Monograph records
https://feeds.library.caltech.edu/people/Dimotakis-P-E/monograph.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 13:32:36 +0000Turbulent Shear Layer Mixing with Fast Chemical Reactions
https://resolver.caltech.edu/CaltechGALCITFM:1987.001
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 1987
DOI: 10.7907/2cnv-2b18
A model is proposed for calculating mixing and chemical reactions in the limit of infinitely fast chemical kinetics and negligible heat release, in fully developed turbulent shear layers. The model is based on the assumption that the topology of the interface between the two entrained reactants in the layer, as well as the strain field associated with it, can be described by the similarity laws of the Kolmogorov cascade. The calculation yields the integrated volume fraction across the layer occupied by the chemical product, as a function of the stoichiometric mixture ratio of the reactants carried by the free streams, the velocity ratio of the shear layer, the local Reynolds number, and the Schmidt number of the flow. The results are in good agreement with measurements of the volume fraction occupied by the molecularly mixed fluid in a turbulent shear layer and the amount of chemical product, in both gas phase and liquid phase chemically reacting shear layers.https://authors.library.caltech.edu/records/ve9bg-j9423Mixing in turbulent jets: scalar measures and isosurface geometry
https://resolver.caltech.edu/CaltechAUTHORS:20140707-154057040
Authors: {'items': [{'id': 'Catrakis-H-J', 'name': {'family': 'Catrakis', 'given': 'Haris J.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 1995
DOI: 10.7907/sfj4-sm73
Experiments have been conducted to investigate mixing and the geometry of scalar isosurfaces in turbulent jets. Specifically, we have obtained high-resolution, high-signal-to-noise-ratio images of the jet-fluid concentration in the far field of round, liquid-phase, turbulent jets, in the Reynolds number range 4.5 × 10^3 ≤ Re ≤ 18 × 10^3, using laser-induced-fluorescence imaging techniques. Analysis of these data indicates that this Reynolds-number range spans a mixing transition in the far field of turbulent jets. This is manifested in the probability-density function of the scalar field, as well as in measures of the scalar isosurfaces. Classical as well as fractal measures of these isosurfaces have been computed, from small to large spatial scales, and are found to be functions of both scalar threshold and Reynolds number. The coverage of level sets of jet-fluid concentration in the two-dimensional images is found to possess a scale-dependent-fractal dimension that increases continuously with increasing scale, from near unity, at the smallest scales, to 2, at the largest scales. The geometry of the scalar isosurfaces is, therefore, more complex than power-law fractal, exhibiting an increasing complexity with increasing scale. This behaviour necessitates a scale-dependent generalization of power-law-fractal geometry. A connection between scale-dependent-fractal geometry and the distribution of scales is established and used to compute the distribution of spatial scales in the flow.https://authors.library.caltech.edu/records/k45z5-hz937Turbulent Mixing in Transverse Jets
https://resolver.caltech.edu/CaltechGALCITFM:2001.006
Authors: {'items': [{'id': 'Shan-Jerry-W', 'name': {'family': 'Shan', 'given': 'Jerry'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul'}}]}
Year: 2001
DOI: 10.7907/t6fq-sd29
Turbulent mixing is studied in liquid-phase transverse jets.
Jet-fluid concentration fields were measured using laser-induced fluorescence and digital-imaging techniques, for jets in the Reynolds number range 1000 <= Re <= 20,000, at a jet-to-freestream velocity ratio of 10. Analysis of the measured scalar fields indicates that turbulent mixing is Reynolds-number dependent, as manifest in the evolving probability density functions of jet-fluid concentration.
Enhanced homogenization is found with increasing Reynolds number. Turbulent mixing is also seen to be flow dependent, based on differences between jets discharging into a crossflow and jets into a quiescent reservoir. A novel technique for whole-field measurement of scalar increments was used to study the distribution of difference (scalar increments) of the scalar field. These scalar increments are found to tend toward exponential-tailed distributions with decreasing separation distance. Finally, the scalar field is found to be anisotropic, particularly at small length scales. This is seen in power spectra, directional scalar microscales, and directional PDFs of scalar increments. The local anisotropy of the scalar field is explained in terms of the global dynamics and large-scale strain field of the transverse jet.https://authors.library.caltech.edu/records/sssj3-ykd55De-aliasing Undersampled Volume Images for Visualization
https://resolver.caltech.edu/CaltechCSTR:1997.cs-tr-97-11
Authors: {'items': [{'id': 'Gornowicz-G-G', 'name': {'family': 'Gornowicz', 'given': 'Galen G.'}}, {'id': 'Laidlaw-D-H', 'name': {'family': 'Laidlaw', 'given': 'David H.'}}, {'id': 'Shan-Jerry-W', 'name': {'family': 'Shan', 'given': 'Jerry W.'}}, {'id': 'Lang-D-B', 'name': {'family': 'Lang', 'given': 'Daniel B.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2001
DOI: 10.7907/Z9C53HWB
We present and illustrate a new technique, Image Correlation Supersampling (ICS), for resampling volume data that are undersampled in one dimension. The resulting data satisfies the sampling theorem, and, therefore, many visualization algorithms that assume the theorem is satisfied can be applied to the data. Without the supersampling the visualization algorithms create artifacts due to aliasing. The assumptions made in developing the algorithm are often satisfied by data that is undersampled temporally. Through this supersampling we can completely characterize phenomena with measurements at a coarser temporal sampling rate than would otherwise be necessary. This can save acquisition time and storage space, permit the study of faster phenomena, and allow their study without introducing aliasing artifacts. The resampling technique relies on a priori knowledge of the measured phenomenon, and applies, in particular, to scalar concentration measurements of fluid flow. Because of the characteristics of fluid flow, an image deformation that takes each slice image to the next can be used to calculate intermediate slice images at arbitrarily fine spacing. We determine the deformation with an automatic, multi-resolution algorithm.https://authors.library.caltech.edu/records/6rzha-w4m53A high-speed quadrature-phase rotation shearing interferometer for imaging through turbulence
https://resolver.caltech.edu/CaltechAUTHORS:KERjpltr01-1307
Authors: {'items': [{'id': 'Kern-Brian-Daniel', 'name': {'family': 'Kern', 'given': 'B.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}, {'id': 'Martin-D-Christopher', 'name': {'family': 'Martin', 'given': 'C.'}, 'orcid': '0000-0002-8650-1644'}, {'id': 'Lang-D-B', 'name': {'family': 'Lang', 'given': 'D. B.'}}, {'id': 'Wadsworth-M', 'name': {'family': 'Wadsworth', 'given': 'M.'}}]}
Year: 2001
A new technique of rotation shearing interferometry has been developed, which is optimized to reduce systematic problems when imaging through turbulence. Key improvements over previous systems are a high-frame-rate, low-noise camera and an optical system which generates four instantaneous interferograms, with instrumental phase shifts of 0°, 90°, 180°, and 270°. The simultaneous quadrature-phase interferograms enable an instantaneous complex visibility measurement in every frame. The camera system has a very short readout time, permitting high duty-cycle recording of short-exposure images, and allows tracking of individual turbulent structures as they translate across the interferograms. By eliminating sources of systematic errors and maximizing the coherence time available, astronomical measurements that far exceed what is possible using ordinary interferometric or direct-imaging techniques are attainable. Laboratory demonstrations as well as first fringes at the Palomar 200" telescope will be discussed.https://authors.library.caltech.edu/records/k5v13-1t594Experiments and modeling of impinging laminar jets at moderate separation distances
https://resolver.caltech.edu/CaltechGALCITFM:2005.003
Authors: {'items': [{'id': 'Bergthorson-J-M', 'name': {'family': 'Bergthorson', 'given': 'Jeffrey M.'}}, {'id': 'Sone-K', 'name': {'family': 'Sone', 'given': 'Kazuo'}}, {'id': 'Mattner-T-W', 'name': {'family': 'Mattner', 'given': 'Trent W.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Goodwin-D-G', 'name': {'family': 'Goodwin', 'given': 'David G.'}}, {'id': 'Meiron-D-I', 'name': {'family': 'Meiron', 'given': 'Dan I.'}, 'orcid': '0000-0003-0397-3775'}]}
Year: 2005
DOI: 10.7907/jaky-fw03
This report describes an experimental and numerical study of impinging, incompressible, axisymmetric, laminar jets, where the jet axis of symmetry is aligned normal to the wall. Particle Streak Velocimetry (PSV) is used to measure
axial velocities along the centerline of the flow field. The jet-nozzle pressure drop is measured simultaneously and determines the Bernoulli velocity. The flowfield is simulated numerically by an axisymmetric Navier-Stokes spectral-element code, an axisymmetric potential-flow model, and an axisymmetric one-dimensional streamfunction approximation. The axisymmetric viscous and potential-flow simulations include the nozzle in the solution domain, allowing nozzle-wall proximity effects to be investigated. Scaling the centerline axial velocity by the Bernoulli velocity collapses the experimental velocity profiles onto a single curve that is independent of the nozzle-plate separation distance. Axisymmetric direct numerical simulations yield good agreement with experiment and confirm the velocity profile scaling. Potential-flow simulations reproduce the collapse of the data, however, viscous effects result in disagreement with experiment. Axisymmetric one-dimensional streamfunction simulations can predict the flow in the stagnation region if the boundary conditions are correctly specified. The scaled axial velocity profiles are well-characterized by an error function with one Reynolds-number dependent parameter. Rescaling the wall-normal distance by the boundary-layer displacement-thickness-corrected diameter yields a collapse of the data onto a single curve that is independent of the Reynolds number. These scalings allow the specification of an analytical expression for the velocity profile of an impinging laminar jet over the Reynolds number range investigated of 200 ≤ Re ≤ 1400.https://authors.library.caltech.edu/records/3tws6-6zk62Experimental investigation of planar strained methane-air and ethylene-air flames
https://resolver.caltech.edu/CaltechGALCITFM:2006.002
Authors: {'items': [{'id': 'Benezech-L-J-M', 'name': {'family': 'Benezech', 'given': 'Laurent J.-M.'}}, {'id': 'Bergthorson-J-M', 'name': {'family': 'Bergthorson', 'given': 'Jeffrey M.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2006
DOI: 10.7907/ef6n-v741
The extinction of planar strained methane-air flames in the stagnation-point flow is studied. A thermal analysis has been conducted in order to build a new copper stagnation plate which can be heated up to 1000K, and allows investigation of downstream heat loss as extinction driving mechanism.
Since premixed stagnation flames are mostly sensitive to the composition of the mixture, axial velocity and CH radical profiles are simultaneously measured for different equivalence ratios, using respectively Particle Streak Velocimetry (PSV) and Planar Laser Induced Fluorescence (PLIF). These are compared to simulations using CANTERA stagnation flow code with a multicomponent molecular transport model, with the following chemical kinetics mechanisms: GRI-MECH 3.0, the C3-Davis, San-Diego 200308 and San-Diego 200503 mechanisms. In methane-air flames, simulations accurately predict the velocity and CH profiles from Phi=0.8 to Phi=1.2, but the flame speed turns out to be overpredicted at Phi=0.7 by all mechanisms except the C3-Davis mechanism (see Bergthorson et al. 2005a). The experiment at Phi=1.3 would need to be reconducted. Also, measured relative concentrations of CH are compared to numerical predictions using each of the four mechanisms cited above. Composition variations impact on ethylene-air flames was also investigated due to a peculiar jump in the overprediction of flame velocities from Phi=1.6 to Phi=1.8 (Bergthorson 2005). This peculiar feature was found to be repeatable, but the cause remains unclear.
Methane-air laminar flame speeds Su0 were computed using CANTERA freely propagating flame code for the following chemical kinetics mechanisms: GRI-MECH 3.0, the C3-Davis mechanism, the San Diego 200308, 200503, and 200506 mechanisms, for variable pressures (1,2,5,10,20 atm) and equivalence ratios (0.6-1.4). Even for methane, whose chemistry is one of the best understood, the scatter between the different mechanisms is significant. Both composition and pressure were found to affect Su0 substantially, although composition variations seem to excite the differences in the predictions among the different mechanisms the most.https://authors.library.caltech.edu/records/16vsf-rgt86Laser Doppler velocimetry momentum defect measurements of cable drag at low to moderate Reynolds numbers: feasibility study
https://resolver.caltech.edu/CaltechAUTHORS:20101022-123953042
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2010
The problem of measuring cable drag coefficients at low to
moderate Reynolds numbers (100 < Re < 30,000) is addressed and
alternative methods of measurement are analyzed. The very low
forces and pressures involved at the lower Reynolds numbers render
conventional measurement methods less suitable candidates. Laser
Doppler velocity measurements, however, of the momentum defect in
the wake appear capable of yielding sufficient accuracy « ± 5%) in
the determination of the drag coefficient. This conclusion assumes
that a test facility can be utilized with a sufficiently uniform
flow field, low turbulence level and a free stream velocity which
either remains stable during the wake survey measurement time
interval or can be monitored independently. Water and air appear
as almost equal in their merits as working fluids. with water
slightly preferable as not requiring scattering particle seeding.https://authors.library.caltech.edu/records/q7z38-m5x25A Greenhouse-Gas Information System: Monitoring and Validating Emissions Reporting and Mitigation
https://resolver.caltech.edu/CaltechAUTHORS:20160602-160820731
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Walker-B-C', 'name': {'family': 'Walker', 'given': 'Bruce C.'}}, {'id': 'Jonietz-K-K', 'name': {'family': 'Jonietz', 'given': 'Karl K.'}}, {'id': 'Rotman-D-A', 'name': {'family': 'Rotman', 'given': 'Douglas A.'}}]}
Year: 2011
DOI: 10.2172/1033495
This study and report focus on attributes of a greenhouse-gas information system (GHGIS) needed to support MRV&V needs. These needs set the function of such a system apart from scientific/research monitoring of GHGs and carbon-cycle systems, and include (not exclusively): the need for a GHGIS that is operational, as required for decision-support; the need for a system that meets specifications derived from imposed requirements; the need for rigorous calibration, verification, and validation (CV&V) standards, processes, and records for all measurement and modeling/data-inversion data; the need to develop and adopt an uncertainty-quantification (UQ) regimen for all measurement and modeling data; and the requirement that GHGIS products can be subjected to third-party questioning and scientific scrutiny. This report examines and assesses presently available capabilities that could contribute to a future GHGIS. These capabilities include sensors and measurement technologies; data analysis and data uncertainty quantification (UQ) practices and methods; and model-based data-inversion practices, methods, and their associated UQ. The report further examines the need for traceable calibration, verification, and validation processes and attached metadata; differences between present science-/research-oriented needs and those that would be required for an operational GHGIS; the development, operation, and maintenance of a GHGIS missions-operations center (GMOC); and the complex systems engineering and integration that would be required to develop, operate, and evolve a future GHGIS.https://authors.library.caltech.edu/records/zpd5a-xhm65Chemical Reactions in Turbulent Mixing Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141020-101605714
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Broadwell-J-E', 'name': {'family': 'Broadwell', 'given': 'James E.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}]}
Year: 2014
The purpose of this research is to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic
and supersonic flows. Our program is comprised of several parts:
a. an experimental effort,
b. an analytical effort,
c. a computational effort,
d. a modeling effort,
and
e. a diagnostics development and data-acquisition effort,
the latter as dictated by specific needs of the experimental part of the overall program.
Our approach has been to carry out a series of detailed theoretical and experimental studies of turbulent mixing in primarily in two, well-defined, fundamentally
important flow fields: free shear layers and axisymmetric jets.
To elucidate molecular transport effects, experiments and theory concern themselves with both reacting and non-reacting flows of liquids and gases, in fully-developed
turbulent flows, i.e., in moderate to high Reynolds number flows. The computational studies are, at present, focused at fundamental issues pertaining to the computational simulation of both compressible and incompressible flows. Modeling has been focused on both shear layers and turbulent jets, with an effort to
include the physics of the molecular transport processes, as well as formulations of models that permit the full chemical kinetics of the combustion process to be
incorporated. Our primary diagnostic development efforts are currently focused on data-acquisition electronics to meet very high-speed, high-volume data requirements,
the acquisition of single, or a sequence, of two-dimensional images, and the acquisition of data from arrays of supersonic flow sensors. Progress has also been
made in the development of a dual-beam laser interferometer/correlator to measure
convection velocities of large scale structures in supersonic shear layers and in a new
method to acquire velocity field data using pairs of scalar images closely spaced in time.https://authors.library.caltech.edu/records/dvnqr-dgg22Chemical Reactions in Turbulent Mixing Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141020-095543611
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Broadwell-J-E', 'name': {'family': 'Broadwell', 'given': 'James E.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}]}
Year: 2014
The purpose of this research has been to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. Progress in this effort thus far has uncovered important deficiencies in conventional modeling of these phenomena, and offered alternative suggestions and formulations to address some of these deficiencies. This program is comprised of an experimental
effort, an analytical modeling effort, a computational effort, and a diagnostics development
and data-acquisition effort, the latter as dictated by specific needs of our experiments.
Our approach has been to carry out a series of detailed theoretical and experimental studies primarily in two, well-defined, fundamentally important flow fields: free shear layers and axisymmetric jets. To elucidate molecular transport effects, experiments and theory
concern themselves with both liquids and gases. Modeling efforts have been focused on both shear layers and turbulent jets, with an effort to include the physics of the molecular transport processes, as well as formulations of models that permit the full chemical
kinetics of the combustion process to be incorporated. The computational studies are, at
present, focused at fundamental issues pertaining to the computational simulation of both compressible and incompressible flows.
This report includes an outline discussion of work completed under the sponsorship of this Grant, with six papers, which have not previously been included in past reports, or transmitted in reprint form, appended.https://authors.library.caltech.edu/records/xk40x-1aw43Chemical Reactions in Turbulent Mixing Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141020-092935685
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}, {'id': 'Broadwell-J-E', 'name': {'family': 'Broadwell', 'given': 'J. E.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'A.'}}]}
Year: 2014
Work is continuing primarily in gas phase turbulent mixing and chemical reactions. The liquid phase work to date is in its final stages of being analyzed and documented for dissemination in the form of archival publications. In the gas phase shear layer work, our investigations are concentrating on shear layer free stream density
ratio effects, finite kinetic rate (Damköhler number) effects, and a design effort in support of the planned extension of the work to supersonic flows. In jet flows, progress has been made in the gas phase laser Rayleigh scattering techniques developed for conserved scalar
measurements down to diffusion space and time scales. A new technique has been developed under joint support with the Gas Research Institute that permits the imaging of soot sheets in turbulent flames and is being
used to describe the combustion flame sheets in methane flames. Theoretical work in progress is addressing the finite chemical rate problem as well as the diffusion-limited shear layer mixing problem.
Advances in our data acquisition capabilities during the last year are permitting higher temporal resolution measurements to be taken with digital image arrays.https://authors.library.caltech.edu/records/f8k3d-e8243Some issues on turbulent mixing and turbulence
https://resolver.caltech.edu/CaltechAUTHORS:20141021-164608550
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/g7fc-f113
Recent data on turbulent mixing suggest that the mixing transition, previously documented to occur in shear layers, also occurs in jets, as well as many
other flows, and can be regarded as a universal phenomenon. The resulting, fully-developed turbulent flow requires a minimum Reynolds number of Re_T ≈ 10^4, or a
Taylor Reynolds number of Re_T ≈ 10^2 to be sustained. Turbulent mixing in this fully-developed state does not appear to be universal, however, with a qualitatively
different behavior between shear layers and jets.https://authors.library.caltech.edu/records/mp1b7-tn298Measurements of scalar power spectra in high Schmidt number turbulent jets
https://resolver.caltech.edu/CaltechAUTHORS:20141021-163918527
Authors: {'items': [{'id': 'Miller-P-L', 'name': {'family': 'Miller', 'given': 'Paul L.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/hpdt-2e37
Single-point, jet-fluid concentration measurements obtained from high Schmidt number (Sc ≃ 1.9 x 10^3) turbulent jets permit an investigation of temporal scalar power spectra, for jet Reynolds numbers in the range of 1.25 ≤ Re x 10^(-4)≤ 7.2. At intermediate scales, we find a spectrum with a logarithmic derivative (slope) that is increasing with Reynolds number, in absolute value, but less than 5/3 at the highest Reynolds number in our experiments. At the smallest scales, our spectra exhibit no k^(-1) power-law behavior, possessing a log-normal region over a range of
scales exceeding a factor of 40, in some cases.https://authors.library.caltech.edu/records/jj3aw-b4f86Image correlation velocimetry
https://resolver.caltech.edu/CaltechAUTHORS:20141021-163502231
Authors: {'items': [{'id': 'Tokumaru-P-T', 'name': {'family': 'Tokumaru', 'given': 'P. T.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}]}
Year: 2014
DOI: 10.7907/ry4g-h059
This paper focuses on the correlation of two successive scalar images for the purpose of measuring imaged fluid motions. A method is presented for deforming,
or transforming, one image to another. Taylor series expansions of the Lagrangian displacement field are used, in conjunction with an integral form of the equations
of motion, to approximate this transformation. The proposed method locally correlates images for displacements, rotations, deformations, and higher order displacement
gradient fields, and applies a global minimization procedure to insure a global consistency in the results. An integral form of the equations of motion is employed
and, as a consequence, no spatial or temporal differentiation of the image data is
required in estimating the displacement field. Successive two-dimensional digital CCD images of fluid motion marked with dye, are used to verify the capabilities of
the method. The utility of the method is also illustrated using a pair of Voyager 2 images of Jupiter.https://authors.library.caltech.edu/records/tjkb9-tm234Chemical Reactions in Turbulent Mixing Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141021-161231721
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}]}
Year: 2014
DOI: 10.7907/akw6-xc58
The purpose of this research is to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic
and supersonic flows. The program during this reporting period was comprised of several parts:
a. an experimental effort,
b. a numerical simulation effort,
and
c. an effort to develop instrumentation and diagnostics; flow and combustion facilities; and data-acquisition systems.
The latter as dictated by the specific needs of the experimental part of the program.
Our approach in this research has been to carry out a series of detailed theoretical and experimental studies of turbulent mixing in primarily in two, well-defined,
fundamentally important flow fields: free-shear layers and axisymmetric jets. To elucidate molecular transport effects, experiments and theory concern themselves
with both reacting and non-reacting flows of liquids and gases, in fully-developed turbulent flows, i.e., in moderate to high Reynolds number flows. A criterion for
fully-developed turbulence was recently developed and will be presented below.
The computational studies are, at present, focused at fundamental formulation and implementation issues pertaining to the computational simulation of both
compressible and incompressible flows characterized by strong fronts, such as shock waves and flames.
Our diagnostic development efforts have recently been focused on improving the signal-to-noise ratio of flow images, in both gas- and liquid-phase flows, as well
as the continuing development of data-acquisition electronics to meet very high-speed,
high-volume data requirements; the acquisition of single, or pairs, of two-dimensional
images in rapid succession; and the acquisition of data from arrays of supersonic flow sensors.https://authors.library.caltech.edu/records/w40cd-dn579Control of Turbulent Mixing Layers
https://resolver.caltech.edu/CaltechAUTHORS:20141028-163232880
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Koochesfahani-M-M', 'name': {'family': 'Koochesfahani', 'given': 'Manoochehr M.'}}]}
Year: 2014
DOI: 10.7907/w891-xv06
This the final report of research conducted at the California Institute of Technology,
by Paul E. Dimotakis, in collaboration with Dr. M. M. Moochesfahani as co-investigator,
and with the assistance of Mr. P. Tokumaru during the last year. The primary goal was to
explore ways in which open loop and closed feedback loop control methods can be utilized to affect the qualitative and quantitative behavior of turbulent shear layers. In particular, we attempted to
i. investigate the dynamic behavior and response of these flows through a study of the feedback control schemes required to produce a given desired outcome,
ii. explore the extent to which specific properties of turbulent shear layer flows, such as growth rate profile and mixing, can be manipulated and altered by such means,
and,
iii. devise schemes for producing turbulent shear layer flows with specific desirable properties, as might be dictated, for example, by the flow specifications for the
efficient operation of a combustion device.
In the course of this work, other derivative and closely related efforts were also undertaken,
some of which will be described below.
The work conducted under the sponsorship of this Grant was primarily experimental and in close collaboration with a broader experimental, numerical and theoretical effort at
Caltech to study unsteady separated flows, and the evaluation and use of control techniques
in these flows in particular.https://authors.library.caltech.edu/records/rs7ww-kd377Whole-Field Measurements in Gas-Phase Turbulent Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141104-110123516
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Fourguette-D', 'name': {'family': 'Fourguette', 'given': 'Dominique'}}]}
Year: 2014
DOI: 10.7907/96et-za81
The purpose of this experimental, nine-month effort was to investigate the scalar field in fully-developed, gas-phase, turbulent flows, using planar index-of-refraction
imaging at elevated pressures (p ≃ 10 atm).
The motivation behind this work is to further our understanding of phenomena that rely on the behavior of scalar gradients, such as aero-optic effects, laser propagation through, and scattering by, gas-phase turbulent flows, as well as turbulent mixing and combustion.
In this effort, we have used planar laser-Rayleigh scattering to image simultaneously the index-of-refraction field of a turbulent jet and the optical degradation of
the planar laser probe beam caused by the turbulent flow-field. From these results, we have demonstrated that conducting these experiments at elevated pressure increases
the index-of-refraction gradients and improves the signal-to-noise ratio over measurements conducted at atmospheric conditions. The optical degradation occurs
in the jet-fluid region and manifests itself as a spatial amplitude modulation (streaks) in the laser sheet. This optical degradation illustrates the same loss of coherence
undergone by laser beams and by coherent information when propagating through the turbulent atmosphere.https://authors.library.caltech.edu/records/qr6n5-qrp73Rate Equation Analysis of Flowing Lasing Systems Part I. Uniform Pumping
https://resolver.caltech.edu/CaltechAUTHORS:20141104-104632359
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
A simple analytical model for flowing laser systems has been developed. The lasing species is modeled as a two-state system with specified pumping and relaxation rates. Threshold requirements and output efficiency are expressed in the form of universal dimensionless functions. In terms of these universal functions, the behavior of particular systems can be studied in a parametric way. The analysis shows that flow would not improve the performance of all laser systems. The transformation ∂/∂t → v ∂/∂x allows one to predict the performance of flowing systems from the behavior of pulsed systems.https://authors.library.caltech.edu/records/2hsv5-z2t10On the convection velocity of turbulent structures in supersonic shear layers
https://resolver.caltech.edu/CaltechAUTHORS:20141104-164138252
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/6wgv-pn56
An ansatz, complemented by appropriate selection rules, is proposed to estimate the convection velocity U_c of turbulent vortical structures in supersonic shear layers. The proposed scheme assumes that, for supersonic convective Mach numbers, shocks will form in one of the two shear layer free streams. The strength of the shocks is estimated by assuming that the flow configuration is stationary with respect to perturbations in the mean flow
quantities caused by the turbulent fluctuations. Given the shock strength, the convection velocity U_c, and the associated convective Mach numbers are calculated by matching the estimated total pressure at the stagnation points in the convected frame. The data indicate
a convection velocity U_c that is close to that of one of the free streams. That appears to be well accounted for by the proposed scheme, which also suggests that the flow can undergo large jumps in configuration with small changes in the flow parameters. This has important implications for supersonic mixing and hypersonic propulsion applications.https://authors.library.caltech.edu/records/1as44-1a738Image correlation velocimetry
https://resolver.caltech.edu/CaltechAUTHORS:20141105-155126556
Authors: {'items': [{'id': 'Tokumaru-P-T', 'name': {'family': 'Tokumaru', 'given': 'P. T.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}]}
Year: 2014
DOI: 10.7907/7q6z-1558
This paper focuses on the correlation of two successive scalar images for the
purpose of measuring imaged fluid motions. A method is presented for deforming,
or transforming, one image to another. Taylor series expansions of the Lagrangian
displacement field are used, in conjunction with an integral form of the equations
of motion, to approximate this transformation. The proposed method locally correlates
images for displacements, rotations, deformations, and higher order displacement
gradient fields, and applies a global minimization procedure to insure a global
consistency in the results. An integral form of the equations of motion is employed
and, as a consequence, no explicit spatial or temporal differentiation of the image
data is required in estimating the displacement field. As a consequence, this
method is appropriate for both continuous scalar as well as discrete particle image
data. Successive two-dimensional digital CCD images of fluid motion marked with
dye, are used to verify the capabilities of the method. The utility of the method is
also illustrated using a pair of Voyager 2 images of Jupiter.https://authors.library.caltech.edu/records/gq8yg-vhn24Whole-Field Measurements of Turbulent Flows for the Study of Aero-Optical Effects
https://resolver.caltech.edu/CaltechAUTHORS:20141111-112204021
Authors: {'items': [{'id': 'Fourguette-D-C', 'name': {'family': 'Fourguette', 'given': 'D. C.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}, {'id': 'Ching-W-K', 'name': {'family': 'Ching', 'given': 'W. K.'}}]}
Year: 2014
DOI: 10.7907/ddnh-6k17
Planar laser-Rayleigh scattering has been employed to simultaneously image the index-of-refraction field of a turbulent jet of ethylene into nitrogen and the
optical degradation of a laser sheet caused by this turbulent-flow field. The optical degradation occurs in t he turbulent-jet region and manifests itself as phase-front
tilts that result in a measurable spatial amplitude modulation (streaks) in the emerging pulsed-laser sheet. The experiments were conducted at elevated pressure,
increasing the index-of-refract ion gradient s and improving the signal-to-noise ratio over measurements conducted at atmospheric pressure. The high index-of-refraction gradients in these experiments placed the optical far field within the field
of view and allowed us to capture caustic formation in the distorted emerging laser sheet, simulating the aero-optics effects expected at large distances from the smaller
index-of-refract ion fluctuations one would more typically encounter.https://authors.library.caltech.edu/records/c9ysw-fnk28Unsplit Schemes for Hyperbolic Conservation Laws with Source Terms in One Space Dimension
https://resolver.caltech.edu/CaltechAUTHORS:20141111-103448502
Authors: {'items': [{'id': 'Papalexandris-M-V', 'name': {'family': 'Papalexandris', 'given': 'Miltiadis V.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/a52f-t488
The present work is concerned with the extension of the theory of characteristics to conservation laws with source terms in one space dimension, such as the
Euler equations for reacting flows. New spacetime curves are introduced on which the equations decouple to the characteristic set of O.D.E's for the corresponding
homogeneous laws, thus allowing the introduction of functions analogous to the Riemann Invariants. The geometry of these curves depends on the spatial gradients
for the solution. This particular decomposition can be used in the design of efficient unsplit algorithms for the numerical integration of the equations. As a first step,
these ideas are implemented for the case of a scalar conservation law with a nonlinear
source term. The resulting algorithm belongs to the class of MUSCL-type, shock-capturing schemes. Its accuracy and robustness are checked through a series
of tests. The aspect of the stiffness of the source term is also studied. Then, the algorithm is generalized for a system of hyperbolic equations, namely the Euler
equations for reacting flows. An extensive numerical study of unstable detonations is performed.https://authors.library.caltech.edu/records/10wr8-na108Turbulence, fractals, and mixing
https://resolver.caltech.edu/CaltechAUTHORS:20141111-113314598
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Catrakis-H-J', 'name': {'family': 'Catrakis', 'given': 'Haris J.'}}]}
Year: 2014
DOI: 10.7907/1tc0-gg58
Proposals and experiment evidence, from both numerical simulations and laboratory experiments, regarding the behavior of level sets in turbulent flows are reviewed. Isoscalar surfaces in turbulent flows, at least in liquid-phase turbulent jets, where extensive experiments have been undertaken, appear to have a geometry
that is more complex than (constant-D) fractal. Their description requires an extension of the original, scale-invariant, fractal framework that can be cast in
terms of a variable (scale-dependent) coverage dimension, D_d(λ). The extension to a scale-dependent framework allows level-set coverage statistics to be related to
other quantities of interest. In addition to the pdf of point-spacings (in 1-D), it can be related to the scale-dependent surface-to-volume (perimeter-to-area in 2-D)
ratio, as well as the distribution of distances to the level set. The application of this framework to the study of turbulent-jet mixing indicates that isoscalar geometric
measures are both threshold and Reynolds-number dependent. As regards mixing, the analysis facilitated by the new tools, as well as by other criteria, indicates enhanced
mixing with increasing Reynolds number, at least for the range of Reynolds numbers investigated. This results in a progressively less-complex level-set geometry,
at least in liquid-phase turbulent jets, with increasing Reynolds number. In liquid-phase turbulent jets, the spacings in one-dimensional records, as well as the
size distribution of individual "islands" and "lakes" in two-dimensional isoscalar slices, are found in accord with lognormal statistics in the inner-scale range. The
coverage dimension, D_d(λ), derived from such sets is also in accord with lognormal statistics, in the inner-scale range. Preliminary three-dimensional (2-D space
+ time) isoscalar-surface data provide further evidence of a complex level-set geometrical structure in scalar fields generated by turbulence, at least in the case of
turbulent jets.https://authors.library.caltech.edu/records/khww4-cyq43Riemann Invariant Manifolds for the Multidimensional Euler Equations Part I: Theoretical Development Part II: A Multidimensional Godunov Scheme and Applications
https://resolver.caltech.edu/CaltechAUTHORS:20141110-161414265
Authors: {'items': [{'id': 'Lappas-T', 'name': {'family': 'Lappas', 'given': 'Tasso'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/yghw-7356
A new approach for studying wave propagation phenomena in an inviscid gas is presented. This approach can be viewed as the extension of the method of characteristics
to the general case of unsteady multidimensional flow. The general case of the unsteady compressible Euler equations in several space dimensions is examined. A family of spacetime manifolds is found on which an equivalent one-dimensional problem holds. Their geometry depends on the spatial gradients of the flow, and they provide, locally, a convenient system of coordinate surfaces for spacetime. In the case of zero entropy gradients, functions analogous to the Riemann invariants
of 1-D gas dynamics can be introduced. These generalized Riemann Invariants are constant on these manifolds and, thus, the manifolds are dubbed Riemann Invariant
Manifolds (RIM). In this special case of zero entropy gradients, the equations of motion are integrable on these manifolds, and the problem of computing the
solution becomes that of determining the manifold geometry in spacetime. This situation is completely to the traditional method of characteristics in one-dimensional flow.
Explicit espressions for the local differential geometry of these manifolds can be found directly from the equations of motion. The local direction and speed of propagation
of the waves that these manifolds represent, can be found as a function of the local spatial gradients of the flow. Their geometry is examined, and in particular,
their relation to the characteristic surfaces. It turns out that they can be space-like
or time-like, depending on the flow gradients. Wave propagation can be viewed as a superposition of these Riemann Invariant waves, whenever appropriate conditions
of smoothness are met. This provides a means for decomposing the equations into a set of convective scalar fields in a way which is different and potentially more useful than the characteristic decomposition. The two decompositions become identical in the special case of one-dimellsional flow. This different approach can be used for computational purposes by discretizing the equivalent set of scalar equations. Such a computational application of this theory leads to the possibility of determining the
solution at points in spacetime using information that propagates faster than the local characteristic speed, i.e., using information outside the domain of dependence.
This possibility and its relation to the uniqueness theorems is discussed.https://authors.library.caltech.edu/records/nbmd4-0dd69Interaction of Chemistry, Turbulence, and Shock Waves in Hypervelocity Flow
https://resolver.caltech.edu/CaltechAUTHORS:20141111-111211793
Authors: {'items': [{'id': 'Candler-G-V', 'name': {'family': 'Candler', 'given': 'G. V.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}, {'id': 'Hornung-H-G', 'name': {'family': 'Hornung', 'given': 'H. G.'}, 'orcid': '0000-0002-4903-8419'}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'A.'}}, {'id': 'Meiron-D-I', 'name': {'family': 'Meiron', 'given': 'D. I.'}, 'orcid': '0000-0003-0397-3775'}, {'id': 'McKoy-V', 'name': {'family': 'McKoy', 'given': 'B. V.'}}, {'id': 'Pullin-D-I', 'name': {'family': 'Pullin', 'given': 'D. I.'}}, {'id': 'Sturtevant-B', 'name': {'family': 'Sturtevant', 'given': 'B.'}}]}
Year: 2014
DOI: 10.7907/wbg4-ra84
Significant progress was made in the third year of an interdisciplinary experimental, numerical and theoretical program to extend the state of knowledge
and understanding of the effects of chemical reactions in hypervelocity flows. The program addressed the key problems in aerothermochemistry that arise from.the interaction between the three strongly nonlinear effects:
Compressibility; vorticity; and chemistry. Important new results included:
• New data on transition in hypervelocity carbon dioxide flows
• New method of free-piston shock tunnel operation for lower enthalpy
• Accurate new method for computation of self-similar flows
• New experimental data on flap-induced separation at high enthalpy
• Insight into mechanisms active in reacting shear layers from comparison of experiment and computation
• Extensive new data from Rayleigh scattering diagnostics of supersonic shear layer
• Comparison of new experiments and computation of hypervelocity double-wedge flow yielded important differences
• Further first-principles computations of electron collision cross-sections of CO, N_2 and NO
• Good agreement between EFMO computation and experiment of flow over a cone at high incidence
• Extension of LITA diagnostics to high temperature.https://authors.library.caltech.edu/records/75kbq-bze72Chemical Reactions in Turbulent Mixing Flows
https://resolver.caltech.edu/CaltechAUTHORS:20141111-095158441
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Leonard-A', 'name': {'family': 'Leonard', 'given': 'Anthony'}}]}
Year: 2014
DOI: 10.7907/z36m-ct61
This is the final report of our program on "Chemical Reactions in Turbulent Mixing Flows," supported under the AFOSR Grant No. F49620-92-J-0290, which
was granted a no-cost extension to permit the completion of the Supersonic Shear Layer Facility upgrade that extended the operating envelope to higher Mach-number
flows. As part of this upgrade, a variety of new diagnostic and safety features were also implemented in this unique facility.
The purpose of this program has been to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. Scientific progress in these areas was documented in our most recent Annual Report (Dimotakis & Leonard 1994).https://authors.library.caltech.edu/records/w16pn-y6q72Two-dimensional NACA 66(MOD) hydrofoil High Speed Water Tunnel tests
https://resolver.caltech.edu/CaltechAUTHORS:20141113-160804180
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'P. E.'}}, {'id': 'Gaebler-H-F', 'name': {'family': 'Gaebler', 'given': 'H. F.'}}, {'id': 'Hamaguchi-H-T', 'name': {'family': 'Hamaguchi', 'given': 'H. T.'}}, {'id': 'Lang-D-B', 'name': {'family': 'Lang', 'given': 'D. B.'}}, {'id': 'Shen-Y-T', 'name': {'family': 'Shen', 'given': 'Y. T.'}}]}
Year: 2014
Two-dimensional tests were conducted on a NACA 66(MOD) hydrofoil in the the GALCIT Hydrolab High Speed Water Tunnel (HSWT) . These tests were conducted using the hydrofoil with
a. a rough leading edge,
and
b. a smooth leading edge,
covering the following range of conditions:
1. Speed range of 30 ft/s to 60 ft/s
2. Angles of attack of 0° to 6°
and
3. static pressures of 3. 03 psiA to 33. 54 psiA, corresponding to cavitating, incipient cavitation thru fully wetted flow conditions.
These tests were performed in the two-dimensional test section of the HSWT and included measurements of:
--Tunnel velocity.
--Tunnel static pressure.
--Lift, Drag and Pitching Moment forces (with tare forces
removed).
--Pressure coefficients on 13 taps, 12 at selected locations on the lifting surface, plus 1 location on the bottom surface.
--High speed (strobe) flow visualization photography under flow cavitation conditions.
--Airfoil gap dependence on static pressure.https://authors.library.caltech.edu/records/g98f0-2kd42The Supersonic Hydrogen-Fluorine Combustion Facility Design Review Report Version 4.0
https://resolver.caltech.edu/CaltechAUTHORS:20141113-153956842
Authors: {'items': [{'id': 'Hall-J', 'name': {'family': 'Hall', 'given': 'Jeffery'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul'}}]}
Year: 2014
DOI: 10.7907/x0n5-he86
This version (4.0) of the report is intended to provide a general overview of the facility
and its capabilities. It includes brief descriptions of all major components, including those
elements of the fluorine gas delivery system that were ignored in the previous versions. More
detailed information on the facility can be found in the appendices, including engineering
drawings, device data sheets and sample calculations.https://authors.library.caltech.edu/records/z9xkj-kxd80Laser Doppler Velocity & Vorticity Measurements in Turbulent Shear Layers
https://resolver.caltech.edu/CaltechAUTHORS:20141113-163459681
Authors: {'items': [{'id': 'Lang-D-B', 'name': {'family': 'Lang', 'given': 'Daniel B.'}}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/kn5k-7234
A Laser Doppler Velocimeter (LDV) system was developed to measure the instantaneous spanwise vorticity, - ω_z, in a turbulent shear layer. It was necessary to design and fabricate the LDV optics and processing electronics, as no commercially available LDV systems met the
specifications of measuring the velocity at four closely spaced points to the requisite accuracy. Measurements were also made of the instantaneous u, v, u', v' and - u'v'. The instantaneous vorticity was processed to obtain an estimate of its probability density function, from which the mean and rms values were estimated. It was also possible to separate the irrotational fraction of the flow (-ω_z = 0)
from the rotational (intermittent) fraction of the flow (-ω_z ≠ O). The development of the intermittency profiles, based on vorticity, as a function of the downstream distance from the splitter plate was studied. A notable feature is that the vorticity is found to have values opposite the mean sense of rotation, i.e., - ω_z(t) < 0, a
significant fraction of the time. Additionally, a detailed study was performed to evaluate the approximation of -∂v/∂x, in terms of various local temporal derivatives ∂v/u(y)∂t. The optimum choice for u(y) can
be found and is influenced by the relative local convection velocities
of the small and large scale structures.https://authors.library.caltech.edu/records/c0swz-mf238Large Structure Dynamics and Entrainment in the Mixing Layer at High Reynolds Number
https://resolver.caltech.edu/CaltechAUTHORS:20141114-134017563
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Brown-G-L', 'name': {'family': 'Brown', 'given': 'Garry L.'}}]}
Year: 2014
DOI: 10.7907/qj0n-bb77
Observations were made on a turbulent mixing layer in a water channel at Reynolds numbers up to 3 x 10^6 . Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observations of the reaction of a base
and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using an LDV, revealed a fundamental
periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that the mixing layer dynamics at any point is coupled to the large structure further downstream, and some possible
consequences about the effects of initial conditions and,. of the influence of apparatus geometry are discussed.https://authors.library.caltech.edu/records/2dgt8-k0321Hydroacoustic Testing of a NACA-66 (MOD) Hydrofoil in the GALCIT High Speed Water Tunnel
https://resolver.caltech.edu/CaltechAUTHORS:20141113-162543069
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}]}
Year: 2014
DOI: 10.7907/az4b-yz08
The work described in this report represents a primarily exploratory effort to assess the feasibility of performing accurate hydroacoustic measurements at high
signal-to-noise ratios, in the GALCIT High Speed Water Tunnel (HSWT), hereafter referred to as the Tunnel, to characterize the hydroacoustic environment in
the HSWT 2-D test section, and to complement the force and flow visualization measurements that were performed using the two-dimensional, NACA 66 (MOD)
hydrofoil in the recent past. See Baloga (1982), Dimotakis et al. (1988), Shen & Dimotakis 1989a, and Shen &. Dimotakis 1989b. This work was also a sequel to
earlier hydroacoustic measurements that were performed by S. Barker (1974, 1975, 1976) in the same facility.https://authors.library.caltech.edu/records/pgbhm-44y25Asteroid Retrieval Technology Development From the Asteroid Return Mission Study
https://resolver.caltech.edu/CaltechAUTHORS:20190211-060216203
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Prince-T-A', 'name': {'family': 'Prince', 'given': 'Thomas A.'}, 'orcid': '0000-0002-8850-3627'}, {'id': 'Brophy-J-R', 'name': {'family': 'Brophy', 'given': 'John R.'}}, {'id': 'Friedman-L', 'name': {'family': 'Friedman', 'given': 'Louis'}}]}
Year: 2019
DOI: 10.26206/Q721-NS02
The Keck Institute for Space Studies (KISS) workshops on the Asteroid Return Mission concept explored and established the feasibility of capturing and returning an entire near-Earth asteroid (NEA) to lunar orbit by the middle of the next decade, and identified the benefits that such an endeavor would provide to NASA, the
nation, and the world. The goal of this technology development program was to start the process of working select technical issues identified in the study to significantly enhance the prospects of making the asteroid capture and return mission a reality.
Key areas of accomplishment:
A) Mission architecture definition:
1. Trajectory design
2. SEP propulsion technology
3. Mission/System Design
4. Solar Thermal Power & Propulsion Technology Introduction
- Study beam-forming deployable reflector designs for
solar concentrators.
- Monitor progress in solar-electric power production
technologies.
B) Small Near Earth Asteroid (NEA) detection:
1. Modifications to the search/detection software employed in the Palomar Transient Factory (PTF).
2. Demonstration of the upgraded PTF as a useful tool for
detecting small NEAs.
C) In-Situ Resource Utilization (ISRU) for asteroids, specifically for power and propulsion.https://authors.library.caltech.edu/records/h80ha-tsb52LES of an Inclined Jet into a Supersonic Turbulent Crossflow
https://resolver.caltech.edu/CaltechAUTHORS:20191016-143406258
Authors: {'items': [{'id': 'Ferrante-Antonino', 'name': {'family': 'Ferrante', 'given': 'Antonino'}, 'orcid': '0000-0002-5336-572X'}, {'id': 'Matheou-Georgios', 'name': {'family': 'Matheou', 'given': 'Georgios'}, 'orcid': '0000-0003-4024-4571'}, {'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul E.'}}, {'id': 'Stephens-Mike', 'name': {'family': 'Stephens', 'given': 'Mike'}}, {'id': 'Adams-Paul', 'name': {'family': 'Adams', 'given': 'Paul'}}, {'id': 'Walters-Richard', 'name': {'family': 'Walters', 'given': 'Richard'}}]}
Year: 2019
DOI: 10.48550/arXiv.0910.3018
This short article describes flow parameters, numerical method, and animations of the fluid dynamics video "LES of an Inclined Jet into a Supersonic Turbulent Crossflow" (this http URL [high-resolution] and this http URL [low-resolution] video). We performed large-eddy simulation with the sub-grid scale (LES-SGS) stretched-vortex model of momentum and scalar transport to study the gas-dynamics interactions of a helium inclined round jet into a supersonic (M = 3.6) turbulent (Re_θ = 13×10^3) air flow over a flat surface. The video shows the temporal development of Mach-number and magnitude of density-gradient in the mid-span plane, and isosurface of helium mass-fraction and λ_2 (vortical structures). The identified vortical structures are sheets, tilted tubes, and discontinuous rings. The vortical structures are shown to be well correlated in space and time with helium mass-fraction isosurface (Y_(He) = 0.25).https://authors.library.caltech.edu/records/m6dcb-3mg09