[ { "id": "authors:h3evj-8y442", "collection": "authors", "collection_id": "h3evj-8y442", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181119-155309490", "type": "book_section", "title": "Jets and mixing layers", "book_title": "A Gallery of Fluid Motion", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Gharib", "given_name": "M.", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Derango", "given_name": "P.", "clpid": "Derango-P" }, { "family_name": "Villermaux", "given_name": "E.", "clpid": "Villermaux-E" }, { "family_name": "Rehab", "given_name": "H.", "clpid": "Rehab-H" }, { "family_name": "Hopfinger", "given_name": "E. J.", "clpid": "Hopfinger-E-J" }, { "family_name": "Parekh", "given_name": "D. E.", "clpid": "Parekh-D-E" }, { "family_name": "Reynolds", "given_name": "W. C.", "clpid": "Reynolds-W-C" }, { "family_name": "Mungal", "given_name": "M. G.", "clpid": "Mungal-M-G" }, { "family_name": "Loiseleux", "given_name": "T.", "clpid": "Loiseleux-T" }, { "family_name": "Chomaz", "given_name": "J.-M.", "clpid": "Chomaz-J-M" }, { "family_name": "Fric", "given_name": "T. F.", "clpid": "Fric-T-F" }, { "family_name": "Roshko", "given_name": "A.", "clpid": "Roshko-A" }, { "family_name": "Gogineni", "given_name": "S. P.", "clpid": "Gogineni-S-P" }, { "family_name": "Whitaker", "given_name": "M. M.", "clpid": "Whitaker-M-M" }, { "family_name": "Goss", "given_name": "L. P.", "clpid": "Goss-L-P" }, { "family_name": "Roquemore", "given_name": "W. M.", "clpid": "Roquemore-W-M" }, { "family_name": "Wernz", "given_name": "S.", "clpid": "Wernz-S" }, { "family_name": "Fasel", "given_name": "H. F.", "clpid": "Fasel-H-F" }, { "family_name": "Gogineni", "given_name": "S.", "clpid": "Gogineni-S" }, { "family_name": "Shih", "given_name": "C.", "clpid": "Shih-C" }, { "family_name": "Krothapalli", "given_name": "A.", "clpid": "Krothapalli-A" } ], "contributor": [ { "family_name": "Samimy", "given_name": "M.", "clpid": "Samimy-M" }, { "family_name": "Breuer", "given_name": "K. S.", "clpid": "Breuer-K-S" }, { "family_name": "Leal", "given_name": "L. G.", "clpid": "Leal-L-G" }, { "family_name": "Steen", "given_name": "P. H.", "clpid": "Steen-P-H" } ], "abstract": "Laser-induced fluorescence (LIF) diagnostics and highspeed, real-time digital image acquisition techniques are combined to map the composition field in a water mixing layer. A fluorescent dye, which is premixed with the lowspeed freestream fluid and dilutes by mixing with the highspeed fluid, is used to monitor the relative concentration of high-speed to low-speed fluid in the layer.\nThe three digital LIF pictures shown here were obtained by imaging the laser-induced fluorescence originating from a collimated argon ion laser beam, extending across the transverse dimension of the shear layer, onto a 512\u2013element linear photodiode array. Each picture represents 384 contiguous scans, each at 400 points across the layer, for a total of 153 600 point measurements of concentration. The vertical axis maps onto 40 mm of the transverse coordinate of the shear layer, and the horizontal axis is time increasing from right to left for a total flow real time of 307 msec. The pseudocolor assignment is linear in the mixture fraction (\u03be) and is arranged as follows: red-unmixed fluid from the low-speed stream (\u03be=0); blue-unmixed fluid from the high-speed stream (\u03be=1); and the rest of the spectrum corresponds to intermediate compositions.\nFigures 1 and 2, a single vortex and pairing vortices, respectively, show the composition field before the mixing transition. The Reynolds number based on the local visual thickness of the layer and the velocity difference across the layer is Re=1750 with U_2/U_1=0.46 and U_1=13 cm/sec. Note the large excess of high-speed stream fluid in the cores of the structures.", "doi": "10.1017/cbo9780511610820.002", "isbn": "9780511610820", "publisher": "Cambridge University Press", "place_of_publication": "Cambridge", "publication_date": "2004", "pages": "1-10" }, { "id": "authors:6085p-6kn38", "collection": "authors", "collection_id": "6085p-6kn38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130911-134434095", "type": "article", "title": "Leonardo's vision of flow visualization", "author": [ { "family_name": "Gharib", "given_name": "M.", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Kremers", "given_name": "D.", "clpid": "Kremers-D" }, { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Kempe", "given_name": "M.", "clpid": "Kempe-M-D" } ], "abstract": "Leonardo's studies of cardiovascular systems, in more than 50 surviving pages from two phases of his research (around 1508\u20131509 and 1513), are a clear demonstration of his observational genius and progressive deduction of cardiac mechanics and the vascular system. He carried out a detailed hemodynamic study of the aortic valve motion and the role of the Sinus of Valsalva in the closure dynamics of the aortic valve, and he accurately correlated the formation of vortices with the separation of a retarded (shear) layer from the lips of the leaflets. In-vivo verification of vortex formation in the Sinus of Valsalva during the systolic phase awaited the application of modern phase-averaged magnetic resonance imaging techniques. Did Leonardo actually build the glass model he twice mentioned, thus performing the first scientific flow visualization of impulsive vortex formation or other fluid mechanical phenomena? Evidence in support of this possibility can be found in both the unusually schematic style he employed for this suite of drawings and the recent flow imaging results obtained in our laboratory through laser-based imaging techniques.", "doi": "10.1007/s00348-002-0478-8", "issn": "0723-4864", "publisher": "Springer", "publication": "Experiments in Fluids", "publication_date": "2002-07", "series_number": "1", "volume": "33", "issue": "1", "pages": "219-223" }, { "id": "authors:rs7ww-kd377", "collection": "authors", "collection_id": "rs7ww-kd377", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-163232880", "type": "monograph", "title": "Control of Turbulent Mixing Layers", "author": [ { "family_name": "Dimotakis", "given_name": "Paul E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Koochesfahani", "given_name": "Manoochehr M.", "clpid": "Koochesfahani-M-M" } ], "abstract": "This the final report of research conducted at the California Institute of Technology,\nby Paul E. Dimotakis, in collaboration with Dr. M. M. Moochesfahani as co-investigator,\nand with the assistance of Mr. P. Tokumaru during the last year. The primary goal was to\nexplore 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\n\ni. investigate the dynamic behavior and response of these flows through a study of the feedback control schemes required to produce a given desired outcome,\n\nii. 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,\n\nand, \n\niii. devise schemes for producing turbulent shear layer flows with specific desirable properties, as might be dictated, for example, by the flow specifications for the\nefficient operation of a combustion device.\n\nIn the course of this work, other derivative and closely related efforts were also undertaken,\nsome of which will be described below.\n\nThe work conducted under the sponsorship of this Grant was primarily experimental and in close collaboration with a broader experimental, numerical and theoretical effort at\nCaltech to study unsteady separated flows, and the evaluation and use of control techniques\nin these flows in particular.", "doi": "10.7907/w891-xv06", "publisher": "California Institute of Technology", "publication_date": "1989-04-30" }, { "id": "authors:82kpr-gbd13", "collection": "authors", "collection_id": "82kpr-gbd13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-160303422", "type": "article", "title": "Effects of a downstream disturbance on the structure of a turbulent plane mixing layer", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" } ], "abstract": "Using a two-dimensional airfoil, a disturbance was introduced into a plane mixing layer some distance\ndownstream of the splitter plate trailing edge. Results indicate that it is possible to induce very large changes in\nthe layer growth rate downstream of the disturbance location, while leaving the portion of the shear layer\nbetween the splitter plate and the disturbance source essentially unaffected. Furthermore, the use of forcing for\nmodification of the mixing layer in the region upstream of the disturbance is demonstrated. It Is shown that two\ndifferent mechanisms are responsible for coupling such disturbances to the flow in the present forcing of\nupstream and downstream regions.", "issn": "0001-1452", "publisher": "AIAA", "publication": "AIAA Journal", "publication_date": "1989-02", "series_number": "2", "volume": "27", "issue": "2", "pages": "161-166" }, { "id": "authors:dt93k-wpc55", "collection": "authors", "collection_id": "dt93k-wpc55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141027-134908693", "type": "book_section", "title": "A Cancellation Experiment in a Forced Turbulent Shear Layer", "author": [ { "family_name": "Koochesfahani", "given_name": "Manoochehr M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "Paul E.", "clpid": "Dimotakis-P-E" } ], "abstract": "Results are presented which demonstrate that it is possible to cancel, using feedback control techniques, the effects of an externally generated disturbance in a fully-developed turbulent two-dimensional shear layer.", "doi": "10.2514/6.1988-3713", "publisher": "American Institute of Aeronautics and Astronautics", "publication_date": "1988" }, { "id": "authors:a4kwj-dxb56", "collection": "authors", "collection_id": "a4kwj-dxb56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-162151046", "type": "book_section", "title": "Vortical Patterns in the Wake of an Oscillating Airfoil", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" } ], "abstract": "The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low speed water channel. it is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude and also the shape of the oscillation waveform. An important observation in this study has been the existence of an axial flow along the cores of the wake vortices. Estimates of the magnitude of the axial flow suggest a linear dependence on the oscillation frequency and amplitude.", "doi": "10.2514/6.1987-111", "publisher": "AIAA", "publication_date": "1987" }, { "id": "authors:bdxqf-c0k71", "collection": "authors", "collection_id": "bdxqf-c0k71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141020-152728708", "type": "book_section", "title": "Inviscid instability characteristics of free shear layers with non-uniform density", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Frieler", "given_name": "C. E.", "clpid": "Frieler-C-E" } ], "abstract": "The linear spatial instability of two-dimensional two-stream plane mixing layers has been studied extensively in the past. In the case of uniform density, Michalke (1965) investigated the single-stream shear\nlayer and Monkewitz & Huerre (1982) considered the effect of the velocity ratio. Maslowe & Kelly (1971) studied the stratified (non-uniform density) shear layers and showed that density variations can be destabilizing. In all these studies, the mean velocity profile\nhas been assumed to be monotonically increasing from the value on the low-speed stream to that on the high-speed stream and usually the hyperbolic tangent form is used. It should be noted, however, that under experimental conditions the initial mean velocity profile almost\nalways has a wake component due to the boundary layers on the two sides of the splitter plate. The effect of the wake component has only recently come into consideration with the investigations of Miau 1984 and Zhang et al. 1984 for the uniform density case.\n\nThe purpose of the present work is to study the instability\ncharacteristics of both uniform and non-uniform density plane shear layers taking into account the wake component of the initial velocity profile. The inviscid, linear, parallel-flow stability analysis of spatially growing disturbances is utilized to numerically calculate the\nrange of unstable frequencies and wave-numbers.", "doi": "10.2514/6.1987-47", "publisher": "AIAA", "publication_date": "1987" }, { "id": "authors:4z34q-fcf57", "collection": "authors", "collection_id": "4z34q-fcf57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120627-085420456", "type": "article", "title": "Mixing and chemical reactions in a turbulent liquid\n mixing layer", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" } ], "abstract": "An experimental investigation of entrainment and mixing in reacting and non-reacting turbulent mixing layers at large Schmidt number is presented. In non-reacting cases, a passive scalar is used to measure the probability density function (p.d.f.) of the composition field. Chemically reacting experiments employ a diffusion-limited acid\u2013base reaction to directly measure the extent of molecular mixing. The measurements make use of laser-induced fluorescence diagnostics and high-speed, real-time digital image-acquisition techniques. Our results show that the vortical structures in the mixing layer initially roll-up with a large excess of fluid from the high-speed stream entrapped in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but its composition also changes. It is found that the range of compositions of the mixed fluid, above the mixing transition and also throughout the transition region, is essentially uniform across the entire transverse extent of the layer. Our measurements indicate that the probability of finding unmixed fluid in the centre of the layer, above the mixing transition, can be as high as 0.45. In addition, the mean concentration of mixed fluid across the layer is found to be approximately constant at a value corresponding to the entrainment ratio. Comparisons with gas-phase data show that the normalized amount of chemical product formed in the liquid layer, at high Reynolds number, is 50% less than the corresponding quantity measured in the gas-phase case. We therefore conclude that Schmidt number plays a role in turbulent mixing of high-Reynolds-number flows.", "doi": "10.1017/S0022112086000812", "issn": "0022-1120", "publisher": "Cambridge University Press", "publication": "Journal of Fluid Mechanics", "publication_date": "1986-09", "volume": "170", "pages": "83-112" }, { "id": "authors:52dhe-qqs16", "collection": "authors", "collection_id": "52dhe-qqs16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160602-172456643", "type": "article", "title": "Laser-induced fluorescence measurements of mixed fluid concentration in a liquid plane shear layer", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" } ], "abstract": "The processes of entrainment and mixing are investigated in a nonreacting, uniform density, liquid mixing layer. Laser-induced fluorescence diagnostics and high-speed, real-time digital image acquisitions techniques are combined to measure the probability density function of the composition field. Results show that the vortical structures in the mixing layer initially roll up with a large excess of high-speed fluid in the cores. It is found that the mixed fluid composition, above the mixing transition, is essentially uniform across the entire transverse extent of the layer and is asymmetric with a bias in favor of the high-speed fluid. Preliminary observations indicate that the composition of the mixed fluid is more uniform across a liquid shear layer than that in the gaseous layer. The important effect of the resolution capability of the measurement apparatus on the results are discussed and comparisons with recent theoretical calculations are presented.", "doi": "10.2514/3.9154", "issn": "0001-1452", "publisher": "AIAA", "publication": "AIAA Journal", "publication_date": "1985-11", "series_number": "11", "volume": "23", "issue": "11", "pages": "1700-1707" }, { "id": "authors:dtp8n-8w135", "collection": "authors", "collection_id": "dtp8n-8w135", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160602-172732465", "type": "article", "title": "A \"flip\" experiment in a chemically reacting turbulent mixing layer", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Broadwell", "given_name": "J. E.", "clpid": "Broadwell-J-E" } ], "abstract": "An experimental investigation of entrainment and mixing in a reacting, uniform density, liquid plane shear layer has been carried out using laser-induced fluorescence diagnostics. Results indicate that the reactants mix on a molecular level and react at a composition that is nearly uniform across the transverse extent of the layer. The composition of the mixed fluid is found to be asymmetric with an excess of high-speed fluid, suggesting that entrainment into the shear layer is also asymmetric. These results are at variance with predictions of conventional models of turbulent transport and mixing.", "doi": "10.2514/3.9063", "issn": "0001-1452", "publisher": "AIAA", "publication": "AIAA Journal", "publication_date": "1985-08", "series_number": "8", "volume": "23", "issue": "8", "pages": "1191-1194" }, { "id": "authors:2s8bb-64q06", "collection": "authors", "collection_id": "2s8bb-64q06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120718-100125180", "type": "article", "title": "Particle streak velocity field measurements in a two-dimensional mixing layer", "author": [ { "family_name": "Dimotakis", "given_name": "Paul E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Debussy", "given_name": "Francois D.", "clpid": "Debussy-F-D" }, { "family_name": "Koochesfahani", "given_name": "Manoochehr M.", "clpid": "Koochesfahani-M-M" } ], "abstract": "Using digital image processing of particle streak photography, the streamwise and perpendicular components of the velocity field were investigated, in the mid\u2010span plane of a two\u2010dimensional mixing layer, with a 6:1 velocity ratio. The Reynolds number of the flow, based on the local vorticity thickness and the velocity difference across the layer, ranged from 1360 to 2520, in the plane of observation. The significant result of this experiment was that the region of vorticity bearing fluid is confined to a small fraction of the flow. A second finding, consistent with the small regions of concentrated vorticity, was the observation of instantaneous streamwise velocity reversal, in the laboratory frame, in small regions of the flow.", "doi": "10.1063/1.863481", "issn": "1070-6631", "publisher": "American Institute of Physics", "publication": "Physics of Fluids", "publication_date": "1981-06", "series_number": "6", "volume": "24", "issue": "6", "pages": "995-999" }, { "id": "authors:s13xs-d4829", "collection": "authors", "collection_id": "s13xs-d4829", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130911-101642275", "type": "article", "title": "Two-Point LDV Measurements in a Plane Mixing Layer", "author": [ { "family_name": "Koochesfahani", "given_name": "M. M.", "clpid": "Koochesfahani-M-M" }, { "family_name": "Catherasoo", "given_name": "C. J.", "clpid": "Catherasoo-C-J" }, { "family_name": "Dimotakis", "given_name": "P. E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Gharib", "given_name": "M.", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Lang", "given_name": "D. B.", "clpid": "Lang-D-B" } ], "abstract": "Investigations into the nature of the large structures in a two-dimensional shear layer were carried out using\nlaser Doppler velocimetry in the GALCIT free-surface water tunnel. By simultaneous measurements of velocity\nat two points outside the turbulent region, above and below the shear layer, it was possible to measure the\nstrength (total circulation) and location of the vorticity center of the large structures. It was found that structures\nnot in the process of pairing convect downstream with the center of their cores close to the ray y/x along which\nthe mean velocity is given by U_m = l/2(U_1 + U_1 ). The determined value of the mean circulation is consistent with\nthe independent measurements of the mean spacing between the structures. Results indicate that if the large\nstructure vorticity distribution is elliptical, the inclination angle of its axis of symmetry with respect to the now\ndirection is small.", "issn": "0001-1452", "publisher": "AIAA", "publication": "AIAA Journal", "publication_date": "1979-12", "series_number": "12", "volume": "17", "issue": "12", "pages": "1347-1351" } ]