Book Section records
https://feeds.library.caltech.edu/people/Bae-Hyunji-Jane/book_section.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenMon, 27 Nov 2023 17:37:15 +0000Numerical scale separation in large-eddy simulation
https://resolver.caltech.edu/CaltechAUTHORS:20210326-095748691
Authors: Verstappen, R. W. C. P.; Rozema, W.; Bae, H. J.
Year: 2014
Large-eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The essence of a scale-separation LES model is that it stops the nonlinear
production of smaller scales of motion at the scale set by the filter: there the modeled
eddy dissipation has to balance the production. Numerical discretization changes both
the nonlinear production and dissipation of sub-filter scales. Therefore, the discrete balance between production and dissipation can deviate from the continuous balance, in
particular if a balance is imposed near the scale set by the numerical grid. This paper
demonstrates that a scale-separation LES model should attain a production-dissipation
balance in the numerical setting. Eddy-viscosity models based on this requirement are
derived and successfully applied in simulations of decaying isotropic turbulence and channel flow.https://authors.library.caltech.edu/records/dds0a-cgz43A low-cost time-advancing strategy for energy-preserving turbulent simulations
https://resolver.caltech.edu/CaltechAUTHORS:20210325-145350953
Authors: Capuano, F.; Coppola, G.; Balarac, G.; Bae, H. J.; de Luca, L.
Year: 2014
Energy-conserving discretizations are widely regarded as a fundamental requirement
for high-fidelity simulations of turbulent flows. The skew-symmetric splitting of the non-
linear term is a well-known approach to obtain semi-discrete conservation of energy in
the inviscid limit. However, its computation is roughly twice as expensive as that of the
divergence or advective forms alone. A novel time-advancement strategy that retains the
conservation properties of skew-symmetric-based schemes at a reduced computational
cost has been developed. This method is based on properly constructed Runge-Kutta
schemes in which a different form (advective or divergence) for the convective term is
adopted at each stage. A general framework is presented to derive schemes with prescribed accuracy on both solution and energy conservation. Simulations of homogeneous
isotropic turbulence show that, on equal results, the new procedure can be considerably
faster than skew-symmetric-based techniques.https://authors.library.caltech.edu/records/fbeny-5mv56Exploring nonlinear subgrid-scale models and new characteristic length scales for large-eddy simulation
https://resolver.caltech.edu/CaltechAUTHORS:20210315-110422387
Authors: Silvis, M. H.; Trias, F. X.; Abkar, M.; Bae, H. J.; Lozano-Durán, A.; Verstappen, R. W. C. P.
Year: 2016
We study subgrid-scale modeling for large-eddy simulation of anisotropic turbulent flows on anisotropic grids.
In particular, we show how the addition of a velocity-gradient-based nonlinear model term to an eddy viscosity model provides a better representation of energy transfer.
This is shown to lead to improved predictions of rotating and nonrotating homogeneous isotropic turbulence.
%We furthermore show that spanwise-rotating turbulent plane-channel flows form a challenging test case for large-eddy simulation.
Our research further focuses on calculation of the subgrid characteristic length, a key element for any eddy viscosity model.
In the current work, we propose a new formulation of this quantity based on a Taylor series expansion of the subgrid stress tensor in the computational space.
Numerical tests of decaying homogeneous isotropic turbulence and a plane-channel flow illustrate the robustness of this flow-dependent characteristic length scale with respect to mesh anisotropy.https://authors.library.caltech.edu/records/6km8j-c4p73Regularity diagnostics applied to a turbulent boundary layer
https://resolver.caltech.edu/CaltechAUTHORS:20210322-152610635
Authors: Bae, H. J.; Gibbon, J. D.; Kerr, R. M.; Lozano-Durán, A.
Year: 2018
Regularity diagnostics for the Navier-Stokes equations based on rescaled high-order
vorticity moments are applied to direct numerical simulation (DNS) of plane turbulent
channel flow and calculations of high-Reynolds-number vortex reconnection. At the
wall-normal height typical of the tips of hairpin vortices, the temporal evolution of the
vorticity moments is qualitatively similar to that of controlled high-Reynolds-number
vortex reconnection in the absence of walls. Both the channel flow and vortex reconnection
data exhibit higher measure of vorticity than previous results from decaying and
forced isotropic turbulence. This allows for future analysis of vortex dynamics based on
new results detailing the vorticity and helicity dynamics of reconnection events.https://authors.library.caltech.edu/records/kqytt-tjs48Studying the effect of wall cooling in supersonic boundary layer flow using resolvent analysis
https://resolver.caltech.edu/CaltechAUTHORS:20200113-074130443
Authors: Bae, Hyunji Jane; Dawson, Scott T.; McKeon, Beverley J.
Year: 2020
DOI: 10.2514/6.2020-0575
Analysis of the resolvent operator is used to study the properties of high-speed turbulent boundary layers for cooled walls. Previous study [1] shows that the resolvent response modes in the relatively subsonic region of high-speed turbulent boundary layers with adiabatic wall boundary conditions follow the same scaling law as those of the incompressible boundary layer case, validating Morkovin's hypothesis on a mode-by-mode basis. Here, we study the effect of the cooled-wall boundary condition on the individual resolvent response modes to understand the underlying mechanisms that cause the failure of Morkovin's hypothesis and velocity transformations for increasingly non-adiabatic walls. In particular, we show that the density and temperature resolvent mode shapes for the cooled-wall case exhibit a secondary peak in the inner and logarithmic layer, which is a result of the non-monotonic mean temperature profile that is absent in adiabatic cases. We also show that the secondary peak becomes more prominent with decreasing surface temperature ratio. The deviation of the mean velocity profiles is attributed to the change in the response modes in the near-wall region, the effect of which is propagated further away from the wall through nonlinear interactions.https://authors.library.caltech.edu/records/xcxb2-wba52Wavelet-based resolvent analysis for statistically-stationary and temporally-evolving flows
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902843000.16
Authors: Ballouz, Eric; Lopez-Doriga, Barbara; Dawson, Scott T. M.; Bae, Hyunji Jane
Year: 2023
DOI: 10.2514/6.2023-0676
This work introduces a formulation of resolvent analysis that uses wavelet transforms rather than Fourier transforms in time. This allows resolvent analysis to be extended to turbulent flows with non-stationary means in addition to statistically-stationary flows. The optimal resolvent modes for this formulation correspond to the potentially time-transient structures that are most amplified by the linearized Navier-Stokes operator. We validate this methodology for turbulent channel flow and show that the wavelet-based and Fourier-based resolvent analyses are equivalent for statistically-stationary flows. We then apply the wavelet-based resolvent analysis to study the transient growth mechanism in the buffer layer of a turbulent channel flow by windowing the resolvent operator in time and frequency. The method is also applied to temporally-evolving parallel shear flows such as an oscillating boundary layer and three-dimensional channel flow, in which a lateral pressure gradient perturbs a fully-developed turbulent flow in a channel.https://authors.library.caltech.edu/records/ee50k-ns830A sparsity-promoting resolvent analysis for the identification of spatiotemporally-localized amplification mechanisms
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902835000.15
Authors: Lopez-Doriga, Barbara; Ballouz, Eric; Bae, Hyunji Jane; Dawson, Scott T. M.
Year: 2023
DOI: 10.2514/6.2023-0677
This work introduces a variant of resolvent analysis that identifies forcing and response modes that are sparse in both space and time. This is achieved through the use of a sparse principal component analysis (PCA) algorithm, which formulates the associated optimization problem as a nonlinear eigenproblem that can be solved with an inverse power method. We apply this method to parallel shear flows, both in the case where we assume Fourier modes in time (as in standard resolvent analysis) and obtain spatial localization, and where we allow for temporally-sparse modes through the use of a linearized Navier--Stokes operator discretized in both space and time. Appropriate choice of desired mode sparsity allows for the identification of structures corresponding to high amplification that are localized in both space and time. We report on the similarities and differences between these structures and those from standard methods of analysis. After validating this space-time resolvent analysis on statistically-stationary channel flow, we next implement the methodology on a time-periodic Stokes boundary layer, demonstrating the applicability of the approach to non-statistically-stationary systems.https://authors.library.caltech.edu/records/1s2nv-jcw28