Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X31: Compressible Instabilities and Turbulence |
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Chair: Salvador Gomez, Center for Turbulence Research Room: 255 C |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X31.00001: Mixing dynamics in two-dimensional acceleration-driven compressible flow Hutson Staggs, Ahmet F Kula, Denis Aslangil The coupled effects of variable density (VD) and flow compressibility on the externally accelerated two-dimensional system are studied with direct numerical simulations (DNS). In this flow configuration, columns of two pure fluids are initially separated by two randomly perturbed thin interfaces parallel to the acceleration field within a neutrally stratified fluid domain with periodic boundary conditions. The fully compressible, multi-species Navier–Stokes equations are solved at various Atwood numbers and isothermal Mach numbers to study the VD effects on compressible acceleration-driven flow. Atwood number represents the normalized molar mass ratio between the mixing fluids, such that a higher number corresponds to a greater difference in molar mass between the mixing fluids. The background isothermal Mach number controls the flow compressibility and is proportional to the square root of the magnitude of the external acceleration field. It is observed that an increase in flow compressibility leads to a slower growth of the shear layer, with this effect becoming more pronounced as the Atwood number increases. In this talk, we will compare the evolution of the shear layer growth, molecular mixing, and enstrophy of the flow for the different DNS cases. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X31.00002: Coupled effects of variable density and isothermal background stratification on vorticity and mixing dynamics of compressible Rayleigh--Taylor instability Orkun Mert Ustun, Man Long Wong, Denis Aslangil Rayleigh-Taylor instability (RTI) occurs at the perturbed interface between fluids with different densities, where the acceleration and density gradient are in opposite directions. RTI is observed in natural flows, such as atmospheric and geological flows, and in engineering applications, such as the mixing stage of ramjets and scramjets and Inertial Confinement Fusion (ICF). We study the coupled effects of compressibility controlled by the isothermal background stratification strength and large molar mass differences between the mixing fluids through Direct Numerical Simulations (DNS) of the two-dimensional, single-mode RTI by solving fully compressible multi-species Navier-Stokes equations. From the low Atwood number cases, it is observed that when the molar mass ratio between the mixing fluids is small, the growth of the mixing layer ceases, and the flow becomes molecularly well-mixed as the background stratification increases. However, our high Atwood number simulations suggest that when the molar mass ratio between the mixing fluids is large, there is a more complex flow evolution where a stronger background stratification leads to a relatively faster mixing growth rate, but it also suppresses the vortical structures within the mixing layer. In addition to the overall flow evolution, we will compare each term of the vorticity transport equation for the low and high Atwood number cases under weak and strong background stratifications at different time instants. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X31.00003: Abstract Withdrawn
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Tuesday, November 26, 2024 8:39AM - 8:52AM |
X31.00004: Analysis of a transonic laminar shock buffet system using a large-eddy simulation Hang Song, Man Long Wong, Aditya S Ghate, Sanjiva K Lele A wall-resolved large-eddy simulation (LES) of transonic shock buffet on the OALT25 supercritical laminar airfoil is configured at a 4-degree angle-of-attack in a Mach 0.735 freestream. The chord-length-based Reynolds number is 1 million. The simulation was conducted using sixth-order compact finite difference methods with an explicit subgrid-scale model and hybrid central-Riemann fluxes for shock-capturing. The data from the LES used for analysis is collected over a range of 260 convective time units at the statistically stationary state. The extended laminar boundary layer, flow separation, transition-to-turbulence, turbulent vortex shedding, and propagation of acoustic waves are well resolved. Signal processing shows that the oscillation of the lift and drag coefficients are dominated by the shock buffet and turbulent vortex shedding at Strouhal numbers of approximately 0.1 and 0.55 respectively. The spectral proper orthogonal decomposition (SPOD) analysis indicates that the flow system exhibits low-rank behavior at the two frequencies. The principal unsteady flow and wave features can be identified from the first SPOD mode at the peak frequencies, and several feedback paths are observed. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X31.00005: Supercritical flow dynamics and mixing of transverse jets Siyu Ding, Jiabin Li, Longfei Wang, Xingjian Wang The present study investigates the flow dynamics of a dodecane jet in crossflow at supercritical pressures, conditions typical of advanced combustors, using large-eddy simulation. The effects of various parameters, including pressure, jet-to-crossflow momentum flux ratios (J), and jet nozzle elevation, on the flow structures and stability characteristics are explored in detail. The results show the supercritical flow dynamics differ substantially from their subcritical counterparts. At a given J of 7.1, the jet's upstream shear layer is absolutely unstable at high supercritical pressure but becomes convectively unstable at low supercritical pressure. Such behavior can be attributed to the intensified real-fluid effect at low supercritical pressure, where the inflection of density variation in the mixing layer creates large density gradients to stabilize the shear layer. Elevating the jet nozzle with a stack alters the jet and crossflow mixing efficiency by introducing intricate interactions between jet and stack wake regions. An analysis of spatial mixing deficiencies demonstrates that incorporating an elevation stack with proper thickness and height can dramatically improve the jet-crossflow mixing efficiency. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X31.00006: Linear disturbance transport and amplification on a hypersonic cone to assess tunnel noise contamination effects on transition Tim J Flint, Parviz Moin Boundary-layer transition measurements in hypersonic wind tunnels are contaminated by noise generated on the tunnel walls which prescribe the free-stream disturbance environment. The level and nature of the free-stream disturbances seen in flight necessarily differs from that in the tunnel, making computational or theoretical estimates necessary. This talk aims to identify how different kinds of disturbances in the free-stream can be transported and amplified, linearly, to a nominal transition location. The Green’s function of the adjoint equations provides insight to the transport of arbitrary free-stream disturbance in a cost-effective way. The results identify the transition location’s domain of dependence and what kinds of disturbances are most effectively received from the free-stream. The Green’s function is used to compute the response in the boundary layer to notional tunnel and flight disturbance environments to compare transition in flight vs that in a tunnel. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X31.00007: Comparative assessment of Global Linear Stability of continuum and kinetic-theory-obtained flows on Short Compression Ramps Vojtech Pezlar, IRMAK TAYLAN KARPUZCU, Vassilis Theofilis, Deborah A. Levin The global linear stability of supersonic flows over short compression ramps was investigated using a continuum-based finite volume solver and BiGlobal modal stability theory. Navier-Stokes-based steady laminar baseflows were obtained at the conditions discussed by Karpuzcu et al. (DOI:arXiv.2405.06775) who used direct simulation Monte Carlo (DSMC) methods at low Knudsen numbers (O(1E-4)).. The respective baseflows show a <4% difference outside of shear-layer and LE shock. The shock and shear layer region has significant differences, mainly in the vertical velocity component. Global stability analysis was performed using a novel Curvilinear Multi-Domain method to discretize the post-ramp region for the first time, and the eigenvalue problem was solved using high-order finite difference schemes.A comparison of the 3D global modes of both continuum-based and particle-based baseflows was conducted. The converged spectra show good agreement within 1% for the leading stationary "C-shape" mode, while comparisons of the Leading Edge mode will be shown at the time of the conference. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X31.00008: High-fidelity numerical simulations of transitional supersonic boundary layers over sinusoidal roughness elements Aishwarya Krishnan, Ivan Bermejo-Moreno As space vehicles enter a planet’s atmosphere at hypersonic speeds, they decelerate due to increasing atmospheric density, leading to increased drag and heat flux on the surface. This heat flux causes the thermal protection system (TPS) to ablate, resulting in surface roughness elements whose sizes and shapes depend on flight conditions and TPS materials (Berry & Horvath, 2008). The surface roughness can disturb the mean flow, leading to a transitional boundary layer that adversely affects aerodynamic performance and structural integrity (Hollis, 2021). This study focuses on high-fidelity numerical simulations of transitional flow over a surface with sinusoidal roughness in both the streamwise and spanwise directions to predict friction and heat flux coefficients in a supersonic transitional boundary layer at Mach 3 and ReΘ ≈ 5000 . Inspired by Muppidi & Mahesh (2012), we extend the surface roughness to the end of the domain and study the effects of varying the ratio of roughness height to boundary layer thickness, mean curvature mimicking blunt body reentry vehicles, and inflow conditions. This research aids in understanding transitional boundary layers due to surface roughness and helps improve the design and performance of the TPS in high-speed reentry vehicles. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X31.00009: Non-equilibrium three-dimensional supersonic boundary layers Salvador Rey Gomez Studies on compressible, wall-bounded turbulent flows largely focus on canonical two-dimensional flows, like boundary layers and channels. In this work, the results of direct numerical simulations of a compressible turbulent channel flow subjected to sudden spanwise pressure gradients at different initial Reynolds and Mach numbers are presented. This study focuses on the transient response during which the channel exhibits three-dimensionality in the mean statistics. During this transient the turbulent kinetic energy decreases, consistent with previous observations in incompressible flow (Lozano-Duran, A., et. al. (2019), Moin, P. et. al. (1990)). The temperature fluctuations also decrease, despite the net increase in the mean temperature. For large spanwise to streamwise pressure gradient ratios, a non-monotonic mean temperature can be observed that creates a positive correlation between the wall-parallel velocities and the temperature fluctuations near the wall and a negative correlation away from the wall. For smaller ratios, the mean temperature is monotonic, and this correlation is positive across the channel. The behavior in the turbulent fluctuations can be explained by tracking the production terms in the kinetic energy, Reynolds stress, and velocity-temperature variance evolution equations. Finally, the validity of Morkovin's hypothesis in this temporal-three-dimensional flow will also be assessed through comparisons with the corresponding incompressible regime. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X31.00010: Transition control of hypersonic boundary layer through non-uniform surface temperature distribution Luca Boscagli, Georgios Rigas, Paul Bruce, Olaf Marxen The location point of laminar to turbulent transition in hypersonic boundary layers has a significant influence on viscous drag and aerodynamic heating of external surfaces of hypersonic vehicles. This is a dominant source of uncertainties during the design process, and it motivates further research on transition control. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X31.00011: DNS of supersonic turbulent boundary layers over rough surfaces Michele Cogo, Davide Modesti, Matteo Bernardini, Francesco Picano Surface roughness effects can significantly alter the mechanical and thermal loads applied on high-speed vehicles. Different superficial treatments can lead to the formation of smooth and rough regions, to which the incoming flow is forced to adjust. In this study, we present direct numerical simulations of smooth and rough zero-pressure-gradient adiabatic turbulent boundary layers at Mach numbers 0.3 and 2, enabling a direct comparison between supersonic and subsonic regimes. The geometry is composed of an initial smooth surface that is followed by a rough wall composed of 3D cubical elements, a structured and well-characterized arrangement. The interaction between compressibility and surface roughness, clearly visible with a pattern of compression and expansion waves, is analyzed considering its implication in turbulence and thermal statistics of the flow. The streamwise adjustment of the turbulent flow to the rough surface is then characterized by assessing the growth of an internal boundary layer (IBL). Preliminary analysis shows profound differences in the outer layer similarity of kinetic and thermal fields with reference smooth cases, as well as the need for more suitable definitions to characterize IBL growth when compressibility effects are present. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X31.00012: ABSTRACT WITHDRAWN
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