Dynamics of a supersonic transitional flow over a backward-facing step
W. Hu, S. Hickel, B.W. van Oudheusden (2019)
Phys. Rev. Fluids 4, 103904. doi: 10.1103/PhysRevFluids.4.103904
The transition mechanism and unsteady behavior behind a backward-facing step (BFS) in the supersonic regime at Ma = 1.7 and Reδ = 13718 is investigated using large-eddy simulation (LES). The visualization of the flow field shows that the transition process behind the step is initiated by a Kelvin-Helmholtz (K-H) instability of the separated shear layer, followed by secondary modal instabilities of the K-H vortices, leading to lambda-shaped vortices, hair-pin vortices and finally to a fully turbulent state.
A priori investigations into the construction and the performance of an explicit algebraic subgrid-scale stress model
A.K. Gnanasundaram, T. Pestana, S. Hickel (2019)
11th International Symposium on Turbulence and Shear Flow Phenomena. TSFP paper 2019-286
We investigate the underlying assumptions of Explicit Algebraic Subgrid-Scale Models (EASSMs) for Large- Eddy Simulations (LESs) through an a priori analysis using data from Direct Numerical Simulations (DNSs) of homogeneous isotropic and homogeneous rotating turbulence. We focus on the performance of three models: the dynamic Smagorinsky (DSM) and the standard and dynamic explicit algebraic models as in Marstorp et al. (2009), here refereed to as SEA and DEA.
A one equation explicit algebraic subgrid-scale stress model
S. Hickel, A.K. Gnanasundaram, T. Pestana (2019)
11th International Symposium on Turbulence and Shear Flow Phenomena. TSFP paper 2019-275
Nonlinear Explicit Algebraic Subgrid-scale Stress Models (EASSMs) have shown high potential for Large Eddy Simulation (LES) of challenging turbulent flows on coarse meshes. A simplifying assumption made to enable the purely algebraic nature of the model is that the Subgrid-Scale (SGS) kinetic energy production and dissipation are in balance, i.e., P/ε = 1. In this work, we propose an improved EASSM design that does not involve this pre-calibration and retains the ratio P~ε as a space and time dependent variable.
Regime transition in the energy cascade of rotating turbulence
T. Pestana, S. Hickel (2019)
Phys. Rev. E 99, 053103. doi: 10.1103/PhysRevE.99.053103
Transition from a split to a forward kinetic energy cascade system is explored in the context of rotating turbulence using direct numerical simulations with a three-dimensional isotropic random force uncorrelated with the velocity field. Our parametric study covers confinement effects in high-aspect-ratio domains and a broad range of rotation rates.
Effectivity and efficiency of selective frequency damping for the computation of unstable steady-state solutions
J. Casacuberta, K.J. Groot, H.J. Tol, S. Hickel (2018)
Journal of Computational Physics 375: 481-497. doi: 10.1016/j.jcp.2018.08.056
Selective Frequency Damping (SFD) is a popular method for the computation of globally unstable steady-state solutions in fluid dynamics. The approach has two model parameters whose selection is generally unclear. In this article, a detailed analysis of the influence of these parameters is presented, answering several open questions with regard to the effectiveness, optimum efficiency and limitations of the method.
Turbulent flow through a high aspect ratio cooling duct with asymmetric wall heating
Kaller, T., Pasquariello, V., Hickel, S., Adams, N.A. (2019)
Journal of Fluid Mechanics 860: 258-299. doi: 10.1017/jfm.2018.836
We present well-resolved large-eddy simulations of turbulent flow through a straight, high aspect ratio cooling duct operated with water at a bulk Reynolds number of Reb = 110 000 and an average Nusselt number of Nu = 371. The geometry and boundary conditions follow an experimental reference case and good agreement with the experimental results is achieved.
Multi-component vapor-liquid equilibrium model for LES of high-pressure fuel injection and application to ECN Spray A
J. Matheis, S. Hickel (2018)
International Journal of Multiphase Flow 99: 294-311. doi: 10.1016/j.ijmultiphaseflow.2017.11.001
We present and evaluate a two-phase model for Eulerian large-eddy simulations (LES) of liquid-fuel injection and mixing at high pressure. The model is based on cubic equations of state and vapor-liquid equilibrium calculations and can represent the coexistence of supercritical states and multi-component subcritical two-phase states via a homogeneous mixture approach.
Unsteady effects of strong shock-wave/boundary-layer interaction at high Reynolds number
V. Pasquariello, S. Hickel, N.A. Adams (2017)
Journal of Fluid Mechanics 828: 617-657. doi: 10.1017/jfm.2017.308
We analyse the low-frequency dynamics of a high Reynolds number impinging shock-wave/turbulent boundary-layer interaction (SWBLI) with strong mean-flow separation. The flow configuration for our grid-converged large-eddy simulations (LES) reproduces recent experiments for the interaction of a Mach 3 turbulent boundary layer with an impinging shock that nominally deflects the incoming flow by 19.6° . The Reynolds number based on the incoming boundary-layer thickness of Reδ ≈ 203 000 is considerably higher than in previous LES studies.
Three-dimensional reacting shock-bubble interaction
F. Diegelmann, S. Hickel, N.A. Adams (2017)
Combustion and Flame 181: 1339-1351. doi: 10.1016/j.combustflame.2017.03.026
We investigate a reacting shock–bubble interaction through three-dimensional numerical simulations with detailed chemistry. The convex shape of the bubble focuses the shock and generates regions of high pressure and temperature, which are sufficient to ignite the diluted stoichiometric H2-O2 gas mixture inside the bubble. We study the interaction between hydrodynamic instabilities and shock-induced reaction waves at a shock Mach number of Ma = 2.83.
Large-eddy simulation of turbulent, cavitating flow inside a 9-hole Diesel injector including needle movement
F. Örley, S. Hickel, S.J. Schmidt, N.A. Adams (2017)
International Journal of Engine Research 18:195-211. doi: 10.1177/1468087416643901
We investigate the turbulent multiphase flow inside a nine-hole common rail Diesel injector during a full injection cycle of ISO 4113 diesel fuel into air by implicit large-eddy simulation (LES). The simulation includes a prescribed needle movement obtained from a one-dimensional multi-domain simulation.
Multi-component vapor-liquid equilibrium model for LES and application to ECN Spray A
J. Matheis, S. Hickel (2016)
Proceedings of the 2016 Summer Program, Center for Turbulence Research, Stanford University. (also available online on arXiv:1609.08533)
We present and evaluate a detailed multi-species two-phase thermodynamic equilibrium model for large-eddy simulations (LES) of liquid-fuel injection and mixing at high pressure. The model can represent the coexistence of supercritical states and multi-component subcritical two-phase states.
Large-eddy simulation of nitrogen injection at trans- and supercritical conditions
H. Müller, C. Niedermeier, J. Matheis, M. Pfitzner, S. Hickel (2016)
Physics of Fluids 28: 015102. doi: 10.1063/1.4937948
Large-eddy simulations (LES) of cryogenic nitrogen injection into a warm environment at supercritical pressure are performed and real-gas thermodynamics models and subgrid-scale (SGS) turbulence models are evaluated. The comparison of different SGS models — the Smagorinsky model, the Vreman model, and the adaptive local deconvolution method — shows that the representation of turbulence on the resolved scales has a notable effect on the location of jet break-up, whereas the particular modeling of unresolved scales is less important for the overall mean flow field evolution. More important are the models for the fluid’s thermodynamic state.
Shock Mach number influence on reaction wave types and mixing in reactive shock-bubble interaction
F. Diegelmann, S. Hickel, N.A. Adams (2016)
Combustion and Flame 174: 85-99. doi: 10.1016/j.combustflame.2016.09.014
We present numerical simulations for a reactive shock–bubble interaction with detailed chemistry. The convex shape of the bubble leads to shock focusing, which generates spots of high pressure and temperature. Pressure and temperature levels are sufficient to ignite the stoichiometric H2–O2 gas mixture. Shock Mach numbers between Ma = 2.13 and Ma = 2.90 induce different reaction wave types (deflagration and detonation).
On the pressure dependence of ignition and mixing in two-dimensional reactive shock-bubble interaction
F. Diegelmann, V. Tritschler, S. Hickel, N.A. Adams (2016)
Combustion and Flame 163:414-426. doi: 10.1016/j.combustflame.2015.10.016
We analyse results of numerical simulations of reactive shock-bubble interaction with detailed chemistry. The interaction of the Richtmyer–Meshkov instability and shock-induced ignition of a stoichiometric H2-O2 gas mixture is investigated. Different types of ignition (deflagration and detonation) are observed at the same shock Mach number of Ma = 2.30 upon varying initial pressure.
Efficient implicit LES method for the simulation of turbulent cavitating flows
C.P. Egerer, S.J. Schmidt, S. Hickel, N.A. Adams (2016)
Journal of Computational Physics 316: 453-469. doi: 10.1017/10.1016/j.jcp.2016.04.021
We present a numerical method for efficient large-eddy simulation of compressible liquid flows with cavitation based on an implicit subgrid-scale model. Phase change and subgrid-scale interface structures are modeled by a homogeneous mixture model that assumes local thermodynamic equilibrium. Unlike previous approaches, emphasis is placed on operating on a small stencil (at most four cells).
A cut-cell finite volume-finite element coupling approach for fluid-structure interaction in compressible flow
V. Pasquariello, G. Hammerl, F. Örley, S. Hickel, C. Danowski, A. Popp, W.A. Wall, N.A. Adams (2016)
Journal of Computational Physics 307: 670-695. doi: 10.1016/j.jcp.2015.12.013
We present a loosely coupled approach for the solution of fluid–structure interaction problems between a compressible flow and a deformable structure. The method is based on staggered Dirichlet–Neumann partitioning. The interface motion in the Eulerian frame is accounted for by a conservative cut-cell Immersed Boundary method. The present approach enables sub-cell resolution by considering individual cut-elements within a single fluid cell, which guarantees an accurate representation of the time-varying solid interface.