10:30
Reacting and compressible flows 2
Chair: Martin Oberlack
10:30
15 mins
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Incorporation of acceleration effects into the one-dimensional-turbulence model, with application to turbulent combustion and shock-turbulence interactions.
Zoltan Jozefik, Alan R. Kerstein, Heiko Schmidt
Abstract: One-dimensional turbulence (ODT) is a stochastic simulation in which 3D turbulence effects are captured on a notional 1D line of sight by introducing instantaneous spatial re-arrangements (maps) that represent advection by notional turbulent eddies. These eddy events incorporate the possibility of kinetic-energy changes that are equal and opposite to changes of other forms of energy such as the gravitational potential energy change due to a re-arrangement of a vertical density profile. This illustrates that motion aligned with an applied force, in this case gravitation $g$, can be associated with energy change. Using this principle, we 1) present a model of turbulence interaction with the dilatational acceleration caused by thermal expansion in flames and show results for a turbulent counterflow flame with comparison to DNS and 2) present a model for shock-induced turbulence and show results for mixing width growth in a shock tube with comparison to experiments.
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10:45
15 mins
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Numerical simulation of Dense Gas Compressible Homogeneous Isotropic Turbulence
Luca Sciacovelli, Paola Cinnella
Abstract: The decay of compressible homogeneous isotropic turbulence for dense gases is studied by means of Direct Numerical Simulations and Implicit Large Eddy Simulations. A family of heavy fluorocarbons, which exhibit non-classical phenomena, is considered. The thermodynamic behavior of the fluids is modeled by the politropic Van der Waals or the five-term Virial Martin-Hou equations of state, and the results are compared to those obtained for a thermally and calorically perfect gas.
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11:00
15 mins
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Explicit algebraic and differential Reynolds stress model application to homogeneously sheared and compressed turbulence
Igor A. Grigoriev, Stefan Wallin, Geert Brethouwer, Arne V. Johansson
Abstract: An explicit algebraic and differential Reynolds stress models (EARSM and DRSM) are used to investigate the influence of homogeneous shear and compression on the behaviour of turbulence in the limit of rapid distortion theory (RDT). EARSM is shown to give realizable results and to preserve RDT regime, unlike the eddy-viscosity model (EVM). The DRSM version of our model is in reasonable agreement with RDT theory.
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11:15
15 mins
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Shadowgraphy of the end-effects regime produced by clustered rockets
Andres Canchero, Raymundo Rojo, Charles Tinney, Nathan Murray, Joseph Ruf
Abstract: The plume produced by a cluster of two high area-ratio thrust optimized parabolic contour nozzles is visualized by way of retroreflective shadowgraphy. Both steady and transient operations of the nozzles (start-up and shut-down) were conducted in the anechoic chamber and high speed flow facility at The University of Texas at Austin. Both nozzles exhibit free shock separated flow, restricted shock separated flow and an end-effects-regime prior to flowing full. Radon transforms of the shadowgraphy images are used to identify the locations in the flow where sound waves are being generated. During these off design operations of the nozzles, most sound waves are generated by turbulence interactions with the shock cells located in the supersonic annular plume. During the end-effects-regime, this supersonic annular plume is shown to flap violently, thus providing a first principals understanding of the sources of most intense loads during engine ignition.
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11:30
15 mins
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DNS of turbulent mixing layers with variable density
Antonio Almagro, Oscar Flores, Manuel García-Villalba
Abstract: We present some preliminary results of direct numerical simulations of three-dimensional, temporal, plane mixing layers with variable density. The simulations are run with a parallel in-house code that solves the Navier-Stokes equations in the Low-Mach number approximation, using a novel algorithm based on an extended version of the velocity-vorticity formulation used by Kim, Moin & Moser (1987) for incompressible flows.
The simulations are run with Pr=0.7 and achieve Re_lambda=90-110 during the self-similar evolution of the mixing layer. Four cases with density ratios s=1,2,4 and 8 are presented. Our results show good agreement with previous experimental and numerical studies, and allow us to characterize the scales in the temperature spectra.
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11:45
15 mins
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Statistics of the subgrid scales after the shock-turbulence interaction
Daniel Livescu, Zhaorui Li
Abstract: The interaction of a normal shock with isotropic turbulence (IT) represents a basic problem for studying some of the phenomena associated with high speed flows, such as hypersonic flight, supersonic combustion and Inertial Confinement Fusion (ICF). In general, in practical applications, the shock width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS)
(Ryu and Livescu, J. Fluid Mech., 756, R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). By using LIA to alleviate the need to solve the shock, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here,
such results with Taylor Reynolds number around $180$ are used to investigate the properties of the subgrid scales (SGS). In particular, it is shown that the shock interaction decreases the asymmetry of the SGS dissipation PDF as the shock Mach number increases, with a significant enhancement in size of the regions and magnitude of backscatter.
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12:00
15 mins
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Symmetry analysis in linear compressible hydrodynamic stability theory
Jan-Niklas Hau, Martin Oberlack
Abstract: We present a unifying solution framework for the linearized gas-dynamical equations for a two-dimensional (2-D) linearly-sheared unbounded homentropic compressible flow using Lie symmetry classification. The full set of symmetries that are admitted by the underlying system of equations are employed to systematically derive three distinct invariant Ansatz functions, which unify the existing ones for normal mode, Kelvin mode analysis, as well as a novel approach. The latter approach considers modes that are localized in the cross-stream and periodic in the streamwise direction and travel on parabola shaped curves at constant velocity in the cross-stream, while being accelerated constantly in streamwise direction by the underlying base flow.
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