LES of an asymmetrically heated high aspect ratio duct at high reynolds number at different wall temperatures

We present the results of well-resolved large-eddy simulations (LES) of an asymmetrically heated high aspect ratio cooling duct (HARCD) with an aspect ratio of AR = 4.3 for two different wall temperatures. The temperature difference with respect to the bulk flow is ∆T = 40 K, respectively ∆T = 60 K. The HARCD is operated with liquid water at a Reynolds number of Reb = 110 ⋅ 103 based on bulk velocity and hydraulic diameter. The generic HARCD setup follows a reference experiment. The main goal of the present study is the numerical investigation of the interaction of turbulent heat transfer and the turbulent duct flow, specifically the heating induced changes in mean flow and turbulent statistics with a spatially developing temperature boundary layer. Furthermore, we investigate the influence of asymmetric wall heating on streamwise vorticity and its dynamics as well as the turbulent Prandtl number and the effect of the secondary flow on its distribution.Aerodynamic

Unsteady effects of strong shock-wave/boundary-layer interaction at high Reynolds number

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. The Reynolds number based on the incoming boundary-layer thickness of is considerably higher than in previous LES studies. The very long integration time of allows for an accurate analysis of low-frequency unsteady effects. Experimental wall-pressure measurements are in good agreement with the LES data. Both datasets exhibit the distinct plateau within the separated-flow region of a strong SWBLI. The filtered three-dimensional flow field shows clear evidence of counter-rotating streamwise vortices originating in the proximity of the bubble apex. Contrary to previous numerical results on compression ramp configurations, these Görtler-like vortices are not fixed at a specific spanwise position, but rather undergo a slow motion coupled to the separation-bubble dynamics. Consistent with experimental data, power spectral densities (PSD) of wall-pressure probes exhibit a broadband and very energetic low-frequency component associated with the separation-shock unsteadiness. Sparsity-promoting dynamic mode decompositions (SPDMD) for both spanwise-averaged data and wall-plane snapshots yield a classical and well-known low-frequency breathing mode of the separation bubble, as well as a medium-frequency shedding mode responsible for reflected and reattachment shock corrugation. SPDMD of the two-dimensional skin-friction coefficient further identifies streamwise streaks at low frequencies that cause large-scale flapping of the reattachment line. The PSD and SPDMD results of our impinging SWBLI support the theory that an intrinsic mechanism of the interaction zone is responsible for the low-frequency unsteadiness, in which Görtler-like vortices might be seen as a continuous (coherent) forcing for strong SWBLI.Aerodynamic

Three-dimensional reacting shock–bubble interaction

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. The chosen shock strength ignites the gas mixture before the shock-focusing point, followed by a detonation wave, which propagates through the entire bubble gas. The reaction wave has a significant influence on the spatial and temporal evolution of the bubble. The misalignment of density and pressure gradients at the bubble interface, caused by the initial shock wave and the subsequent detonation wave, induces Richtmyer–Meshkov and Kelvin–Helmholtz instabilities. The growth of the instabilities is highly affected by the reaction wave, which significantly reduces mixing compared to an inert shock–bubble interaction. A comparison with two-dimensional simulations reveals the influence of three-dimensional effects on the bubble evolution, especially during the late stages. The numerical results reproduce experimental data in terms of ignition delay time, reaction wave speed and spatial expansion rate of the bubble gas. We observe only a slight divergence of the spatial expansion in the long-term evolution.Aerodynamic

Turbulent flow through a high aspect ratio cooling duct with asymmetric wall heating

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 × 103 and an average Nusselt number of Nuxz = 371. The geometry and boundary conditions follow an experimental reference case and good agreement with the experimental results is achieved. The current investigation focuses on the influence of asymmetric wall heating on the duct flow field, specifically on the interaction of turbulence-induced secondary flow and turbulent heat transfer, and the associated spatial development of the thermal boundary layer and the inferred viscosity variation. The viscosity reduction towards the heated wall causes a decrease in turbulent mixing, turbulent length scales and turbulence anisotropy as well as a weakening of turbulent ejections. Overall, the secondary flow strength becomes increasingly less intense along the length of the spatially resolved heated duct as compared to an adiabatic duct. Furthermore, we show that the assumption of a constant turbulent Prandtl number is invalid for turbulent heat transfer in an asymmetrically heated duct.Aerodynamic

Large-eddy simulation of the high-Reynolds-number flow through a high-aspect-ratio cooling duct

We present well-resolved large-eddy-simulations (LES) of a straight, high-aspect-ratio cooling duct (HARCD) at a bulk Reynolds number of Re = 110 • 103 and an average Nusselt number of Nu = 371. The geometry and boundary conditions have been defined together with Rochlitz et al. (2015), who conducted the experimental measurements for this case. Water was chosen as coolant. The current investigation focuses on the influence of asymmetrical wall heating on the flow field and specifically on the influence of the turbulence-induced secondary flow on turbulent heat transfer, the spatial development of the temperature boundary layer and the accompanying viscosity modulation. Due to the viscosity drop in the vicinity of the heated wall we observe a decrease in turbulent length scales and in turbulence anisotropy, resulting in a decrease of turbulent mixing and the secondary flow strength along the duct.Aerodynamic