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

Adaptive reduced-order modeling for non-linear fluid–structure interaction

We present an adaptive reduced-order model for the efficient time-resolved simulation of fluid–structure interaction problems with complex and non-linear deformations. The model is based on repeated linearizations of the structural balance equations. Upon each linearization step, the number of unknowns is strongly decreased by using modal reduction, which leads to a substantial gain in computational efficiency. Through adaptive re-calibration and truncation augmentation whenever a non-dimensional deformation threshold is exceeded, we ensure that the reduced modal basis maintains arbitrary accuracy for small and large deformations. Our novel model is embedded into a partitioned, loosely coupled finite volume–finite element framework, in which the structural interface motion within the Eulerian fluid solver is accounted for by a conservative cut-element immersed-boundary method. Applications to the aeroelastic instability of a flat plate at supersonic speeds, to an elastic panel placed within a shock tube, and to the shock induced buckling of an inflated thin semi-sphere demonstrate the efficiency and accuracy of the method.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

GPU-accelerated simulations for eVTOL aerodynamic analysis

The demand for fast, high-fidelity, scale-resolving computational fluid dynamics (CFD) simulations is continuously growing. Especially new emerging aviation technologies, such as electrical vertical take-off and landing aircraft (eVTOL), strongly rely on advanced numerical methods to retain development life-cycle costs and achieving design targets more quickly. This paper presents a cutting-edge large-eddy simulations (LES) solver developed to enable over-night turnaround times for full aircraft simulations on advanced graphics processing unit (GPU) architectures. The solver models weakly compressible fluid flows over complex three-dimensional bodies based on an immersed boundary method with geometry-based and flow-based automatic mesh adaption. Its high accuracy and unprecedented performance is demonstrated for high Reynolds number aerodynamic benchmark cases and compared to recent results from literature. In addition, the successful validation against experimental data for the Lilium Jet canard is discussed.Aerodynamic