January 15, 2025
16:15
Louvain-la-Neuve
Place Sainte Barbe, auditorium BARB 94
Wall-modeling in LES is of crucial importance to allow scale-resolving simulations of turbulent flows in industrial-scale devices. Numerous models were developed and validated for incompressible flows, including the simple quasi-analytical model based on Reichardt formula to approximate the ``law of the wall’’ (which covers the laminar sublayer, the transition region and the log layer). This work presents a new scaling of Reichardt formula to properly take into account strong compressibility effects in wall-modeled LES (wmLES). The newly developed wall-model is validated against wall-resolved LES (wrLES) on three adiabatic turbulent channel flow cases at moderate Reynolds number, and with increasing Mach number: ranging from a quasi-incompressible regime at M=0.25 up to a supersonic regime at M=1.5. The wall-model is also used to perform wmLES of channel flow cases at high Reynolds number, and the velocity profile is seen to match the expectations.
The wall-model is then used to perform a high-fidelity wmLES of a rectangular supersonic air ejector, using periodic boundary conditions in the spanwise direction. The results are compared to those obtained using a 2-D RANS simulation, and also to those obtained experimentally in a setup with transparent side-walls (also used for flow visualization). The structure of the mixing layers is analyzed and the postprocessing tools using total exergy fluxes are presented. The discrepancies between the RANS simulation and LES results are explained using an analysis of the turbulent fluctuating contributions for both frameworks: those being resolved in our LES; yet only modeled in RANS.
Finally, the design of a new cylindrical supersonic ejector experiment is presented; which is really the design used for industrial applications. The characteristic curves are obtained experimentally. They are also compared to those obtained
using axisymmetric RANS simulations. It is found that such RANS simulations allow to predict quite well the global behavior of the ejector, in on- and off-design operations. We however observe large deviations between the experimental and numerical wall-pressure profiles. To gain additional insight into the flow physics, and also help explain the observed differences, a high-fidelity wmLES of the full ejector is performed for an operating point at the end of the on-design regime, just before the critical point. The results of this simulation are presented, and are also used to provide an explanation for the consistent underestimation of the wall-pressure profile in RANS simulations, using an extension of the compound-choking theory.
Jury members :
- Prof. Yann Bartosiewicz (UCLouvain, Belgium), supervisor
- Prof. Grégoire Winckelmans (UCLouvain, Belgium), supervisor
- Prof. Hadrien Rattez (UCLouvain, Belgium), chairperson
- Dr. Matthieu Duponcheel (UCLouvain, Belgium)
- Dr. Koen Hillewaert (ULiège, Belgium)
- Prof. Stephan Hickel (TUDelft, Netherlands)