METTU, BALACHANDRA REDDY. Wall Modeled LES of Compressible Flows in Non-Equilibrium Conditions. (Under the direction of Pramod Subbareddy.)A turbulent boundary layer is composed of a wide range of length scales and time scales. To resolve all these scales of motion, as with a DNS or traditional wall resolved LES, the grid sizes required scale roughly as the square/cube of the Reynolds number (Re). These requirements make high Re flows computationally very expensive. By modeling the effect of the motions close to the wall, as is proposed in wall modeled LES (WMLES) methods, the computation of high Re flows can be made significantly cheaper. To date, WMLES has been relatively less studied in application with strong compressibility effects.In this study, we implement state-of-the-art wall models for these flows and examine the different challenges which are common to high-speed flow applications: isothermal cold wall conditions, the transition to turbulence, and shock boundary layer interactions (SBLI). It is observed that for cold-wall flows, a more empirical "mixed" scaling for the length scale appearing in the eddy viscosity formulation outperforms the classical semi-local scaling for obtaining predictions of heat-flux and skin-friction. For transitional flows, we develop a modified transition sensor that gave robust predictions for the high Mach number cases we examined. We find that the more computationally expensive non-equilibrium model with an eddy viscosity formulation based on the pressure gradient outperformed the standard equilibrium model for skin-friction predictions in SBLIs. A sensor for detecting regions of non-equilibrium flow was developed based on the resolved Reynolds stress. By using this sensor and switching to an exchange location closer to the wall in the non-equilibrium region for the equilibrium model gave skin-friction and heat flux results close to or even better than the non-equilibrium model at a far cheaper cost. WMLES was performed for SBLI at moderate to high Re with different wall temperature conditions. It was observed that WMLES was able to capture the expansion and shrinking of the separation bubble size when the wall was heated and cooled. Also observed was that using WMLES the low-frequency characteristics of SBLI at high Re was now possible. As a whole, it was seen that WMLES can become a promising tool for exploring the complex physics involved in turbulent high-speed flows at a significantly lower cost than wall resolved LES/DNS and with much higher fidelity compared to pure RANS simulations.

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