Shock-boundary Layer Interaction (sbli) Cfd Research and Applications

Preamble Interaction of shock waves with turbulent boundary layers is important in many aerospace applications. Examples in external aerodynamics include control surfaces, wing body junctions, and multi-body aerodynamics. In high-speed propulsion systems, shock-boundary layer interaction (SBLI) can occur in intakes, supersonic combustion chambers and nozzles. Computational fluid dynamics (CFD) is routinely used to study SBLI flows and predict such interactions in geometries of practical interest. Simulation of SBLI flows in engineering applications rely mostly on Reynolds-averaged Navier Stokes (RANS) methods. The reliability of the CFD results are primarily determined by the accuracy of the turbulence model used in the computation. Traditional turbulence models, even with compressibility corrections, often fail to predict dominant features in SBLI flows accurately. These include flow separation and reattachment, peak pressure and heat transfer. Several modifications are proposed in literature, but their performance vary from one test case to another. The interaction of turbulent fluctuations with a shock wave involves complex physical processes. General purpose turbulence models do not account for many of these mechanisms, and therefore lead to inaccurate predictions. For example, most RANS models treat the shock wave as steady and neglect the effect of unsteady shock oscillation in an otherwise steady mean flow. Upstream temperature fluctuations, inherent in a high-speed boundary layer, result in additional physics which is usually not modeled. Research is underway at IIT Bombay to systematically study different aspects of shockturbulence interaction and model the underlying physics. Most notably, the effect of unsteady shock oscillations has been modeled in a simple and physically consistent way. The new model has been validated against experimental measurements available in literature for a range of Mach numbers and geometric configurations. It has shown good potential in matching the experimental data on separation bubble size, shock structure and wall pressure distribution. Additional aspects of SBLI flows that are of practical relevance are currently under investigation. These include three dimensional effects, numerical implementation issues, and surface heat transfer rates. Such indigenous efforts at developing and validating turbulence models for targeted CFD application can be valuable to the relevant space and defense programmes. Close interaction and feedback between industry and academia can harness the full potential of these developments. The SBLI meeting at IIT Bombay is an effort in this direction.