Large Eddy Simulation of Tandem Blade Stator Cascades

Abstract

Large eddy simulations of tandem blade compressor cascades have been performed with an explicit filtering method. A low speed case was simulated using the public domain code Incompact3d which solves incompressible flow with an immersed boundary method for embedded solid bodies, obviating the effort expended on preparing good quality meshes around blading. The LES successfully captures transition on the front blade and yields a significantly different loading compared with RANS solutions obtained before. The less substantial impact on the rear blade is traced to rapid transition forced by the turbulent wake of the front blade. LES with a refined grid was found to shorten the transition width due to the crucial role of small scales during transition. A complementary study with an in-house compressible LES solver was conducted for a transonic tandem cascade at the inlet Mach number of 0.89. Flow expands around the leading edge of the front blade and is terminated by a shock which interacts with the suction surface boundary layer. The beneficial effect of tandem blading was found to be achieved by limiting this separation. The shock-induced separation also marks a rapid transition of the suction surface boundary layer that is readily captured in the LES, showing pre-transitional streaks, but could prove difficult even for current transition-sensitive RANS.