Investigations on Aerodynamic Loading Limits of Subsonic Compressor Tandem Cascades: End Wall Flow

Abstract

An optimized subsonic compressor tandem cascade was investigated experimentally and numerically. Since the design aims at applications under incompressible flow conditions, a low inlet Mach number of 0.175 was used. The experiments were carried out at the low speed cascade wind tunnel at the Technische Universität Braunschweig. For the numerical simulations, the CFD-solver TRACE of DLR Cologne was used, together with a curvature corrected k-ω turbulence model and the γ-Reθ transition model. The aerodynamic loading was varied by incidence variation. Results are presented and discussed for different inlet angles: spanwise loss coefficient, turning, pressure rise coefficient and AVR together with contour plots of the wake plane, flow visualization and oil flow pictures. Experimental and numerical results were compared and found to be in good agreement. The secondary flow topology of the front blade is considerably altered by the aerodynamic loading variation, whereas the topology of the rear blade surface is almost unchanged. The effect of the nozzle between the tandem blades, was observable up to the end wall for all investigated incidences. In addition, a comparison is made to published results of previous experimental and numerical investigations of a transonic tandem compressor cascade [1] and its reference single compressor cascade [2]. The comparison of the tandem cascades revealed that the general structures of the secondary flow seem to be similar for similar loading.