Secondary Flows in a Compressor Cascade with Fillet Radius
M. Hoeger, U. Schmidt-Eisenlohr, S. Gomez, H. Sauer
abstract:
Large fillet radii are typically found at modern blisk compressor rotors to ensure structural integrity. The objective of the present paper is to investigate the impact of such real geometry effects on the flow at the hub section. Investigations were performed numerically for the idealized case of a plane compressor cascade with the 3D (multistage) Navier-Stokes code TRACE_S for realistic inlet boundary layer displacement thickness and typical loading levels.
Two different fillet radii are considered as well as a 3D leading edge configuration. The results are discussed in terms of secondary flow patterns, span wise losses and turning. A complex 3D vortex system is demonstrated to rise from the fillet radius which alters the aerodynamic behavior of the cascade end wall sections. The vortex system has an impact on the discharge flow angle distribution as well as on the radial location of the low energy region typically found on the suction surface close to the end wall.
For the 3D leading edge configuration an amplification of the suction surface horse shoe vortex leg was observed. This vortex is counter-rotating compared to the passage vortex and it is demonstrated to weaken the secondary flow at the end wall. By that less low energy fluid is driven across the blade passage and the hazard of severe suction surface boundary layer separation and corner stall is reduced.
reference:
Summer School on CFD for Turbomachinery Application, Gdansk, 31.8.-3.9.2001.