Commencement and Development Processes of Flow Unsteadiness at Tip Clearance Region of a Low Speed Axial Compressor Rotor Blade Row
Commencement and development processes of unsteadiness, caused by blade row tip leakage flow in a low speed axial compressor, are investigated and results are presented in this paper. Analyses are based on results obtained through numerical simulation of unsteady three dimensional viscous flows. Discretization of the Navier-Stokes’s equations has been carried out based on upwind second-order scheme and k-ω-SST turbulence modeling was used for estimation of eddy viscosity.
Three different circumstances, including design point and two near stall conditions are considered for investigation and discussion. Tip leakage flow frequency spectrums were examined through surveying instantaneous static pressure signals imposed on the blades surfaces. Focusing on time dependent flow structure results signified existence of some pressure peaks at near stall conditions. These regions, which are created as a result of interaction between main inflow and tip leakage flow, lead to occurrence of self-induced unsteadiness. However, at design condition, flow is more affected by the main inflow instead of the tip leakage flow. By occurrence of self-induced unsteadiness, which occurs at near stall condition, tip leakage vortex flow starts to fluctuate at a frequency about the blade passing frequency. Further decrease in the flow rate up to a specified value showed no significant variations in the leakage flow frequency, but, on the other hand, magnified amplitudes of this unsteadiness.