Stall inception in a contra-rotating fan under radially distorted inflows

Abstract

The fan of a gas turbine engine is often subject to distortion due to non-uniformities in the incoming flow which could eventually result in an early stall of the fan. Contra-rotating fans have potential aerodynamic advantages and could replace the conventional fan configurations of gas turbine engines. Understanding the phenomenon prior to stall is important to characterise the behaviour of the stage at low mass flow rates. This paper investigates the phenomena leading to stall in a low-aspect ratio contra-rotating fan stage operating at different speed combinations under radially distorted inflows. Unsteady casing static pressure measurements obtained at a location upstream of rotor-1 leading edge are analysed using wavelet and Fourier analysis techniques. The results primarily concluded that a higher speed of rotation of rotor-2 could possibly suppress the pre-stall disturbances. The fluid structures leading to stall are initially associated with the blade passing frequency (BPF). These frequencies stretch to lower frequencies during the onset of fully developed stall and fully developed stall finally occurs at low frequencies.