Oscillatory Tip Leakage Flows and Stability Enhancement in Axial Compressors

Abstract

Rotating stall axial compressor is a difficult research field full of controversy. Over the recent decades, the unsteady tip leakage flows had been discovered and confirmed by several research groups independently. This paper summarizes the research experience on unsteady tip leakage flows and stability enhancement in axial flow compressors. The goal is to provide theoretical bases to design casing treatments and tip air injection for stall margin extension of axial compressor. The research efforts cover (1) the tip flow structure at near stall that can explain why the tip leakage flows go unsteady and (2) the computational and experimental evidences that demonstrate the axial momentum playing an important role in unsteady tip leakage flow. It was found that one of the necessary conditions for tip leakage flow to become unsteady is that a portion of the leakage flow impinges onto the pressure side of the neighboring blade near the leading edge. The impediment of the tip leakage flow against the main incoming flow can be measured by the axial momentum balance within the tip range. With the help of the theoretical progress, the applications are extended to various casing treatments and tip air recirculation.

Steady and Unsteady Numerical Characterization of the Secondary Flow Structures of a Highly Loaded Low-Pressure Compressor Stage

“…In this context, they classified the hub corner separation as a critical secondary structure that could possibly lead to aerodynamic stall, especially in highly loaded machines like the one presented in this paper. A similar analysis was proposed for the unsteady characterization of the tip clearance flow [4][5][6][7]. The flow redistribution observable at the casing prior to the stall and its impact on the development of spike-type stall inception mechanisms was proposed, together with suggestions for stability enhancement.…”

Effects of the Shock Wave Structure on the Tip Clearance Leakage Flow in Transonic Compressor Rotors

“…The leakage flow streamlines at 97% clearance height under the minimum and maximum tip clearances (0.25 mm and 1.00 mm) are shown in Figure 30. There is an obvious double-leakage tip clearance flow (that is, the leakage flow generated by adjacent blades flows into the local tip clearance [21,27,30]). At the same time, Figures 15 and 16 show that there is a secondary leakage phenomenon in the leakage flow.…”

“…More recent research was performed in the field of tip clearance leakage flow field structure and flow mechanism, which were the basis of understanding the effect of the tip clearance on compressor performance [21,22]. The tip clearance flow of Rotor37 rotor was simulated and compared with the experiment by Chima [23].…”