Rotor tip stall from a designer's perspective

Abstract

The operating range of a compressor is the most critical aspect to consider when dealing with new designs. Two distinct routes to compressor stall are known in literature: modal-stall that occurs near the peak of the overall characteristic and spike-stall that initiates on the negatively-sloped part of the characteristic curve. Modal type stall can be taken into account from the very beginning during the design process. The basic mechanisms that drive the phenomena are essentially 2D in nature and there are well-established and experimentally validated design criteria available. Unfortunately this statement no longer applies when dealing with spike-type stall. This short length-scale instability is related to a threedimensional breakdown of the flow that appears at rotor tip. Since when firstly observed, much effort has been expended trying to understand the flow features underlying this abrupt stall. Nevertheless, a well-established and validated design criterion is still missing. This paper deals with the topic from a designer's perspective. A discussion which tries to highlight the design variables affecting the spike-stall is presented in the first part of the paper. Then CFD results on core stages of an heavy-duty axial compressor are discussed. The aim is to derive useful considerations for the designer work and discuss which design actions are more effective to successfully complete a spike-stall safe design.

Retrofittable Solutions Capability for Gas Turbine Compressors

“…This flow structure is more visible for the fourteenth stator row and increases its dimension on the CV15 and OGV. Increasing the back-pressure, the hub corner stall increases both in terms of size and spanwise penetration, indicating that the last stages are about to give up [23].…”

Retrofittable Solutions Capability for a Gas Turbine Compressor

“…This flow structure is more visible for the fourteenth stator row and increases its dimension on the CV15 and OGV. Increasing the back-pressure, the hub corner stall increases both in terms of size and spanwise penetration, indicating that the last stages are about to give up [17].…”