Predicted and measured performance and stability of two variants of a military fan

Abstract

Adequate stability margin is a key issue in the design of compact, highly loaded transonic fans needed for future combat engines, especially for operation with high levels of inlet distortion. Stability prediction is difficult, and modern three-dimensional multi-row flow calculation methods are being increasingly applied. Following a fairly comprehensive review of previous such applications, this paper describes studies on baseline and redesigned versions of an advanced fan stage. The predictions capture the main features of the test results, including the increased stability margin of the revised design. The results indicate that whereas the critical region affecting surge for the baseline case is the rotor tip, the stability of the revised stage design can be affected by the stator, and a mechanism for this is suggested. Further insight is gained from solutions using a closely-coupled, choked-nozzle exit boundary condition and from calculations with radial total pressure distortion at inlet, including its development from an upstream generating screen.