Prediction of the Fluid Induced Instability Force of an Axial Compressor

Numerical calculations of a rotor row of a low speed axial compressor with an asymmetric tip clearance distribution were carried out. Asymmetric tip clearance induces blade loading and downstream pressure redistribution along the circumferential direction while upstream pressure field is maintained. At small flow coefficients, blade loading redistribution patterns are highly affected by upper 50% blade span region. High pressure difference at the small clearance region causes high blade loading at the small clearance region. On the other hand, at a high flow coefficient, blade loading redistribution is almost coincident with the asymmetric tip clearance distribution. In contrast to lower flow coefficients, the contribution of the lower 50% blade span region increases. A higher axial velocity induces a higher axial momentum, which delivers the upstream pressure field downstream without any circumferential redistribution. Blade loading redistribution due to increased axial momentum overcomes the redistribution caused by local tip clearance performance due to high pressure difference at the small clearance and becomes the dominant term of blade loading redistribution. As a result, the redistributed blade loading synchronizes with the tip clearance distribution and the strength of the blade loading redistribution increases as the flow coefficient increases.