Effect of a Gap Between Inner Casing and Stator Blade on Axial Compressor Performance

The small gap at stator hub section of 10-stage axial compressor of small power class industrial gas turbine engine was studied to confirm its effect on compressor analysis result. This gap is allowed for manufactural tolerance and thermal expansion during engine operation. For the convenient purpose of CFD geometric modeling, such gap was simplified and the 3D Navier-Stokes code was used to predict the compressor performance then compared the results with the case without a gap. In the case of calculation without a gap, the performance was estimated to be lower than that of test result. It is because of the presence of 3D separation at hub corner of every stator except on the 1st and 2nd stator. The CFD calculation shows that, with a gap, the stall observed at hub corner vanished and the predicted compressor performance agrees well with the test result. From this, it is concluded that the existence of a gap between inner casing and stator brings a considerable effects on the compressor flow distribution and must be taken into account in the design.