THE IMPACT OF REDUCED BLADE COUNT AND TIP CLEARANCE VARIATION ON THE FLOW FIELD OF AXIAL COMPRESSOR BLADE ROWS

Abstract

The aerodynamic design of axial compressor blades requires a careful trade-off between aerodynamic loading and efficiency. Fewer blades increase the aerodynamic load on each blade, while a reduced rotor blade count can lower profile losses due to the smaller number of wakes—potentially improving efficiency. It can also intensify secondary flows because of the higher local loading. To evaluate these opposing effects during preliminary design, three-dimensional RANS simulations remain common practice, although they are known to have weaknesses when predicting secondary flow phenomena. This paper presents experimental results from a four-stage, low-speed research compressor. Tests were carried out with two different blade counts and with both small and enlarged tip clearances to validate the numerical models. The rotor blade count was reduced by roughly 30%, and the rotor stagger anglewas increased to maintain the design-point pressure ratio and mass flow while compensating the stronger deviation. The study focuses on the influence of these changes on the tip-clearance vortex of the rotor blades; the measured data are used to validate simulations that support deeper analysis. The chosen reduction in blade count led to an overall efficiency gain and a markedly lower sensitivity to tip-clearance increases. Although the higher loading produces a steeper tip-leakage vortex, the operating range is not substantially narrowed. The larger blade pitch allows the vortex to traverse the passage with reduced interaction with adjacent blades. These results improve understanding of tip-clearance vortex behavior and can inform future compressor design.