Overall Performance and Loss Analysis of a Low-Speed Research Compressor with Different Nonaxisymmetric Tip Clearance Layouts

This paper mainly investigates the aerodynamic effect of two different average sizes and three specific nonaxisymmetric rotor tip clearance arrangements on the overall performance and loss mechanism of a four-stage low-speed research compressor (LSRC) at Shanghai Jiao Tong University. The stage was modeled for the steady simulations as a seventh entire annulus computation domain of the inlet vane and the first stage rotor row. The numerical method was validated using experimental data on the radial profiles of total pressure and flow angle at the rotor outlet. Results illustrate that a size increase (from 1.2% span to 2.3% span) in uniform clearance layout will bring adverse effects. The specific degradation in isentropic efficiency is 1.11% and 1.77% at the design and near stall points, respectively. The nonaxisymmetric rotor tip clearance arrangement significantly increases the stall margin by 25%-31% relative to the uniform layout, and the benefit is more pronounced in the case of a larger average clearance size of 48%-57%. However, there are no visible changes in the global performance characteristics. The zigzag-distributed clearance layout has a better performance impact than the other two linearly arranged schemes. Detailed analyses based on the streamwise and spanwise efficiency deviation were carried out to interpret the aerodynamic improvement. Moreover, the differentiated distribution of aerodynamics and specific flow behaviors at the rotor tip were investigated in detail over each rotor passage. Circumferentially averaged performance and radial profiles were performed. Because of the nonaxisymmetric layout, the inlet mass flow and incidence were redistributed in both radial and circumferential directions, further causing a significant alleviation of the blockage arising from the tip leakage flow, especially the region at the first 0.5 axial chord and above 80% span. The loss caused by the nonaxisymmetric tip clearance included not only the leakage flow loss, but also the interference between the leakage flow and the incoming main flow, or the low-energy fluid in the corner region of the casing, and even the loss on the suction surface of the adjacent rotor blade.