Numerical investigation of boundary layer suction on certain highly loaded aspirated compressor at low speeds

Abstract

Boundary layer suction is considered to be an available approach to restraining or even eliminating flow separation and to improve the aerodynamic performance of the compressor. In this paper, a highly loaded axial-flow aspirated compressor based on a low-reaction design concept is investigated in detail to find an appropriate flow control strategy for boundary layer suction to achieve significant performance benefit. The flow control strategy consists mainly of the arrangement of suction hole and the aspirated flow rate. The geometrical models including aspiration cannulas, stator cavity and aspiration channel are novelly applied in this research to approach a real engineering application. Complete compressor maps are predicted by a three-dimensional computational fluid dynamics simulation. The distribution of the typical aerodynamic parameters and the partial flow structures are analysed at design and off-design conditions. Three-dimensional separation near the stall point is effectively suppressed by the aspiration on both hub and shroud, and better performance is achieved by a reasonable increase of aspirated flow rate; a peak efficiency of 0.91 and a total pressure ratio of 1.055 are attained at a total aspirated flow rate of 0.024 kg/s per passage. However, sudden turning of compressor maps at low inlet flow rate occurs without the aspiration on shroud, and a noticeable deterioration in performance occurs with the decreasing of the inlet flow rate. The main reason of performance deterioration is that the flow control efficiency of aspiration is not enough for effectively suppressing three-dimensional separation near the casing corner. The difference in the aspirated flow source is owed to the distinct flow feature at various locations caused by the aspiration efficiency of suction holes. A partial auto-readjustment feature of the suction flow rate with increasing flow separation has been found. The boundary layer suction with an appropriate flow control strategy is necessary for a higher efficiency, highly loaded aspiration compressor.