Effect of prewhirl on the performance of centrifugal compressors

摘要

In comparison with axial flow compressors, centrifugal compressors have distinct relative merits such as: higher stage pressure ratio, simplicity and ruggedness of construction, shorter length, better resistance to foreign object damage, less vulnerable to blockage, handling small volume flows, better matching characteristics, and less manufacturing costs. However, the axial flow compressor has a large flow capture per unit area which is important to aircraft applications. In this study, prewhirl is introduced to alleviate the compressibility effect at the convex side of the eye to avoid the formation of shock waves and the consequent losses. However, this caused reduction of work absorbing capacity W and pressure ratio R. This problem was overcome by twisting the prewhirl vanes between the tip and the root linearly, then parabolically, where the prewhirl angle α{sub}(w1) is maximum at tip α{sub}(w1t) and zero at root α{sub}(w1r)·α{sub}(w1t) was varied over a range of 20°- 50°. Computations showed that the linear variation recovered about 40% of W and R, whereas the parabolic variation of α{sub}(w1t) up to 40° recovered Wand R totally.