Effects of Curvature Continuity of Compressor Blade Profiles on Their Performances

Curvature discontinuity may exist in the surface, especially at the leading edge, of a compressor blade. The importance of curvature continuity or discontinuity has been realized, but its definite influences and mechanisms still need research. In this paper, an optimization method is proposed to design continuous-curvature blade profiles from datum blades, and a Reynolds-Averaged Navier-Stokes (RANS) solver with a transition model is used to examine the flowfields and performances of different blade profiles. Large eddy simulations of several cases are also presented to validate the RANS results. The effects of leading-edge-blend-point curvature continuity and the main-surface curvature continuity are studied separately. The results show that the curvature continuity at the leading-edge blend point helps to eliminate the separation bubble, and thus improves the blade performance. The main-surface curvature continuity is also found beneficial, although its effects are much smaller than those of the blend-point curvature continuity. Boundary-layer equations of the blade profiles are analyzed in terms of order of magnitude to further study the different curvature-continuity effects of the blend point and main surface theoretically. The analysis reveals the physical facts that produce the pressure spike around a leading-edge blend point with a discontinuous curvature, and thus explains how the optimized continuous-curvature leading edge removes the pressure spike and the related separation. The analysis also finds that the high spike appearing near the nose of a continuous-curvature leading edge at larger incidences is controlled by the large nose curvature rather than curvature discontinuity. The dual separation mechanisms also help to solve the so-called sharp leading edge paradox.