The Bowed-blade Designing Of The Guide Vane In A Small Flow Rate Turboshaft Engine Power Turbine

The helicopter receive much concern in both military and civilian use, becauseof its excellent features of lightness and flexibility, especially its ability to dominimum altitude flying. As the main power supply of the modern helicopter, theturboshaft engine should have a compact structure, light weight, large power, lowfuel consumption and a fine varying duty performance to guarantee the overallperformance of the helicopter. Because of the flow area of the turboshaft engine hasbeen restricted by the small size, the aspect ratio of the turbo blade become lower.In this kind of turbo cascade, the secondary flow constituted a high proportion ofthe flow area and the main flow has been heavily affected. The second flow reducethe throughflow ability of the cascade and raise the cascade loss.Traditional bowed-blade design reduces the loss by change the pressuredistribution in the cascade in order to control the intensity and scale of the vortexstructures in the cascade. But we cannot control the intensity of the secondary flowonly by bowed-blade because the boundary layer constituted a high proportion ofthe flow area of the low aspect ratio cascade. It may be a good choice that we canbuild a pressure gradient to push the low energy fluid towards the endwall region inorder to improve the main flow.The subject of the study in this paper is a turboshaft engine, and we redesignthe guide vanes of both the two stages of the power turbine by using thebowed-blade theory. We compare the effects brought by positive dihedral andnegative dihedral and then determine that the two guide vanes should be designed asnegative dihedral blades in order to achieve a better performance. After analyzingand comparing different plans which are different in bowed angle and bowed height,we acquire the best design and propose a constructive suggestion in low aspect ratio turbo blade designing.