Performance Improvements of Compressor Cascades by Controlling the Profile and Sidewall Boundary Layers

For increasing the thrust-to-weight ratio of modern turbojet engines, the number of stages of the turbo components or at least the number of blades per stage have to be minimized. This inevitably forces a higher loading of the remaining blades, for which — especially in the compressor — even the use of modern controlled diffusion airfoil concepts is limited due to the danger of flow separation. Therefore, boundary layer control can be taken into consideration. The use of blowing proves to be most obvious for applications in turbojet engines, because the required pressurized air is — due to the working process — already available. Basic investigations on this topic are described in this paper, and both the midspan and the sidewall region are covered. As a review of the pertinent literature disclosed the lack of reliable design criteria, fundamental experiments in a cascade wind-tunnel were performed. The results of these measurements are reported and recommendations concerning the application of blowing in compressor cascades are given.