Advances in High-Speed Linear Design Technology: Novel Approach to Sidewall Geometry Design for Erosion Tests

Test rigs for compressor cascade testing reported in literature are characterized by a high level of complexity. This is especially the case if a variable incidence should be allowed for or the flow conditions reach transonic or supersonic flow regimes. Incidence alteration capability is preferable for obtaining a more comprehensive picture of cascade properties. However, it necessitates a complex kinematic set-up in order to rotate the blades and to adjust the sidewall setting such that flow periodicity across the passages is ensured. Additionally, a complex sealing system is usually required to guarantee minimum flow disturbance. Often, a suction system is also introduced for boundary layer control and regulation of flow conditions. In the case of erosion testing the situation is exacerbated as the application of such conventional adjustment devices is ruled out due to the presence of solid particles in the flow. In this work an investigation of a new cascade design for erosion testing with variable incidence was conducted. A fixed sidewall geometry is proposed which ensures periodic flow conditions in the speed range of M = 0.5 up to M = 0.78 while allowing incidence adjustments in the range of i = ±10° as assessed by means of CFD. The novel design paradigm enables such flexibility by virtue of a self-regulating flow induced by flow separation from the fixed sidewall geometry. The latter has the benefit of not requiring a specialized mechanical setup and sealing due to the absence of movable parts in the flow. The calculated results show acceptable periodicity of various flow parameters within the passage at 50 percent blade height for all incidence settings considered. The conducted investigation has demonstrated that specially designed fixed sidewalls may enable sufficiently accurate transonic erosion testing under various incidence angles while making cascade erosion testing more economical and time efficient.