Design and Testing of Two Supercritical Compressor Cascades Free

Based upon a blade pressure distribution similar to that one proposed by D. Korn, a supercritical cascade blade section was developed for a transonic compressor stator. The design inlet Mach number of M₁ = 0.8 and the flow turning of Θ = 36.8 deg resulted in a diffusion factor around D = 0.5 and the blade suction surface pressure distribution was optimized with the aid of a boundary-layer calculation. In order to obtain the related cascade geometry, an inverse blade calculation was performed by E. Schmidt (University of Stuttgart) solving the potential flow equation with a finite difference relaxation method. In the experimental cascade tests, reasonable performance could be obtained at design point conditions for reduced loading (increeased axial velocity density ratio). However, the performance at lower inlet Mach numbers and different inlet flow angles was not acceptable. This was attributed to the measured blade pressure distribution, which differed from the design in the leading edge region. Based upon these results, a second supercritical cascade blade section was developed for the same inlet flow conditions and identical flow turning. The modified pressure distribution included also an axial stream tube contraction. The design intent was verified by the cascade tests which showed an improved performance at design and off-design. The combination of boundary layer and inverse blade-to-blade computation promises to become an effective design tool for axial flow compressors.