Time resolved simulation and experimental validation of the flow in axial slot casing treatments for transonic axial compressors

Building on the experience of previous investigations, a casing treatment was developed and applied to an axial tran- sonic compressor stage, in literature referred to as Dannstadt Rotor I. The aerodynamics of the experimental compressor stage was improved by applying axially orientated semicircular slots to the original plain casing, which both enhanced the operating range and design point efficiency. A gain in total pressure ratio along the entire design speed line was also observed. Within the scope of this study four dfferent axial casing treatments were designed. Their effect on the flow in a tran- sonic axial compressor stage was investigated parametrically using time-resolved 3D-FANS simulations with a mesh ofapprox- imately 4.8 106 grid points. This research aims to identify cor- relations between the geometrical cavity design and the changed channel flow. The findings help to formulate parameters for eva- luating the performance of casing treatments. These criteria can further be used as target functions in the design optimisation pro- cess. The predicted behaviour of the transonic compressor was validated against experiments as well as an alternative numer- ical model, the non-linear harmonic method. Both confirmed the effect of the slots in raising efficiency as well as moving the design speed line towards higher pressure ratios. In the experi- ments, the addition of the slots increased the total pressure ratio at stall conditions by more than 5% and reduced mass flow from 87.5% of the design mass flow to less than 77.5% compared to the origizal geometry.