Performance Characterizations Of A High Speed Axial Flow Compressor Stage Implemented With Diverse Porosities Of Axial Slotted Casing Treatment

Abstract

The design of transonic axial flow compressor is primarily centered on the reduction of stage numbers, which usually points to the problem of how to prevent the instabilities of flow due to rotating stall. In addition to the inventiveness employed in aerodynamic blade design, various methods and devices have been demonstrated. Among them, casing treatment with axial skewed slots made on the endwall, has been proved to have a favorable effect on increasing stable operating range of compressors. In the current study, the effect of porosities in axial skewed slot casing treatment at specified axial locations on the flow field and the stability enhancement of transonic axial compressor, have been investigated and examined through CFD analysis. The interpretation of the performance conditions is done through a standardized steady state 3-dimensional numerical study using a commercial solver tool with SST K-ω Turbulence model. The obtained results are distinguished with the case results of solid casing of the compressor stage comprising of rotor and stator blade blades. The transonic compressor stage chosen for study has a competence of generating 1.36 stage total pressure ratio, absorbing air mass flow rate of 23 kg/s at rated design speed of 12930 RPM. Steady calculation for solid casing condition for baseline compressor was conducted first to clarify its stall inception mechanism and thereby selecting the required grid independence and mesh conditions for further stages forward to result analysis. Prior selecting the suitable grids size for the analysis the grid independence test has been carried out for the baseline case at 100% design speed for three different meshed sizes. After selecting the suitable grid size the performance map of the compressor stage is evaluated for the baseline model for the three operating speed of 80%, 90% and 100%. This study deals with the study of effect of porosity concerned on a transonic compressor rotor. Slotted casing treatment, made with axial and radial skew angles of 15° and 45° respectively at 40% of the axial location w.r.t rotor leading edge is considered. To study the effect of porosity, 39%, 43% and 47% is taken into account. The steady state CFD simulations were performed at 100%, 90%, 80% design speed. The obtained results are contrasted with those acquired on the base line compressor with solid casing and identifying the potentiality of casing treatment in modifying the efficiency of rotor and stall margin when analyzed to the solid casing. The present work has been carried out at AFCR, Propulsion Division, NWTC, CSIR-National Aerospace Laboratories, Bangalore.