Numerical simulation of using combined active and passive stall control techniques in centrifugal compressors

Abstract

This study presents a numerical simulation of stall control by using the casing treatment method which represents the passive control technique and also by using the air injection method which represents the active control technique. The casing treatment types used are the holed casing treatment and the casing skewed slots. There are four proposed numerical models; the first model is the regular shape model without casing treatments, the second model combines the holed casing treatment with the skewed slots, the third model is similar to the second one but enhanced by air injection at specified locations at the slot wall while the fourth model contains casing slots only. Results showed that the holed casing treatment helps in reducing the tip leakage flow by transferring it from the blades tip area to the impeller inlet. Also, it was found that the casing slots can cause a flow circulation and increase the kinetic energy around the position of slots and this leads to decreasing the number of stall cells. Results indicated also that the air injection at the casing slots increases the circulated flow rate inside the slots and minimizes the flow separation. It was found that the third model which contains casing slots only is the best comparing with other models in terms of decreasing the stall areas and increasing the compressor stability. Final results confirmed also that the casing treatment method increases the stability but reduces the isentropic efficiency.