Injection profile effects on low speed axial compressor stability enhancement

This study presents stability enhancement of a four-stage low speed axial compressor with different injection profiles. The injection profiles include one-step injection, multi-step injection, and continuous injection. For the tip injection, eight Coanda-shaped nozzles have been installed at eight equally spaced circumferential locations upstream of the first stage rotor. Two external blowers injected air steadily through the Coanda-shaped nozzles. With tip injection, the compressor operation range has been extended. To analyze stall margin improvement, spatial Fourier transform (SFT) has been performed. The coefficient of SFT (SFC) is a complex number, containing information about the magnitude and the phase of SFC. By analyzing the distribution of the magnitude and the phase of SFC, the stall onset point has been verified. Furthermore, the injection flow rate has been changed during injection process to examine the possibility of attaining an additional flow extension. Increasing the injection rate during stabilization can bring about additional operation range extension. These results suggest a new injection method to reduce the total amount of the injection air.