Effects of Air injection at Rotor Blade Row Tip Region of an Axial Compressor on its Performance under Inlet Distortion Conditions

Improvement of an axial compressor performance through suppression of flow disturbances due to inlet flow blockage, utilizing air injection at the blade tip region, is the subject of the present study. Method of investigation is based on experimental measurements conducted in a low speed isolated axial compressor rotor blade row. Four different blockage screens of different blockage ratios ranged between 5 and 20 percent of the inlet area are located at the compressor entrance. Instantaneous and time-averaged static pressure are recorded at different locations of compressor casing. Frequency analyses of pressure signals, show that the flow disturbances are being created in the presence of the blockage screens. These disturbances cause to appearance of rotating stall in the flow field when the compressor operates under distorted inflow with low blockage ratios (5 and 10%). To reduce the destructive effects of the inlet distortion, air is injected at the tip region of the rotor through 12 injectors which are located evenly spaced around the compressor circumference. Air injection in small quantities, 1.5% of main flow, has considerable effects on the compressor performance under inlet distortion. The rotor performance and compressor delivery pressure is improved up to 35% than to the no injection case. By implementation of Short-Time Fourier Transform (STFT) technique effects of air injection on elimination or reduction of flow disturbances are demonstrated, too.