High-frequency pressure oscillations of rotating stall type. Part 2: Fields of high-frequency oscillations

High-frequency oscillations with main oscillating frequency greater than that of rotor rotation and less than that of blade passing frequencies were discovered before, during and after rotating stall. These high-frequency oscillations existed only at high rotor speeds (n/n(d) = 0.8 and n/n(d) = 0.95). The oscillation amplitudes of high-frequency and main blade passing components were identical. Therefore, both components are considered simultaneously. In this paper, the variations of filtered signals of both components in compressor circumference and time are demonstrated. It is shown that circumferential modes of parameter (especially pressure) perturbations perfectly represent the structure of parameters in compressors during high-frequency oscillations. In general, the numbers of circumferential modes of pressure perturbation oscillating with high-frequency and main rotor blade passing frequency are usually not equal. (In one compressor transverse cross-section may rotate different, usually unequal numbers of modes oscillating with different frequencies.) Thus, the rotational speeds of these modes are also not equal. In the investigated cases, the second, third, fourth and fifth modes of high-frequency oscillations rotate simultaneously with the fourth mode of the blade frequency component.