Ledovskaya N.

As is known, the compressor noise is attributed to the sources connected with unsteady flow pattern that forms in compressor flow path, in particular under action of propagating upstream and downstream disturbances. The experimental investigation of unsteady flow pattern in stages being models of fans having different gasdynamic and geometrical design parameters was conducted. The investigations were performed with the fast-response pressure sensors. The frequency ranges when measuring oscillations of total pressure and static pressure was 25-40kHz. The special methodology for processing the readings of fast-response sensors was developed. It permits: to visualize unsteady flow pattern in the tip section of rotor blade passages, in the inlet and outlet ducts by constructing pressure isolines; to determine unsteady flow parameters in the tip section of the wheel and in the inlet and outlet ducts, such as flow velocity in absolute and relative motions, blade angles, values of tip clearances for each blade, fields of losses and pressure ratios; to create cartoon films visualizing location and displacement of shock in blade passages. It was shown: 1-flow dynamics intensification in the zone of shocks formation in blade passages, change in amplitude-frequency contents of oscillation at change in operating mode. 2-the flow disturbances upstream of the stage at shock expulsion are 6-12 times higher than those with flow having subsonic velocity. 3-as the upstream distance from the rotor increases, the energy of oscillations shifts from band at blade passing frequency to band at rotor frequency, and near the stability boundary the fluctuation energy increases 2–3 times as compared with the optimal point. When flow over the leading edges is shock-free, the pressure fluctuations in the inlet duct can be 5-15 db lower than those with shocked flow over.