Youichi Ando

Detection of a Rotating Stall Precursor in Isolated Axial Flow Compressor Rotors

Statistical characteristics of pressure fluctuation on the casing wall of two axial flow compressor rotors have been investigated experimentally to find a precursor of rotating stall. Near stall, the casing wall pressure across a flow passage near the leading edge is characterized by a highly unsteady region where low-momentum fluid accumulates. The periodicity of the pressure fluctuation with blade spacing disappears and an alternative phenomenon comes into existence, which supports the disturbance propagating at a different speed from the rotor revolution. The precursor of rotating stall can be detected by monitoring collapse of the periodicity in the pressure fluctuation. To represent the periodicity qualitatively, a practical detection parameter has been proposed, which is easily obtained from signals of a single pressure sensor installed at an appropriate position on the casing wall during operation of a compressor.

Pressure Fluctuation on Casing Wall of Isolated Axial Compressor Rotors at Low Flow Rate

The pressure fluctuations on the casing wall of two axial flow compressor rotors with various tip clearances have been analyzed by the use of two kinds of correlation functions. The behavior of the pressure fluctuation varies depending on tip clearance and blade solidity. In the case of small tip clearance, the nature of disturbances becomes random as the flow rate is reduced to a stall condition. For moderate tip clearance, coherent-structured disturbances appear intermittently at low flow rate. They appear more frequently as the solidity is increased and the flow rate becomes lower. For large tip clearance, the coherent structured disturbances exist even at considerably higher flow rates. Corresponding to these features, there are peculiar patterns in the correlation designated as phase-locked correlation functions.

Detection of a sign prior to rotating stall in an axial flow compressor rotor.

Pressure fluctuation on the casing wall of an axial flow compressor rotor has been investigated experimentally to find a sign prior to rotating stall. Statistical characteristics of the pressure have been obtained by a phase-locked data logging technique with high frequency response pressure sensors. Periodicity of the fluctuation, which has been examined in the phase-locked patterns of cross-correlation between two points in the relative reference frame, disappears near the stall. In order to monitor collapse of the periodicity qualitatively during operation of a compressor, a detection parameter has been presented which can be obtained from signals of a single pressure sensor mounted on the casing wall.

Tip clearance flow in axial flow impellers at low flow rate.

In two axial flow impellers with various tip clearances, behavior of tip clearance flow has been investigated experimentally by varying the flow rate from the deslgn point to a stall inception. As the flow rate decreases, a rolling-up axis of leakage vortex becomes more inclined towards the circumferential direction and fluctuates intermittently. Near stall, the rolling-up vortex disappears and the casing wall pressure is characterized by a highly fluctuating region across a flow passage near the leading edge where low-momentum fluid accumulates. Skewness of fluctuation is a negative value on the pressure side and tends to be positive on the suction side, probably due to the intermittent local separation at the leading edge.