Experimental Analysis of Unsteady Blade Rows Interaction in a Multistage Turbomachine

The object of our investigation is an experimental analysis of the unsteady interactions between a fixed row (stator) and the moving blade rows (rotors) in turbomachines. Two methods are developed for data processing. The first one which is based on spectral analysis is developed to identify periodic and random flow fluctuations. Using this method, the data acquisition period needed is reduced four times comparing to the one needed by ensemble averaging method used until now. The second method takes into account some characteristics of periodic disturbances identified by the first method, to determinate the instantaneous flow fields in all stator passages by using space time measurement in one passage. An important gain of measurement duration and grid is obtained. These methods are applied for unsteady measurements carried out upstream and downstream of the first stator of a four stage axial flow compressor. The results show the importance of rotor/rotor and rotor/stator blade numbers ratio on flow unsteadiness