Investigation of separating and utilizing the influences of upand downstream blade rows

The superimposed influences of the blade rows in multistage compressor are important, because different matching status of upstream and downstream blades can result in significant differences in unsteady pressure fluctuations. Numerical investigation of the unsteady pressure distributions on axial stator blade, which affect by the axial rotor in the upstream and the radial rotor in the downstream, was performed in an axial-radial combined compressor. Unsteady pressure fluctuation was investigated. When rotors have equal blade numbers, the unsteady pressure fluctuates periodically versus time within T time. On contrast, it fluctuates irregularly within T time when they have different blade numbers. A model-split subtraction method to separate the influences of the individual blade rows on the profile pressure distribution of the axial stator was presented. Analysis from the rotor-stator configuration showed that the unsteady pressure fluctuation response caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady pressure fluctuations were influenced by up- And downstream blade rows. With the model-split subtraction method, the up- And downstream influences on the unsteady pressure could be clearly separated and quantified. High amplitudes were observed when the influences from up- And downstream moving rows were superimposed with "positive peakpositive peak" type wave. In contrast, the amplitudes were decreased by the opposite superimposition phase ("positive peak-negative peak" type wave). Clocking investigations were carried out for two goals. One is to show the isolated influence from up- or downstream rotor by eliminating down- or upstream influence components. This is called clocking subtraction method. The other one is to change the relative superimposed phase of influences from the surrounding blade rows. Thus, the physical mechanism of the unsteady pressure fluctuation amplitude modulation by means of clocking was put forward.