Study on Unsteady Flow Induced by Annular Cascade

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To investigate phenomena of an unsteady flow induced by annular cascade of inlet guide vanes for a centrifugal compressor, experiments and numerical analysis were conducted. In experiments, fluctuating wall pressure distributions were measured by small semi-condustor pressure transducers and instantaneous velocity distributions at 10% chord length after the cascade were gotten by a hot-wire anemometer and flow streak lines around the vanes were visualized by sheet light of an argon ion razor and smoke. As a result, the followings are found : (1)In case that blade setting angle from radial direction is smaller than 30 degrees, the unsteady flow with noise is not induced, but in case that the angle is larger than 50 degrees, the unsteady flow is produced. (2)A core installed in center of a pipe passage to reduce unsteadiness of a swirling flow does not affect occurrence of the unsteady flow with noise. (3)Both blade width and chord length also have no influence for the occurrence of the unsteady flow. (4)Fundamental frequency of the unsteady flow almost has a linear relation to flow velocity. (5)Strouhal number is constant and independent of Reynolds number in some flow conditions. (6)The occurrence of the unsteady flow is considered to have a relation to flow separation from blade surface. (7)Flow direction of blade wake strongly fluctuates under the occurrence of the unsteady flow. (8)The unsteadiness travels counter direction of swirling stall cell. (9)A tab protecting the unsteady flow with noise is quit effective. Furthemore, numerical analysis was success in simulation of pressure fluctuations corresponding to be experimental results in 60 degrees of angle. Accuracy of calculation is not yet sufficient but it is say that the numerical opens the way to establish a flow model for the unsteady flow induced by annular cascade.