Experiments were conducted to investigate the effects of using small exit vanes on the characteristics of an otherwise vaneless radial diffuser of outer radius and width-to-inlet radius ratios of 1.75 and 0.116, respectively. The steady and unsteady characteristics of the diffuser were evaluated as the angle of the vanes was varied continuously at several diffuser inlet conditions. The measurements showed that the influence of the adjustable exit vanes on the diffuser flow field increased as the diffuser inlet flow angle was decreased. Elimination of the self-excited flow oscillations in the diffuser was possible for all operating conditions by appropriate setting of the exit vane angle. Moreover for the diffuser investigated here and with optimum setting of the exit vanes angle the static pressure rise coefficient was significantly improved compared to the case of a pure vaneless diffuser and was found to remain almost constant at low values of diffuser inlet angles. Relative to other techniques for controlling flow instability in vaneless diffusers the proposed method offers mechanical simplicity and improved overall performance.

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