Experimental and numerical investigations on flow losses of a U-bend and return channel system for centrifugal compressor

The flow losses in a U-bend and return channel system of an inter stage has an important influence on the stage performance. To study the flow characteristics in such system, a pseudo-stage which consists of pseudo guide vanes, U-bend and return channel, combined with a normal stage, was designed and its performance curves were measured at different machine Mach numbers. Simultaneously, the numerical simulations, in which different data processing methods of CFD post process were adopted, were performed and the prediction accuracy was verified by comparison with the experimental results. The results indicated that the design of pseudo guide vanes provides an approximately constant flow direction at the inlet of U-bend with the variation of inlet Reynolds number, which matches the blade metal angle of the return channel well. The further analyses on the measured and numerical results showed that the loss characteristics vary with the inlet Reynolds number. When the Reynolds number is greater than a critical Reynolds number, the loss coefficient in the U-bend and return channel keeps nearly constant. The non-uniformity of flow angle and total pressure at the outlet of return channel were also illustrated and discussed.