Optimization of A Recirculation Flow Type Casing Treatment with Guide Vanes for Centrifugal Compressors

A wider operating range as well as higher performance are necessary for turbocharger compressors so as to meet demands of modern engines. Recirculation flow type casing treatment is one of the most effective devices that have been widely investigated. Recirculating flow type casing can extend the operating range of the compressor to the low flow rate region by sucking the reverse flow at shroud wall side at small flow rate condition. The advantages of the recirculation flow type casing treatment are well known as (1) a low energy fluid is sucked out from the down-let slot located near a throat of a rotating impeller (2) flow incidence is reduced because that recirculation flow merges with incoming main flow upstream of the impeller inlet. However, increase in friction loss and mixing loss resulted from the casing treatment can be considered as the disadvantages of the casing treatment. In the present study, an application of three-dimensional guide vane with 14 blades inside the casing treatment is presented to overcome the disadvantages of the casing treatment. And it shows improvement compared with the guide vanes with 7 blades. The shape of the guide vanes were optimized by using a surrogate model assisted optimization code. Numerical results showed that the optimized guide vanes hold a possibility to improve off-design performance by reducing the excessive pre-whirl at the compressor inlet.