Abstract

Blade loading on a single stage high pressure centrifugal compressor is limited due to separation that might occur on the suction side of the airfoil at mass flow rates lower than design point. A novel configuration of centrifugal compressor is designed and analyzed to overcome this issue by placing multiple rotors on the same hub with a stator vane in between similar to a multi-stage axial compressor blade arrangement. By having independent rotors, blade loading can be distributed more efficiently and higher pressure rise can be achieved through this design. As the blade chord length is reduced due to splitting of single impeller blade, the effective turning angle is divided through several stages thereby lowering the adverse pressure gradient reducing the chance of separation. Stator vanes are placed in between the rotors so that the successive rotor receives the flow at desired incidence angle. The attempt here is to apply the same principle of axial compressor multi-staging on a centrifugal compressor and compare the performance with single stage using low to high fidelity analysis framework developed in-house. A low fidelity 1D analysis tool CIMdes is used for evaluating blade angles and stage degree of reaction which are exported to T-blade3, in-house parametric geometry tool, for 3D blade generation. These blades are further analyzed using 3D CFD analysis using an in-house automated multifidelity framework. Loss quantification revealed that diffuser losses are higher in singlestage and the novel design increased the backsweep angle resulting in lower diffuser losses. Splitting the single rotor facilitated the increase in backsweep angle to a larger range as compared to single rotor impeller configurations. Two configurations with different shroud height for the single stage compressors are investigated and compared with the novel compressor with respective flowpaths at 100% speedline using a multi-fidelity design analysis suite. The flow capacity is extended near the stall with a penalty in efficiency for configuration-1. Configuration-2 showed an improvement in efficiency at design mass flow rate. The preliminary analysis demonstrates the advantages of the multi-staging on the same hub and extends the design space for performance range improvement with some trade-offs.

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