The ram-rotor presented by Ramgen Power Systems, Inc. is a new kind of compression system based on shock wave compression technology commonly used in supersonic intakes. Compared to conventional axial and centrifugal compressors, it has a simple and compact configuration, and also has advantages of the higher single stage pressure ratio, small volume and light weight. However, its efficiency should be further improved. Based on its inherent advantages, the ram-rotor can be widely used in small aero-engine, medium and small shipping power system, micro gas turbine employed by distributed energy system and power plant in the future. In this paper, the flow field and performance of a ram-rotor with different tip clearance sizes are simulated numerically by adopting the three dimensional Reynolds-averaged Navier-Stokes equations and the Spalart-Allmaras turbulent model at the design condition. The purpose of numerical simulation is to investigate the flow details and performance parameters of the ram-rotor under different tip clearance sizes, including the structure of the shock wave, the size and location of flow separation zone, radial distribution of flow parameters at the outlet of the ram-rotor, the characteristics of tip clearance leakage flow, and so on. It has been found that the performance of the ram-rotor is very sensitive to the tip clearance size. The overall performance parameters of the ram-rotor decrease greatly with the increase of the tip clearance size. So, the selection of suitable tip clearance size is one of the key issues in obtaining a high performance of the ram-rotor in the design process. For the ram-rotor with tip clearance, the reflection structure of the shock wave will be destroyed. The flow loss of tip region will be increased with the increase of the tip clearance size. For the ram-rotor with and without tip clearance, the flow parameters distribution trend along the radial direction at the outlet is different.
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