The design methods of typical supersonic aircraft intakes and shock wave compression technology have been applied to ram-rotor, a new attractive compression system. A ram-rotor is a typical structure including the compression ramp, the throat and the subsonic diffuser; a scrampressor is similar to ram-rotor, the only different is that scrampressor has no subsonic diffuser. Base on the preparatory work, it has been found that these two structures have different advantages respectively. So, in this paper, the three dimensional Reynolds-averaged Navier-Stokes equations and the Spalart-Allmaras turbulent model are used to simulate numerically the flow field of the ram-rotor and the scrampressor at the design and at the off-design conditions. The back pressure and rotational speed are mainly considered which may affect the flow field and the total performance. It has been found that back pressure can not have influence on the flow field before the throat outlet obviously. With increasing of the back pressure, the position of the flow separation zone and shock train move forwards to the inlet. The rotational speed changes the shock wave structure of the ram-rotor and scrampressor evidently. With the rotational speed increasing, each shock wave moves to the outlet and the shock wave number decreases. The ram-rotor and scrampressor structure is similar, except the ram-rotor flow structure has a large flow separation zone after the throat outlet. The compression capability of the ram-rotor is higher than that of the scrampressor. The total performance of the scrampressor is better than the ram-rotor.
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