GB920260A - Improvements in supersonic compressors - Google Patents

Abstract

920,260. Centrifugal land axial - flow compressors. COMMISSARIAT A L'ENERGIE ATOMIQUE. July 2, 1959 [July 7, 1958], No. 22802/59. Class 110 (1). In a supersonic compressor in which the velocity of flow through a blade passage is reduced to a subsonic value by means of a normal shock wave, the passage so shaped upstream of the shock wave as to produce a succession of expansion waves producing an acceleration upstream of the normal shock wave. This stabilizes the position of the shock wave. In the axial-flow compressor shown in Fig. 1, the velocity V a at the exit from the guide blades 1 may be Mach 0.7, the rotor peripheral velocity U is Mach 1.2, and the relative velocity V r at entry to the rotor blades 2 is Mach 1.6. The initial portion AB of the suction face of each blade 2 is substantially straight and parallel to V r . The following portion BC is slightly convex, preferably with constant curvature, the tangent at B making an angle of about 7 degrees with that at C. The end C preferably occurs at the termination of a shock wave A‹C starting from the leading edge A ‹ of the following blade 2. The portion CD is straight, and the portion DF beyond the normal compressive shock wave D‹ may be a continuation of CD or may be curved. The pressure face I may be substantially straight. Expansion waves, such as d 1 , d 2 , d 3 occur at the curved region BE, and accelerate the flow upstream of the normal shock wave D‹, producing a non-uniformity of flow velocity which causes the shock wave D‹ to be convex towards the downstream direction. This convexity is stated to assist the stabilization of the shock wave D ‹. Any displacement of the shock wave D ‹ produced by an alteration in the flow velocity causes a variation in the suction exerted on the shock wave by the expansion waves in the sense opposing the displacement, thereby stabilising the new position of the shock wave. The flow is subsonic downstream of the shock wave D‹. The pressure face I may have an initial curved portion, this portion and the portion BC of the suction face then each being curved through an angle of 3.5 degrees. In the centrifugal compressor shown in Fig. 4, the suction face of each diffuser blade 4 comprises a concave spiral portion AB producing compression waves directed towards the impeller 3, the end B corresponding to the last compression wave BA‹ capable of reaching the impeller without being intercepted by the leading edge A‹ of the next blade. As in the previous embodiment, expansion waves are produced at a curved portion BC of the suction face of each blade 4, the portion BC being curved through 7 degrees and preferably terminating at the place where an oblique shock wave starting from A ‹ reaches the suction face. The remainder of the suction face is straight. The pressure face of each blade 4 may be convex, with an initial straight portion. Subsonic diffusion occurs downstream of the normal shock wave D ‹, and guide blades 5 may be provided.