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A model has been assumed to predict the hydraulic and disc friction losses in a radial compressor stage. A potential three dimensional flow field inside the impeller is solved, by using TSONICMR program. Then, the hydraulic and disc friction losses sere predicted for the impeller, vaneless diffuser and the collector. Experimental investigation has been carried out for a radial compressor stage, in order to verify the validity of the assumed model. The pressure ratio and efficiency were measured for different mass flow ra•3s. at different rotating speeds. The results showed satisfactory agreement with that predicted . INTRODUCTION The centrifugal compressors are today playing an essential role in the gas turbine applications. In small gas turbines, single stage radial compressor is usually replacing the multistage axial compressor. However, much work remains to be elaborated such that the flow inside the compressor is fully understood to predict it's behaviour. The main part of the compressor is the impeller, as it delivers the energy to the fluid flowing through it. In the same time, it affects the flow upstream the diffuser stage and hence it's performance. The difficulties of predicting the flow inside the impeller 'nee be partly attributed to the complex geometry of the flow passages. They are rotating curved passages from the axial to the radial direction. Also for open, or semi—open, impellers the tip leakage has an important effects on the flow field. Furthermore the viscosity and flow separation affect the build—up of the boundary layer and the deviation of the flow from potential. behaviour. Herein, the ideal potential compressor characteristics has been predicted, by using the modified version of the TSONICMR program, (1l. A loss model for both hydraulic and disc friction has been * Senior Engineer of a Power workshop, Armed Forces. ** Assoc. Prof.. Mech. Power Dept., *** Prof., Aircraft Dept.. Military Tech. College **** Head of Aircraft Group. Tech. Ins. Of Armed Forces. Egypt. FOURTH ASAT CCI4FEI=ENCE 14-16 May 1991, CAIRO PR-2 192 developed for the impeller, vaneless diffuser and for the collector. The losses have been assumed to occur due to incidence, viscous and mixing losses, as well as mechanical disc friction around the impeller. A computer program RISTIC has been written to evaluate the actual characteristics of the compressor stage, [5]. The obtained results have been verified experimentally for a model compressor stage of outer diameter of 100 mm. IPOTENTIAL FLOW SOLUTION It has been established earlier that the flow through stationary or rotating cascade cannot be axisymmetric if the flow has to exert a moment on the blades. It is for this reason an arbitrary flow through a cascade does not have stream surfaces of revolution or axisymmetric shape. Exceptions are the incompressible flow in radial cascades with stream surfaces of planes perpendicular to the axis, (2). I.1QUASI 3-DIMENSIONAL FLOW Quasi 3-dimensional flow may be evaluated by combining the flow fields in the meridional plane and for the blade-to-blade surface of revolution. The meridional flow solution is firstly evaluated for the meridional streamlines. The stream sheets are then defined as that bound the streamlines. The blade-to-blade solution has been evaluated for each stream sheet by using the TSONICMR program, [1]. On the other hand the stream sheets geometries may be obtained by assuming equal flow areas. For 3-dimensional potential flow, the flow equation may be written in a rotating cylindrical coordinates, ( m, and r ), as, (3] : d W 1 d(Ln R) 0 R2 d d m2 R2 a d a (Ln. R) (,d d d 2 b P =o =0-z. (1) st:-eam function could be normalized by writing : U / (2) where w is the mass flow rate per stream sheet. Then equation (1) could be reduced to 1 d 2 U d 2 1 1 a u ._4 2 '7in .Lt 3f . J .; z + r t_L_L. ] --R` d a al R d i) 0 ,:r R 2 b o 4.0 • min (3) while If the flow is entirely subsonic, equation (3) for supersonic flow it is hyperbolic. The boundary conditions could be defined meridional flow channel, Fig.(1), is divided tr.: FOURTH ASAT CONFERENCE 14-16 May 1991, CAIRO PH-2 193

EXPERIMENTAL AND THEORETICAL INVESTIGATION OF LOSSES IN A RADIAL COMPRESSOR STAGE