EN Fluid dynamic design of centrifugal compressor diffusers

Abstract

Diffusers are used to convert the kinetic energy of the gas flow into potential energy, i.e. to reduce the velocity and to increase the pressure. The most common types of diffusers are vaneless, vaned, and channel ones. Each type of diffuser has its design features and its performances. Improving the operational cha­racteristics of vaneless diffusers is possible by using stepped diffusers with flow injection. The developed mathematical model of gas flow in a vaneless diffuser with flow injection provides design of the stage of centrifugal compressor with the wider range of stable operation. Traditional methods of designing vaned and channel diffusers of turbomachines are focused on the use of simple geometric lines and surfaces, such as a straight line, arc of a circle, plane, cylindrical surface, etc. The design is performed according to recommendations based on experimental data. The other way of designing the vaned and channel diffusers of turbomachines is related to solving the inverse problem of fluid dynamics, when the shape of the surfaces is determined by the given distribution of velocities along the surfaces of the channel. This paper describes the design principles for the centrifugal compressor diffusers based on physical and mathema­tical models of the flow of swirling viscous compressible fluid. According to the presented method, the designing diffusers are based on the preseparation condition of the boundary layer along one of the surfa­ces. Such a design ensures a reduction in separation zones in the channels of the diffusers and, accor­dingly, a reduction in total pressure losses and an expansion of the range of stable operation. A new method of designing the vaned and channel diffusers provides an improvement in the gasdynamic characteristics of diffusers compared to traditional geometry diffusers