Abstract
This paper deals with a theoretical approach to study the non-steady flow and wave action in a centrifugal impeller and vaneless diffuser, and also to predict the non-steady flow performance of a centrifugal compressor. This was carried out by replacing the compressor unit by a model which consisted of a simplified rotating duct, a vaneless diffuser, and a cone-shaped pipe which replaced the scroll.
A theoretical technique using the method of characteristics and the development of the non-steady flow equations to a rotating duct and radial diffuser is given. The development of the theory and the difficulties encountered are described. In particular, the techniques developed for starting a computer calculation are described.
In order to maintain homentropic flow in the impeller and diffuser all losses were assumed to occur at the impeller inlet. A pressure loss boundary condition was developed to enable the steady pressure ratio-mass flow characteristics to be computed. When these values agreed with the experimentally determined characteristics, the boundary condition at the rotor inlet was such that the pressure loss terms allowed for the impeller and diffuser losses.
The theoretical results obtained are compared with corresponding experimental results, and the possibility of using this theoretical technique as a design tool is discussed.
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