Three types of annular diffusers associated with radial and mixed flow turbocharger compressors have been studied both experimentally and theorticaly. The investigations have been carried out on model diffusers six times larger than the normal turbocharger in order to enable detailed flow traverse measurements to be carried out. These measurements have been obtained using both a five hole yaw probe and a hot wire anemometer in order to observe the development of the flow profiles throughout the diffuser with particular reference to flow stability. To measure the onset and development of unstable flow flush mounted wall pressure transducers were employed. Radial, curved annuler and straight annuler diffusers have been tested in order to study their relative merits. Two curved diffusers, which are used with mixed flow compressor impellers, have been studied. It has generally been observed that the straight annular diffuser was the least stable, with the radial diffuser having the best stability characteristics. For mixed flow compressor designs, therefore, the curved annular diffuser, which turns the flow from the conical to radial direction, is to be prefered. The theoretical analysis employed the finite element method to solve the basic Navier-Stokes equations using a stream function-vorticity formulation, with the common two equation, k- turbulence model. In order to obtain solutions at high Reynolds numbers a dynamic mesh system was used which solved for the required properties at the centre node only using the variational method. The mesh was then regenerated so that each non-boundary node become a centre node in turn. The theoretical analysis has been used to study the effect of inlet velocity profiles upon the stability of the diffuser. The analysis indicated the type of velocity profiles which should be avoided if possible.
|Date of Award||1983|