AERODYNAMIC STUDY OF AXIAL DIFFUSER

Abstract

A diffuser is a device which is generally used to convert the kinetic energy of the moving fluid into pressure energy. When a fluid passes through diffuser it is retarded and diffusion comes into picture. Diffuser is an important member in a power plant, which generally increases the efficiency of the power plant by increasing the pressure. The requirements of fuels and water can be reduced and saved for the society with the help of good design diffuser. So, diffuser is a very important device. Lot of experimental research work has been done on the diffuser, but mathematical modelling is scantly available. Work on annular diffuser is also scantly available. The analysis of flow through annular diffuser are not studied at intermediate areas ratios 2.5, 3.5 and 4,5 etc. The present study involves the Computational Fluid Dynamic (CFD) analysis of annular diffuser with parallel hub and diverging casing. The characteristic quantities such as longitudinal velocity, swirl velocity, pressure recovery coefficient, flow patterns, flow separation and flow reversals have been analyzed graphically and numerically by using FLUENT Code. Variation of longitudinal velocity and Swirl velocity have been analyzed along the different diffuser passages heights at different traverses of (x/L) =10%, 20%, 40%, 60%, 80% and 90% along the axial direction of the annular diffuser. The variation of pressure recovery coefficient has been also analysed along the walls of Casing and Hub of the annular axial diffuser. We used vii second order scheme for momentum, swirl velocity and turbulent kinetic energy and Presto scheme for pressure. The Residual have been taken as 10-6 for x-velocity. Different turbulence models were used to obtain the results and finally it was found that the results of RNG k-ɛ turbulent model shows good agreements with the experimental results .So RNG k-ɛ turbulent model have been used to analyse the flow through the annular diffuser. Parametric investigations have been done at different area ratios of (2, 3, 2.5 & 4) and different swirl angles at the inlet (00, 7.50, 120, 170 & 250). Finally, the results are presented in terms of non-dimensional longitudinal velocity, swirl velocity and Pressure recovery coefficients and with the help of these results separation and development of flow through annular diffuser have been discussed.