Aerodynamic Study of Axial Diffuser

Abstract

A diffuser is a device which is generally used to convert the kinetic energy of the newlinemoving fluid into pressure energy. When a fluid passes through diffuser it is retarded newlineand diffusion comes into picture. Diffuser is an important member in a power plant, newlinewhich generally increases the efficiency of the power plant by increasing the pressure. newlineThe requirements of fuels and water can be reduced and saved for the society with the newlinehelp of good design diffuser. So, diffuser is a very important device. Lot of newlineexperimental research work has been done on the diffuser, but mathematical modelling newlineis scantly available. Work on annular diffuser is also scantly available. The analysis of newlineflow through annular diffuser are not studied at intermediate areas ratios 2.5, 3.5 and newline4,5 etc. The present study involves the Computational Fluid Dynamic (CFD) analysis newlineof annular diffuser with parallel hub and diverging casing. The characteristic quantities newlinesuch as longitudinal velocity, swirl velocity, pressure recovery coefficient, flow newlinepatterns, flow separation and flow reversals have been analyzed graphically and newlinenumerically by using FLUENT Code. Variation of longitudinal velocity and Swirl newlinevelocity have been analyzed along the different diffuser passages heights at different newlinetraverses of (x/L) =10%, 20%, 40%, 60%, 80% and 90% along the axial direction of newlinethe annular diffuser. The variation of pressure recovery coefficient has been also newlineanalysed along the walls of Casing and Hub of the annular axial diffuser. We used newlinevii newlinesecond order scheme for momentum, swirl velocity and turbulent kinetic energy and newlinePresto scheme for pressure. The Residual have been taken as 10-6 newlinefor x-velocity. newlineDifferent turbulence models were used to obtain the results and finally it was found that newlinethe results of RNG k-and#603; turbulent model shows good agreements with the experimental newlineresults .So RNG k-and#603; turbulent model have been used to analyse the flow through the newlineannular diffuser. Parametric investigations have been done at different area ratios of (2, newline3, 2.5 and 4) and different swirl angles at the inlet (00 newline, 7.50 newline, 120 newline, 170 and 250 newline). Finally, the newlineresults are presented in terms of non-dimensional longitudinal velocity, swirl velocity newlineand Pressure recovery coefficients and with the help of these results separation and newlinedevelopment of flow through annular diffuser have been discussed. newline newline