The Calculation of Turbulent Flow in Wide-Angle

A method of calculating the properties of axisymmetric swirling and nonswirling turbulent recirculating flows in wide-angle diffusers is described and appraised. It is based on the numerical solution of differential equations in orthogonal curvilinear coordinates with a two-equation model to represent turbulence characteristics of the flows. The appraisal is achieved by comparing calculated results with measurements obtained In wide-angle diffusers with expansion half-angles of 20° and 45° and swirl numbers of 0 and 0.93. The results show that the mean velocity is represented within measurement accuracy for zero swirl number but, mainly due to the two-equation turbulence model, becomes less satisfactory with increasing swirl. Calculated values of the kinetic energy of turbulence are always significantly different from measurements, and the difference Increases with swirl The defects of the turbulence model, particularly its isotropic characteristic and inability to represent large streamline curvature and rotation, are examined and discussed, but the procedure is shown to be able to calculate symmetric, large-angle diffuser-type flows with precision adequate for many engineering purposes.