Experimental and Numerical Investigation into Turbulent High Reynolds Number Flows Through a Square Duct with 90-Degree Streamwise Curvature - II Numerical Methods

Abstract

A square duct with a 90-degree streamwise curvature is representative of complex flow domains. Such flow domains are encountered in the designs of fluids engineering systems, especially in the aerospace turbo-machinery components. Examples include the gas turbine engine axial compressor interstage spaces, where the rise in air pressure (and hence compressor efficiency) is dependent on suppression of turbulence. In the case of the centrifugal compressor, pressure rise in the Ushaped diffuser assembly where the suppression of turbulence is critical to the attainable pressure ratio. The results obtained from numerical calculations are analysed and discussed along with the corresponding hot-wire measurements and flow visualization result from a wind-tunnel of identical configuration. Calculations are implemented in four turbulent models, i.e. Standard k-e Module, Algebraic Stress Model (ASM), Non-linear Renormalization Group (RNG) - k-e Model and Differential Stress Model (DSM). The discretization up-winding scheme is the Quadratic Up-winding with Interpolation Kinematics (QUICK). Two high Reynolds number turbulent flows are investigated, with mainstream velocities of 12.3 m/s and 20.4 m/s, representing Re=3.56x105 and Re=6.43x105 respectively. Generally strong correlation between theory and experimental data are recorded. Further, as reported in similar studies, the turbulence modules that are formulated to account for turbulence anisotropy return results that more closely match experimental measurements. Uniquely for this configuration, a massive flow detachment is predicted along the convex wall at about the 90˚ position. Also, the core of the fluid flow is observed to shift from the outer to the inner areas of the bend in proportion to the secondary (recirculating) flow generated by the bend.