Numerical Analysis of Reynolds Stresses for Developing Turbulent Flow in a Square-Sectioned 90 Degree Bend.

Abstract

A computational study on developing turbulent flow in a square-sectioned 90 degree bend at Reynolds number of 4×104 is reported. The ratio of bend mean radius of curvature to hydraulic diameter is 2.3 and straight ducts 45 and 30 hydraulic diameters long are attached to the inlet and outlet planes of the bend, respectively. In calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulence precisely, and a boundary fitted coordinate system was introduced as the method of coordinate transformation. Calculated results were compared with the experimental data measured separately by two research groups. In this resarch, special attention is paid to the comparison of calculated results with the distribution of the Reynolds stresses. Moreover, the production mechanism of streamwise velocity fluctuation is examined by evaluating its production term for calculated results. In consequence of this calculation, it was found that the present method predicted relatively well the characteristic features of Reynolds stresses, although there are a few points of discrepancy. The examination of the production term for streamwise velocity fluctuation suggests that the production term including the streamwise velocity gradient with respect to bend angle plays an important role in its generation near the both side walls.