Numerical analysis of developing turbulent flow in a rotating U-bend of strong curvature with roughened walls

A numerical analysis has been performed for three-dimensional developing turbulent flow in a rotating U-bend of strong curvature with rib-roughened walls by using an algebraic Reynolds stress model. In this calculation, an algebraic Reynolds stress model is adopted in order to predict preciously Reynolds stresses and boundary fitted-coordinate system is introduced as the method for coordinate transformation to set exact boundary conditions along complicated shape in rib-roughened walls. Calculated results of mean velocity and Reynolds stresses are compared with the experimental data in order to examine the validity of the presented numerical method and an algebraic Reynolds stress model. It has been pointed out as a characteristic features from the experimental result that positive rotation leads to a more uniform velocity distribution within bend, whereas, the high momentum fluid remains closer to the inner side with negative rotation. The present method can relatively predict such velocity profiles and reproduce the separated flow generated near the outer wall which is just located at downstream of curved duct. Besides, calculated results suggest clearly that the flow pattern of secondary flow is greatly influenced by the rotational direction and the flow pattern with negative rotation is similar to that without rotation. As for the comparison of Reynolds stresses, the present turbulent model relatively predicts the experimental data well except for the flow separated region which is located near the outlet cross section of curved duct. (author)