Large eddy simulation of turbulent flow in a square annular duct

The fully developed turbulent flow in a straight square annular duct is simulated using large eddy simulation (LES). The flow Reynolds number is 200 based on the mean friction velocity and half the hydraulic diameter of the annular duct. A grid refinement study is carried out using 130x66x66 (0.57 million) and 130x130x130 (2.2 million) control volumes, respectively. The mean flow field and the turbulent statistics are compared with existing experimental and numerical data for square duct flow. Acceptable agreement is obtained. A universal relation between the mean streamwise velocity and the distance away from a concave 90 degrees corner along the corner bisector is derived by curve-fitting the results from both LES in a square annular duct and direct numerical simulation in a square duct. The results from the present investigation exhibit the distinctive secondary flow of Prandtl second kind, which consist of a chain of counter-rotating vortex pairs around both convex and concave 90 degrees corners in the annular duct. Mechanisms responsible for the generation of the secondary flow are interrogated by analyzing the anisotropy of the Reynolds stress distributions. (C) 2001 American Institute of Physics.