Large eddy simulation of turbulent flow in a square annular duct

The fully developed turbulent flow in a straight square annular duct is sim ulated using large eddy simulation (LES). The flow Reynolds number is 200 b ased on the mean friction velocity and half the hydraulic diameter of the a nnular duct. A grid refinement study is carried out using 130x66x66 (0.57 m illion) and 130x130x130 (2.2 million) control volumes, respectively. The me an flow field and the turbulent statistics are compared with existing exper imental and numerical data for square duct flow. Acceptable agreement is ob tained. A universal relation between the mean streamwise velocity and the d istance 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 pre sent investigation exhibit the distinctive secondary flow of Prandtl second kind, which consist of a chain of counter-rotating vortex pairs around bot h convex and concave 90 degrees corners in the annular duct. Mechanisms res ponsible for the generation of the secondary flow are interrogated by analy zing the anisotropy of the Reynolds stress distributions. (C) 2001 American Institute of Physics.