DIRECT SIMULATION OF TURBULENT-FLOW IN A SQUARE DUCT - REYNOLDS-STRESS BUDGETS

The data base from a direct numerical simulation of turbulent flow in a square duct is used to calculate all the terms in the Reynolds stres s transport equations. The simulation of this complex turbulent flow w as performed at a Reynolds number of 600 based on the friction velocit y and the duct width. The distributions of the Reynolds stress budget terms along the wall bisector show similar dynamics to wall-bounded tu rbulent flows with one inhomogeneous direction. Budget terms in the vi cinity of the corner demonstrate how transport and redistribution of e nergy and shear stresses between the Reynolds stress components takes place, promoting the turbulence characteristics of secondary flows of the second kind. The redistribution of energy by pressure velocity cor relations can be explained by the low pressures at the cores of stream wise vortices. The data base is also used to evaluate a nonlinear turb ulence model in its ability to accommodate the anisotropy of the Reyno lds stress tenser in this flow. This anisotropy is known to be entirel y responsible for the formation of the secondary flow in noncircular d ucts and cannot be captured by linear models.