CRITICAL COMPARISON OF 2ND-ORDER CLOSURES WITH DIRECT NUMERICAL SIMULATIONS OF HOMOGENEOUS TURBULENCE

Recently, several models have been proposed for closing the second-mom ent equations, in which the velocity-pressure gradient tensor and the dissipation rate tensor are two of the most important terms. In the li terature, these correlation tensors are usually decomposed into a so-c alled rapid term and a return-to-isotropy term. Models of these terms have been used in global now calculations together with other modeled terms. However, their individual behaviors in different flows have not been fully examined because they are unmeasurable in the laboratory. Recently, the development of direct numerical simulation (DNS) of turb ulence has given us the possibility to do this kind of study. With dir ect numerical simulation, we may use the solution to calculate exactly the values of these correlation terms and then directly compare them with the values from their modeled formulations. In this paper, we mak e direct comparisons of five representative rapid models and eight ret urn-to-isotropy models using the DNS data of 45 homogeneous flows, whi ch were done by Rogers et al. (1986) and Lee and Reynolds (1985). The purpose of these direct comparisons is to explore the performance of t hese models in different flows and identify the ones that give the bes t performance. The paper also describes the modeling procedure, model constraints, and the various evaluated models. The detailed results of the direct comparisons are discussed, and a few concluding remarks on turbulence models are given.