RESEARCH ON IMPROVEMENTS OF LRN TURBULENCE MODEL BASED ON FLOW AROUND AUTOMOBILE BODY

The flow around automobiles was modularized into typical local flows in this paper. Through analyzing the characteristics of typical local flows, it is verified that the capture ability of turbulence model to transition is the key to accurately simulate the flow around automobiles. The paper optimized the solutions of steady-state and transient-state problems by analyzing the separation and transition mechanism of the flow, promoted the prediction ability of turbulence model for transition and improved the accuracy of turbulence model for automobile flow field simulation. For the steady-state solution of the flow around automobiles, by introducing the streamline curvature factor and the response threshold into the low Reynolds number (LRN) k-\varepsilon model proposed by Jones and Lauder, a modified low Reynolds number turbulence model (modified LRN k-\varepsilon ) which can predict transition more accurately was obtained. This model alleviated the problems of the original model's over-dependence on the turbulent dissipation rate and the insufficient prediction of the total stress development. For the transient-state solution, by analyzing the characteristics of the RNAS(Reynolds-averaged Navier-Stokes equations)/LES(large eddy simulation) mixed turbulence model, introducing the constrained large eddy simulation (CLES) method and the modified LRN k-\varepsilon turbulence model proposed in this paper, a transition LRN CLES model that can accurately predict the transition was proposed. These improved models were applied to the simulation of the external flow field and buffeting noise of a real automobile model respectively. Computations were carried out using the ANSYS Fluent solver. The calculation results were compared with the simulation results of the commonly turbulence models, HD-2 wind tunnel test results and real vehicle road test results, it show that the improved turbulence models can more accurately simulate the steady-state and transient-state characteristics of the complex real automobiles, which provides a reliable theoretical basis and effective numerical solution method for the study of automotive aerodynamic.