RESEARCH ON IMPROVEMENTS OF LRN TURBULENCE MODEL BASED ON FLOW AROUND AUTOMOBILE BODY 1)

doi:10.6052/0459-1879-20-095

Abstract

Abstract:

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.

Key words: transition mechanism, low Reynolds number turbulence model, RANS/LES mixed turbulence model, constrained large- eddy simulation

CLC Number:

O368

Qiang Guanglin, Yang Yi, Chen Zhen, Gu Zhengqi, Zhang Yong. RESEARCH ON IMPROVEMENTS OF LRN TURBULENCE MODEL BASED ON FLOW AROUND AUTOMOBILE BODY ¹⁾[J]. Chinese Journal of Theoretical and Applied Mechanics, 2020, 52(5): 1371-1382.

Figures/Tables 19

Fig. 1 Computational results for approximate simple models

Fig. 2 Comparison of the computational results of commonly used turbulence models

Fig. 3 Test model

Fig. 4 Unstructured (left) and structural grid (right) of the simplest automobile model

Table 1 Computational results based on structural and unstructured grids

Fig. 5 Model size, simulation computational domain and boundary conditions

Table 2 Drag coefficient and computational time based on different grid numbers

Fig. 6 Model computing grids

Table 3 Aerodynamic drag coefficient and aerodynamic lift coefficient ($\beta =0^\circ$)

Fig. 7 Aerodynamic drag and lift coefficient of the model

Fig. 8 Surface pressure distribution (continued)

Fig. 9 Streamline diagram at the head

Fig. 10 Vorticity diagram at the head

Fig. 11 Streamline diagram at the tail

Fig. 12 Numerical calculation for buffeting noise of the automobile model

Fig. 13 Model size, calculation domain and boundary conditions

Fig. 14 Aerodynamic noise computing grids

Fig. 15 SPL of the simulation and test

Table 4 Peak frequency of SPL

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RESEARCH ON IMPROVEMENTS OF LRN TURBULENCE MODEL BASED ON FLOW AROUND AUTOMOBILE BODY ¹⁾

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