A LES Study of a Simplified Tractor-Trailer Model

Abstract

A numerical study using large eddy simulation (LES) of the flow around a simplified tractor-trailer model has been done. The model is that from the experimental investigation [1] and consists of two boxes placed in tandem arrangement. The Reynolds number based on the height of the rear box and free stream velocity is 0.51 x 106. The first box has normalized height, width and depth of 0.92, 0.92 and 0.67, respectively, and represents the cab of a truck. The second box has height, width and depth of 1, 1, and 2.5, respectively, and represents the load of a truck. The front box is lifted 0.21 above the simulated moving ground and the rear box is lifted 0.5. The aim of the present study has been to investigate the influence of the size of the gap between the tractor and the trailer on the flow physics and the resulting aerodynamic performance of the tractor-trailer model. Two different models have been investigated. One model with sharp front edges of the front box and one with rounded front edges of the front box. Experimental results [1] have shown that the two cases exhibit large differences in the drag coefficient depending on the gap width between the boxes. For smaller gap widths, the model with rounded front edges has a considerably smaller drag, while for larger but still practical gap widths the drag exceeds that of the sharp-edged model significantly. Simulations with three different gap widths for each model has been simulated using LES. The results has shown good agreement with the available experimental data from [1] for the sharp model but less accurate results for the rounded model even though the general trend is in agreement. The mean velocity field has been analysed and the flow physics responsible for the difference in drag for the models has been found.