Computational Analyses of the Effects of Wind Tunnel Ground Simulation and Blockage Ratio on the Aerodynamic Prediction of Flow over a Passenger Vehicle

Abstract

With the fast-paced growth of computational horsepower and its affordability, computational fluid dynamics (CFD) has been rapidly evolving as a popular and effective tool for aerodynamic design and analysis in the automotive industry. In the real world, a road vehicle is subject to varying wind and operating conditions that affect its aerodynamic characteristics, and are difficult to reproduce in a traditional wind tunnel. CFD has the potential of becoming a cost-effective way of achieving this, through the application of different boundary conditions. Additionally, one can view wind tunnel testing, be it a fixed-floor or rolling road tunnel, as a physical simulation of actual on-road driving. The use of on-road track testing, and static-floor, and rolling-road wind tunnel measurements are common practices in industry. Subsequently, we investigated the influences of these test conditions and the related boundary conditions on the predictions of the aerodynamic characteristics of the flow field around a vehicle using CFD. A detailed full-scale model of Hyundai Veloster with two vehicle configurations, one with the original and the other with an improved spoiler, were tested using a commercial CFD code STAR-CCM+ from Siemens. Both vehicle configurations were simulated using four different test conditions, providing overall eight different sets of simulation settings. The CFD methodology was validated with experimental data from the Hyundai Aero-acoustic Wind Tunnel (HAWT), by accurately reproducing the test section with static floor boundary conditions. In order to investigate the effect of the blockage ratio on the aerodynamic predictions, the vehicle models were then tested with moving ground plus rotating wheel boundary conditions, using a total of four virtual wind tunnel configurations, with tunnel solid blockage ratios ranging from 1.25%, which corresponds to the actual HAWT, to 0.04%, which presents an open air driving condition.

CNN-based flow field prediction for bus aerodynamics analysis

“…The bus and Ahmed body geometries combined with the domain defined according to the specified wind-tunnel dimensions amount to a blockage-ratio of around . Furthermore, the effect of the BR for ground vehicle simulations in open jet wind tunnels has been studied by Fu et al 15 , concluding that increasing the BR yields and overprediction in drag compared with the free air drag. The larger the BR the greater the interference effect is, and therefore drag predictions are less accurate.…”

Drag on Passenger Cars: Computational Fluid Dynamics Analysis of 2D Body Design Using ANSYS Fluent

“…1.1.2. Computational Fluid Dynamics Computational Fluid Dynamics (CFD) is an innovation that is 70+ years old, developed in the 1950s, that has revolutionized the analysis of the drag forces (Fu et al, 2020). CFD was popularized with ANSYS Fluent software in the late 1970s and with many other packages thereafter.…”

Research on precise and standardized numerical simulation strategy for vehicle aerodynamics

“…Based on the improved delayed detachment simulation (IDDES) model, Wang et al (2018) studied the effect of relative ground motion on a slipstream with three different ground/ wheel configurations. Combined with the elliptical equation, an algebraic mesh generation method was introduced to construct a high-quality mesh for the simulation of vehicle aerodynamics (ElCheikh and ElKhoury, 2019;Fu et al, 2020) conducted a comparative analysis of the influence of ground boundary conditions on the simulation accuracy of airflow around a vehicle. The effect of an air deflector on the aerodynamic drag of a truck has been studied using a hybrid grid technique (Li et al, 2008).…”