Multi-Disciplinary Aerodynamics Analysis for Vehicles: Application of External Flow Simulations to Aerodynamics, Aeroacoustics and Thermal Management of a Pickup Truck 2007-01-0100

During the design process for a vehicle, the CAD surface geometry becomes available at an early stage so that numerical assessment of aerodynamic performance may accompany the design of the vehicle's shape. Accurate prediction requires open grille models with detailed underhood and underbody geometry with a high level of detail on the upper body surface, such as moldings, trim and parting lines. These details are also needed for aeroacoustics simulations to compute wall-pressure fluctuations, and for thermal management simulations to compute underhood cooling, surface temperatures and heat exchanger effectiveness. This paper presents the results of a significant effort to capitalize on the investment required to build a detailed virtual model of a pickup truck in order to simultaneously assess performance factors for aerodynamics, aeroacoustics and thermal management. This type of multi-disciplinary approach using a single virtual model is referred to as “total vehicle analysis” or “TVA”, and allows for optimization across disciplines. Simulations are carried out using the commercial code PowerFLOW from Exa Corporation for a prototype pickup, and are used to produce performance metrics for each TVA discipline. For aerodynamics, the drag coefficient, front-end cooling flow rate (with cooling fan off), and static pressures are computed; for aeroacoustics wall-pressure fluctuation spectra are produced on the upper body and underbody, and for thermal management, cooling flow performance and surface temperatures of underhood components and are produced. Thorough analysis and visualization of the simulation results show the importance of detailed geometry for prediction of flow structures and surface pressures which are critical for accurate prediction of aerodynamic and aeroacoustic performance. Coupling between the PowerFLOW simulation and thermal simulation tools are also used: Exa PowerCOOL is used to compute the 1-D coolant performance, and RadTherm from ThermoAnalytics, Inc., (TAI) is used to compute radiation from hot surfaces in the underhood and underbody, leading to surface temperatures for the underhood cooling simulations. Visualization of underhood flow shows the relationships between flow features at the fascia and underbody with cooling airflow within the underhood region. Finally, the process for incorporating this type of simulation data into the design process for vehicles is explored.