The Simulation On Aerodynamic Characteristics Of A Car With The Underhood And Bottom Details Considered

Recent years, with the improvement of vehicle design level and the rapiddevelopment of high-grade highway, the running speed and aerodynamic force ofvehicles are gradually increasing, which has a great effect on the dynamic property, fueleconomy and handling stability of vehicles. Therefore, the study of aerodynamiccharacteristics of vehicle becomes an important research task during the development ofa new model. Generally, numerical simulation and wind tunnel test are integrated toresearch automotive aerodynamics. With the use of CFD numerical simulationtechnology, aerodynamic characteristics and flow regime distribution of automobilescan be easily obtained in a short period of time, which may provide straightforwardbasis for vehicle design.At present, the domestic CFD simulation of car is generally conducted withouttaking interference and influence of airflow through the underhood and complex shapeof the car bottom into account, which cannot guarantee calculation accuracy and theaerodynamic modeling details. To this end, theory-based on computational fluiddynamics and automobile aerodynamics, a research is carried on in this thesis to studythe aerodynamic characteristics of a new car model considering the internal flowinfluence of underhood and bottom structure details. The specific research and resultsare as follows:1. The theory study of the car external flow field is conducted. In addition, SSTk-ω turbulence model and SIMPLE calculation method are confirmed to run thesimulation.2. The geometry models of two CFD simulation schemes are established. Thecalculation domain and grid layout are also set up.3. The simulation of external flow field around a car is conducted regardless of theinfluence of underhood and bottom structure details. Body surface pressure distributionis gained. Furthermore, flow separation phenomenon and the trailing vortex flows arestudied in detail based on the velocity vector diagram. The air drag coefficient and liftcoefficient are calculated. And the car body is divided into11boundaries to analyze thecontribution rate to the air drag coefficient of each boundary.4. The numerical simulation calculation of flow field is carried on considering the influence of underhood and bottom structure details. The pressure distribution of bodysurface and underhood are analyzed, as well as the influence of internal flow on theflow field around the car. Also, the air drag coefficient and lift coefficient are got. Thecontribution rates to drag coefficient of14body boundaries with underhood componentand bottom structure considered are gained as well.5. Quantitative analysis of the aerodynamic characteristics of the car is conductedwith the internal flow influence considered or not. The error of Cd and Cl are23.5%and111%respectively. In addition, the main parameters of aerodynamic modeling whichhave great effect on the aerodynamic characteristics are extracted on the basis of eachboundary’s Cd value, they are front end, rear end, car body and grill.6. Based on aerodynamic modeling parameters, aerodynamic shape optimization isproceeded. And the effectiveness of the optimization is verified according to the Cdvalue of new simulation result, which is decreased7.8%than the original model.