Aerodynamics analysis around a car by CFD Hayato Suzuki
ForecastRecently, automobile industry started utilizing computersimulations like CFD(Computational Fluid Dynamics) todevelop and design car body. Previously, it prepared actualcar body model, and it evaluated car body aerodynamiccharacter by running wind tunnel test. To prepare actual carbody model takes time and cost. Therefore, it tended todecrease wind tunnel test and increase computer simulation.But, to re-enact actual car running had difficulty in CFD, and ithad some problems like computational result accuracy.
OutlineI use an open source simulation software which name isOpenFOAM. Here is how to simulate. First, I get the 3D data ofa car. I can not make whole car body 3D model on my own. SoI get it from web. Next, I decide a size of virtual wind tunneland position of car model in it. After that, I generate some gridsfor calculation, it is called “mesh”. Next, I set boundarycondition like inlet of air flow. After that, I execute a simulation. Finally, I display a result by visualize software called“paraView” after finished simulation. It can display stream line,cut by X or Y or Z axis, and so on.
Motivation and Problem StatementPast CFD were a lot of simulations when a car running straightline, but they were not so real. First, a car model is not real.For example, it is too simple, its appearance like box. Or, it hasonly car body, no tires. My car model is normal sedan car.Second, my simulation software is open source and freesoftware. It name is OpenFOAM. Past business engagementsimulation software are too expensive. OpenFOAM was madepossible simple simulation of student level like me. Finally, Iuse k-omegaSST turbulent model. It is hybrid turbulent modelk-epsilon and k-omega. Past CFD were a lot of standard k-epsilon model. It can calculate quickly. But, accuracy is not sogood. K-omegaSST can realize more good accuracy.
MethodsFirst, creating a model data. Creating 3D or 2D model by CADdata. This model will be simulation objective. Second, meshgeneration. CFD expresses calculational space in mesh. Thisnumber of mesh is very important for accuracy. A lot of meshprovide good accuracy, but it needs long calculation time. So Imust find good balance. Third, running calculation. Mylaboratory has super computer. In CFD, calculation time isvery long. So I need high spec computer. Finally,visualization. Calculation result is difficult for human eyes tounderstand.
ResultsPressure around a car. High pressure is looked front of car. Butlow pressure is looked over a car. It is negative pressure.
ResultsThis is air stream line graphic. It is not easy for us tounderstand. So I will fix it.
SummaryFrom CFD simulation, I can look air flow around a car. And, Ican find high pressure point around a car.Additional, I want to calculate drag force and lift force. They areimportant for aerodynamics. I will write them on my thesis.But, this is low quality simulation. To save time, I reduce meshnumbers. So I want to do more high quality simulation. Twographics shows air flow and pressure around a car. But theyare not easy to understand. So I will fix graphics to post it onmy thesis.