19-01-2013, 04:09 PM
AERODYNAMIC ANALYSIS OF THE CAR BODY FOR MINIMUM FUEL CONSUMPTION
AERODYNAMIC ANALYSIS.doc (Size: 476 KB / Downloads: 73)
ABSTRACT:
The potential for energy savings by reducing the aerodynamic drag of rail cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of empty cars would correspond to a 5% fuel savings for a round trip. The aerodynamic drag of scale rail cars was measured in a wind tunnel experimentally but it is cost oriented and more time and effort consuming work. In this paper Computational Fluid Dynamics (CFD) predicts the drag over the car body numerically which can be validated with existing wind tunnel experimental work. The goal of the study was to measure the drag reduction of various car cover designs. The reduction in drag corresponds to the uniform pressure distribution over the body. The analysis yields a tremendous saving of the fuel consumption.
INTRODUCTION
During the recent past, significant progress in the field of computational fluid dynamics (CFD) has also been made, and CFD is gradually becoming established as an efficient tool in vehicle design. It is recognized that complex flow fields are not easily represented in terms of a closed solution. CFD technology allows for the visualization of complex flow phenomena in a virtual environment that can significantly enhance the learning experience. It has the potential to explore cause-effect relationships through open-ended analyses, and extends analyses beyond what is possible using traditional experimentation, because the end user can easily visualize complex flow phenomena using color contour plots and velocity vector plots. Additional features available to compute many derived parameters along with user-friendly graphical operations allow highlighting the region of interest for detailed analyses.
FUEL CONSUMPTION RELATES THE AERODYNAMICS
A moving vehicle encounters resistance from the air. This drag is made up of pressure drag and skin friction drag. The oncoming airflow pushes against the front, creating a high-pressure region, just as it does on the wheels and the front of the semi-trailer. The car moving forward in the airflow creates a low-pressure region behind the tractor and the semi-trailer: these areas ‘suck’ the vehicle backwards, as it were. Interestingly, the high-pressure region at the front contributes just as much to drag as the low-pressure region at the rear: with or without crosswind, each accounts for about 1/3 of the overall drag. The remaining 1/3 of the overall drag is created by the vehicle’s under-body [3].
CFD FLUENT AS SOLVER
CFD Fluent is used for calculating the drag over the car body for different slant angles varying from 20 degree to 35 degree with a span of 5. The slant angle plays an important role by decreasing the drag over the body but it increases the skin friction of the car body. Optimization is performed for the slant angle for minimum of drag. Here inlet velocity is taken as 40 m/s and k-e turbulence model is selected for capturing turbulent motion of vortices [5].
CONCLUSION
From the above experiment & result analysis it is very clear that the fuel consumption can be significantly reduced by appropriate change in slant angle for the car body. Fuel consumption is directly dependent on the drag force resistance acting over the car body. The drag force depends on the vortices shed generated at the back of the car body which causes separation and produces less pressure areas at the back of the car body as a result the body is resisted by the air moving over the car body. The drag is directly dependent on the slant angle of the body. The larger the slant angle more pressure difference of the front and back surfaces generates more drag but less slant angle allows more surface of the body to be in contact with the fluid and more skin friction is resulted.