IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 _______________________________________________________________________________________________ Volume: 05 Issue: 07 | Jul-2016, Available @ http://ijret.esatjournals.org 158 CFD ANALYSIS OF DIFFUSER IN A CAR FOR DOWNFORCE GENERATION Asif Ahmed A 1 , Murtaza M.A 2 1 Research Scholar, Automobile Engineering, Amity University (Lucknow Campus),Uttar Pradesh, India 2 Professor, ASET, Amity University (Lucknow Campus), Uttar Pradesh, India Abstract Many accidents take place on our highways on a daily basis where the driver loses control of his/her vehicle. Highways being the arteries of a nation are used widely by the people to travel and at faster speeds causing many such accidents. While drag reduction is essential on its own, downforce generation plays a pivotal role in improving handling characteristics of the given vehicle. The objective of this paper is to understand how a diffuser works and what advantages it may give to any given vehicle pertaining to its role in altering the drag and lift characteristics of the said vehicle. Computational Fluid Dynamics technique was utilized to determine optimum diffuser angle for maximum downforce that it can create. Ansys 14.0 Fluent was utilized to analyze the drag and lift acting on the vehicle at different diffuser angles at different vehicle speeds. Keywords: Downforce, Diffuser, CFD, Drag, Ansys, Fluent. ---------------------------------------------------------------------***--------------------------------------------------------------------- 1. INTRODUCTION India has world’s second largest road network with roads totaling a length of over 3,300,000 kms [1]. And at the same time fatalities due to road accidents jumped from 91,376 in 2004 to 118,239 in 2008 which is more than any other country in the world [2]. Narrowing it down further we come across a startling fact that while the National Highways constitute just 2% of the total road lengths they carry 40% of the nation’s road traffic and added to that estimates suggest that around 40% of road fatalities occur at National Highways [1]. This averages to about one fatality per kilometer per year on the National Highway which highlights the dangers of highway driving [3]. Since 2005 UK has been studying crashes and segregating them according to the crash type. It showed that cause of vehicle crash because of any vehicle defect was at a measly 2.8% whereas due to driver error or reaction it rises to 65.3% in fatalities. The driver error has been further broken down into different causes among which the most prominent are: -Loss of control: 34% -Poor Turn: 12% - Swerved: 6.2% [4] All these data suggest that drivers usually struggle to get to grips with the car at higher speeds. This is mostly because of the very large amount of turbulence being created behind the car body and also the effect of lift forces causing the driver to lose traction. Lift forces increase with increase in velocity and drivers then feel like the rear of the car is “floating around” while at cruising speeds. Remedies have been made by using Electronic Stability Control (ESC). While it has been an effective tool to reduce loss of control of the car by the driver, the loss of traction at the rear wheels due to lift forces is still present and it causes drop in confidence of the driver which can be dangerous. This can be improved impressively by incorporating the use of diffusers in car bodies. The simulations have been carried out using Computational Fluid Dynamics (CFD) which is flexible method to study effects of wind flow on a car body. Ansys Fluent was used to conduct the simulations. 2. OBJECTIVE This paper focuses on the CFD analysis of a diffuser in a production car. The vehicle selected for the simulation is Honda City as it is a very popular vehicle and is among the most used vehicles for highway travels. Also availability of its dimensions for CAD design was an advantage. The vehicle model was created in Solidworks 2014 and then was imported into Ansys Fluent Workbench which is a solver. The target was to simulate the air flow around the vehicle body and obtain the drag and lift coefficients for the body. Then a diffuser was designed and incorporated to the car body and the same simulations were performed for different diffuser angles at different wind velocities in order to create downforce on the vehicle allowing it to handle better at high speeds. 3. THEORY 3.1 Drag and Lift Forces When a vehicle is travelling on the road it is subjected to a lot of forces be it mechanical or aerodynamic which acts upon the vehicle from all directions. In case of aerodynamic forces they are split up into various directions as the wind flows around the body of the vehicle. Lift is the component of this aerodynamic force that is perpendicular to the oncoming flow direction. On the other hand the force component which is parallel to the flow direction is termed as drag force.