Vehicle Aerodynamics of the cwru sae baja Team Car



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Vehicle Aerodynamics of the CWRU SAE Baja Team Car

Nicholas A. Jones



Abstract

This project is an aerodynamic study of the CWRU Baja Team’s car. The aerodynamic study is a potential way of increasing the car’s performance without the need for expensive mechanical devices and exotic materials. I will be requesting access to the CAD (Computer Aided Design) files of the car, the ability to change the design of the files, and potential funding. The proposal will cover the basic principles of aerodynamics, aerodynamic design, and aerodynamic tuning methods. The proposal will also cover the methodology of how the study will be carried out and the potential budget.


Introduction

The CWRU SAE Baja team is being outspent by powerhouse Baja teams such as the University of Michigan Baja team. The UM Baja budget is at least 3 times larger than ours. This financial discrepancy means that UM can spend money on expensive mechanical devices and materials that make their car faster while we are having to make cost saving cuts in design. We need to find other solutions to this problem and I believe an aerodynamic study of the car would help us build a faster car that is not much more expensive than the current design. To do this study I request access and authorization to use and change the car’s design and run it through the Solidworks CFD program. If a dedicated aero package proves to be a worthwhile venture I request funding to build a wind tunnel that can and will be used in this year and future year’s designs. In order to study the aerodynamics of the Baja car we must establish the basic concepts of aerodynamics, how aerodynamic principles affect vehicle design, and learn what CFDs and wind tunnels are and how they are used.



Basics

First and foremost air can be considered a fluid. This assumption allows us to use fluid dynamic principles and equations. One of these fluid dynamic equations is the Bernoulli Equation [3].



The Bernoulli Equation is a conservation of energy in fluid flow and states that as a fluid increases in speed the pressure of the fluid decreases. This principle is the basis for flight. Airplane wings are designed to have slower air flow on the bottom half of the wing than the top half. This creates a pressure differential and allows for lift. The lift force can be measured using this equation [3].



These concepts and equations can be used in automobile body and chassis design to obtain results such as fuel efficiency and speed.



Automobile Aerodynamics

Air flow also creates other forces such as drag and downforce. These forces can be found the same way as lift but instead of a coefficient of lift we have coefficients of drag and downforce [5]. Downforce is the opposite lift [5]. Most high performance and racing vehicles are built like upside-down wings [5]. Instead of generating an upward force these vehicles generate a downward force which pushes the vehicle into the ground. This allows for greater traction without needing to add extra weight which makes the car handle better and go faster [5]. Drag is a resistance force that pulls and tugs on a vehicle going through a fluid and slows the vehicle down [5]. These tugs and pulls are caused by air resistance and a phenomenon called flow detachment [10]. As a vehicle drives down a road at speed the cockpit, mirrors, when, etc. create a vacuum behind the car called a flow detachment [10]. This means that the vehicle creates a “hole” behind it and the air molecules cannot fill the hole fast enough and creates a force that pulls the vehicle back. Wind resistance is basically friction caused by air flow. The Vehicle’s purpose will determine which of these aerodynamic forces are most important.

If you are designing a vehicle to get great fuel economy you will need to create a chassis and body that lowers the drag at the expense of lowering downforce or even generating lift. Reducing the drag, in this case, means that you need less horsepower to overcome drag which means you do not need as much fuel [4]. If you are designing a vehicle that is meant to drag race you will want to generate enough downforce so that the vehicle is stable and has enough traction to keep it under control while drastically reducing drag. This reduction in drag means that more power produced by the engine can be used in acceleration and top end speed instead of overcoming drag [4]. If you are designing a vehicle that is designed to race on ovals or road courses you will want to create as much downforce as possible with the side effect of increasing drag [4]. In oval and road racing increasing drag will slow down straight line speed but being able to go through the turns faster has a bigger effect on lap times than straight line speed [4]. When tuning an aero package to meet these needs we can use several tools such as CFD programs (computational fluid dynamics) and wind tunnel testing.

CFDs

CFDs (Computational Fluid Dynamics) are computer programs that take the geometry of a body and perform fluid dynamic computations to see how the body reacts when exposed to fluid flow [1]. This allows us to see how downforce/lift and drag is generated by our aero package. One of the big benefits to using CFDs is the ability to tune and make addition changes to the aero package before we spend money on manufacturing it.





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