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Adaptive automotive aerodynamics By Rual Abreu (Student Number: 200941474) A dissertation submitted in partial fulfilment for the degree Of Masters In Technology (Engineering: Mechanical) In Mechanical & Industrial Engineering Technology Faculty of Engineering and the Built Environment Supervisor: Dorina Ionescu 2013 University of Johannesburg | Adaptive Automotive Aerodynamics 2013 R.Abreu DECLARATION I Rual Abreu hereby submit this dissertation in partial fulfilment of the requirements for the degree M.Tech Mechanical Engineering at the University of Johannesburg. I declare that the content of this dissertation is my own unaided work and has not been submitted to any other academic institution for review. Rual Abreu Adaptive Automotive Aerodynamics 2013 2 ABSTRACT This dissertation focuses on understanding the relation between aerodynamic drag and aerodynamic lift in modern passenger cars and explores what effect these forces have on a vehicle. Modern cars are capable of exceptionally high speed and are subjected to large destabilizing lift forces at these speeds. To counteract the effects of positive lift, various aerodynamic devices and body design details are included in the typical car design. These devices often increase the vehicles aerodynamic drag, reducing energy efficiency as speed increases. The problem that this project aims to address is that at typical commuting speeds where lift forces are low these counter lift devices are not required, however because these devices are fixed the losses associated with their increased drag is still incurred. The devices can however not be excluded from the design as they are required on occasions that the vehicle is driven at abnormally high speed and lift forces become large. The losses associated with the increased drag of such devices are incurred over the vehicles full range of speeds even though the devices are only required at higher speed. The objective of this project is to develop an aerodynamic system that allows the vehicle to continuously and autonomously adjust its drag vs. lift properties to an optimal compromise that suits the vehicles instantaneous aerodynamic requirements. The system offers improvements in both handling and breaking performance as well as increased energy efficiency. The feasibility and effectiveness of the developed system is compared against the performance of a standard test vehicle and against the same test vehicle equipped with various traditional fixed aerodynamic devices. The methods used to develop, analyse and compare the various test models include both practical testing of a physical vehicle and computer based simulation using a digitized model of the same vehicle. Practical testing was conducted at Gerotek test facilities in Pretoria, South Africa and includes measuring the flow rate through the engine cooling system to determine the drag contribution of the cooling system to total vehicle drag. Coast-down testing is used to characterise the test vehicles rolling resistance and skid-pan or circuit tests are used to characterise the vehicles handling properties. Acceleration and breaking tests are also performed. Data from these tests are recorded through various on-board data logging units with pitot tube, GPS and accelerometer devices as inputs. A 3D model of the test vehicle is compiled using photogrammetry software to capture the profile and dimensions of the test vehicle into digital form. A 3D CAD model is developed from the vehicle scan and is used for CFD simulations to solve for the vehicles aerodynamic properties and to assist in the design and incorporation of the various adjustable aerodynamic devices required for the project. The data accumulated through computer simulation and practical testing is combined to form a statistical computer model of the standard vehicle. Research is conducted on existing aerodynamic devices common to passenger cars and suitable devices are adapted to three additional computer models: One with an adaptive aerodynamic system and two with fixed aerodynamic configurations of different intensities. The performance and energy efficiency of the four models are analytically simulated and the results are compared directly. The study shows that in terms of sporting performance around a theoretical road circuit, the adaptive model outperforms both the standard vehicle and fixed configuration models by a small degree, +- 2.3%. The standard vehicle is found to have a lift coefficient CL=0.43 with a drag coefficient of Cd=0.31. The dynamic model is able to realize combinations of low drag or low lift between the limits of Cd=0.3, CL=0.34 and Cd=0.32, CL=0.03. The variable aerodynamic properties allow for a 5.5% increase in maximum cornering speed and a 20% improvement in acceleration time from standstill to terminal speed. The percentage improved lap time would be greater if the effects of breaking from the higher terminal speed achieved by the dynamic model were ignored for the simulation. Adaptive Automotive Aerodynamics 2013 3 This improvement in cornering speed, acceleration and terminal speed is available along with increased energy efficiency when cruising in a straight line. The adaptive system allows for an additional 15km range to be gained per tank of fuel when compared to the standard vehicle range of 727km, an improvement of approximately 2.5%. This is attributed to the dynamic model reducing its drag coefficient to Cd=0.3 when streamlined as opposed to the standard vehicles Cd=0.31. Although gains are small they are realized on both ends of the spectrum, performance and efficiency, without compromise on either. The system is also designed to incorporate discreetly into the vehicle body so as not to interfere with current body styling trends and is also sufficiency compact not to interfere with the vehicles ergonomics and usable volumes. The results suggest that the system would be of little use to vehicles that typically commute at speeds less than 120km/h and would only be suitable to luxury segment sports cars or sports saloons that drive at high speed frequently and fall in a price bracket where the increase cost of such a system would be acceptable. The project leaves scope to further explore the dynamic effects on vehicle handling that would arise from rapidly changing the aerodynamic forces acing on the vehicle. The control system and response time of the system is also to be further developed and analysed. Adaptive Automotive Aerodynamics 2013 4 Acknowledgments: I would like to thank the following people for their time and assistance in the undertaking of this thesis: Special thanks to: Ms. Dorina Ionescu : Project supervisor and - University of Johannesburg Engineer And to: Zahn-Michelle Bredenkamp : Experiment assistant David Taylor : Aerodynamic and Mechanical - Epsilon Engineering Services (PTY) Engineer, Director Ltd Johan Badenhorst : Aerodynamic and Mechanical - Epsilon Engineering Services (PTY) Engineer, Director Ltd Ernst Bielfeld : Mechanical Engineer and - Epsilon Engineering Services (PTY) Motorsports expert Ltd Gerhard Smit : Mechanical and Systems - Carl Zeiss optronics Ltd Engineer Dries Laas : Mechanical, Composite and - Epsilon Engineering Services (PTY) Aerodynamics Engineer Ltd Marcel Maree : Mechanical Engineer and - Toyota motor sport (PTY) Ltd Motorsports expert Leonard A Beukes : Test facility manager - Gerotek Test facilities Armscor Business (PTY) Ltd Jarred Spies : Experiment assistant and Test vehicle owner Adaptive Automotive Aerodynamics 2013 5 Contents ABSTRACT ...................................................................................................................................................... 3 Acknowledgments: ........................................................................................................................................... 5 Nomenclature .................................................................................................................................................15 Variables relating to CFD Results ..................................................................................................................16 1 INTRODUCTION: ......................................................................................................................................17 1.1 Problem definition ....................................................................................................................................17 1.2 Problem discussion ..................................................................................................................................19 1.3 Project Goals ............................................................................................................................................20