1 Project on Heavy Vehicle Aerodynamic Drag ATTABENE Amine 3 rd AUTOMOTIVE Engineering student Amine.ATTABENE@uir.ac.ma 1. INTRODUCTION: In order to increase the fuel efficiency get a better cooling , improved engine compartment packaging and lower production costs . during the good era of vehicle’s development there is a common practice to test a prototype vehicle in a wind tunel after reworking the surfaces and components adding some and avoiding some in order to reduce the drag coefficient 2. ESSENTIAL KNOWLEDGE : - Aerodynamics : Aerodynamics is the study of forces and the resulting motion of objects through the air. ... Because aerodynamics involves both the motion of the object and the reaction of the air around it . - Drag force : In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. o CD : The drag coefficient is a number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and flow conditions on aircraft drag . ... The drag coefficient then expresses the ratio of the drag force to the force produced by the dynamic pressure times the area. 2 - Flow separation : Flow separation or boundary layer separation is the detachment of a boundary layer from a surface into a wake. ... In aerodynamics , flow separation results in reduced lift and increased pressure drag, caused by the pressure differential between the front and rear surfaces of the object. - Wind Tunnel testing : Wind tunnel testing was invented by Frank H. Wenham in 1871 and since then it was routinely used by the large automotive companies employ wind tunnels to analyze their latest models. While these companies may test an entire vehicle , they will also evaluate the aerodynamics of individu al components, such a s grilles, rear - deck spoilers and roof racks. In wind engineering, wind tunnel tests are used to measure the velocity around, and forces or pressures upon structures. Wind Tunnel Testing Aerodynamicists use wind tunnels to test models of proposed vehicles and engine components. During a test , the model is placed in the test section of the tunnel and air is made to flow past the model. ... In some wind tunnel tests , the aerodynamic forces and moments on the model are measured directly. Aerodynamicists use w ind tunnels to test models of proposed vehicles and engine components. During a test , the model is placed in the test section of the tunnel and air is made to flow past the model. Various types of instrumentation are used to determine the forces on the model. - Means to reduce the Aerodynamic Drag Types of controle 3 3. PRESENTATION OF THE PROTOTYPE - The prototype: 4 Up view Side view Front View Back view - Components and devices added on : Diffuser 5 Vortex Generator Rear Spoiler With taking into consideration the dimensions of the prototype the devices added should not be bigger of smaller otherwise we may have misleading results - Dimentions Height : 8 cm Lenght :15 cm Width : 7cm Frontal Area = 8*7 *10^( - 6) =5.6*10^( - 5)m^2 - Test operated: **Part1 6 - Results 7 ** Part 2 Results Obtained: 8 4. DISCUSSION : - Drag Decreasing ratio D1 = 3.49 Cd1=0.4 D2 = 1.34 Cd2=0.15 Delta (D) = 2.15 Decreasing ratio = Delta D/D1 =61% So we can consider that the efficiency of the added component is 61% = 0.61 - Error Probabilities Mistakes Leading to errors : Common sources of error include instrumental, environmental, procedural, and human. All of these errors can be either random or systematic depending on how they affect the results. Instrumental error happens when the instruments being used are inaccurate, such as a balance that does not work so here some of the mistakes that we may have done leading to some miscalculations : **miss reading ** displacement of the prototype in the machine **wrong combinations of devices 5. CONCLUSION As known this testing made automotive companies avoid big During all this time while using it so instead of creating real cars And risking the probabilities of human mistakes in calculations Assumptions it allowed them to maximize the benefits and Minimize the waste of money .