MEC3458 Final Report

Project Report

ContentsAcknowledgement2Abstract2Introduction3Background4Problem Statement4Literature Review5Methodology7Experimental Setup Apparatus and Materials7Part A Determining the Aerodynamic forces of control model8Designing a mount for model8Calibration of the sensors9 Determining humid air density and wind velocity9Flow Visualization10Part B Optimization of the car surface11Analyzing The Data Obtained11Designing The New Cowl11Results and Discussion12Conclusion12Future Works12References13

Acknowledgement

Abstract

Chapter 1IntroductionThe field of aerodynamics has been around since the seventeenth century but its application has been utilized for centuries throughout recorded history, from the use of sailboats and windmills by ancient societies to the flying machines designed by Leonardo Da Vinci during the Renaissance.[1] Although the foundations of aerodynamics were formulated over the past 200 years, not all principles were immediately utilized for car design. When the carriage horse was replaced by a thermal engine more than 100 years ago, nobody thought about aerodynamics. The purpose of the body of a car was to shelter the driver and passengers from outside elements such as wind and rain. The concept of applying aerodynamics to road vehicles came up much later after flight technology had made considerable progress.[2] Naturally, the desire for low drag was recognized first followed by the need for higher negative lift. One of the earliest car design to have a streamlined designed was the 1899 Camille Jenatzy that went on to break the 100 kilometer/hour (km/h) barrier. The car itself was electrically powered and had a design that was oddly shaped as a long cigar in an effort to reduce aerodynamic drag. The rapidly developing automotive industry followed and one of the most significant designs of that era is the 1924 Tropfenwagen (droplet shape in German). This automobiles shape was dominated by the airfoil shape (particularly from the top view) and recent tests in the Volkswagen wind tunnel showed a drag coefficient of CD = 0.28, which is outstanding even by todays standards.[3]Figure 1: Camille Jenatzy at the helm of his la jamais contente

Fast forward to almost a century later and we can see how the principles of aerodynamics has become a multifaceted field that governs a lot of the design choices we see on the road today. Economics, safety and even environmental concerns has driven the need for optimizing the aerodynamic design of vehicles. It is estimated that around 80km/h the aerodynamic drag begins to have significant effect on a vehicle, and by 110km/h 65 percent of the power generated by the car is used to overcome aerodynamic drag.[4] The motion of air around a moving vehicle affects all of its components in one form or another. Engine intake and cooling flow, internal ventilation, tire cooling, and overall external flow all fall under the umbrella of vehicle aerodynamics. The present discussion, however, focuses on the effects of external aerodynamics only.

BackgroundImprovements on vehicle drag is an important aspect in car design because of its potential to improve fuel economy. However, for this experiment, the focus is on the aerodynamic forces acting on a scale model of a mini 4 wheel drive (4WD) race car in order to improve its performance on the tracks and also to better understand aerodynamic principles in car design. The use of rapid-prototyping is also a main aspect of this experiment to show that the use of this technology is cheaper, faster and more reliable than using computer aided simulations such as FLUENT.The field of rapid-prototyping, especially Fused Deposited Modelling (FDM), is becoming more accessible to the general public as it has becomes less complex and more affordable to build. There is also no lack in the materials that it is able to use in printing. Polylactic acid (PLA), Acrylonitrile butadiene styrene (ABS), rubber, porcelain and metal clay are but a few of the material that is able to be used in rapid-prototyping. The list of material is ever-expanding as the field is becoming ever more popular and more research are being conducted.[5] The use of CFD to determine the aerodynamics forces acting on a 3D model of the mini 4WD cowl requires complex understanding of the accurate perimeters that it will be subjected to in real life condition. Long simulation time coupled with the requirement of expensive computer hardware to run these simulations makes the use of low cost FDM 3D printing machine a much more appealing alternative as the cost is cheaper, the printing time is shorter and the result is testing is actual working conditions. Problem StatementThe purpose of this project is to measure and optimize the live scale model of mini 4 Wheel Drive (4WD) car toys aerodynamic forces. The measurement of aerodynamic forces of car model is taken using wind tunnel testing. The data is processed and body parts that contribute to drag and lift are identified. Rapid prototyping using Fused Deposited Modelling (FDM) is used to build modified parts/body and re-tested to measure the optimized models aerodynamic.The specific objectives of this work are to: To apply proper flow visualization technique suitable toward identifying separation of flow on the models body parts. To measure the aerodynamic forces of the model using wind tunnel testing rig. To analyse the data and identify the parts contributing to the drag and lift forces of the model To build an improved model by rapid prototyping using FDM the new parts/body and assemble it together. To compare the successful percentage of reducing drag and lift forces of model.

Chapter 2Literature ReviewHalil Sadettin Hamut et al. conducted a study on the aerodynamic effects of rear spoiler geometry on a sports car and the results from the CFD analysis are compared with the wind tunnel experimentation. Uncertainty analysis is carried out to ensure the reliability of the obtained results. The experiment was conducted by creating a 2-D vehicle geometry of a race car and it is solved using computational fluid dynamics (CFD) solver FLUENT version 6.3. Analysis of the aerodynamic effects is carried out with and without the rear spoiler under different vehicle speeds. Comparison of the main results with the wind tunnel experiment is conducted with 1/18 replica of a Nascar. The drag coefficient is found to be 0.31 by using CFD analysis and it increases to 0.36 when the spoiler is added to the geometry. A good agreement is obtained within 5.8 percent error band for the comparison of the computational results with the spoiler and the experimental data. For the wind tunnel testing, the uncertainty related to the drag coefficient is calculated to be 6.1 percent. In the experiment conducted, it is found that the addition of the spoiler in the CFD model caused a decrease in the lift coefficient from 0.26 to 0.05.[6] Yihua Cao and Xu Zhu carried out a research on the effects of characteristic geometric parameters on parafoil aerodynamic performance with the aid of computational fluid dynamic (CFD) technique. The planform geometry, arc-anhedral angle, basic airfoil and leading edge-cut are the main characteristic geometric parameter for this study. A large number of numerical parafoil models with different geometric parameters are created by using CFD technique to study the relationship between the parameters and parafoil aerodynamic performance. Finding showed that an increase in arc-anhedral angle decreases the lift of a parafoil but has little effect on lift-drag ratio, the model with smaller leading-edge radius and thinner thickness of parafoil section achieves larger lift-drag ratio and the leading-edge cut has little effect on lift but increase drag dramatically; meanwhile, its effect on flowfield is confined to the nearby region of leading edge. Besides that this study found that the model which has the lowest drag tends to have the largest lift-drag ratio which shows that drag plays a leading role in parafoil gliding performance.[7]K.S. SONG et al. carried out a research on aerodynamic design optimization of rear body shapes of a sedan for drag reduction. Artifial Neural Network (ANN) is used for this study to optimize the outer shape of a sedan aerodynamically which focused on the rear body shapes of the sedan. To obtain the variables for the optimization, CFD simulation was used to analyse the unsteady flow field around the sedan which moves at high speed and the fluctuations of the drag coefficient (CD) and pressure around the car was calculated. After consideration of the baseline result of CFD, 6 local parts from the end of the sedan were chosen as the design variable for optimization. The studies found that as the shapes are aerodynamically optimized, the aerodynamic performance is improved by 5.64 percent compared to the proposed baseline vehicle. Yang Zhigang et al. conducted a study on aerodynamic design optimization of race car rear wing. The research conducted states that the process of design and numerical calculation for rear wing is traditionally carried out by manual interference, and the numerical results normally will be about the relationship of aerodynamic forces and a single design parameter of a rear wing. In this study, computer program of wing profiles and two scripts were created such that the process of design analysis of a rear wing ranging from geometry generating and meshing to the numerical calculation can be fully automatically handled. As stated by (Yang, Gu and Li, 2011), this automatic design and analysis process was applied to the PACE 2008 global vehicle collaboration project and there were 4725 numerical cases due to the variations of five parameters were calculated using the computer program. It is found that compared to the original design, the process yielded a design with a 6 percent increase in downward force and 5 percent decrease in drag.[8]

Chapter 3MethodologyExperimental Setup Apparatus and MaterialsFigure 2: wind tunnel schematic with dimensions

The area for the test section part at the wind tunnel is 0.25 m x 0.25 m.Apparatus: Manometer Barometer Force Transducer (KYOWA LSM-B-10NSA1 ) Weights Pitot tubes Tamiya Mini 4WD 3D printerMaterials: Thread Cotton Polylactic acid (PLA) filament Double sided tape Super Glue CyanocrylatePart A Determining the Aerodynamic forces of control model

The dimension for the model is as belowTable 1: Specification of the setupSpecificationDescription

Chassis and bodyMade from ABS plastic

Maximum car widthUnder 105 mm

Overall car heightUnder 70 mm

Overall car lengthUnder 165 mm

Minimum car weight (including batteries and motor)At least 90 g

Front and rear tyres diameter22 - 35 mm

Front and rear tyres width8 - 26 mm

Designing a mount for model

[SOLIDWORKS PICTURE OF MOUNT]

The model for the mount of the car is designed by using the solid work software. Then, the mount was print out by using the 3D printing device as shown in Figure 1 above. Polylactic acid (PLA) material is used as a filament in the 3D printing device to create this mount. This is because the material is harder than other material such as Acrylonitrile Butadiene Styrene (ABS). Besides that, PLA material also is used because it is easier to use PLA material for the 3D printing process. Then, this mount was attached under the car model so that the model will held upside down in the wind tunnel as shown in Figure 2 above. It is easier to set up the sensor when the car is held in this position. Figure 3: left - 3D Printed mount for model; right - mounted model inside the wind tunnel

Calibration of the sensors The KYOWA LSM-B-10NSA1 device was set up as shown in Figure 3 above and connected to the computer. Value of 50g increments weights was put onto that device to calibrate the sensor. From the computer, software for calibration was run and observed to obtain the strain unit in x-direction (channel 1), y-direction (channel 2) and z-direction (channel 3). Then the results obtained were plotted by using Microsoft Excel. The graph of strain unit in z-direction against mass (g) is plotted to find the relationship equation between the strain unit and mass (g). Then, this graph and the equation obtained will be used as the reference to obtain drag force and lift force based on the strain unit for drag and lift.Figure 4: Kyowa force sensor and bronze weights

Determining humid air density and wind velocityFigure 5: from left - barometer; table of humid air temperature; wet and dry bulb thermometer

Dry bulb and wet bulb temperature were taken from the thermometer as shown in Figure 6 above in lab. The difference between these two temperatures were defined and referred to the humidity air table as shown in Figure 5 above to obtain percentage of humidity. Then, barometric pressure reading was taken from barometer as shown in Figure 4 above in lab. All the values obtained were key in to the air density calculator. During the wind tunnel testing, the pitot tube was connected to the manometer reading as shown in Figure 7 and Figure 8 above to find the change in height. Then, the values for change in height and air density were used in Bernoullis Principle equation to obtain air velocity. The velocity of air used for the wind tunnel is 20 m/s.

Flow VisualizationFor the flow visualization techniques where the process of making the physics of fluid flows are visible. Some specials methods are needed to make the flow patterns visible because most fluids are transparent and their flow patterns are invisible to us. This technique is very critical to study in order to understand the flow patterns on the surface. The key features that can be investigated using the flow visualization are stagnation point location, separation point, location of boundary layer transition, extent of separation zones and etc. In this experiment, we choose the simplest and frequent method for surface flow visualization which is to attach tufts to the surface of interest. Figure 6: side view of model with tuff

The surface of the car model was painted with black color. Then, cotton wool was attached by glue to the surface of the car model to make the color different from the surface of the car so that the flow patterns clearer to observe as shown in the Figure 7 and Figure 8 above. Then, the flow separation in the rear portion was observed from the flow pattern of the cotton wool during the wind tunnel testing through the experiment. Flow separation visualization was recorded and type of flow separation areas occurs was defined due to geometry of the car. Then, the geometry of the car was modified in order to optimize the drag and lift force.Figure 7: Top view of model with tuff

Part B Optimization of the car surface

Analyzing The Data ObtainedIn data analysis, the value for drag coefficient and lift coefficient were found. There are 4 strain unit readings that will be shown in Microsoft Excel which are Channel 1, Channel 2, Channel 3 and Channel 4. However, for this project only reading from channel 2 and channel 3 will be taken into consideration as channel 2 represents the drag reading (Y-axis) and channel 3 represent the lift reading (Z-axis). The wind tunnel test was run two times to get more accurate result. The average reading for channel 2 and channel 3 was used to plot the graph of strain unit (drag) against time (s) and strain unit (lift) against time (s). Based on these two graphs, the strain unit (drag) and strain unit (lift) can be obtained. Then, by using the relationship of strain unit and mass (g) that was found during the calibration of the sensor, the value for drag force and lift force can be obtained. Next, the drag coefficient and lift coefficient is found by using the above formula

Designing The New Cowl

Chapter 4Results and Discussion

Conclusion

Future Works

References[1]J. G. Leishman, Principles of Helicopter Aerodynamics with CD Extra: Cambridge university press, 2006.[2]W.-h. Hucho and G. Sovran, "Aerodynamics of road vehicles," Annual review of fluid mechanics, vol. 25, pp. 485-537, 1993.[3]J. Katz, "Aerodynamics of race cars," Annu. Rev. Fluid Mech., vol. 38, pp. 27-63, 2006.[4]D. Singh, J. Toutbort, and G. Chen, "Heavy vehicle systems optimization merit review and peer evaluation," Annual Report, Argonne National Laboratory, vol. 23, pp. 405-411, 2006.[5]H. Lipson and M. Kurman, Fabricated: The new world of 3D printing: John Wiley & Sons, 2013.[6]H. S. Hamut, R. S. El-Emam, M. Aydin, and I. Dincer, "Effects of rear spoilers on ground vehicle aerodynamic drag," International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24, pp. 627-642, 2014.[7]X. Zhu and Y. Cao, "Numerical simulation of platform geometry effect on parafoil aerodynamic performance," Acta Aeronautica et Astronautica Sinica, vol. 32, pp. 1998-2007, 2011.[8]Z. Yang, G. Wenjun, and Q. Li, "Aerodynamic design optimization of race car rear wing," in Computer Science and Automation Engineering (CSAE), 2011 IEEE International Conference on, 2011, pp. 642-646.