Alistair Duff, for technical assistance Mr. Andrew Crockett, for strain gauge assistance
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ACKNOWLEDGEMENTSThe Author would like to thank the following: Dr. Matt Stickland, for project guidance Mr. Chris Cameron, for technical assistance Mr. Alistair Duff, for technical assistance Mr. Andrew Crockett, for strain gauge assistance Mr. Jim Doherty, for supplies assistance ABSTRACTThis paper studies the aerodynamic properties of a Range Rover L319 wing mirror, both through experimental means in a wind tunnel and through the use of CFD software. The results from each method are compared and consequently the accuracy of the CFD analysis is validated. From there, two design alterations are applied to the CFD model in an aim to reduce both the wing mirror drag and the sources of aerodynamically created noise on the wing mirror surfaces. The design alterations are proven to have a beneficial impact on the wing mirrors aerodynamic performance with regards to many features and therefore the usefulness of CFD software in engineering design is underlined. A simplified CFD analysis of the flow over the car is also performed and therefore a better understanding of the flow over the A-Pillar region is achieved. The possibilities of further optimization of the wing mirror design and potential alterations to the A-Pillar geometry are then discussed, along with the potential for further study with regards to aeroacoustic modelling. ContentsACKNOWLEDGEMENTS 1 ABSTRACT 2 Contents 3 NOMENCLATURE 5 1. INTRODUCTION 6 2. THE WING MIRROR 8 2.1 HISTORY 8 2.2 DESIGN IMPROVEMENT 8 3. THE A-PILLAR 9 4. AERODYNAMIC NOISE 10 4.1 SIGNIFICANCE & SOURCES 10 4.2 NOISE REDUCTION 11 5 DEBRIS/DROPLET SHEDDING 11 6. COMPUTATIONAL FLUID DYNAMICS 12 6.1 FUNCTION 12 6.2HISTORY 13 6.3 ENGINEERING APPLICATIONS 13 7. WIND TUNNEL TESTING 14 7.1 CLOSED RETURN 14 7.2 TESTING METHOD 15 7.3 WING MIRROR & BAR CONNECTION 15 7.4 RIGGING TO DATA ACQUISITION 16 7.5 DATA ACQUISITION SOFTWARE 17 7.6 STRAIN GAUGE BAR CALIBRATION 17 7.8 WIND TUNNEL SAFETY & OPERATING PROCEDURE 22 8. CFD – WING MIRROR ON FLAT PLATE 24 8.1 GAMBIT: MODELLING 24 8.2 GAMBIT: MESHING & EXPORTING 26 8.3 FLUENT: ANALYSIS SETUP 28 8.4 FLUENT: SOLVING 29 9. WIND TUNNEL RESULTS & CFD VALIATION 31 9.1 RESULTS COMPARISON 31 9.2 ERRORS 32 9.3 VALIDATION 32 14. DESIGN PERFORMANCE ASSESMENT 34 14.1 PRESSURE DRAG 34 14.2 AEROACOUSTICS 35 15. OPTIMIZATION (I) 36 15.1 MODELLING 36 15.2 RESULTS 37 16. OPTIMIZATION (II) 38 16.1 MODELLING 39 16.2 RESULTS 40 17. A-PILLAR MODELLING 41 17.1 A-PILLAR INFLUENCE 41 17.2 GAMBIT: MODELLING 42 17.3 GAMBIT: MESHING & SOLVING 43 17.4 FLAT PLAT & A-PILLAR COMPARISON 44 17.5 FLOW OVER THE A-PILLAR 44 17.6 WATER DROPLET & DEBRIS SHEDDING 45 17.7AERO ACOUSTIC NOISE SOURCES 46 18. DISCUSSION AND FURTHER STUDY 48 18.1 WIND TUNNEL TESTING 48 18.2 OPTIMIZATION EFFORTS 48 18.3 A-PILLAR 49 18.4 AEROACOUSTICS 50 19. CONCLUSION 50 REFERENCES 52 NOMENCLATUREAir Density (kg/m3) ………………………………………………………….........ρ Area (m2) ……………………………………………………………………...…...A Constant …………………………………………………………………………….k Drag Coefficient………………………………………..…………………………CD Drag Force (N)……………………………………………………………………D Lift Coefficient …………………………………………………………………….CL Normal Force on Strain Gauge Bar (N)………………………………………...Fs Skin Friction Drag Coefficient ………………………………………………… Cd0 Velocity (m/s)……………………………………………….……………………..V
The wing mirror in most motor vehicle designs is, in essence, an exposed bluff body, and thus produces high levels of pressure drag. A wing mirror typically represents about 2.5% of the vehicle frontal area but has been found to contribute up to 5% of the total vehicle drag [1] which can be considered significant. Furthermore, a typical modern production vehicle usually has a drag coefficient value of around 0.3 to 0.5 [2], and the wing mirrors of the vehicle can make a contribution to this value at around the order of 0.01[3]. This drag contribution has a detrimental effect on vehicle acceleration and top speed, with the most noticeable reduction in acceleration occurring at speeds of around 60 miles per hour and higher (motorway cruising speed). For example, studies have shown that a particular vehicle with an overall drag coefficient of 0.45 can reach a speed of 75 miles per hour in 20 seconds. However, if this value of drag coefficient is improved to 0.25, the time taken to reach 75mph is reduced by 3 seconds [4], which is a noticeable improvement in the vehicle’s acceleration performance. Due to the detrimental effects of drag on vehicles at motorway cruising speeds, another negative impact on the vehicle’s performance is fuel economy. Wing mirrors can also influence cabin comfort for passengers and drivers within the vehicle due to the aeroacoustic effects produced by the airflow over the A-Pillar and wing mirror. The aerodynamic noise created is more significant now in modern cars due to the mechanical noise present within the cabin being reduced as a result of enhanced quality engines. Poor wing mirror/A-Pillar design can also result in debris and water droplets being shed from the wing mirror onto the front side windows resulting in impairment of visibility for the driver and therefore a reduction in vehicle safety. This report will study the aerodynamic characteristics of a Range Rover L319 wing mirror (Figure 1) through wind tunnel testing as part of a small A-Pillar configuration. The wing mirror will then be analyzed both in isolation on a flat plate and connected to the Range Rover car body through use of Computational Fluid Dynamics software. 
Figure 1 - L319 Wing Mirror The results from wind tunnel testing and CFD modelling on the flat plate will then be compared to validate the accuracy of the CFD results. With the results validated the software will then be utilised in design optimization efforts, with the aim of reducing the wing mirror pressure drag. Changes will also be made in an effort to minimize the sources of aerodynamically created noise on the surfaces of the wing mirror. The flow over the A-Pillar will also be studied to better understand the nature of the flow over this region and to assess whether applying and testing the design optimizations on the wing mirror in isolation is a valid approach to design improvement.
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