Epler 420 - Anotações da utilização do peril aerodiâmico Eppler PDF

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Anotações da utilização do peril aerodiâmico Eppler...

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2014-2015 MAAE 4907 Formula Student AERODYNAMICS

Preethi Nair CARLETON UNIVERSITY Department of Mechanical and Aerospace Engineering 2014-2015

TABLE OF CONTENTS PART 1 – FALL SEMESTER ---------------------------------------------------------------------------------- 6 1.0

INTRODUCTION ---------------------------------------------------------------------------------------- 7

2.0

THEORY ---------------------------------------------------------------------------------------------------- 7

3.0

DESIGN STEPS ------------------------------------------------------------------------------------------- 8

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11

BASELINE TESTING ---------------------------------------------------------------------------------- 8 HYRDOGEN BUBBLES FLOW VISUALIZATION ------------------------------------------- 9 INK DYE TESTING ---------------------------------------------------------------------------------- 10 SYMMETRICAL AIRFOILS VS. CAMBERED AIRFOILS ------------------------------- 11 ANGLE OF ATTACK -------------------------------------------------------------------------------- 12 SELECTION OF AIRFOIL -------------------------------------------------------------------------- 12 CONCEPT DESIGNS -------------------------------------------------------------------------------- 14 SIZING --------------------------------------------------------------------------------------------------- 15 THEORETICAL LIFT CALCULATIONS ------------------------------------------------------ 17 HYPOTHESIS ------------------------------------------------------------------------------------------ 19 COAST DOWN TESTING -------------------------------------------------------------------------- 20

4.0

CONCLUSION ------------------------------------------------------------------------------------------ 22

5.0

REFERENCES ------------------------------------------------------------------------------------------- 23

PART 2 – WINTER SEMESTER --------------------------------------------------------------------------- 24 1.0

INTRODUCTION -------------------------------------------------------------------------------------- 25

2.0

XFOIL ------------------------------------------------------------------------------------------------------ 25

2.1 2.2 3.0 3.1 3.2 3.3

EPPLER 423 -------------------------------------------------------------------------------------------- 25 EPPLER 420 -------------------------------------------------------------------------------------------- 27 WIND TUNNEL TESTING -------------------------------------------------------------------------- 29 EXPERIMENTAL SETUP -------------------------------------------------------------------------- 30 TESTING RESULTS --------------------------------------------------------------------------------- 31 FLOW VISUALIZATION – SMOKE MACHINE --------------------------------------------- 33

4.0

WORKBENCH ANSYS ------------------------------------------------------------------------------- 34

5.0

ENDPLATE DESIGNS -------------------------------------------------------------------------------- 39

6.0

CONCLUSION ------------------------------------------------------------------------------------------ 40

7.0

REFERENCES ------------------------------------------------------------------------------------------- 40

APPENDIX A ----------------------------------------------------------------------------------------------------- 41

LIST OF FIGURES FIGURE 1. The hydrogen bubbles flow visualization experimental setup and the battery source that provides the voltage…………………………………………………………………………...9 FIGURE 2. Ink dye testing on symmetrical airfoil at zero angle of attack…………………….....10 FIGURE 3.Ink dye testing on symmetrical airfoil at an increased angle of attack, a)…………....10 FIGURE 4. Ink dye testing on symmetrical airfoil with an increased angle of attack, b)……..….11 FIGURE 5. Ink dye testing on symmetrical airfoil with an increased angle of attack, c)……..….11 FIGURE 6. Eppler 420 obtained from the NACA Database……………………………………..12 FIGURE 7. Eppler 423 obtained from the NACA Database……………………………………..13 FIGURE 8. Concept 1 – single element wing…………………………........................................14 FIGURE 9. Concept 2 – multiple element wing (based on a previously designed wing a few years prior)…………………………………………………………………………………………….. 14 FIGURE 10. Concept 3 – dual element wing…………………………………………………….15 FIGURE 11. Concept 4 – multiple element wing (main element and 2 flaps) …………………....15 FIGURE 12. Concept 1 – 3 Views and Isometric drawing (dimensions in millimeters)………...16 FIGURE 13. Concept 3 – 3 Views and Isometric drawing (dimensions in millimeters)…………16 FIGURE 14. An approximate relationship between lift and velocity for Concept 1……………..18 FIGURE 15. An approximate relationship between lift and velocity for Concept 3……………..19 FIGURE 16. The data for Eppler 423 at alpha of 0 degrees using XFOIL……………………….25 FIGURE 17. The data for an alpha of 0 degrees and Reynolds No. of 3e6……………………….26 FIGURE 18. The pressure distribution of Eppler 423 at alpha 0 degrees and 3e6 Reynolds No....26 FIGURE 19. The data for an alpha of 18 degrees and Reynolds No. of 3e6……………………...27 FIGURE 20. The data for Eppler 420 at alpha of 0 degrees using XFOIL……………………….27 FIGURE 21. The pressure distribution of Eppler 420 at alpha 0 degrees, and 2e6 Reynolds No...28 FIGURE 22. The data for an alpha of 0 degrees and Reynolds No. of 2e6.....................................28 FIGURE 23. The pressure distribution of Eppler 420 at alpha 0 degrees, viscous flow and 2e6 Reynolds No……………………………………………………………………………………...29 FIGURE 24. The mounting setup for Concept 4 wing…………………………………………...30

FIGURE 25. The mounting setup for Concept 1 wing…………………………………………...30 FIGURE 26. The strain gauge mounting setup underneath the floor of the wind tunnel…………31 FIGURE 27. The single results……………………..32

element

wing’s

(printed

model)

downforce

FIGURE 28. The multiple element wing's (printed model) downforce results………………….32 FIGURE 29. The multiple element wing’s (printed model) downforce results – extrapolated…...33 FIGURE 30. The streamlines of the airflow over the wing produced by the use of a smoke machine…………………………………………………………………………………………..34 FIGURE 31. The velocity contour for a multiple element wing design using Eppler 420 profile shape and flaps at 40 and 60 degrees deflections…………………………………………………34 FIGURE 32. The pressure contour for a multiple element wing design using Eppler 420 profile shape and flaps at 40 and 60 degree deflections…………………………………………………..35 FIGURE 33. The airflow over the wing represented by streamlines and its velocity contour……35 FIGURE 34. The airflow over the wing from the front view…………………………………….36 FIGURE 35. The airflow over the wing from the back view……………………………………..36 FIGURE 36. The vortices formed by the endplates of the wing shown by the streamlines………36 FIGURE 37. The velocity contour on the front wing design – upper surface…………………….37 FIGURE 38. The velocity contour on the front wing design – bottom surface…………………...37 FIGURE 39. The pressure contour on the front wing design – upper surface……………………37 FIGURE 40. The pressure contour on the front wing design – bottom surface…………………..38 FIGURE 41. The force contour on the front wing design – upper surface………………………..38 FIGURE 42. The force contour on the front wing design – bottom surface……………………...38 FIGURE 43. Three different types of endplate designs, created to redirect airflow and produce more downforce………………………………………………………………………………….39 FIGURE 44. The single element wing’s (printed model) downforce results – raw data………….41 FIGURE 45. The single element wing’s (printed model) downforce results – raw data smoothened………………………………………………………………………………………41 FIGURE 46. The multiple element wing’s (printed model) downforce results – raw data.............42

FIGURE 47. The multiple element wing’s (printed model) downforce results – raw data smoothened………………………………………………………………………………………42

LIST OF TABLES TABLE 1. Airfoil characteristics for Eppler 420 obtained from the NACA Database……….......13 TABLE 2. Airfoil characteristics for Eppler 423 obtained from the NACA Database……….......13 TABLE 3. Values calculated and determined for Concept 1……………………………………..17 TABLE 4. Values calculated and determined for Concept 3……………………………………..18

PART 1 – FALL SEMESTER

1.0

INTRODUCTION

Aerodynamics, the study of flow around an object, is important and relevant to race cars because it can improve the car’s performance on the track. Altering the body shape of the car to be more streamline and having a smooth external surface, the drag effects on the car can be reduced which ultimately can have potential improvements in the fuel economy. With the addition of aerodynamic components like front and rear wings, aerodynamic downforce can be created. Aerodynamic downforce is created through the use of inverted wings, in other words, negative lift. This is beneficial as increasing car’s weight negatively affects straight line racing, as the goal is to reduce the overall weight of the car. However, more weight is required for the car to maintain speed in a skid-pad to avoid sliding. Therefore, downforce increases tires’ cornering ability by increasing loads on the tires without actually increasing the car’s weight. Aerodynamics is also known to improve the vehicle stability and high speed braking. The effects of aerodynamics are significant when the speeds at which the car is travelling at is high. Hence, the purpose of A1 – Aerodynamics this year, is to prove the benefits of front and rear wings for the low speeds at which Carleton’s Formula Student car travels at. To determine the effectiveness of wings for low speeds, a design process must be followed. First step is to understand the theory of flow around an airfoil then with that understanding, create conceptual designs of wings, following, calculate theoretical lift and drag values for those designs. Then a hypothesis will be made before obtaining experimental and computational fluid dynamic data of whether wings are beneficial. The initial focus will be on front wings; unlike the rear, front wings not only provides downforce, but since it precedes the entire car, it is responsible for directing the airflow back towards the rest of the car. In addition, it can be used to manipulate the air above the front tires to decrease wheel drag. The front wings are known to produce approximately 25-40% of the car’s downforce [2]. The report has been divided into sections: theory, design process, future work and conclusion. Theory section will include information of wings, design process section has been broken down to subsections that will discuss the process in detail, and future work section will state the work that needs to be completed.

2.0

THEORY

This section outlines some of the basic theory needed before starting the design process. As mentioned before, downforce is negative lift due to the airfoils in wings being inverted for cars. Therefore, in this report when wings are discussed, the term, lift, will be used in certain cases but with the understanding that lift is similar to downforce. For example, if it states lift is higher, that directly suggests the downforce is higher when the airfoils are inverted. The effect of downforce increases with ground proximity. The effect becomes noticeable when the ground clearance is less than one chord length of an airfoil. Chord length is the distance from the leading edge of the airfoil (the rounded edge) to the trailing edge (the streamlined portion). Therefore, the closer the wings are to the ground, the more downforce the wing will produce. When incorporating wings to the design of the car, an important factor is the front/rear lift ratio. The ratio needs to be close to one, or more precisely, it needs to be close to the front and rear weight distribution in order to keep the balance of the car with its increasing speed. Thus, lift can be analyzed by further dividing it into front axle lift, Clf and Clr [1].

Another important part of the front wing design is the endplate design. Endplates are significant because it redirects the flow around the front tires, as tires are one of the biggest sources of drag on the car. By redirecting the flow, it minimized the amount of drag resistance produced and allows the airflow to continue back towards the rest of the car. The endplates are responsible for also providing additional downforce. To also help redirect the flow around the front tires, the front wing designs can have multiple elements. Having, for example, a main wing and a flap, can help reduce the drag by directing the flow above the front tires. The elements are separated by slot gaps, and the gaps allow the airflow under the wing where the air pressure is lower, therefore resulting in higher downforce and reducing the chances of wing “stalling”. Stalling is when there is a loss of lift and a dramatic increase in drag produced. The main wing and the flaps are not connected directly to the endplates at either end of the front wings. Instead, the elements form their own endplates in the form of a turning vane. This allows improved airflow redirection and also improves the efficiency of the overall endplate design. When designing the wing flaps for either side of the nose cone of the car, they are to be asymmetrical. It being asymmetrical suggests that the flaps reduce in height nearer to the nose cone as this would allow air to flow into the radiators if they were to be mounted in the sidepods. However, this is not required as the radiator for the RR15 is not being placed in the sidepods, therefore the wing flaps can have their height maintained right to the nose cone [3]. Effects that need to be considered created by the front wings and the front wheels include the tip vortex on the front wing and the front wheel wake. The objective is to avoid the creation of vortexes and the front wheel wake to places of the car that could possibly get damaged. To comply with the rules of SAE for aerodynamics, front wings ends overlap the front wheels when viewed from the front. This can cause unnecessary turbulence in front of the wheels, contributing to reduced aerodynamic efficiency and increased drag. To overcome this design problem, the inside edges of the endplates must be curved in order to direct the air away from the chassis and around the wheels. In addition to the previously mentioned functions of endplates, they are part of wing designs to eliminate induced drag which is created by the development of high-pressure air on top of the wing rolling over to the low pressure air beneath at the end of the wing. The aim through the design of incorporating endplates is to ultimately discourage “dirty”, meaning clean, undisturbed flow created by the front tire going into the floor of the car [2].

3.0

DESIGN STEPS 3.1

BASELINE TESTING

A baseline test was performed with the RR14 car to collect data, so that final outcome of the project can be effectively be compared to the start situation. Initially, pitot tubes and flow visualization methods were to be used at the test, but was unable to collect any data. The flow visualization method consisted of using a paraffin-based light solution to be sprayed on the car to determine the airflow over the bodywork of the car. This is the solution F1 cars use, even transparent oil based paint of non-gelling characteristic and with a specific viscosity chosen in a way that the solution will not flow downwards when the

car is stationary, could be used. Through this method, details like direction and attached/non-attached flow can be observed. The disadvantage of this flow visualization is only the surface airflow can be determined, and therefore would be more beneficial if it were to be used to confirming wind tunnel and computational fluid dynamic findings [4].

3.2

HYRDOGEN BUBBLES FLOW VISUALIZATION

To understand how the flow behaves around an airfoil, a method called hydrogen bubbles flow visualization was looked into. This flow visualization occurs in a water channel and will show areas of smooth flow, areas of flow separation and flow structures that form around the airfoil. The water channel to be used is a re-circulating type, with the water continuously being pumped and filtered in a circuit. Wind tunnel and water channel studies are directly comparable. Water being approximately 1000 times denser than air which means the flow speed can be lowered to achieve the same conditions. Using this method, it would provide a clear picture of the dynamics of how the flow structure is occurring around the geometry [5]. The process used in hydrogen bubbles flow visualization is called electrolysis. Placing two electrodes in the water channel and applying a DC current through them splits the hydrogen and oxygen gas that breaks up the water molecules into separate gases. The creation of hydrogen gas bubbles is on a very small diameter wire, and with the flow of the water in the channel, the visualization of the bubbles moving can be seen [5]. The method was tested in a small scale, using a battery source and two coins, which represented the two electrodes, and the method proved to work. However, when the experimental setup was created, shown in the Figure below, and tested in the water channel, the hydrogen bubbles did not appear on the thin diameter steel wire. Therefore, for the flow visualization, the ink-dye method was performed in the water channel with the same airfoil.

FIGURE 1. The hydrogen bubbles flow visualization experimental setup and the battery source that provides the voltage.

3.3

INK DYE TESTING

Since, the hydrogen bubble flow technique did not work, the ink dye was used to visualize how the flow behaves around a symmetrical airfoil, which are illustrated below in the following figures.

FIGURE 2. Ink dye testing on symmetrical airfoil at zero angle of attack.

FIGURE 3. Ink dye testing on symmetrical airfoil at an increased angle of attack, a).

FIGURE 4. Ink dye testing on symmetrical airfoil with an increased angle of attack, b).

FIGURE 5. Ink dye testing on symmetrical airfoil with an increased angle of attack, c).

3.4

SYMMETRICAL AIRFOILS VS. CAMBERED AIRFOILS

Airfoils are a two dimensional cross sections of three dimensional wings that have a finite span length. Airfoils are designed to have an overall effect on the surrounding fluid to result in faster flow on the upper surface and slower flow on the lower surface (reversed when the wings are inverted). The velocity differences is caused by the pressure variation between the two surfaces, creating suction on the higher velocity surface. This suction causes the resultant force to act upward, thus creating lift (downforce when wings are inverted). Therefore, the pressure distribution is directly related to the velocity distribution

of the airfoil. This shape of the pressure distribution can be altered by changing the angle of attack of the airfoil and the camberline shape. Camberline shape determines the curvature difference between the two surfaces. Hence, airfoils could be either symmetrical or cambered. Symmetrical airfoils produce zero lift at a zero angle of attack unlike cambered airfoils. This is because cambered airfoils for the same angles of attack compared to the symmetrical will produce larger lift. The trailing edge of the camberline has the largest effect on the airfoil’s ability to produce lift, compared to the rest of the camberline. Higher lift can be achieved also by just changing the camberline geometry without increasing the an...