570 Lab 1 Report

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570

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Mechanical Engineering

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Dec 6, 2023

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1 Aerodynamic Characteristics of Aerofoils ENME 570 Lab B02 October 20, 2023 Marcus Gregory UCID: 30115997 Rachel Mah UCID: 30114083 James Williams UCID: 30061201 Ayman Malkawi UCID: 30117701

2 TABLE OF CONTENTS EXECUTIVE SUMMARY 3 1 – INTRODUCTION & BACKGROUND 3 2 – METHODS & PROCEDURE 5 3 - RESULTS 6 4 - DISCUSSION 12 5 - CONCLUSION 17 6 - REFERENCES 18

3 EXECUTIVE SUMMARY The purpose of this laboratory experiment is to gain a better understanding of wind tunnel testing and to analyze the collected data to gain further knowledge regarding the pressure distribution around an aerofoil. Further objectives include analyzing how lift is generated by different aerofoils and how shape and angle of attack affect the lift and drag forces. Two aerofoils are tested in the wind tunnel; a symmetrical aerofoil NACA 0012 with pressure taps and a cambered airfoil NACA 2412 with a variable flap. An open-loop, subsonic wind tunnel is used which contains a force transducer to measure lift or drag as well as a 32-way manometer to obtain the 20 pressure measurements for NACA 0012. In completing this lab, the coefficient of lift for NACA 0012 was obtained using the pressure distribution for each angle of attack and compared with the values from the force transducer measurements. The plot showed that discrepancies between the two methods increased at higher angles of attack. Plots of lift coefficient vs angle of attack, drag coefficient vs angle of attack, and lift coefficient vs drag coefficient were produced for both aerofoils and compared. Many conclusions were drawn from the plots. Firstly, the coefficient of lift for the symmetric airfoil was approximately zero at zero angle of attack as opposed to the cambered aerofoil which did produce lift initially. It was expected that the cambered airfoil would produce a greater amount of lift than the symmetrical airfoil however, the trend in the data showed that as the angle of attack increased, the coefficient of lift was greater in the symmetric aerofoil which could be due to a variety of sources of error present in the experiment. It is concluded that a cambered aerofoil can generate a greater amount of lift than a symmetric aerofoil before stalling. The plots reinforced that the cambered aerofoil produced less drag than the symmetric. Multiple sources of error were identified in the experiment including bias errors found in the calibration of certain tools, misalignment in the system, and instrument drift. Additional random errors could be due to turbulence within the wind tunnel, environmental fluctuations, vibrations, as well as human error. Overall, the lab was a success and the trends found in the results were similar to those found in literature. 1 – INTRODUCTION & BACKGROUND Aero foil theory and wind tunnels play integral roles in the field of aerodynamics, shaping our understanding of how objects interact with fluids, particularly in the field of aerospace engineering. The airfoil theory serves as a fundamental framework for understanding and predicting these aerodynamic behaviors. Wind tunnels, on the other hand, are invaluable tools that allow engineers and scientists alike to conduct controlled experiments, test models, and collect data to better understand, validate, and refine aerodynamic concepts including the airfoil foil theory. Airfoil theory revolves around the study of airfoils, which are specifically designed shapes that optimize lift and minimize drag when an object moves through a fluid, particularly in air. The distinctive shape of an airfoil is characterized by a curved upper surface and a flatter lower surface, designed to manipulate the airflow around it. This manipulation leads to the generation of lift, a force that enables aircraft to overcome gravity and achieve flight. This manipulation also attempts to minimize the drag forces acting upon it. There are 2 main components of drag, both of which arise due to the viscosity of the fluid:

5 1. Frictional Drag: This component results from the resistance of air as it flows over the surface of an object, such as the wing of an aircraft. 2. Pressure Drag: This component emerges from the variations in air pressure around the object. This pressure difference results in an aerodynamic force that acts in the direction of the higher pressure, which is typically towards the upper surface. The shaping of immersed bodies is crucial for generating lift. This lift is produced by manipulating pressure distributions around the body. Symmetric bodies can also create lift by adjusting the angle of attack, which is the angle relative to the free stream direction (α). An airfoil serves as a prime example of a body that is designed to generate lift. They can be symmetric or asymmetric in cross-section. Importantly, asymmetric airfoils can produce lift even at α = 0 degrees, while symmetric airfoils require a nonzero α to generate lift. This foundational knowledge underpins aerodynamics and is pivotal in designing wing profiles and optimizing performance. The drag and lift forces can be found by taking the surface integral of the body and is represented by equations 1 and 2. 𝐹 ? = ∮ 𝑃 ? sin 𝜃 ?𝐴 + ∮ 𝜏 𝑜 cos 𝜃 ? ?𝐴 (1) 𝐹 𝐿 = ∮ 𝑃 ? cos 𝜃 ?𝐴 − ∮ 𝜏 𝑜 sin 𝜃 ? ?𝐴 (2) In computing the drag and lift forces, the coefficient of lift and the coefficient of drag can also be determined using the relations in equations 3 and 4. 𝐶 ? = 𝐹 𝐷 1 2 𝜌 ∞ 𝑈 ∞ 2 𝐴 (3) 𝐶 𝐿 = 𝐹 𝐿 1 2 𝜌 ∞ 𝑈 ∞ 2 𝐴 (4) Wind tunnels are controlled environments for simulating the flow of air over objects, providing an experiment to further verify and refine the airfoil theory. They typically consist of a test section, where the models or prototypes are placed, and a powerful fan system to propel air over these objects at controlled speeds. Wind tunnels allow engineers and researchers to study the effects of factors such as airspeed, angle of attack, and airfoil shape in a consistent manner. Wind tunnels can appear in many different fashions depending on the use. The wind tunnel in this lab is an open-loop, subsonic wind tunnel with a square intake, test section, and outtake. The speed ranges from 0 to 36 m/s, and the 600 mm-long test section has a 305 mm by 305 mm cross-section. An important parameter for any wind tunnel testing is the freestream velocity (U∞), which can be measured using a pitot tube, by placing it normal to the flow which creates a stagnation point at the tip where the stagnation pressure may be measured. On the side of the pitot tube, the flow closely approximates the velocity of the free stream, and it is possible to measure the static pressure of the fluid. The difference between these values represents a pressure corresponding to the reduction in potential energy from stagnation to static. Assuming energy conservation, this reduction is equivalent to the kinetic energy of the flow at the free stream velocity.

6 2 – METHODS & PROCEDURES For the experiment the two aerofoils being tested in the wind tunnel are NACA 0012 with pressure taps and NACA 2412 with a variable flap. The open-loop, subsonic wind tunnel contains a force transducer to measure lift or drag as well as a 32-way manometer to obtain the 20 pressure measurements for NACA 0012. Figure 1: Schematic of Wind Tunnel Setup 1. Turn on the power for the data acquisition system, the fan, and the force transducer. 2. Connect the force transducer using TeqQuipment’s data acquisition s oftware on the computer. 3. After ensuring the lift and drag balance are in the lift position, level the aerofoil at an angle of attack of 0 degrees. To ensure it is level and secure, use the screws and ensure the tip of the edges of the aerofoil are 153mm from the bottom wall of the wind tunnel. 4. Record the tare value of the pressure in manometers one to twenty as well as the last manometer (static pressure), this value should be approximately 300 mm. 5. Ensure the pitot tube is pointed upstream and lowered to 30 mm from the tunnel wall to measure accurate air speed. 6. Next, tare the force balance and turn the fan speed dynamometer completely counterclockwise. 7. After switching on the fan, turn the speed up until the pitot tube manometer has reached 40 mm and avoid touching or moving the equipment as it will affect the accuracy of the results obtained. 8. After waiting two minutes for the air speed to steady, use the software to collect force data at a frequency of 2 Hz for 60 seconds. 9. Pressure data can now be collected for the corresponding angle of attack. Record each pressure measurement in the data table provided. 10. Repeat steps 1-9 for the required angle of attacks.

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