# Pressure Distribution and Lift on a Piercy Aerofoil

School of Engineering and Materials Science

Den233

Low Speed Aerodynamics

Pressure Distribution and Lift on a Piercy Aerofoil

Abstract

In this experiment in a low speed flow the static pressure around an aerofoil will be observed and discussed. The lift on the aerofoil will also be calculated and compared with the theoretical value. The aerofoil being used in this particular experiment is symmetrical and is taking place in a wind tunnel with a speed of 18.5m/s, therefore the flow is assumed to be incompressible. The different pressures along the surface of the aerofoil will be measured at an angle of attack of 4.1 degrees and 6.2 degrees. These values of pressure will then be analysed and graphs and calculations will be produced, the lift being calculated using the trapezium method in excel and these values and graphs will then be compared to the theoretical results for an inviscid flow from the thin aerofoil theory. The errors in the experiment will be quantified and any improvements to the experiment will be discussed.

Table of Contents

1. Introduction

2. Experiment Description

3. Apparatus

4. Calculations and Results

5. Discussion

6. Conclusion

7. References

Introduction

The thin aerofoil theory is very useful as it relates values of lift to small angles of attack for aerofoils with low camber and thickness without taking into account the viscosity of the flow. The thin aerofoil theory assumes that the flow is 2 dimensional, inviscid and incompressible. It can be used to predict pressures and forces on very thin cambered surfaces with the thickness approaching zero, along with finding the lift. The assumptions for this theory is that the flow must be inviscid, two dimensional, incompressible, a small angle of attack, the maximum camber less than one, the maximum thickness to chord ratio must be less than one, and the Kutta condition is satisfied. The Kutta condition generally applies to bodies with sharp edges such as the trailing section of an aerofoil. The definition of this condition is that if an aerofoil has a sharp trailing edge moving through a fluid it will create circulation to hold the stagnation point at the trailing edge in place. The fluid will approach the trailing edge from both surfaces and will flow away from the body with none of the flow remaining attached. Implementing this condition generally means there will be no pressure difference at the trailing edge between the upper and lower surfaces. In the thin aerofoil theory the changes in flow direction are small relative to the free stream and the velocity changes are small. The 2nd order terms in the velocity components are neglected and therefore the result is linear. An aerofoil generally has a streamlined and thin cross section with a round leading edge to prevent separation of the flow and a sharp trailing edge to fix circulation. The chord of the aerofoil is the straight line joining the leading edge to the trailing edge with a length of c. The mean camber line is the line joining the points halfway between the upper and lower surfaces of the aerofoil. The camber is the biggest distance between the chord and the mean camber line and the greater this distance is the more camber the aerofoil has. The aerofoil thickness is the distance between the upper and lower surfaces. In this report the theoretical results for an inviscid flow in relation to the thin aerofoil theory will be compared with the experimental results of an aerofoil in a low speed flow. The lift for both cases will be found and graphs will be plotted. This experiment is to test the theory of thin aerofoil with a small angle of attack.

Experiment Description

In this experiment the pressure distribution...

References: [1] Queen Mary University of London, DEN233, Low Speed Aerodynamics, Lab Handout, November 2013, (Accessed on 13th November 2013)

[2] Queen Mary University of London, DEN233, Low Speed Aerodynamics, Lecture Notes, 2013, (Accessed on 13th November 2013)

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