AE 331 Lab Manual.pdf

7/29/2019 AE 331 Lab Manual.pdf

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CONTENTS

1. Wind tunnel calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2. Pitot static tube calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3. Smoke Flow visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4. Surface flow visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5. Flow over a symmetric airfoil . . . . . . . . . . . . . . . . . . . . . . . . . 8

6. Flow through a pipe bend . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7. Flow over a circular cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8. Lift measurement from wall pressure distribution . . . . . . . . . . . . . . 14

9. Drag estimation by wave survey . . . . . . . . . . . . . . . . . . . . . . . . 16

10. Strain gauge balance: Drag measurement . . . . . . . . . . . . . . . . . . . 18

11.Studies on Jet Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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Wind tunnel calibration

IntroductionWind tunnels are devices which can generate a controlled steam of air with the

required velocity and are used to simulate the flow conditions encountered in real

flight [1]. In the open-circuit low speed wind tunnel, air is sucked into the tunnel and

made to flow through the test-section by an axial fan. The flow conditions in the

test section are controlled by varying the fan rpm. The wind tunnel design should

ensure a uniform flow in the test-section, and precise control of the flow conditions.

The utility of a wind tunnel clearly depends on the accuracy with which the flow

conditions in the test section can be controlled. Wind tunnel calibration involves

characterisation of the flow conditions in the test section such as, the velocity profile

in the test-section and the variation in the test conditions with the fan rpm.

Aim

To calibrate the Flight demonstration wind tunnel[2] by measuring the velocity

profile in the test-section and also to find an empirical correlation between the mean

flow speed in the test section and the fan rpm.

Deliverable

1. The velocity profile at a particular cross section clearly showing the extent of

inviscid core and the mean flow speed

2. Variation of the mean flow speed in the test section and the fan rpm, along

with the empirical correlation obtained using a least square fit on the data.

3. The operating Reynolds number range of the wind tunnel

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Equipment provided

The experiments are to be performed in the Flight demonstration wind tunnel.

Further details of the facility can be found in [2] .

The flow velocity can be calculated from the dynamic pressure measured using

the Pitot static tube and the manometer

Questions?

1. Compute the losses in various sections of the wind tunnel and obtain a rough

estimate of power required to run the tunnel at various speeds.

References

1. Low speed wind tunnel testing, Pope, Barlow

2. The flight demonstration wind tunnel, Users Manual

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Pitot static tube calibration

IntroductionA pitot static tube is used to determine the dynamic pressure and thereby the

velocity of the flow. The pitot probe axis needs to be aligned to the flow direction,

in order to provide meaningful measurements

Aim

To quantify the sensitivity of the pitot- static probe to the orientation with

respect to flow.

Deliverable

1. The variation of pitot and static probe pressure with angle of yaw of the probe

Equipment provided

The experiments are to be performed in the Flight demonstration wind tunnel.

Further details of the facility can be found in [2] .

References

1. Low speed wind tunnel testing, Pope, Barlow


**

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Smoke Flow visualization

IntroductionSmoke flow visualization involves introducing streaks of smoke (soot particles)

into the flow field [4]. The particles are carried along with the flow and give an

approximate picture of the streaklines. This simple technique can be applied to

analyze the qualitative features of flow over aerodynamic objects of interest like the

airfoil.

Aim

The streamline pattern over the airfoil and the circular cylinder with and

without the splitter plate needs to be visualized, using the smoke generator set-

up. In addition, the effect of introducing a boundary layer trip also needs to be

investigated.

Deliverables

1. Photographs of the streamline pattern

Equipment provided

1. Flight demonstration wind tunnel

2. Airfoil and cylinder models

3. Smoke generator

Questions?

1. Explain the reasons behind the observed behavior of the flow-field over the

airfoil and the cylinder

2. What is happening when the splitter plate is introduced?

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References


2. Maltby.R.L, Flow visualization in wind tunnels using indicators, AGARDograph-

70, 1962

3. Edwin Abbott, Theory of wing sections, Dover

4. Anderson John.D, Fundamentals of Aerodynamics,Mc Graw Hill

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3. Paint solution and brushes

Questions?

1. Explain major flow features of a finite wing, as the angle of attack is increased

References

1. Maltby.R.L, Flow visualization in wind tunnels using indicators, AGARDograph-

70, 1962

2. Flight demonstration wind tunnel, Users Manual

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Flow over a symmetric airfoil

IntroductionAirfoils are generic aerodynamic shapes with high lift to drag ratio and are

used as lift generating surfaces on aircraft. The non-dimensional lift of an airfoil is

a function of the angle of attack and the flow Reynolds number.

Aim

The objective of this experiment is to study the pressure distribution over

on an airfoil its variation with free stream velocity and angle of attack. The netlift and drag force on the airfoil is then calculated from the pressure distribution.

Using this data characterize the stall behavior of the airfoil. The results are also to

be presented in a non dimensional form (lift, drag and pressure co-efficients) The

pressure distribution obtained can be compared with inviscid flow predictions made

using open source programs such as Xfoil and Xflr5.

Methodology

1. Measure the static pressure distribution over the airfoil surfaces for a fixed

angle of attack and a fixed free stream velocity.

2. Repeat the above for different angle of attack and different free stream velocity.

Deleverables

1. The variation of lift and drag coefficient with angle of attack ()

2. The variation of stalling angle with Reynolds number

3. Comparison of the measured values with xfoil/xflr5 predictions

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Equipment


2. Airfoil model with pressure tappings

3. Inclined tube manometer

Questions

1. Why stalling happens in the airfoil?

2. What are the classifications of drag?

3. Does the drag calculated from the experimental measurements represent the

net drag on the airfoil?

4. What is the effect of introducing tripwire (on lift and drag)

5. Identify the parameters specified in the NACA nomenclature of the airfoil

supplied

References

1. Abbott, I. H., and von Doenhoff, A. E., Theory of wing sections, including a

summary of Airfoil data, McGraw-Hill, 1949.

2. Anderson, J. D., Fundamentals of Aerodynamics, 5th edition, Tata McGraw-

Hill Education, 2010.


4. http://web.mit.edu/drela/Public/web/xfoil/

5. http://www.xflr5.com/xflr5.htm

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Flow through a pipe bend

IntroductionGeneral equations of motion for inviscid in compressible flows can be written

in streamline co-ordinates as

P

s+ V

V

s= 0 (6.1)

P

n=

V2

r(6.2)

r is the streamline radius of curvature and s, n are directions along and normal

to the streamline respectively. From these equations, it could be seen that, if the

streamlines are curved a pressure gradient is set up normal to flow direction also.

Aim

Flow through a 90 degree, constant area circular bend is studied, in order

to understand the effect of streamline curvature on the pressure distribution. In

the flow through the bend provided, the streamlines could be assumes as circular

arcs, and the pressure distributions across the streamline can be solved form these

equations and compared with the experimental data.

Methodology

1. Measure the static pressure distribution along the wall in the flow direction

and perpendicular to it

2. Repeat the above for different free stream velocities.

Deleverables

1. The variation of static pressure for different velocities.

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2. Pressure variation predicted by inviscid theory and its comparison with ob-

served results

3. A schematic representation of the pressure variation on the walls, superim-

posed on the scale drawing of the bend.

Equipment

1. Modular flow apparatus

2. Circular bend


Questions

1. Consider the part of the pipe where it transitions for a straight duct to the

circular bend. What is the pressure distribution in this region?

2. Explain how the apparatus can be used as a flow meter. Calculate the dis-

charge co-efficient for this set-up

References

1. Ain.N.Sonin, Equation of Motion in Streamline Coordinates

2. http://web.iyte.edu.tr/ unverozkol/Fluid lab/Flow around a bent duct-theory.pdf

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Flow over a circular cylinder

IntroductionThe drag force on a circular cylinder is mainly due to the asymmetry in pres-

sure distribution about the vertical axis, resulting due to flow separation in the wake

region of the cylinder. For in compressible flows the drag co-efficient is a function

of Reynolds number. The variation depends on whether the flow is laminar or

turbulent ahead of the separation point.

Aim

To determine the drag over a circular cylinder and to compute the variation

of CD with Re. Drag force on the cylinder can be estimated from the pendulum

set-up provided.

Methodology

1. Measure angular defection of the model

2. Repeat different free stream velocities.

Deleverables

1. Plot showing the variation ofCD vs Re

2. Free body diagram of the model support. with an explanation of drag calcu-

lation

Equipment


2. Circular cylinder and support mechanism


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Questions

1. Explain the observed behavior of drag co-efficient

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Lift measurement from wall pressure distribution

IntroductionThe lift force acting on a model placed in a wind tunnel can be indirectly

determined by the application of momentum equation to a control volume containing

the model.

Aim

To determine the variation of CL with angle of attack for the given airfoil

model, by the application of momentum equation. The pressure distribution overthe wind tunnel walls is used for this purpose.

Methodology

1. Measure the pressure distribution over the top and bottom walls of the wind

tunnel, for various angles of attack of the airfoil

2. Repeat at different free stream velocities.

Deleverables

1. Theoretical basis for lift estimation by integral momentum balance

2. Plots showing the pressrue dustributionover the wind tunnel walls

3. Plot showing the variation ofCL vs at various Re

Equipment


2. Airfoil model


4. Drawing indicating the pressure tapping locations on the wall (wall pressure tap.pdf)

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Questions

1. Does the presence of viscosity introduce any error in the lift calculations?

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Drag estimation by wave survey

IntroductionThe drag force acting on a model placed in a wind tunnel can be indirectly

determined by measuring the momentum deficit in the wake region of the model.

Aim

To determine the variation ofCD with Reynolds number for the given circular

cylinder, by the application of the integral momentum equation. The wake velocity

profile is measured for this purpose.

Methodology

1. Measure the velocity profile in the wake region using the pitot rake provided

2. Repeat at different free stream velocities.

3. Determine the momentum flux in the wake region and calculate the drag force.

Deleverables

1. Theoretical basis for drag estimation by integral momentum balance

2. Wake velocity profile

3. Plot showing the variation ofCD vs Re

Equipment


2. Circular cylinder model

3. Pitot rake with inclined tube manometer

4. Dimensioned drawing of the pitot wake rake (wake rake.pdf)

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Questions

1. Does the measured drag include the skin friction drag?

References

1. Pijush Kundu, Iram.M.Cohen, Fluid Mechanics,Third Edition, Elsevier, Sec.5.7,

2004

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Strain gauge balance: Drag measurement

IntroductionThe drag force acting on a model placed in a wind tunnel can be directly

measure by using force balances. In a strain gauge balance, the drag force acting on

the model is deduced from the strain produced in the model support as a result of

the aerodynamic forces on the model. The balance structure is configured so as to

enable the measurement of the individual component forces and moments. In order

to facilitate this, the balance need to be calibrated by the application of known loads

and moments

Aim

To get familiarized with the use of strain gauge balances and the balance

calibration procedure.

Methodology

1. Calibrate the given strain gauge balance and obtain the calibration constants

relating the strain gauge voltages and the applied forces and moments

2. Measure the strain gauge voltage output at varying free stream velocities

3. Using the calibration data estimate the corresponding drag force on the wind

tunnel model

Balance calibration

A 2 component balance for measuring drag and pitcing moment is provided for

this pupose. It consists of a set of 2 strain gauge circuits in wheatstones bridge

configuation. The voltages V1 and V2 from these strain gauges corresponds to

the strain at the locations on the balance structure. These voltages are affected

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by the load D and the pmment about the loading point M. Assuming a linear

relationship, the dependance can be expressed as

V1 = K11D + K12M

V2 = K21D + K22M

The constants K11, K12K21K22 are to be estimated by performing the cali-

bration through the application of known loads and moments to the balance

structure.

Deleverables

(a) Calibration charts for the balance provided

(b) Plot showing the variation ofCD vs Re

Equipment

(a) Subsonic wind tunnel

(b) Circular cylinder model

(c) Stain gauge balance with multimeter and power supply

(d) Balance calibration rig (calibration.png)

References

(a) Cameron Tropea, Alexander.L.Yarin, John F Foss, Springer handbook of

experimental fluid mechanics,Chapt.8, Springer,

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Studies on Jet Propagation

Introduction

Jet is a free shear layer which is generated by the pressure difference across

the nozzle/orifice/pipe. A shear layer is formed in the interface between the

jet and the surrounding flow due to the velocity difference between them. The

surrounding flow may be at rest or have some velocity.

Aim

To understand the subsonic jet spread and velocity distribution along and

normal to the jet direction.

Methodology

(a) Measure the total pressure along the centerline of the jet up to 20D,

where D is the nozzle exit diameter.

(b) Measure the velocity profile across the jet at different axial location, e.g.

0.1D, 3D and 6D

Deliverables

(a) Plot the non-dimensional velocity (velocity/velocity at nozzle exit) along

the centerline of the jet

(b) Plot the non-dimensional velocity profile (velocity/velocity at center) atdifferent axial location

Equipment

(a) Nozzle connected with blower

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(b) Pitot tube

(c) Traverse mechanism for the movement of pitot probe

Questions

(a) Give three practical examples of jet mixing

(b) Discuss the similarity and difference between the boundary layer and the

free shear layer

(c) Discuss the variations of static and total quantities of pressure and tem-

perature across and along the jet

(d) Discuss the variation of mass, momentum and energy along the jet

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