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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
2. The flight demonstration wind tunnel, Users Manual
**
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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
1. The flight demonstration wind tunnel, Users Manual
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
1. Flight demonstration wind tunnel
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.
3. The flight demonstration wind tunnel, Users Manual
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
3. Inclined tube manometer
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
1. Modular flow apparatus
2. Circular cylinder and support mechanism
3. Inclined tube manometer
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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
1. Modular flow apparatus
2. Airfoil model
3. Inclined tube manometer
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
1. Flight demonstration wind tunnel
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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