Thursday, May 29, 2014

Questions from previous year Question Papers I for WTT




 PART – A (10 x 2 = 20)
Answer All the Questions
1. Define Reynolds number?
2. Define Mach number?
3. What is meant by subsonic and transonic speed regime?
4. Define critical Mach number?
5. Name any two equipments used in the calibration of wind tunnels.
6. What is meant by LDA?
7. What is meant by PIV?
8. Name any two equipments used for the measurement of force?
9. How are the surface streamlines and turbulence measured in wind tunnels?
10. What is the technique adopted to visualize Shock waves.
PART – B (5 x 16 = 80)
Answer All the Questions
11. Explain the Buckingham’s Pi Theorem.
(or)
12. Briefly discuss the scale effects of similarities.
13. Discuss the classification of wind tunnels in detail.
(or)
14. Explain with a neat diagram the layout of a subsonic wind tunnel.
15. Explain the techniques used for Turbulence measurements in a wind tunnel.
(or)
16. Explain in detail the calibration of a supersonic tunnel.
17. Explain with a neat sketch the working of a hot wire anemometer.
(or)
18. Briefly explain the measurement of pressure, velocity and force in a wind tunnel.
19. Discuss the smoke and tuft grid techniques used for flow visualization.
(or)
20. Briefly explain the optical methods used for flow visualization.
PART - A (10 X 2 = 20)
Answer ALL the Questions
1. Explain the term dynamic similarity.
2. Define Mach number.
3. Define laminar and turbulent flow.
4. What are the classifications of wind tunnel?
5. Name any two equipments used in the calibration of wind tunnels.
6. Define horizontal buoyancy.
7. What is meant by LDA?
8. Name any two equipments used for the measurements of velocity.
9. How are the surface streamlines and turbulence measured in wind tunnels?
10. What is meant by PIV?
PART – B (5 x 16 = 80)
Answer All the Questions
11. Explain the Buckingham’s Pi theorem.
(or)
12. Explain the dynamic similarity between a wind tunnel model and the prototype to be flight-tested. What are the essential conditions to be satisfied for the results to be carried from the model to the prototype? Are there any limitations or preconditions involved?
13. What is understood by the term low speed wind tunnel in aerodynamic testing? Describe with brief details through sketches and plots, various types of low speed wind tunnels based upon the details of the flow in test section.
(or)
14. Write notes on:
(a) setting Mach number in a transonic wind tunnel
(b) Measurements of turbulence level in a transonic wind tunnel. Explain the techniques used for turbulence measurements in a wind tunnel.
15. Describe the basis for the measurement of pressure and instruments used for the purpose. What are its advantages and applications? Illustrate with theory and an example. It is desired to obtain pressure distribution of a rotating circular cylinder kept in the test section of a wind tunnel.
(or)
16. Explain in detail the calibration of a supersonic wind tunnel.
17. Explain with a neat sketch the working of a hot wire anemometer.
(or)
18. What types of wind tunnel balances are used to ascertain forces and moments on an airplane model in a low speed wind tunnel? Hence describe the underlying principles of an external type wind tunnel balance for measuring lift, drag and pitching moments over a finite span wing.
19. Explain the phenomenon of separation of flow over a 2D wing with the help of liquid paraffin generated smoke wire technique with good sketches. What are its merits over kerosene generated smoke?
(or)
20. Briefly explain the optical methods used for flow visualization.
PART – A (10 x 2 = 20)
Answer All the Questions
1. What is geometrical similarity in wind tunnel testing of models?
2. What is boundary layer correction in the test section design of wind tunnels?
3. What is turbulence factor of a subsonic wind tunnel?
4. How is test section speed measured in case of a subsonic wind tunnel?
5. How are wind tunnel balances classified?
6. What is the basic principle involved in the interferometer method of flow visualization?
7. What are the advantages of flow visualization methods?
8. How is total pressure estimated in the test section of a super sonic wind tunnel?
9. What is horizontal buoyancy?
10. What are the limitations of dye injection method for flow visualization?
PART – B (5 x 18 = 60)
Answer All the Questions
11. (a) State Buckingham theorem. How is thus theorem useful in the experiments using wind tunnels?
(b) What is the basic principle behind hot wire anemometer? What are its limitations?
(or)
12. Define the following non-dimensional numbers: force coefficient, Euler number, Reynold’s number and moment coefficient. How do the model scale effects influence the wind tunnel test results?
13. How are the wind tunnels classified? What are the special problems of testing in hypersonic wind tunnels?
(or)
14. Sketch the typical layout of a supersonic wind tunnel and mark all the components and subsystems. What is starting problem in supersonic tunnels?
15. Write short notes on the following topics:
(a) Flow angularities in wind-tunnel testing.
(b) Turbulence intensity measurements in wind tunnel test section.
(or)
16. With a neat illustration explain the objective of calibration of a wind tunnel. In what way the calibration procedure for a supersonic tunnel different from that of a subsonic wind tunnel?
17. Distinguish between internal and external wind tunnel balances. Briefly explain how force measurements are carried out using an external strain gauge balance.
(or)
18. Bring out the essential features of a strain gauge based six component internal wind balance. Explain how the six components are measured using the balance.
19. With neat illustration explain the basic principles of Schelieren method of flow visualization. What are the advantages and limitations of the method?
(or)
20. Write short notes on the following techniques:
(a) Smoke technique for flow visualization.
(b) Use of tufts and electrical techniques for flow visualization studies.

B.Tech I Semester Regular Examinations, November 2006
WIND TUNNEL TECHNIQUIES (Aeronautical Engineering) Time: 3 hours Max Marks: 80
Answer any FIVE Questions All Questions carry equal marks
1. Explain the term Dynamic similarity in aerodynamic testing. Does it influence the aerodynamic characteristics of a model under testing? Hence state the PI theorem and work out dimensionless groups upon which depend the aerodynamic characteristics of a model under tests in a wind tunnel. [16] 2. Show with good sketches a comparison of the aerodynamics of a closed ckt , open jet wind tunnel with an open test section ,open ckt wind tunnel for the same capabilities. Which of the two is economical in the longer run? Illustrate with reference to operational charges and fabrication cost. [16] 3. Show with a detailed sketch salient features of a continuous type supersonic wind tunnel. What are its similarities with a continuous, return type subsonic tunnel; explain with a sketch. [16] 4. You are in the process of designing and fabricating a new low speed wind tunnel. What is the right location of pressure taps for conducting experiments for speed setting of this tunnel? Describe theory and the procedure to be followed in this case. [16] 5. Describe an electronic manometer for recording pressures simultaneously from multiple pressure ports with neat sketches. How does it differ from an ordinary multi- tube manometer? [16] 6. Describe a platform type external balance with line diagrams and sketches for measuring all six components on airplane and missile models. Draw good sketches and plots in support of your answer. [16] 7. A tuft grid is considered a supplementary flow visualization technique and used in conjunction with smoke flow visualization. Make use of this technique for explaining flow over a circular cylinder and in its field of influence by arranging tuft grid as deemed fit. [16] 8. Explain the superiority of oil flow visualization technique over some other surface flow visualization techniques. What are the factors that contribute to realistic results from this technique? Apply this method for viewing stalled flow over a finite span wing model:sting mounted in the test section in laminar and turbulent flows with pitch-changing mechanisms and present the results in the form of good sketches.
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Sunday, March 23, 2014

Define Horizontal Buoyancy ?

It is well known that the static-pressure-coefficient values obtained from tests of axisymmetric bodies in, for example, a large water tunnel indicate the existence of tunnel wall interference. This interference is due to blockage experienced by the body operating within the boundaries of the test section walls and to the skin friction on both the tunnel walls and the surface of the body, which, in turn, causes finite-thickness boundary layers to develop. These factors result in a decrease in static pressure along the test section, which leads to a spurious horizontal buoyancy on the body.
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Monday, March 3, 2014

SET of TWO MARK QUESTIONS

TWO MARK QUESTIONS

1. DEFINE MACH NUMBER?
 It’s defined as the square root of the ratio of the inertia force of a flowing fluid
to the elastic force.
Also it is defined as the ratio between Velocity of the Body and the Velocity of Sound.

2. DEFINE REYNOLDS NO?
It’s defined as the ratio of an inertia force of the flowing fluid and the viscous force of the fluid

3. DEFINE EULER’S NO?
It’s defined as the square root of the ratio of the inertia force of a flowing fluid to the pressure force

4. DEFINE WEBER’S NO?
It’s defined as the square root of the ratio of the inertia force of a flowing fluid to surface tension force

5. DEFINE FROUDE’S NO?
It’s defined as the square root of the ratio of the inertia force of a flowing fluid to the gravity force

6. DEFINE BUCKINGHAMS Л THEOREM?
If there are n variables in a physical phenomenon and if this variables contain m fundamental dimension (M, L, T) then the variables are arranged to (n-m) dimensionless terms, each term is called л-term

7. WHAT IS MEANT BY SIMILARITIES?
Model and prototype have similar properties or model and prototype are similar

8. WRITE DOWN THE TYPES OF SIMILARITIES?
 Geometric similarity
 Kinematic similarity
 Dynamic similarity 

9. WHAT ARE THE CLASSIFICATIONS OF WIND TUNNEL?
 Low speed wind tunnel,
 High speed wind tunnel,
 Special type tunnel.

10. WHAT IS FUNCTION OF EFFUSER?
It converts available pressure energy into kinetic energy and its located upstream of the test section.

11. WHAT IS FUNCTION OF DIFFUSER?
It converts the kinetic energy to pressure energy and it’s downstream of the test section.


12. WHAT IS BREATHER?
It is attached with an one way valve so that it take the air and by propeller suction, flow is maintained inside the return type.

13. WHAT ARE THE MERITS AND DEMERITS OF OPEN CIRCUIT?
 Construction cost less,
 It no surging problem is open to the free atm.

 DEMERITS.
 Tunnels much noisy,
 Make cost environment problem.

14. DEFINE ENERGY RATIO.
It is defined as the ratio between the total kinetic energy of the flow to the energy loss.
ER = 1/K0

15. WHAT ARE THE ADVANTAGES OF BLOW DOWN TYPE WIND TUNNEL?
 This is the simplest among the supersonic tunnel and most economic to build.
 Constant blowing press can be maintaining for considerable running by throttle valve.

16. WHAT ARE THE APPLICATION OF VERTICAL WIND TUNNEL?
 It is used to study the spinning motion of the aircraft,
 Ejection of pilots from seats,
 Parachute flying,
 Helicopter operation.

17. WHAT ARE THE LOSSES IN SUPERSONIC TUNNEL?
 Friction losses,
 Expansion losses,
 Losses in the contraction cone and test section,
 Losses in guide vanes,
 Losses in cooling system.

 18. WHAT ARE THE TYPES OF FLOW ANGULARITIES?
 Sphere type yaw meter,
 Claw type yaw meter.

19. WHAT ARE THE TURBULENT MEASUREMENTS?
 Turbulence sphere,
 Pressure sphere,
 Hot wire anemometer.

20. WHAT ARE THE METHODS TO REDUCE TURBULENCE INSIDE W/T.
 Using max. no of fan blades,
 Using a very long and gradual nacelle,
 Anti swirl vanes,
 Providing max. Possible distance between propellers and test section.

21. PRINCIPLE OF HOT WIRE ANEMOMETER.
The rate of heat from an electrical heated wire and placed in an airstream is
proportional to the velocity.
22. WHAT ARE THE TYPES OF FLOW ANGULARITIES?
 Sphere type yaw meter,
 Claw type yaw meter.

23. WHAT ARE THE TURBULENT MEASUREMENTS?
 Turbulence sphere,
 Pressure sphere,
 Hot wire anemometer.

24. WHAT ARE THE METHODS TO REDUCE TURBULENCE INSIDE W/T.
 Using max. no of fan blades,
 Using a very long and gradual nacelle,
 Anti swirl vanes,
 Providing max. Possible distance between propellers and test section.

25. DEFINE WIND TUNNEL BALANCE
Wind tunnel balance is a device to measure the actual forces &moments acting on a model placed in the test section stream

26. WHAT ARE THE CLASSIFICATIONS OF WIND TUNNEL BALANCE?
 Wire type balance
 Strut type balance
 Platform type balance
 Yoke type balance
 Strain gauge type balance

27. WHAT DO YOU MEAN BY WIRE BALANCE?
In wire type wind tunnel balances only wires are used to support the model. All the load components are transmitted to the measuring device by these wires.

28. WHAT ARE THE CLASSIFICATIONS OF STRUT TYPE BALANCES?
 Yoke type
 Platform type
 Pyramid type

29. WHAT ARE THE TYPES OF STRAIN GAUGE BALANCE?
 Internal balance
 Semi internal balance
 External balance

30. WHAT IS THE PRINCIPLE OF LIQUID MANOMETER?
The principle is that the pressure is balanced by the weight of a liquid column.

31. WHAT ARE THE TYPES OF BAROMETERS?
 Syphon barometer
 Fortin barometer
 Aneroid barometer

32. GIVE SOME DISADVANTAGES OF DIAL TYPE PRESSURE GAUGE?
 They must be calibrated periodically to ensure that they continue to read correctly
 The manometers are less expensive when there is a large number of pressures to be read
 Like manometers, they cannot be easily read electronically

33. WHAT ARE THE TYPES OF PRESSURE TRANSDUCERS?
They are classified as mechanical, electrical & optical type

34. LIST OUT SOME ADVANTAGES OF PRESSURE TRANSDUCERS?
 They provide signal proportional to the applied pressure which can be automatically recorded by acquisition system
 They are relatively low volume devices & consequently respond more rapidly to
pressure changes
 They are small enough to be mounted inside wind tunnel models

35. STATE THE PRINCIPLE OF LDA?
The principle is that a moving particle illuminated by a light beam scatters light at a frequency different from that of the original beam. This difference in frequency is known as Doppler shift & it’s proportional to the velocity of the particle.
36. WHAT ARE THE SCATTERING SUBSTANCES USED FOR LDA?
 Micro polythene spheres
 Diluted milk droplets
 Diluted smoke particles
 Aerosol
 Fine alumina powder
37. WHAT ARE THE ADVANTAGES OF LDA?
 It has high frequency response
 It has negligible probe interference
 It is applicable to the wide range of application
 The measurement with LDA is absolute, linear with velocity and require no pre calibration.

38. GIVE SHORT NOTES ON REFERENCE BEAM SYSTEM?
In reference beam system the scattered beam of light is optically mixed with original  beam & the difference is obtained as the Doppler shift in frequency. This technique is known as heterodyning & it’s the characteristic of a photo multiplier.

39. WHAT IS THE ADVANTAGE OF VORTEX SHEDDING TECHNIQUE?
It is capable of measuring low speeds of air which cannot be measured accurately with a
conventional manometer.
40. DEFINE PATHLINE?
The path of a point or particle convected with the flow is called a path line. If we could
release a tracer particle at any selected point and record its subsequent path, this would be
a path line.

41. DEFINE STREAKLINE?
It is a curve which represents the instantaneous motion of the fluid particle from the
given point.

42. DEFINE STREAMLINE?
A streamline through a point at an instant in time is the line whose tangent is the velocity
at that point and that follows a path through the fluid such that the tangent at every point
is the local instantaneous velocity.

43. DEFINE TIMELINE?
A timeline is generated by simultaneously emitting a short burst of tracers along a line
perpendicular to the local flow. This marks a line of elements that are in a straight line at
the initial time.

44. HOW CAN WE CLASSIFY FLOW VISUALISATION?
The flow visualization can be broadly classified into two, they are
 surface flow visualization
 flow field visualization

 45. WHAT ARE THE KEY ASPECTS OF SURFACE FLOW THAT CAN BE
INVESTIGATED FROM SURFACE FLOW VISUALISATION?
 Key aspects of surface flows that may be investigated using visualization techniques
include
 Stagnation point location
 Separation lines
 Location of boundary layer transition
 Characteristic unsteadiness
 Extent of separation zones
 Types of critical points

46. WHAT ARE THE REQUIREMENTS OF TUFTS?
The Tufts must be of light, flexible material that will align itself with the local surface
flow as a result of direct of direct aerodynamic force.

47. WHAT ARE THE MATERIALS USED FOR MAKING TUFTS?
The most commonly used material is light yarn with weights and lengths chosen
according to model size and test speed.

48. WHAT ARE THE MATERIALS USED FOR MAKING MINITUFTS?
The tuft material is monofilament nylon that has been treated with a fluorescent dye.

49. WHAT ARE THE ADVANTAGES OF USING TUFTS?
 Easily producible
 Once the tufts are installed the model can be repositioned and indications studied visually & photographed for as long as desired.

50. WHAT ARE THE METHODS OF OPTICAL FLOW VISUALISATION?
 Shadow graph
 Schlieren technique
 Interferometer

51. WHAT ARE THE APPLICATION OF SMOKE VISUALISATION?
 Flow over an aerofoil
 Study vortex motion

52. WHAT ARE THE ADVANTAGES OF OPTICAL TECHNIQUES?
 Non intrusive
 Avoiding the formation of unwanted shockwaves
 Avoid problems associated with the introduction of foreign particles

53. WHAT IS THE FUNDAMENTAL PRINCIPLE OF THE INTERFEROMETER?
From corpuscular properties of light, we know that when light travels through a gas the velocity of propagation is affected by the physical properties of the gas.

C=fλ

54. WHAT IS THE FUNDAMENTAL PRINCIPLE OF SCHLIEREN TECHNIQUE?
The speed of a wave front of light varies inversely with the index of refraction of the medium through which the light travels.
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Unit III Wind Tunnel Measurements

Pressure Measurements

Introduction
  • Pressure measurement is important in many fluid mechanics related applications. 
  • From appropriate pressure measurements velocity, aerodynamic forces and moments can be determined. 
  • Pressure is measured by the force acting on unit area. Measuring devices usually indicate differential pressure i.e. in relation with atmospheric pressure.This is called gauge pressure. 
  • The measured pressure may be positive or negative with reference to the atmospheric pressure .
  • A negative gauge pressure is referred to as vacuum.






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Sunday, March 2, 2014

Unit II Hypersonic Wind Tunnel


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Unit II Hypersonic flow


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SET II SHORT QUESTIONS

1. What do you mean by dimensionless numbers? Name some of it.

Dimensionless numbers are those numbers which are obtained by dividing the inertia force by viscous force or gravity force or pressure force or surface tension force or elastic force.  As this is a ratio of two forces, it will be dimensionless number.  These dimensionless numbers are also called non – dimensional parameters.

The following are the important dimension less numbers:
    1.      Reynolds numbers
  1. Froude’s number
  2. Euler’s number
  3. Weber’s number
  4. Mach’s number
2. What are the different laws on which models are designed for dynamic similarity?

Model laws or laws of similarity are the laws  on which the models are designed for dynamic similarity.  Models are designed on the basis of ratio of the force, which is dominating in the phenomenon.
The following are the model laws:

  1. Reynolds model law
  2. Froude model law
  3. Euler model law
  4. Weber model law
  5. Mach model law 
3. Explain the terms: distorted models and undistorted models.  What is the use of distorted models?

Undistorted Models: Undistorted models are those models which are geometrically similar to their prototypes or in other words the scale ratio for the linear dimensions of the model and its prototype is same.  The behaviour of the prototype can be easily predicted from the results of undistorted model.

Distorted Model:

            A model is said to be distorted if it is not geometrically similar to its prototyped model. Different scale ratios for the linear dimensions are adopted.  For example, incase to rivers, harbours, reservoirs etc.  two different scale ratios, one for horizontal dimensions and other for vertical dimensions are taken. Thus the models of revivers, harbors and reservoirs will become distorted models.

The followings are the advantages of distorted models.

  1. The vertical dimensions of the model can be measured accurately.
  2. The cost of the model can be reduced.
  3. Turbulent flow in the model can be maintained. 
4. Write the drawbacks of analytical methods.

            The following are the disadvantages of analytical methods used for study and analysis of many problems in fluid mechanics.

1.          It involves a number of approximations and assumptions and hence application of the analytical methods are restricted.
2.                  It involves highly complicated equations which cannot be solved.
3.                  The solutions to various complex flow patterns cannot be obtained by analytical methods alone.
4.              It is impossible or impracticable in some cases to make a satisfactory and complete mathematical analysis of the problems 

5. What you mean by hydraulic similitude?

            The observations made on the performance of the model are useful to predict the performance of the prototype. Hence it is very necessary that the model should represent the prototype in every respect i.e. the model should represent the prototype should have similar properties. The similarity between a prototype and its model is called similitude.

            For absolute similitude between a model and the prototype the following types of similarities should exist.
 a)      Geometric similarity
 b)      Kinematics similarity and
 c)      Dynamic similarity 

6. What are the demerits of distorted models?

The following are the demerits of distorted models:

i)                    Due to unequal horizontal and vertical scales the pressure and velocity distribution are not truly reproduced in the model.

ii)                  The wave pattern in the model will be different from that in the prototype due to depth distortion.

iii)                Slopes, bends and earth cuts are not truly reproduced.

7. What do you mean by scale effect?

            This is a defect which occurs in certain models due to which the computed properties of the prototype from model experiments deviate much from the actual properties of the prototype.

            For example, a model cannot match with prototype if it large depths, high velocities, surface tension factor, flow conditions and force. Here the models do not have exact properties with prototype. Hence, the scale effect occurs.

8. What are the different types of forces acting in moving fluid?

Types of Forces Acting in Moving Fluid:

For the fluid flow problems, the forces acting on fluid mass may be any one, or a combination of several of the following forces :

  1. Inertia Force Fi.
  2. Viscous force Fv.
  3. Gravity force Fg.
  4. Pressure force Fp.
  5. Surface tension force,
  6. Fs Elastic force Fe.
  1. Inertia Force (F1) :
 It is equal to the product of mass and acceleration of the flowing fluid and acts in the direction opposite to the direction of acceleration. It is always existing in the fluid flow problems.

  1. Viscous Force (Fv) :
 It is equal to the product of shear stress (t) due to viscosity and surface area of the flow. It is present in fluid flow problems where viscosity is having an important role to play.

  1. Gravity Force (Fg) :
 It is equal to the product of mass and acceleration due to gravity of the flowing fluid. It is present in case of open surface flow.

  1. Pressure Force (Fp)  :
 It is equal to the product of pressure intensity and cross sectional area of the flowing fluid. It is present in case pipe flow.

  1. Surface Tension Force(Fs) :
 It is equal to the product of surface tension and length of surface of the flowing fluid.

  1. Elastic Force (Fe) :
 It is equal to the product of elastic stress and area of the flowing fluid.

For a flowing fluid, the above – mentioned forces may not always be present. And also the forces, which are present in a fluid flow problem, are not of equal magnitude. There are always one or two forces which dominate the other forces. These dominating forces govern the flow of fluid.







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