16

ARUNAI ENGINEERIN COLLEGETHIRUVANNAMALAI

AE6412 AERODYNAMICS LABORATORY LAB MANUALFor 4rd semester B.E/B.Tech students

Department of Aeronautical Engineering

LIST OF EQUIPMENTS(for a batch of 30 students)SI.NOREQUIRMENTQUANTITY

1Venturimeter1 each

2Orificemeter1 set

3Pipe friction apparatus1 No.

4Subsonic Wind tunnel1 each

6Aerofoil Model- rough1 each

7Aerofoil Model- smooth1 No.

8Aerofoil Model- cylinder1 No.

9Aerofoil Model- flat plate1 No.

UNIVERSITY PRACTICAL EXAMINATION

ALLOTMENT OF MARKSInternal Assessment= 20 marksPractical Examination= 80 marksINTERNAL ASSESSMENT[20 Marks]Staff should maintain the assessment Register and the Head of the Department should monitorit.SPLIT UP OF INTERNAL MARKSRecord Note10 marks

Model Exam5 marks

Attendance5 marks

Total20 marks

UNIVERSITY EXAMINATIONThe examination will be conducted for 100 marks. Then the marks will be calculated to 80 marks.ALLOCATION OF MARKSAim and Procedure30 marks

Modeling30 marks

Simulation20 marks

Result10 marks

Viva Voce10 marks

Total100 marks

LIST OF EXPERIMENTS AS PER SYLLABUS1. Application of Bernoullis Equation venturimeter and orifice meter.2. Frictional loss in laminar flow through pipes.3. Frictional loss in turbulent flow through pipes.4. Calibration of a subsonic Wind tunnel.5. Determination of lift for the given airfoil section.6. Pressure distribution over a smooth circular cylinder.7. Pressure distribution over a rough circular cylinder.8. Pressure distribution over a symmetric aerofoil.9. Pressure distribution over a cambered aerofoil.10. Flow visualization studies in subsonic flows.Total: 45 PERIODS

TABLE OF CONTENTS

EXCERSISE NO.

TITLEPAGE NO.

LIST OF NOMENCLATURES

1Application of Bernoullis Equation venturimeter and orifice meter.

2Frictional loss in laminar flow through pipes.

3Frictional loss in turbulent flow through pipes.

4Calibration of a subsonic Wind tunnel.

5Determination of lift for the given airfoil section.

6Pressure distribution over a smooth circular cylinder.

7Pressure distribution over a rough circular cylinder.8. Pressure distribution over a symmetric aerofoil.

8Pressure distribution over a cambered aerofoil.

10Flow visualization studies in subsonic flows.

LIST OF NOMENCLATURES

SI.NO.SYMBOLDESCRIPTION

1

Cp

Pressure coefficient

2

VFree stream velocity of the fluid

3

PTTotal pressure

4

PSStatic pressure

5

q

Dynamic pressure

6

air

Free stream fluid density (Air at sea level and 15 C) is 1.225 kg / m3

7

water

Water density is 1000 kg / m3

8

g

Acceleration due to gravity is 9.81 m / s2

9

CL

Coefficient of lift force

10

CD

Coefficient of drag force

11

CS

Coefficient of side force

12

FT

Theoretical force

13

FL

Lift force

14

FD

Drag force

15

FS

Side force

16

S

Surface Area (S ) = Span (b) Chord (C)

17

Angle of attack

Ex. No.: 01APPLICATION OF BERNOULLIS EQUATION VENTURIMETER AND ORIFICEMETER.Date:

Aim:To understand the concept in generation Bernoullis Equation venturimeter and orifice meter.

Apparatus Required: venturimeter and orifice meter Differential U-tube Collecting tank Stop watch

FORMULAE:

1. ACTUAL DISCHARGE:

Q act = A x h / t (m3 / s)

2. THEORTICAL DISCHARGE:Q th = a 1 x a 2 x 2 g h / a 12 a 22 (m3 / s)

Where:

A= Area of collecting tank in m2

h = Height of collected water in tank = 10 cm

a 1= Area of inlet pipe in,m2

a 2= Area of the throat inm2

g= Specify gravity inm / s2

t= Time taken for h cm rise of water

H = Orifice head in terms of flowing liquid = (H1 ~ H2) (s m / s 1 - 1)

Where:

H1 = Manometric head in first limb

H2 = Manometric head in second limb

s m = Specific gravity of Manometric liquid

(i.e.) Liquid mercury Hg = 13.6

s1 = Specific gravity of flowing liquid water = 1

ManometricManometricTime taken forActualTheoretical

reading

headCo-efficient of

h cm rise ofdischargedischarge Qth

DiameterH=(H1~H2)discharge Cd

S.NowaterQ act x 10-3x 10-3

in mmH1 cmH2 cmx 12.6 x 10-2(no unit)

t Secm3/ sm3/ s

of Hgof Hg

Mean Cd =

3. CO EFFICENT OF DISCHARGE:

Co- efficient of discharge = Q act / Q th(no units)

DESCRIPTION:

Orifice meter has two sections. First one is of area a1, and second one of area a2, it does not have throat like venturimeter but a small holes on a plate fixed along the diameter of pipe. The mercury level should not fluctuate because it would come out of manometer.

PROCEDURE:

1. The pipe is selected for doing experiments

2. The motor is switched on, as a result water will flow

3. According to the flow, the mercury level fluctuates in the U-tube manometer

4. The reading of H1 and H2 are noted

5. The time taken for 10 cm rise of water in the collecting tank is noted

6. The experiment is repeated for various flow in the same pipe

7. The co-efficient of discharge is calculated

RESULT:

The co efficient of discharge through Venturimeter and Orificemeter is (No unit)

Ex. No.: 02 FRICTIONAL LOSS IN LAMINAR FLOW THROUGH PIPES.Date:

Aim: To find the frictional loss in laminar flow through pipes.Apparatus Required: A pipe provided with inlet and outlet and pressure tapping

Differential u-tube manometer

Collecting tank with piezometer

Stopwatch

Scale

FORMULAE:

1.FRICTION FACTOR ( F ):

f = 2 x g x d x h f / l x v2(no unit)

Where,

g = Acceleration due to gravity(m / sec2)

d = Diameter of the pipe(m)

l = Length of the pipe(m)

v = Velocity of liquid following in the pipe(m / s)

hf = Loss of head due to friction(m)

= h1 ~ h2

Where

h1 = Manometric head in the first limbs

h2 = Manometric head in the second limbs

2.ACTUAL DISCHARGE:

Q = A x h / t(m3 / sec)

Where

A = Area of the collecting tank(m2)

h = Rise of water for 5 cm(m)

t = Time taken for 5 cm rise(sec)

Manometer readingsTime forActual discharge

5cmVelocityFriction

Qact x 10-3V2

Diameter ofrise ofVfactor

m2/ s 2

S.Nopipe mmwaterm3 / sm/sf x 10-2

h1xh2 xhf = (h1-h2)

t sec

10-210-2x 10-2

Mean f =

3. VELOCITY:

V = Q / a(m / sec)

Where

Q = Actual discharge(m3/ sec)

A = Area of the pipe(m2)

DESCRIPTION:

When liquid flows through a pipeline it is subjected to frictional resistance. The frictional resistance depends upon the roughness of the pipe. More the roughness of the pipe will be more the frictional resistance. The loss of head between selected lengths of the pipe is observed.

PROCEDURE:

1. The diameter of the pipe is measured and the internal dimensions of the collecting tank and the length of the pipe line is measured

2. Keeping the outlet valve closed and the inlet valve opened

3. The outlet valve is slightly opened and the manometer head on the limbs h1 and h2 are noted

4. The above procedure is repeated by gradually increasing the flow rate and then the corresponding readings are noted.

Result: RESULT:

1.The frictional factor f for given pipe =x 10-2 (no unit)

2.The friction factor for given pipe by graphical method = x 10-2 ( no unit )

Ex.No : 03FRICTIONAL LOSS IN TURBULENT FLOW THROUGH PIPES.DATE:

Aim: To find the frictional loss in turbulent flow through pipes.Apparatus Required: A pipe provided with inlet and outlet and pressure tapping

Differential u-tube manometer

Collecting tank with piezometer

Stopwatch

Scale

FORMULAE:

1.FRICTION FACTOR ( F ):

f = 2 x g x d x h f / l x v2(no unit)

Where,

g = Acceleration due to gravity(m / sec2)

d = Diameter of the pipe(m)

l = Length of the pipe(m)

v = Velocity of liquid following in the pipe(m / s)

hf = Loss of head due to friction(m)

= h1 ~ h2

Where

h1 = Manometric head in the first limbs

h2 = Manometric head in the second limbs

2.ACTUAL DISCHARGE:

Q = A x h / t(m3 / sec)

Where

A = Area of the collecting tank(m2)

h = Rise of water for 5 cm(m)

t = Time taken for 5 cm rise(sec)

Manometer readingsTime forActual discharge

5cmVelocityFriction

Qact x 10-3V2

Diameter ofrise ofVfactor

m2/ s 2

S.Nopipe mmwaterm3 / sm/sf x 10-2

h1xh2 xhf = (h1-h2)

t sec

10-210-2x 10-2

Mean f =

3. VELOCITY:

V = Q / a(m / sec)

Where

Q = Actual discharge(m3/ sec)

A = Area of the pipe(m2)

DESCRIPTION:

When liquid flows through a pipeline it is subjected to frictional resistance. The frictional resistance depends upon the roughness of the pipe. More the roughness of the pipe will be more the frictional resistance. The loss of head between selected lengths of the pipe is observed.

PROCEDURE:

1. The diameter of the pipe is measured and the internal dimensions of the collecting tank and the length of the pipe line is measured 2. Keeping the outlet valve closed and the inlet valve opened

3. The outlet valve is slightly opened and the manometer head on the limbs h1 and h2 are noted

4. The above procedure is repeated by gradually increasing the flow rate and then the corresponding readings are noted.

RESULT:

1.The frictional factor f for given pipe =.x 10-2 (no unit)

2.The friction factor for given pipe by graphical method = x 10-2 ( no unit )

Ex.No : 04 CALIBRATION OF A SUBSONIC WIND TUNNEL.Date:

Aim: To find the velocity at attest section in a subsonic wind tunnel and to plot the graph for rpm is test section velocity.

Apparatus Required: Subsonic Wind Tunnel Multimeter Scale Pitot static tube Pitot tube

Formula Used: m/sWhere,g- acceleration due to gravitylw- density of waterlu- density of airv-velocity of test sectionH- pressure head

Procedure: 1) The static and dynamic pressure varies at different velocity due to kinetic energy change in the wind tunnel2) But the total pressure in the wind tunnel remains the section.3) After taking the values, calculate the velocity by using and same constant.4) From the table, it seen that for varying RPM sand static pressure, the total pressure remains the same 5) Finally plot the graph between RPM and velocity.

Tabulation:

S.NoSpeedrpmStatic pressurehs(mm)Total Pressureho(mm)H(Velocitym/s

Graph:

Plot for RPM vs. Test section Velocity

Result: Thus the plot for RPM vs. Test section Velocity has been drawn. Ex. No. : 05 DETERMINATION OF LIFT AND DRAG FOR THE GIVEN AIRFOIL SECTION.Date :

Aim: To determine the coefficient of lift and drag using section type wind tunnel for the given aerofoil section.

Apparatus Required: Subsonic Wind Tunnel Multimanometer Angle scale Aerofoil sectionFormula Used:1) Coefficient of pressure

Where-Load pressure at point in m of water-Ambient pressure in m of water-Density of air kg/-Velocity of wind in wind tunnel m/s

2) Velocity of wind tunnel for given rpm m/sWhere,g- acceleration due to gravitylw- density of waterlu- density of airv-velocity of test sectionH- pressure head3) Coefficient of normal force and axial force

Where, =Coefficient of pressure at lower chamber=Coefficient of pressure at upper chamber

4) Coefficient of lift(L) and coefficient of Drag(D)

Where,5) To determine the lift and drag

(N)

(N)

Upper side:

S.Nox/cy/c in m of

Lower side:S.Nox/cy/c in m of

S.No normal axial

Procedure:

1) Wind tunnel is checked for its working initially.2) The given aerofoil is fixed in the test section at angle of attack 0 to chord line.3) Wind tunnel is turned on is fixed at req speed4) The static and total pressure is first measured.5) Using attained multimanometer, the pressure of a rise aerofoil for 12 sport is taken.6) Formatting the pressure reading in the formula, the velocity of wind and there coefficient of lift and drag is calculated.

Result: Thus the calculated for coefficient of lift and coefficient of drag from 0 angle of attack.

1) Coefficient of lift=2) Coefficient of drag=..

Ex. No. : 06PRESSURE DISTRIBUTION OVER SMOOTH CIRCULAR CYLINDERDate :

Aim: To find the Coefficient of pressure over smooth circular cylinder

Apparatus Required: Subsonic Wind Tunnel Smooth Circular Cylinder with Pressure taps

Procedure: Switch ON the Main which is connected to the 440 V, 32 A, 3 ph, AC power supply with neutral and earth connection. Check all the switches of the controller are in OFF position before starting. Switch ON the MCB (Miniature Circuit Breaker) of Console Board. Put-on the mains and observe the main indicator lights are glowing at the bottom of the control panel. Fix the circular cylinder in the test section, at required orientation. Connect the pressure taps of manometer to the respective taps of model. Control the main flow of air in the test section by increasing the AC motor speed gradually. Set the speed as constant and note the velocity from the RPM vs.Test section Velocity plot. Measure and note the readings from the manometer. After the experiment switch OFF all accessories. Find the coefficient of pressure at each point from calculation.

Plot a graph for Cylinder Surface Pressure vs. Pressure Tapping Points by taking x-axis for Pressure Tapping Points and y-axis for Cylinder Surface Pressure.

Tabulation: Values of pressure Coefficient over smooth circular cylinder Air at velocity = ________ m/s for frequency = ________ Hz

Location

Refer.Pressure,Pr (cm)CylinderSurface Pressure,P(i) (cm)PressuresPT -PS(cm)Cp=(PT-PSv2

Pm = ( Pr-P(i) ) (cm)PT=Pm (cm)PS = ( Pr P13 ) (cm)

1

2

3

4

5

6

7

8

9

10

11

12

13

Graph: Plot for smooth Cylinder Surface Pressure vs.Pressure Tapping Points

Result: Thus the pressure Coefficient over the smooth circular cylinder has been found and required plot has been drawn. Ex. No: 07 PRESSURE DISTRIBUTION OVER ROUGH CIRCULAR CYLINDERDate :

Aim: To find the Coefficient of pressure over rough circular cylinder

Apparatus Required: Subsonic Wind Tunnel Rough Circular Cylinder with Pressure taps

Procedure: Switch ON the Main which is connected to the 440 V, 32 A, 3 ph, AC power supply with neutral and earth connection. Check all the switches of the controller are in OFF position before starting. Switch ON the MCB (Miniature Circuit Breaker) of Console Board. Put-on the mains and observe the main indicator lights are glowing at the bottom of the control panel. Fix the circular cylinder in the test section, at required orientation. Connect the pressure taps of manometer to the respective taps of model. Control the main flow of air in the test section by increasing the AC motor speed gradually. Set the speed as constant and note the velocity from the RPM vs.Test section Velocity plot. Measure and note the readings from the manometer. After the experiment switch OFF all accessories. Find the coefficient of pressure at each point from calculation.

Plot a graph for Cylinder Surface Pressure vs. Pressure Tapping Points by taking x-axis for Pressure Tapping Points and y-axis for Cylinder Surface Pressure.

Tabulation: Values of pressure Coefficient over rough circular cylinder Air at velocity = ________ m/s for frequency = ________ Hz

Location

Refer.Pressure,Pr (cm)CylinderSurface Pressure,P(i) (cm)PressuresPT -PS(cm)Cp=(PT-PSv2

Pm = ( Pr-P(i) ) (cm)PT=Pm (cm)PS = ( Pr P13 ) (cm)

1

2

3

4

5

6

7

8

9

10

11

12

13

Graph: Plot for Cylinder Surface Pressure vs.Pressure Tapping Points

Result: Thus the pressure Coefficient over rough circular cylinder has been found and required plot has been drawn. Ex. No.: 08 PRESSURE DISTRIBUTION OVER SYMMETRICAL AIRFOIL AND ESTIMATION OF CpDate: Aim: To find the Coefficient of pressure over Symmetrical Airfoil

Apparatus Required: Subsonic Wind Tunnel Symmetrical Airfoil model with Pressure taps

Formulae Used:

1. Total Pressure = Static Pressure + Dynamic Pressure

2. For manometer readings,

Procedure: Switch ON the Main which is connected to the 440 V, 32 A, 3 ph, AC power supply with neutral and earth connection. Check all the switches of the controller are in OFF position before starting. Switch ON the MCB (Miniature Circuit Breaker) of Console Board. Put-on the mains and observe the main indicator lights are glowing at the bottom of the control panel. Fix the symmetrical Airfoil model in the test section, at required orientation. Connect the pressure taps of manometer to the respective taps of model. Control the main flow of air in the test section by increasing the AC motor speed gradually. Set the speed as constant and note the velocity from the RPM vs. Test section Velocity plot. Measure and note the readings from the manometer for different Angle of Attacks. After the experiment switch OFF all accessories. Find the coefficient of pressure at each point from calculation.

Plot a graph for symmetrical Airfoil Surface Pressure vs. Pressure Tapping Points by taking x-axis for Pressure Tapping Points and y-axis for symmetrical Airfoil Surface Pressure at certain Angle of Attack.

Tabulation: Values of pressure coefficient over Symmetrical Airfoil Air at velocity = ______ m/s for frequency = ________ Hz

Graph: Plot for Symmetrical Airfoil Surface Pressure vs. Pressure Tapping Points

Result: Thus the pressure Coefficient over the symmetrical Airfoil model has been found and required plot has been drawn.

Ex. No.: 09PRESSURE DISTRIBUTION OVER CAMBERED AIRFOIL AND ESTIMATION OF CpDate: Aim: To find the Coefficient of pressure over Cambered Airfoil

Apparatus Required: Subsonic Wind Tunnel Cambered Airfoil model with Pressure taps

Formulae Used:

1. Total Pressure = Static Pressure + Dynamic Pressure

2. For manometer readings,

Procedure: Switch ON the Main which is connected to the 440 V, 32 A, 3 ph, AC power supply with neutral and earth connection. Check all the switches of the controller are in OFF position before starting. Switch ON the MCB (Miniature Circuit Breaker) of Console Board. Put-on the mains and observe the main indicator lights are glowing at the bottom of the control panel. Fix the cambered Airfoil model in the test section, at required orientation. Connect the pressure taps of manometer to the respective taps of model. Control the main flow of air in the test section by increasing the AC motor speed gradually. Set the speed as constant and note the velocity from the RPM vs. Test section Velocity plot. Measure and note the readings from the manometer for different Angle of Attacks. After the experiment switch OFF all accessories. Find the coefficient of pressure at each point from calculation.

Plot a graph for Asymmetrical Airfoil Surface Pressure vs. Pressure Tapping Points by taking x-axis for Pressure Tapping Points and y-axis for Asymmetrical Airfoil Surface Pressure at certain Angle of Attack.

Tabulation: Values of pressure coefficient over Asymmetrical Airfoil Air at velocity = ______ m/s for frequency = ________ Hz

Graph: Plot for Asymmetrical Airfoil Surface Pressure vs. Pressure Tapping Points

Result: Thus the pressure Coefficient over the Cambered Airfoil model has been found and required plot has been drawn.

Ex. No.: 10USE OF SCHLIEREN SYSTEM TO VISUALIZE SHOCKDate :

Aim: To study the use of Schlieren system to visualize shock

Apparatus Required: Supersonic Wind Tunnel Schlieren system

Introduction:Schlieren method visualizes the distribution of fluid density within a fluid, as fluid density controls the index of refraction. Regions of density gradient deflect light beams, shifting their position on the image plane. The relative change in light intensity can be used to infer the original density and flow field.Optical Principle:There are several methods commonly used to visualize refractive index or density changes in liquids, gases, liquids and solids. Generically these include shadowgraphs, schlieren and interferometric techniques. These systems are used to visualize temperature gradients, shock waves in wind tunnels, nonhomogeneous areas in sheet glass, convection patterns in liquids, etc. Shadowgraph systems are often used where the density gradients are large. This technique also can accommodate large subjects, is relatively simple in terms of materials required and in terms of cost is probably the least expensive technique to set-up and operate. Interferometric techniques are usually highly sensitive, complex in set-up, can provide quantitative information but are expensive systems and can only deal with relatively small subjects. Schlieren systems are intermediate in terms of sensitivity, system complexity and cost. Schlieren systems can be configured to suit many different applications and sensitivity requirements. Typically, however, they are still considered too complex and expensive to implement in many cases where a simple density visualization system is needed. While discussed and introduced in the early '50's, the focusing schlieren method is one that uses no unusual or expensive optical elements and yet achieves high sensitivity at relatively low cost. Plus it relies on low-tech system "ingredients". As you can see by the attached illustration showing two students setting up a demo system, it is perfect for use in teaching situations where cost tends to be a primary concern. Unlike other systems, the focusing schlieren technique uses a broad light source instead of a small or point light source. This source is usually made up of a regular array of black and white elements. To make one requires simply a large translucent, opalescent, sheet of plastic onto which opaque stripes are fastened creating a black line/bright line effect. This screen is illuminated from behind with a single flood lamp or a flash, or a bank of them. If this screen is located closer to the "imaging" lens than infinity, then the image of this screen is reproduced at a distance somewhat larger than 1 focal length of the lens. If one makes a high contrast negative photograph of the image of the screen, then the bright areas of the subject will reproduce as dark, opaque, lines at the location of the image of the screen and the black lines will reproduce as clear lines. Then, if a subject of some kind is placed between the source and the camera lens, the image of this subject will be reproduced sharply at a distance larger then that at which a sharp image of the screen is reproduced. This essentially means that image points of this closer subject are made up, at the focus of the image of this closer subject, by light rays that come to the camera lens from a large number of source locations. Before these light rays become part of the sharply focused image of the subject they are part of the sharply focused image of the source. Now if the negative reproduction of the light source or screen is placed in the position where it was when its photograph was made, then at any position farther away from the camera lens no light will be seen because all the light from the clear areas of the source would be stopped by the dark lines of the reproduction of the source. If during the "steady state" condition of the systems the interfering physical reproductions of the gridlines of the source are displaced slightly from the pint where they cause a total extinction of light, then a grayish field of uniform brightness will be perceived. This field will become brighter until the physical lines completely cover the dark lines of the image of the source grid allowing all the light present in the clear, bright, areas of the source grid to pass. If the system is adjusted so that the obstruction and the image of the source grid are slighly misaligned and a uniform, grey field is seen, then local variations in refractive index that cause the light beam to move will become visible as local areas in the image plane that are brighter or darker than the middle grey selected that indicates the "steady state" condition. Thus local variations in density can be visualized. They can be recorded with simple auxiliary photographic equipment.

Figure 9. Operating principle of schlieren systemLight rays are bent whenever they encounter changes in density of a fluid. Schlieren systems are used to visualize the flow away from the surface of an object. The schlieren system shown in this figure uses two concave mirrors on either side of the test section of the wind tunnel. A mercury vapor lamp or a spark gap system is used as a bright source of light. The light is passed through a slit which is placed such that the reflected light from the mirror forms parallel rays that pass through the test section. On the other side of the tunnel, the parallel rays are collected by another mirror and focused to a point at the knife edge. The rays continue on to a recording device like a video camera. Now if the parallel rays of light encounter a density gradient in the test section, the light is bent, or refracted. In our schematic, a shock wave has been generated by a model placed in the supersonic flow through the tunnel test section. Shock waves are thin regions of high gradients in pressure, temperature and density. A ray of light passing through the shock wave is bent as shown by the dashed line in the figure. This ray of light does not pass through the focal point, but is stopped by the knife edge. The resulting image recorded by the camera has darkened lines that occur where the density gradients are present. The model completely blocks the passing of the light rays, so we see a black image of the model. But more important, the shock waves generated by the model are now seen as darkened lines on the image. We have a way to visualize shock waves. The earliest schlieren photographs of shock waves were black and white images. The image shown here is a color schlieren image produced by putting a prism near the slit and breaking the white light into different colors. Notice that the resulting image is two dimensional while, in reality, shock waves are three dimensional. So the schlieren photograph provides some valuable information about the location and strength of the shock waves, but it requires some experience to properly interpret the results of the process. Procedure: It is desirable to use a large aperture, relatively long focal length lens for the imaging lens. Some surplus copier lenses can be applied for this purpose. The source grid should be placed at a distance equal to four focal lengths of the lens. The subject field will be located at two focal lengths from the lens. Therefore the lens will be making a life sized reproduction of the subject. Due to this choice of distances, the lens will make an image of the source grid at a distance of 16 inches from the lens. This can be determined from the basic relationship that the reciprocal of the lens' focal length is equal to the reciprocal of the object distance plus the reciprocal of the image distance. To make a reproduction of the source grid a piece of high contrast film material (possibly stiffened by a piece of glass or held in or taped to a frame) is placed where the source grid comes to a sharp focus. It goes without saying that this must be done in such a manner that only light from the source grid falls on the photosensitive emulsion. This can be accomplished by baffling or building a light tight box around the lens to film area. It is important to note that the reproduction of the source grid will reflect any refractive index inhomogeneities present due to the inclusion of imperfect windows in the system and this feature alone often results in major cost benefits in terms of system setup since relatively low quality optical components can be used between the one lens in the system and source. After the film is exposed and developed, it is replaced in its original position. This can be checked by visually examining the registration between the image of the source grid and its physical negative reproduction as well as tracking the appearance of the subject field on a ground glass placed, as mentioned above, at two focal lengths from the lens. It should be noted that slight misregistration between the two grids allows the operator to vary the brightness of the subject field on the ground glass. Once this relationship has been established, placing a density gradient two focal lengths from the camera lens will cause this gradient to be visible on the ground glass. If the source of the gradients is a hot soldering iron, for example, the warm air rising from the iron should be clearly visible as rising plumes of light and dark from the iron itself.

Figure 9.1 Shock captured by schlieren system A camera can be aimed at the ground glass and images of the disturbances created by the rising density gradients can then ultimately be photographed. Conversely, if the whole system (from the lens back to the ground glass) is built in a light tight container and the lens is equipped with shutter, then film can be the ultimate image and exposures are made by simply operating the shutter or firing a flash that illuminates the source grid for a brief instant. This is a focusing schlieren photograph made directly onto film showing warm air rising from hot soldering irons. Result: Thus the use of schlieren system to visualize the shock is studied.

Viva questions: What is wind tunnel balance? How the shock induces? What are the types of shock? What are flow visualization techniques? Explain schlieren operating technique?Ex. No.: 11USE OF SHADOWGRAPH SYSTEM TO VISUALIZE SHOCKDate:

Aim: To study the use of Shadowgraph system to visualize shock

Apparatus Required: Supersonic Wind Tunnel Shadowgraph system

Introduction:The density of a fluid varies with temperature, salinity, and pressure. And, the index of refraction changes with fluid density. Variations in the refractive index deflect or phase shift light passing through the fluid. If a screen is placed opposite the light source, these effects create shadows one the screen creating an image called a Shadowgraph. Operating principle:The shadowgraph is the simplest form of optical system suitable for observing a flow exhibiting variations of the fluid density. In principle, the system does not need any optical component except a light source and a recording plane onto which to project the shadow of the varying density field. A shadow effect is generated because a light ray is refractively deflected so that the position on the recording plane where the undeflected ray would arrive now remains dark. At the same time the position where the deflected ray arrives appears brighter than the undisturbed environment. A visible pattern of variations of the illumination (contrast) is thereby produced in the recording plane. From an analysis of the optics of the shadow effect it follows that the visible signal depends on the second derivative of the refractive index of the fluid. Therefore, the shadowgraph as an optical diagnostic technique is sensitive to changes of the second derivative of the fluid density.

Figure 10. Operating principle of shadowgraphProcedure: It is evident that the shadowgraph is not a method suitable for quantitative measurement of the fluid density. Owing to its simplicity, however, the shadowgraph is a convenient method of obtaining a quick survey of a flow in which the density changes in the described way. This applies particularly to compressible gas flows with shock waves that can be considered as alterations of the gas density with an extremely intense change in curvature of the density profile, i.e., a change of the respective second derivative. The observation of shock waves in gases by means of shadowgraphy goes back to the 19th century when these flow phenomena were discovered by means of this optical technique.

Figure 10.1 Shadowgraph setup Due to the very simple optical setup, the shadow effect resulting from inhomogeneous density fields can be observed also outside a laboratory, with the sun serving as the light source, e.g., the sun light may project onto a solid wall shadow patterns that are caused by fuel vapor rising in the air. The camera that records a down-scaled picture is focused onto a plane at distance l from the test field. This plane corresponds to the position of the recording plane. The intensity of the shadow effect, or the sensitivity of the shadowgraph, increases with the distance l. On the other hand, the flow picture is the more out of focus the greater l, so that a compromise between optical sensitivity and image quality has to be found. The optical sensitivity of the shadowgraph is, in principle, an order of magnitude lower than that of schlieren or interferometric techniques.

Figure 10.2 Shock captured by shadowgraph systemResult: Thus the use of shadowgraph system to visualize the shock is studied.

Viva questions: Explain schlieren operating technique? How the shock induces? What are the types of shock? What type of flow visualization techniques is more accurate?

UNIVERSITY QUESTIONS

How the lift is generates? How the vortices generates? Explain the inducement of lift and drag? Visualize the flow using water channel. Visualize the flow using smoke tunnel. Calibrate the subsonic wind tunnel using RPM method. Calibrate the subsonic wind tunnel using test section velocity method. Determine the pressure distribution over a circular cylinder. Determine the pressure distribution over symmetrical aerofoil. Determine the pressure distribution over a symmetrical aerofoil. Also find the CP and CD. Determine the pressure distribution over asymmetrical aerofoil Determine the pressure distribution over a symmetrical aerofoil. Also find the CP and CD. Determine the force over the symmetrical aerofoil using wind tunnel balance technique. Determine the force over the asymmetrical aerofoil using wind tunnel balance technique. Explain Schlieren photography method. How the shock is captured in Schlieren photography method. Explain Shadow graphy method. How the shock is visualized in shadow graphy method.