Pitot tube velocimetry PDF

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Summary

Lab report...

Description

1.1.

PURPOSE The purpose of this experiment is to study and learn how to implement a pitot static tube for air speed velocimetry. A Pitot tube is used for measuring the airspeed of an aircraft.

1.2.

THEORY

Figure 1 Pitot Static System Fig.1 shows a schematic drawing of a pitot-static tube. Pitot-Static tubes, which are also called Prandtl tubes, are used on aircraft as speedometers. The actual tube on the aircraft is around 10 inches (25 centimeters) long with a 1/2 inch (1 centimeter) diameter. Several small holes are drilled around the outside of the tube and a center hole is drilled down the axis of the tube. The outside holes are connected to one side of a device called a Manometer. The center hole in the tube is kept separate from the outside holes and is connected to the Manometer. The pitot-static tube is mounted on the aircraft, or in a wind tunnel , so that the center tube is always pointed in the direction of the flow and the

outside holes are perpendicular to the center tube. On some airplanes the pitot-static tube is put on a longer boom sticking out of the nose of the plane or the wing.

Difference in Static and Total Pressure: Since the outside holes are perpendicular to the direction of flow, these tubes are pressurized by the local random component of the air velocity. The pressure in these tubes is the static pressure (

PS

) discussed in Bernoulli's equation. The center tube,

however, is pointed in the direction of travel and is pressurized by both the random and the ordered air velocity. The pressure in this tube is the total pressure ( PT ) discussed in Bernoulli's equation. The difference in total and static pressure can be measured from the manometer which is called the dynamic pressure q. Measurement q PT  PS

Solve for Velocity With the difference in pressures measured and knowing the local value of air density from pressure and temperature measurements, we can use Bernoulli's equation to give us the velocity. Bernoulli's equation states that the static pressure plus one half the density times the velocity V squared is equal to the total pressure.

V 

2( PT  PS )  =

√

2 ρwater g(h2−h1 ) ρair

or PT  PS 

2.

REQUIRED EQUIPMENT 

Wind Tunnel



Manometer

V 2 2



3.

Pitot Tube

OBSERVATIONS AND READINGS

Position 1 Position 2 Position 3 Position 4 Position 5 T = 298 K

4.8 4.8 4.8 4.8 4.8 R = 287

P = 101300 Pa

Density of air = P/RT = 101300/ (287*298) = 1.184 kg/m^3

4.

CONCLUSIONS AND RESULTS

Position 1 

V = √ ((2*1000)(0.048-0.044) / 1.184 ) = 2.6 m/s

Position 2 

V = √ ((2*1000)(0.048-0.040) / 1.184 ) = 3.68 m/s

Position 3 

V = √ ((2*1000)(0.048-0.036) / 1.184 ) = 4.5 m/s

Position 4 

V = √ ((2*1000)(0.048-0.030) / 1.184 ) = 5.51 m/s

Position 5 

V = √ ((2*1000)(0.048-0.026) / 1.184 ) = 6.1 m/s

4.4 4.0 3.6 3.0 2.6

7

Flow Velocity

6 5 4 3 2 1 0 0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

Position

Potential source of error is misalignment of the pitot static tube axis and the flow vector....