Week 3 - Pitot tube

Aim

1. A pitot static tube geometry is attached below.

a.You are required to do a literature review of pitot-static tube. Also establish a relationship between Total (stagnation) pressure and static pressure

b.You are required to create surfaces and fill it separately for Total pressure port and static pressure port as shown below.

2. For the values of velocity given below calculate the total and static pressures and find the error in percentage for velocity.

Velocity(m/s)	Gauge Pressure (Pa)
240	-2817
100	33287
62	65780

Introduction

A pitot tube, is a flow measurment device used to measure fluid flow velocity. It is widely used to determine the airspeed of an aircraft,^[3] water speed of a boat, and to measure liquid, air and gas flow velocities in certain industrial applications.

The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure.

The measured stagnation pressure cannot itself be used to determine the fluid flow velocity (airspeed in aviation). However, Bernoulli's equation states:

Stagnation pressure = static pressure + dynamic pressure

Which can also be written

Solving that for flow velocity gives

where

• is the flow velocity;
• is the stagnation or total pressure;
• is the static pressure;
• is the fluid density.

Mesh

Setup

• Viscous model set to laminar
• Air density is changed to 0.86 and the dynamic viscosity to 1.678e-5
• Coupled model is selected
• Hybrid initialisation is done and given 700 iterations to start solving

Outputs

Case 1

Inlet velocity = 240 m/s

Guage pressure = -2817 pa

Calculation

Pt = 22952.189 pa

Ps = -1815.7962 pa

Hence U = `((2(22952.189-(-1815.7962)))/0.86)^0.5`

U = 239.9999 m/s

Case 2

Inlet velocity = 100 m/s

Guage pressure = 33287 pa

Calculation

Pt = 33461.373 pa

Ps = 37761.37 pa

Hence U = `((2(33461.373-(37761.37)))/0.86)^0.5`

U = 100.00430 m/s

Case 3

Inlet velocity = 62 m/s

Guage pressure = 65780 pa

Calculation

Pt = 67501.748 pa

Ps = 65848.829 pa

Hence U = `((2(67501.748-(65848.829)))/0.86)^0.5`

U = 61.99998m/s

Discussion

Cases	Velocity at inlet (m/s)	Calculated velocity	Percentage of error
1	240	239.9999	4.1e-5 %
2	100	100.00430	4.3e-3 %
3	62	61.99998	2e-5%

• Since the deviation of calculated value of velocity is small the results can be validated

Conclusion

• Literature review on pitot tube is done
• established the relationship between Total (stagnation) pressure and static pressure
• Velocity is calculated using total pressure and static pressure and percentage of error is calulated