Week 3 - Pitot tube

Aim

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

Velocity(m/s)	Gauge Pressure (Pa)
240	-2817
100	33287
62	67580

Introduction

A pitot tube is a flow measurement device used to measure fluid flow velocity. It is widely used to determine the airspeed of an aircraft, 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;
• and is the fluid density.

Pitot tube Model

After extracting fluid volume, because by removing unwanted parts we could reduce computational time, for this simulation we have removed the casing by considering only the volume where the fluid flows

Pitot tube inside the enclosure.

Cfd Models used in simulation

Solver - Pressure based
Velocity Formulation - Absolute
Time - Steady
Viscous - Laminar flow

Boundary conditions
Inlet - Velocity inlet
Outlet - Pressure outlet
Enclosure wall - Symmetry
Static pitot tube- Wall (No slip condition)

No. of Iteration - 1000

Case 1

For 240 m/s & press -2817pa

Total press after 1000 iter= 20320.543 pa

Static press after 1000 iter = -3536.1238 pa

putting in the above formula we get 244 m/s

Case 2

For 100 m/s & press 33287pa

Total press after 1000 iter= 37319.846 pa

Static press after 1000 iter=33174.343 pa

putting in the above formula we get 101 m/s

Case 3

For 62 m/s & press 67580pa

Total press after 1000 iter = 69132.175 pa

Static press after 1000 iter= 67541.476 pa

putting in the above formula we get 63 m/s

Percentage error