Week 3 - Pitot tube

Aim

To perform a fluid flow simulation in the given enclosed pitot-static tube and to calculate the error percentage for velocity .

Introduction

This page 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 pressure transducer. The center hole in the tube is kept separate from the outside holes and is connected to the other side of the transducer. The transducer measures the difference in pressure in the two groups of tubes by measuring the strain in a thin element using an electronic strain gauge. 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.

V = sqrt [2 * {pt – ps} / r ]

V --> Velocity

pt --> Total pressure

ps --> Static pressure

r --> Density of the medium (Here it is air = 1.225 kg/m^3)

Procedure

1.The file was loaded into Ansys-FLUENT as it is.

2.The viscous model was selected as laminar.

3.The above values of velocity and pressure were given and the simulation was done in 3 cases as given below

Case 1

Velocity = 240 m/s Gauge pressure = -2817 Pa

Total Pressure = 29683.79 Pa

Static pressure = -2169.42 Pa

By substituting the values in the above formula we get V = 228.04 m/s

The % error in velocity is 5.23 %

Case 2

Velocity = 100 m/s Gauge pressure = 33287 Pa

Total Pressure = 39269.097 Pa

Static pressure = 33942.21 Pa

By substituting the values in the above formula we get V = 93.25 m/s

The % error in velocity is 7.23 %

Case 3

Velocity = 62 m/s Gauge pressure = 65780 Pa

Total Pressure = 67865.65 Pa

Static pressure = 65820.691 Pa

By substituting the values in the above formula we get V = 57.78 m/s

The % error in velocity is 7.3 %

Result

The simulation was done using the above velocity and pressure values and the given error percentage in velocities were found out .