Week 3 - Pitot tube

Stagnation Pr = Static Pr + Dynamic Pr

Which can also be written

From above equation flow velocity can be written as

where

• = flow velocity;
• = stagnation or total pressure

Three types of pitot tubes are used:

(a) Simple pitot tube which measures total pressure of the incoming fluid

(b) Static tube which measures the static pressure of the incoming fluid

(c) Pitot static tube is used in measuring flow speed. It is a tube that has two holes on it. The front hole is placed in the airstream to find the stagnation pressure. The side hole is used to measure the static pressure. The difference between these pressures will give the dynamic pressure, and this can be used to calculate the speed of incoming air.

Solution methods:

Mesh file is imported to ANSYS Fluent.

Under operating conditions default value of operating pressure is 101325Pa. So we get gauge pressure.

But this operating pressure value is set to zero and this gives us absolute pressure.

Under the report definitions create area weighted average of static pressure at:

• tube-walls-fff-small fluid volume and
• tube-walls-fff-big fluid volume.

Standard initialization

FMG initialization procedure can be accessed using the text user interface (TUI) once the standard flow initialization is performed.

To customize the FMG initialization, type the following command :

solve initialize fmg-initialization

Viscous model: Laminar

Boundary conditions:

Case1:

Velocity Inlet: 240m/sec

Pressure outlet: -2817

Velocity inlet: 100m/s

pressure: 33287 Pa

Input values		Output values		Calculated
Velocity	Gauge pressure	P total	Pstatic	Velocity
240	-2817	22121.5	-2845.6	240.12
100	33287	37631.43	33331.1	99.82
62	67580	69253.5	67627.8	61.3