Week 3 - Pitot tube

AIM: To perform simulation on the pitot tube using Ansys Fluent.

OBJECTIVE:

• To do a literature review of the pitot-static tubes. Also, establish a relationship between Total (stagnation) pressure and static pressure
• To 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:

Pitot tube :

• A pitot tube, also known as a pitot probe, is a flow measurement device used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy.
• Pitot Static Tubes are used to measure Pressure.
• Pressure measurement is used for other readings for the pilot,

1. Altimeter,
2. AirSpeed Measurement.

Types of Pitot Tubes:

1. Simple Pitot Tube (measures total pressure of the fluid incoming)
2. Static Pitot Tube (measures static pressure of fluid)

iii.Pitot Static Tube

• Tip Measures total pressure.
• The side measures Static pressure.
• pressure transducers sense pressure.
• measurements will be accurate at low Mach conditions. (Incompressible Flow)
• Used in low-speed Aircraft.

Theory of operation:

• The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, 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 be used to determine the fluid flow velocity (airspeed in aviation). However, Bernoulli's Equation states:

The difference between Static and Total Pressure:

• Since the outside holes are perpendicular to the direction of travel, these tubes are pressurized by the local random component of the air velocity.
• The pressure in these tubes is the static pressure 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 discussed in Bernoulli's equation. The pressure transducer measures the difference in total and static pressure.
• measurement = pt - ps
• Stagnation pressure = static pressure + dynamic pressure.

Solve for Velocity

• With the difference in pressures measured and knowing the local value of air density (r) 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.

Solving for V:

Case setup:

Results:

- Post-processing (Plots and contours)

a. Velocity at 240m/s and gauge pressure at 2817Pa:

- Residuals:

- Velocity :

- Static pressure:

- Total pressure:

b. Velocity at 100m/s and gauge pressure at 33287Pa:

- Residuals:

- Velocity:

- Static pressure:

- Total pressure:

c. Velocity at 62m/s and gauge pressure at 65780Pa:

- Residuals:

- Velocity:

- Static pressure:

- Total pressure:

- Results and Conclusion:

After calculating the Velocities by usng the formula, we get:

Velocity m/s (Given)	Gauge Pressure Pa (Given)	Static pressure Pa	Total pressure Pa	Velocity m/s	Error percentage (%) Velocity
240	2817	478.26	31500.44	225.05	6.22
100	33287	84.461	5454.99	93.63	6.37
62	65780	33.57	2093.99	57.99 ~ 58	6.45

The comparison of the actual and analytical results of velocity is performed by calculating the error and the error is around 5% which is acceptable for this kind of simulation.