Module 8 - Pressure Probes

Question 1

What are common issues with pressure taps?

Answer 1

• Burrs resulting in higher or lower pressure readings
• chamfers/fillets
• hole angle
• “cavity flow”

Question 2

What are sources of errors in Pitot tube measurements near a wall?

Answer 2

• Bias towards high velocity due to large velocity gradient
• Viscous effects: low V can result in viscous effects in the Pitot tube

Question 3

What is the advantage of a shrouded Kiel probe?

Answer 3

Reduced sensitivity to misalignment with flow direction

Question 4

What determines the placement of static holes for a Pitot-static probe?

Answer 4

• must be far downstream of nose so flow is parallel
• must be far upstream of stem to ensure flow around stem doesn’t affect it

Question 5

How would you measure the air speed using a Pitot tube and wall-static pressure tap?

Answer 5

• Connect pitot tube and tap to a pressure transducer to get dynamic pressure
• Connect tap to an absolute pressure transducer to get Pstatic
• Use thermocouple to measure T
• Use ideal gas law to solve density
  Solve for velocity given q and rho

Question 6

Which situation will read a static pressure higher than the actual value?
A) burr upstream of pressure tap
B) burr downstream of pressure tap
C) no burr

Answer 6

B

Question 7

How might the choice of Pitot tube affect measurements in the turbulent wake of an automobile?

Answer 7

• Choosing a small pitot tube may lead to viscous effects in the low momentum wake
• turbulence intensity can lead to large fluctuations which can affect calibration of the probe
• Highly three dimensional flow may lead to misalignment with flow direction