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Unformatted text preview: the flow around the probe is nearly
frictionless and Bernoulli’s relation, Eq. (3.77), applies with good accuracy. For incompressible flow
2 V2 gzs p0 1
2 (0)2 gz0 Assuming that the elevation pressure difference g(zs
V 2 ( p0 ps) z0) is negligible, this reduces 1/2 (6.117) This is the Pitot formula, named after the French engineer who designed the device in
The primary disadvantage of the pitot tube is that it must be aligned with the flow
direction, which may be unknown. For yaw angles greater than 5°, there are substantial errors in both the p0 and ps measurements, as shown in Fig. 6.30. The pitot-static
tube is useful in liquids and gases; for gases a compressibility correction is necessary
if the stream Mach number is high (Chap. 9). Because of the slow response of the fluidfilled tubes leading to the pressure sensors, it is not useful for unsteady-flow measurements. It does resemble a point and can be made small enough to measure, e.g.,
Static ≈ Free-stream
V θ ps Stagnation
pressure 4 to 8
holes Error +10% v v p0 pS Stagnation pressure Fig. 6.30 Pitot-static tube for combined measurement of static and
stagnation pressure i...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08