Bernoulli effect Pitot (P -t ) Pitot tubes (seen in Fig. 12-7 of the text) are u

Question

Bernoulli effect

Pitot (P -t ) Pitot tubes (seen in Fig. 12-7 of the text) are used to measure fluid speeds on aircraft and other equipment using the Bernoulli effect. They work by measuring the pressure difference between fluid moving past the device at a relative velocity and fluid moving with the device (relative velocity = 0). If I read a pressure difference of 8.1 kPa at sea level (pair = 1.22 kg/m^3), what is my speed relative to the fluid (i.e. airspeed)? Would the operation of this device change as I change altitude, assuming the temperature stays constant?

Explanation / Answer

a) Velocity V = sqrt(2*pressure difference/air density) = sqrt(2*8.1*10^3/1.22) = 115.233 m/s

b)As altitude changes pressure decreses and hence air density decreases (since d air = Patm /(R*Tatm)

Therefore, velocity will increase for the same pressure difference as altitude rises.

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