5 Experimental Fluid Mechanics
369
Fig. 5.27 LDA velocimetry device
5.6 Experimental Measurement Method
for Dynamic Forces
(1) Pressure measurement method
Pressure measurement in the wind tunnel was first measured by a liquid
pressure gauge such as a U-tube pressure gauge. The most commonly used
measure of total air pressure and static pressure is the Pitot tube. In the supersonic flow, a positive shock wave is generated before the Pitot tube, so only
the total post-wave pressure can be measured. Nowadays, pressure sensors
have been widely used to measure pressure. There are many types of pressure sensors, which can be divided into resistance strain type, capacitive type,
inductive type, diaphragm type, solid state piezoresistive type, and piezoelectric type according to the conversion principle. When a very low pressure is
encountered in a hypersonic wind tunnel, a diaphragm or solid piezoresistive
sensor is often used. Piezoelectric sensors are mainly used for pulsed wind
tunnels or for measuring transient pressures. When measuring multi-point
pressure, a pressure measuring system consisting of a pressure sensor and a
pressure scanning valve or an electronic scanning pressure measuring system
(as shown in Fig. 5.28) is widely used.