| 摘要 |
For the measurement of low-fluid velocities, especially velocities which are very low, a probe is oscillated in the stream of fluid in a simple harmonic motion and in a plane that is parallel to the fluid flow. The probe carries a transducer of a type whose output is some function of relative air flow over the transducer. The frequency or amplitude of the oscillation is chosen so that at some point in the cyclic movement, the velocity of the transducer relative to the fluid stream will be zero. The output of the transducer is compared with the mechanical oscillation of the probe to find the angular positions of the probe at which there is zero relative speed and these positions are related to fluid velocity in accordance with the expression Vf=A omega cos theta , WHERE Vf is the velocity of the fluid medium, A is the amplitude of the vibration of the probe, omega is the angular frequency of the vibration and theta is the angular position of the probe when velocity of transducer relative to the fluid medium is zero.
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