Hot-Wire Anemometry

A thermal anemometer is a method of measuring fluid velocities by measuring heat transfer from a small wire or film immersed in the fluid. The rate of which heat is removed from the sensor is directly related to the velocity of the fluid flowing over the sensor. So by measuring the amount of current required to maintain the sensor at a constant temperature, you can obtain the fluid velocity. The advantages of thermal anemometry include high accuracy, an easily-automated collection procedure, and a high frequency response allowing measurement of turbulent flows.

Boundary Layer
Anemometer One such thermal anemometer used by our research group is a boundary layer probe. In this probe, a single anemometer (or "hot wire") is mounted on a curved base (see figure), allowing measurements of the streamwise component of velocity in boundary layer-type flows. Due to the high frequency response of the sensor, time profiles of instantaneous velocity can be collected, allowing measurement of both average velocity and the rms value of the velocity fluctuation.

Triple Wire Anemometer Another anemometer used by our group is a triple-wire probe. In this probe, three orthogonal hot films are mounted on a single support. By measuring the simultaneous response of all three sensors, instantaneous time traces of all three components of velocity can be measured. From these time traces, a number of flow features can be measured, including average velocity, turbulence intensity, and turbulent shear stresses.

(anemometer images courtesy of the TSI, inc. Web site)

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