Position sensitivity of hot-film shear probes

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Abstract
The position sensitivity of hot-film shear probes was studied with the use of pulse-echo ultrasound. The ultrasonic probe was placed opposite the hot-film probe across a rigid tube. The accuracy of measuring hot-film probe position by ultrasonic methods was studied with the aid of a mechanical micrometer. A similar study was conducted in vivo on the thoracic aorta of dogs to maintain flush conditions between the hot-film probe and arterial wall. The sensitivity of hot-film probes to position with respect to a rigid wall was studied. Probe position was determined by ultrasonic methods. The results showed a 20% deviation in hot-film anemometer bridge voltage with a change in probe position of 0.3 mm from the wall. This could result in a 50% error in computed wall shear stress. Resolution of the method of ultrasonic positioning of the hot-film probe was determined to be 0.1 mm.