The validation and testing of a thermal-tuft probe is described in detail. The thermal tuft consists of three parallel wires where the middle wire is heated and the two lateral wires act as resistance thermometers, thereby sensing the flow direction. The probe's function principle is validated in an acoustic resonator that generates a nearly sinusoidal velocity perturbation with zero mean. It is shown that the variation in electrical resistance of the sensing wires is a measure of the flow direction. The probe's sensitivity to the heater current in the central wire and to the flow angle is also investigated. The electronic circuit is validated by placing the probe on a mechanical shaker. The output voltage is shown to be consistent with the variation in electrical resistance of the sensing wires. The flow direction can thus simply be measured by recording the probe's output voltage with a single digital data-acquisition channel. Finally, the thermal tuft is evaluated in a low-speed, pressure-driven, turbulent, separation-bubble flow. It is shown that the forward-flow fraction and the intermittent frequency can be measured with an uncertainty of about . The positions of separation and reattachment in the test section, measured with the thermal tuft, are consistent with flow-visualization experiments reported elsewhere.
Evaluation of a Thermal-Tuft Probe for Turbulent Separating and Reattaching Flows
Department of Mechanical Engineering,
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received December 2, 2013; final manuscript received May 6, 2014; published online September 10, 2014. Assoc. Editor: Mark R. Duignan.
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Schwaab, Q., and Weiss, J. (September 10, 2014). "Evaluation of a Thermal-Tuft Probe for Turbulent Separating and Reattaching Flows." ASME. J. Fluids Eng. January 2015; 137(1): 011401. https://doi.org/10.1115/1.4027642
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