Unsteady flows measurements using a calorimetric wall shear stress micro-sensor
Abstract
A microscale low power high temperature gradient calorimetric (HTGC) sensor measuring both mean and fluctuating bidirectional wall shear stress is presented. The micromachined sensor is composed of three free-standing 3 µm × 1 mm micro-wires mechanically supported using perpendicular micro-bridges. The static and dynamic characterisations were performed in a turbulent boundary layer wind tunnel on a flat plate configuration, and compared to the one obtained with a conventional hot-film probe. The results demonstrated that the calorimetric sensor behaves similarly to the hot-film in constant temperature anemometry with nonetheless lower power consumption and better spatial resolution and temporal response. Additionally, its calori-metric measurement detected the direction of the wall shear stress component orthogonal to the wires, corresponding to the shear stress sign in 2D flows. The 2 Cecile Ghouila-Houri et al. calibrated HTGC micro-sensor was then used for unsteady flow separation detection downstream a 2D square rib for Re h = 2.56 × 10 4. The calorimetric micro-sensor enabled self-correlated measurements and consequently successfully achieved the detection of flow separation and the reattachment point around x/h = 10.7.
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