Simulation and Testing of a Family of Calorimetric Wall Shear Stress Microsensors

A family of calorimetric wall shear stress microsensors is investigated numerically and experimentally to determine their static response curves and their capacity to detect reattachment in a turbulent separated air flow. Four sensor designs are considered: a “Gap” design that features three separated beams suspended over a cavity, a “NoGap” design where the three beams are mechanically connected for enhanced robustness, a “Membrane” design where the cavity is closed, and finally, a “Kapton” design without any cavity. The results show that connecting the beams by removing the gap, adding a membrane, or getting rid of the cavity altogether lowers the sensor’s sensitivity. This is explained by the enhanced conductive heat transfer between the beams. Furthermore, while all designs can detect the average reattachment line in a turbulent flow, only the sensors featuring a cavity are sensitive enough to accurately measure the small-scale regions of backflow characterizing turbulent separated flows. These findings will help the design of both robust and sensitive calorimetric shear stress sensors for aerodynamic applications.