Design, manufacturing, calibration, and basic characterization of a microelectromechanical systems (MEMS) wall hotwire sensor on a flexible polyimide substrate are presented. A configuration exhibiting bondpads on the top side of the foil, as well as an improved setup featuring a through-foil metallization and bottom side bondpads were established. Both sensor designs make use of a highly sensitive nickel thin-film resistor spanning a reactive ion etched cavity in a polyimide substrate. The polyimide base material enables the sensor to be adapted to curved aerodynamic surfaces, e.g., airfoils and turbine blades. A mismatch of curvature of aerodynamic surface and silicon sensor surface, as observed with previously presented MEMS hot-wire anemometers is avoided. The combination of polyimide's low thermal conductivity and a cavity featuring FEM-optimized dimensions accounts for a very low-power consumption (<25 mW). Fluctuations in wall shear stress up to 85 kHz can be resolved in constant-temperature mode. An average sensitivity of 0.166 V/(N/m 2 ) is achieved in a wall shear stress range from 0 to 0.72 N/m 2 . The specifically designed through-foil metallization process allows for electrical contacts to be positioned on the backside of the substrate, thus effectively minimizing aerodynamic disturbances.Index Terms-Microelectromechanical systems (MEMS), polyimide, via, wall hot-wire.
This paper describes a joint experimental and numerical investigation of the control of the flow over the flap of a three-element high-lift configuration by means of periodic excitation. At Reynolds numbers between 0.3 × 10 6 and 1 × 10 6 the flow is influenced by periodic blowing or periodic blowing/suction through slots near the flap leading edge. The delay of flow separation by periodic vertical excitation could be identified in the experiments as well as numerical simulations based on the Unsteady Reynolds-averaged Navier-Stokes equations (URANS). As a result, the mean aerodynamic lift of this practically relevant wing configuration could be significantly enhanced. By investigating different excitation frequencies and intensities optimum control parameters could be found. The behaviour of the aerodynamic forces with varying flap deflection angle are measured on a finite swept wing. Scientific visualisation of the numerical simulations of an infinite swept wing allows a detailed analysis of the structures in this complex flow field and the effect of flow control on these. Nomenclature c, c k clean chord length, flap length (c k = 0.254c) c L , c Lmax lift coefficient, maximum lift coefficient C µ momentum coefficient C µ = 2 H c ua u∞ 2
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