IEMN/LEMAC magneto-mechanical microjets and micro-hotwires and aerodynamic active flow control
ABSTRACT An overview of the microjet and micro-hot wire solutions developed by IEMN/LEMAC during these last ten years for active flow control is presented. The IEMN/LEMAC microjet solutions are based on micro-magneto-mechanical systems (MMMS) and concern integrated devices delivering pulsed microjets, continuous microjets with bistable 'On-Off' actuation, and synthetic microjets. These devices were combined in arrays of eight to 32 elements distributed near the leading edge of a physical model of air wing, within an engine blade, inside an S-duct, around an engine exhaust and at the rear end of an Ahmed car model. Several wind tunnel experiments were made for separation control, and aero-acoustic control. It was demonstrated that the microjets satisfied the functional specifications defined by the industrial partners, as well as good robustness in severe wind tunnel environments. In addition, MEMS micro-hot wires for very local flow characterisations were also developed.
Article: A robust thermal microstructure for mass flow rate measurement in steady and unsteady flows A robust thermal microstructure for mass flow rate measurement in steady and unsteady flows[show abstract] [hide abstract]
ABSTRACT: A silicon micro-machined thermal gas flow sensor operating in anemometric mode has been designed, fabricated and investigated for continuous and pulsatile flows. The sensor is specifically designed to achieve high sensitivity, fast response time and high robustness. It is composed of four metallic resistors interconnected to form a Wheatstone bridge. Two of them act simultaneously as the heating and sensing elements and the two others are used as a temperature reference. The heating element consists of a metallic wire of platinum Pt (2 μm width, 2 mm length) maintained on each lateral side by periodic silicon oxide SiO 2 micro-bridges. Finite element simulations show that this structure achieves a fast thermal response time of 200 μs in constant current operating mode and a coefficient of temperature rise close to 25 • C/120 μW based on bulk electrical resistivity and when the Pt wire and SiO 2 thicknesses are close to 100 nm and 500 nm, respectively. This design allows the fabrication of a robust thermal flow sensor with heating elements as long as possible, which enables accurate measurements with high signal to noise ratio. The sensor is then characterised experimentally; its electrical and thermal properties are obtained in the absence of fluid flow. These results confirm the effectiveness of the thermal insulation as predicted by the simulations. In a second step, the fluidic characterizations are reported and discussed for both continuous and pulsatile flows. In continuous mode, the sensor response was studied for gas flow rate ranging from 0 L min −1 to 10 L min −1 . In pulsatile mode, the sensor is integrated inside a channel of a micro-valve actuated at 200 Hz. The measurements are compared with those obtained by a classical commercial hot wire. (Some figures may appear in colour only in the online journal)Journal of Micromechanics and Microengineering 05/2013; 23(065016). · 2.11 Impact Factor