Open-loop cavity flow control with Micro-Magneto-Mechanical Systems (MMMS) microvalves
Creators: name:  T. ARNOULT 
name:   C. LECLERCQ 
name:   C. GHOUILA-HOURI 
name:   Q. GALLAS 
name:   R. VIARD 
name:   E. GARNIER 
name:   D. SIPP 
name:   A. MERLEN 
name:   A. TALBI 
name:   P. PERNOD 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLOW CONTROL
AEROSPACE

description: The open cavity is a common geometry in weapon bays, wheel wells or landing gear doors. The flow developing over such a geometry has been extensively studied since Roshko [1] and complex dynamic phenomena develop in it. The shear layer destabilises over the cavity and impacts the downstream corner of the cavity. The acoustic waves generated from this location propagate upstream the cavity exciting the shear layer instabilities. This results in self-sustained oscillations in the flow, which can induce structural vibrations and noise radiation [2] [3].Therefore damping these oscillations is of interest. We propose a design of micro-valve based on MMMS technology and integrate an array of 15 of these microfluidic device to the upstream wall of an open-cavity, placed in a wind tunnel at the ONERA (Office National dEtudes et de Recherches Aerospatiales), in order to implement an open-loop flow control strategy. The MMMS design consist in a pressurised air inlet, a channel surmounted by a flexible resonator made in elastomer material (Silastic) and a submillimetric outlet. A NdFeB permanent magnet is fixed on the flexible resonator enabling the channel height modulation and hence modulating the outlet velocity, when an electrical current runs in the coil surrounding the magnets. The microvalve can deliver a high-speed jet with an outlet velocity of 150 m/s (with a submillimetric outlet) pulsed at frequencies up to 500Hz [4]. The actuators outlet design was enhanced and adapted to the control of cavity flow. Therefore, the submillimetric outlet was modified in order to obtain an outlet velocity spread over a slot. Performances of these adapted actuators were assessed with hot wire measurements performed at the ONERA Lille. For a chosen flow regime, effects of quasi-steady and pulsed jets on the cavity oscillations were assessed through hot wire and unsteady pressure measurements, performed at the cavity downstream corner, where the cavity dynamics is the most amplified. Depending on the microvalves performances and the flow regime, quasi-steady jets enabled a decrease of 20dB in the cavity oscillations sound pressure level, deduced from the unsteady pressure measurements. Regarding pulsed jets, depending on the forcing induced by the actuators a locking phenomenon was observed. Therefore, the actuators authority proved to be sufficient to shift the cavity natural oscillation frequency towards the microvalves actuation frequency. The open-loop experiments campaign aims at preparing the closed-loop flow control campaign. Therefore, the system transfer function identification was performed with the pulsed jets in the linear limit assumption. Harmonic forcings were used to identify the transfer function in a given flow regime with different forcing amplitudes. References: [1] A. Roshko, Some measurements in a rectangular cutout, National Advisory committee for aeronautics, Technical note 3488, 1955. [2] J. E. Rossiter, Wind tunnel experiments on the flow over rectangular cavities at subsonic and transonic speeds, RAE Technical Report No. 64037, 1964. [3] C.K.W. Tam and P.J.W. Block, On the tones and pressure oscillations induced by flow over rectangular cavities, J. Fluid Mech., vol. 89, peed 2, pp. 373-399, 1978 [4] VIARD R., TALBI A., PERNOD P., PREOBRAZHENSKY V., MERLEN A., Magnetostatic microvalve for high momentum rate pulsed jet generation, Eurosensors XXIII, Lausanne, Switzerland, september 6-9, 2009, Procedia Chem. 1, 1 (2009) 421-424.