Overview of IEMN micro-sensor technologies: from turbulence measurement to aerodynamic flow control
Creators: name:  C. GHOUILA-HOURI 
name:   A. TALBI 
name:   T. ARNOULT 
name:   A. MAZZAMURRO 
name:   M. BENEDITO 
name:   R. VIARD 
name:   Q. GALLAS 
name:   E. GARNIER 
name:   A. MERLEN 
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: Turbulence has been a complex field of study in fluid mechanics, characterized by disorderly behaviour with vortices whose size, location and orientation vary constantly. In fact, understanding, predicting and controlling turbulence are the three major goals of research in this area. The consequences are crucial: predicting the behaviour of turbulent flows in order to control and manipulate them would, in many fields of application, save energy, improve system performance and protect the environment. The most obvious example is the one of transport industry, which is confronted to the problem of aerodynamic drag on vehicles. However, turbulence is an unresolved problem in classical physics that does not present a simple solution and numerical simulation used to predict the behaviour of turbulence highly rely on empirical data1. Turbulent high Reynolds numbers flows generate very short spatial and temporal scales: spatial scales whose order of 100 ?m or less and time scales require a bandwidth of at least 10 kHz2. Experiments thus require small, fast, implementable sensors in various configurations and models, and allowing non-intrusive measurements of the flow. In this paper, we present the different technological solution developed by the IEMN (Institute of Electronics Microelectronics and Nanotechnology) to address this challenge. Based on microtechnology, the devices present submillimetre characteristic lengths. We will present two main sensor technology: an original nano-crystalline diamond based micro-hot-wire probe designed for freestream flow velocity measurement3, and skin friction and direction sensitive micro-transducers designed for flow separation control strategies46. We will first focus on the micro scale thermal anemometer based on Nano Crystalline Diamond (NCD) thin film. For proof of concept, we chose a sensitive element that consist of a self-compensated stress multilayer (Ni/W) patterned to form a wire with length, width, and thickness respectively close to 200 m, 5 m and 2 m. The wire is deposited and supported by prongs made of NCD thin film. Due to its high young modulus, NCD allows a very high mechanical toughness without the need of a thicker support for the hot wire. Also, depending on grain size, the NCD is able to present thermal conductivity smaller than 10W/mK, providing good thermal insulation from the substrate and less conductive end losses to the prongs. The sensors were characterized experimentally. Its electrical and thermal properties were obtained in the absence and presence of fluid flow. The results confirm the effectiveness of thermal insulation and the mechanical robustness of the structure. The test of the probe in wind tunnel will be performed shortly, with various flow configurations during the few coming months. Then, we will present robust micro-machined high temperature gradient calorimetric transducers that were developed for flow separation control strategies. Also based on thermal principle, the transducers measure the mean and fluctuating skin friction and is sensitive to the flow direction, both making them particularly useful for flow separation detection. More than a hundred micro-sensors were simultaneously micro-machined using MEMS technology in the IEMN cleanroom facilities. Tested in a turbulent boundary layer wind tunnel, they were calibrated between -2.5 and 2.5 Pa of wall shear stress and demonstrated a bandwidth of about 15 kHz. A flexible array of calorimetric micro-sensors was implemented with miniaturized electronics on a flap model also equipped with pulsed jet actuators. Flow control experiments were successfully conducted as the natural separation occurring on the model was detected by the micro sensors network and controlled by pulsed jet actuation. Ongoing work aims at increasing the bandwidth of the transducers and at implementing a closed-loop separation control on the flap model. References: 1 L. Lofdahl and M. Gad-el-Hak, Prog. Aerosp. Sci. 35, 101 (1999). 2 N. Kasagi, Y. Suzuki, and K. Fukagata, Annu. Rev. Fluid Mech. 41, 231 (2009). 3 A. Talbi, L. Gimeno, J.-C. Gerbedoen, R. Viard, A. Soltani, V. Mortet, V. Preobrazhensky, A. Merlen, and P. Pernod, J. Micromechanics Microengineering 25, 125029 (2015). 4 C. Ghouila-Houri, J. Claudel, J.-C. Gerbedoen, Q. Gallas, E. Garnier, A. Merlen, R. Viard, A. Talbi, and P. Pernod, Appl. Phys. Lett. 109, 241905 (2016). 5 C. Ghouila-Houri, A. Talbi, R. Viard, Q. Gallas, E. Garnier, A. Merlen, and P. Pernod, Exp. Fluids 60, 67 (2019). 6 C. Ghouila-Houri, A. Talbi, R. Viard, Q. Gallas, E. Garnier, A. Merlen, and P. Pernod, Smart Mater. Struct. 28, 125003 (2019).