Boundary Layer Separation and Reattachment Detection on Airfoils by Thermal Flow Sensors

Sturm, Hannes; Dumstorff, Gerrit; Busche, Peter; Westermann, D.; Lang, Walter

doi:10.3390/s121114292

Cited by 36 publications

(22 citation statements)

References 25 publications

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“…In the case (b) the flow separation due to a geometrical obstacle that leads by construction to a separation bubble [3]. As shown on Figure 1 and according to Equation (1), the wall shear stress, and particularly its orientation, is directly linked with the flow separation phenomena and its measurement is a key point to detect the state of the flow, either attached or separated.…”

Section: Figure 1: (A) Schematic Of a Flow Separation On An Airfoil Lmentioning

confidence: 99%

High temperature gradient calorimetric wall shear stress micro-sensor for flow separation detection

Ghouila-Houri

Gallas

Garnier

et al. 2017

Sensors and Actuators A: Physical

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The paper describes and discusses the design and testing of an efficient and high-sensitive calorimetric thermal sensor to measure simultaneously the magnitude and the direction of wall shear stress in aerodynamic flows. The main technical application targeted is the back flow and the flow separation detection for active flow control. The measurement principle is based on the flow-induced forced heat convection transfer on a heater element. The sensor is micro-structured with three parallel substrate-free wires presenting a high aspect ratio and supported by periodic perpendicular SiO2 micro-bridges ensuring a mechanical toughness and a thermal insulation relatively to the bulk substrate with high thermal inertia. The central wire is made of a multilayer structure (Au/TiSiO2/Ni/Pt/Ni/Pt/Ni/SiO2) and is composed of a heater element (Au/Ti) and a thermistor (Ni/Pt/Ni/Pt/Ni) enabling to measure the heater temperature. The upstream and downstream wires are thermistors enabling to operate in the calorimetric mode. This design provides a high temperature gradient and a homogeneous temperature distribution along the wires. The sensor operates in both constant current mode and constant temperature mode, with a feedback on current enabled by uncoupling heating and measure. Welded on a flexible printed circuit, the sensor was flush mounted on the wall of a turbulent boundary layer wind tunnel. The experiments, conducted in both attached and separated flow configurations, demonstrate the sensor sensitivity to the wall shear stress up to 2.4 Pa and the ability of the sensor to perform flow direction sensing for back-flow detection in a separated flow configuration.

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Section: Figure 1: (A) Schematic Of a Flow Separation On An Airfoil Lmentioning

confidence: 99%

High temperature gradient calorimetric wall shear stress micro-sensor for flow separation detection

Ghouila-Houri

Gallas

Garnier

et al. 2017

Sensors and Actuators A: Physical

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…”

mentioning

confidence: 97%

Improved sensitivity of micro thermal sensor for underwater wall shear stress measurement

Zhu

Jiang

et al. 2014

Microsyst Technol

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Knowledge of such wall shear stress is essential for understanding the dynamics of the fluid flow, and its measurement holds great importance for investigating and controlling wall-bound turbulence and flow separation (Bellhouse and Schultz 1966;Goldstein 1996;Kimura et al. 1999;lin et al. 2005;Wang et al. 2007;Sturm et al. 2012). Presently, there are many measurement techniques for shear stress. however, most of them will greatly interfere with fluid flow during measurement (Zhang et al. 2008). Miniaturized shear stress sensors fabricated using MeMS technology offer superior spatial resolution, fast time response and minimized interference with fluid flow (liu and Yuan 2007;liu and Zhu 2009;Beutel et al. 2013a). Therefore, MeMS sensors will play an important role for studying gaseous or liquid fluid flows experimentally.Micro thermal shear stress sensors are based on measurement of heat transfer from a heated thin-film element to the fluid flow (Osorio and Silin 2011). constant current (cc) mode can be used to drive them. There are many reported thermal shear-stress sensors working in cc mode. The shear-stress sensitivity of a micromachined thermal shear stress sensor reported by chang liu is 15 mV/Pa at a power consumption of 12 mW (I = 2 ma) when the shear stress input was about 0.2 Pa (liu et al. 1994). Mark Sheplak has presented a characterization of a silicon-micromachined thermal shear-stress sensor (Sheplak et al. 2002). The sensitivity of this sensor is 11 mV/Pa at a power consumption of 9 mW (I = 10 ma) when the shear stress input was about 0.2 Pa.In this paper, we studied how to improve sensitivity of thermal shear stress sensor working underwater with allowable drive currents. They were obtained by analyzing I-V characteristic and output voltage-shear stress relationship. and they were be allied to drive the sensor in two different shear stress input ranges to explore the advancement of sensitivity.Abstract Drive current is an important parameter of thermal shear stress sensor. Increasing drive current is helpful for enhancing its sensitivity. however, there must be an allowable drive current for the sake of safe working temperature of the sensor. how to make full use of drive current to increase the sensor's sensitivity working underwater was studied. If the allowable drive current in still water and the current in stream water are used to drive the sensor in lower and higher shear stress input ranges, respectively, sensitivity of the sensor will be enhanced with the sensor working under a safe temperature. The both currents were separately determined by analyzing I-V characteristic and output voltage-shear stress relationship. We can improve the sensor's sensitivity from 11.8 to 27.5 mV/Pa when shear stress input was 0.4 Pa.

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“…Data acquisition has again been carried out with a USB-6212 digital acquisition card at a sampling rate of 1 kHz and a measurement period of 1 s. As shown in Fig. 10, four sensor boards have been integrated on the airfoil to get a more precise position of the flow separation point [34].…”

Section: Application: Flow Separation and Reattachment Detectionmentioning

confidence: 99%

Membrane-based thermal flow sensors on flexible substrates

Sturm¹,

Lang²

2013

Sensors and Actuators A: Physical

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Boundary Layer Separation and Reattachment Detection on Airfoils by Thermal Flow Sensors

Cited by 36 publications

References 25 publications

High temperature gradient calorimetric wall shear stress micro-sensor for flow separation detection

High temperature gradient calorimetric wall shear stress micro-sensor for flow separation detection

Improved sensitivity of micro thermal sensor for underwater wall shear stress measurement

Membrane-based thermal flow sensors on flexible substrates

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