Unsteady flows measurements using a calorimetric wall shear stress micro-sensor

Abstract

A microscale low power high temperature gradient calorimetric (HTGC) sensor measuring both mean and fluctuating bidirectional wall shear stress is presented. The micromachined sensor is composed of three freestanding 3 µm × 1 mm micro-wires mechanically supported using perpendicular micro-bridges. The static and dynamic characterisations were performed in a turbulent boundary layer wind tunnel on a flat plate configuration, and compared to the one obtained with a conventional hot-film probe. The results demonstrated that the calorimetric sensor behaves similarly to the hot-film in constant temperature anemometry with nonetheless lower power consumption and better spatial resolution and temporal response. Additionally, its calorimetric measurement detected the direction of the wall shear stress component orthogonal to the wires, corresponding to the shear stress sign in 2D flows. The

MEMS High Temperature Gradient Sensor for Skin-Friction Measurements in Highly Turbulent Flows

“…In terms of Mach number, which is the ratio of the airflow velocity to the velocity of sound in air, it corresponds to a maximum Mach number of 0.1. Previous works presented the wind tunnel geometry and the way we evaluated the corresponding wall shear stress in the test section ( [14], [15]). The range of skin-friction considered here is 0 to 2.5 Pa.…”

High temperature gradient micro-sensors array for flow separation detection and control

“…We characterized the micro-sensors the same way as it was done in [16] by evaluating their response to wall shear stress variation. We first indirectly evaluated the wall shear stress variation with the flow velocity.…”

“…This method links the hot-wire measurements at the center of the wind tunnel test section with the shear stress or the wall velocity. The package used for implementation on models, with front side contacts, differs from the one used in [16], which was perfectly flush but fragile. In the present configuration, the micro-sensors are not perfectly flush mounted but in a 100 µm deep cavity.…”

“…In (a), the amplitude of the response is measured using the central wire via constant temperature anemometry, and the sign is given by the difference of resistance (equivalent to the difference of temperature) between the two lateral wires. The sensitivity of the micro-sensor is less important as obtained in [16] due to the different package, but it is sensitive enough to fit the classical third-order polynomial curve [5]. We also evaluated the sensor response to wall shear stress fluctuations by measuring the power spectral density (PSD).…”

“…The purpose of this work is to use an array of such micro-sensors for detecting flow separation on a flap model and characterizing flow separation control. The first part of the paper introduces the micro-sensors design whose technology was published in previous works [14][15][16]. The second part is devoted to characterizations in a turbulent boundary layer wind tunnel.…”