Sensing flow separation on a typical aerofoil by MEMS flexible thermal sensor array

Abstract

When a fluid flows over a solid surface, viscous effects generate shear stress, or skin friction, on the surface. Knowledge of such wall shear stress is essential for understanding the dynamics of fluid flow, and its measurement holds great importance for investigating and controlling wall-bound turbulence and flow separation in aerodynamic control. MEMS play an important role for studying gaseous or liquid fluid flows experimentally due to device dimensions on the μm-scale. For aerodynamic applications, the realization of sensor-actuator networks on airfoils is a challenging task to improve the lift properties of aircrafts by the precise detection and the systematic manipulation of the transition point from laminar to turbulent airflow conditions. Based on the well-established principle of thermal anemometry, an array of thermal sensors on a flexible polyimide substrate was developed. The first application of this technology has produced a flexible shear-stress sensor array. Apparently, this technology can be applied to produce a flexible skin with other sensing elements, such as temperature or pressure sensors. In addition, two signal processing methods of the sensor array signals have been proposed to detect the location of the flow separation point on curved surface for the positive flow control purpose. The computation parameter is based on thermal method measurement the surface local shear stress. The flexible sensor array has also been used to detect instantaneous separation region on the surface of a NACA0012 typical aerofoil. In a first step, CFD (Computational Fluid Dynamics) simulations were performed to estimate the corresponding shear stress distribution within the NACA0012 typical aerofoil at flow conditions is the velocity 40m/s and AOA 16° .To illustration the method, the low speed wind tunnel testing data was used to analysis the accuracy and effectively of the method presented in this paper, which can demonstration that the method provides an applicable, efficient tool for the flow separation analysis in the it's location decision aspect. Copyright © 2007 by ASME.