Abstract
A sensor concept for detection of boundary layer separation (flow separation, stall) and reattachment on airfoils is introduced in this paper. Boundary layer separation and reattachment are phenomena of fluid mechanics showing characteristics of extinction and even inversion of the flow velocity on an overflowed surface. The flow sensor used in this work is able to measure the flow velocity in terms of direction and quantity at the sensor's position and expected to determine those specific flow conditions. Therefore, an array of thermal flow sensors has been integrated (flush-mounted) on an airfoil and placed in a wind tunnel for measurement. Sensor signals have been recorded at different wind speeds and angles of attack for different positions on the airfoil. The sensors used here are based on the change of temperature distribution on a membrane (calorimetric principle). Thermopiles are used as temperature sensors in this approach offering a baseline free sensor signal, which is favorable for measurements at zero flow. Measurement results show clear separation points (zero flow) and even negative flow values (back flow) for all sensor positions. In addition to standard silicon-based flow sensors, a polymer-based flexible approach has been tested showing similar results.
Highlights
Boundary layer separation on overflowed surfaces is a common effect in fluid mechanics
A non-flexible and a flexible approach based on silicon and polyimide as substrate material has been tested during the work
The integration process shows significant benefits of the flexible approach, which does not need the drilling of a cavity for flush mounting the sensor
Summary
Boundary layer separation ( flow separation, stall) on overflowed surfaces is a common effect in fluid mechanics. Due to its unstable flow profile combined with drag increase, high energy loss and—in case of airfoils—reduced lift, this effect is mostly unwanted for most applications and even dangerous in aviation [1,2]. The use of shear stress sensors for online detection and even prevention of flow separation could give a better understanding of this still incompletely understood effect
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have