A team of researchers has developed a multidirectional, thin, and flexible sensor that characterizes high-speed airflows on curved surfaces to create efficient fluid machinery
Inefficient fluid machinery used in the energy and transportation sector, including pumps, turbines, and aircraft engines results in greenhouse gas emissions that are majorly responsible for global warming. To improve the efficiency of industrial-scale fluid machinery, it is essential to identify and suppress flow separation on curved surfaces. To overcome this challenge, Prof. Masahiro Motosuke from the Tokyo University of Science (TUS) in Japan and his colleagues, Mr. Koichi Murakami, Mr. Daiki Shiraishi, and Dr. Yoshiyasu Ichikawa from TUS, in collaboration with Mitsubishi Heavy Industries, Japan, and Iwate University, Japan, have developed a flexible, thin-film microelectromechanical system-based airflow sensor that can be implemented to analyze complex, three-dimensional flow separation in curved walls for high-speed airflows. The sensor measures the wall shear stress and flows angle in subsonic airflow which results in the improvement of the efficiency of fluid machinery which further reduces greenhouse gas emissions and hence provides environmental sustainability.
Prof. Motosuke states, “Sensing the shear stress and its direction on curved surfaces, where flow separation easily occurs, has been difficult to achieve in particular without using a novel technique.”
The team invented a polyimide thin film-based flexible flow sensor that can be easily fabricated on curved surfaces without disturbing the surrounding airflow, which is essential for efficient measurement. The sensor was manufactured using microelectromechanical system (MEMS) technology. This novel design integrated multiple sensors for simultaneous measurement of the wall shear stress and flow angle on the surface of the wall. The sensor measured the heat loss from a micro-heater to measure the shear stress on the walls. At the same time, the flow angle was estimated using an array of six temperature sensors around the heater that facilitated multidirectional measurement. The team conducted numerical simulations of the airflow to optimize the geometry of the heaters and sensor arrays.
“The circuits around the sensor can be pulled out using a flexible printed circuit board and installed in a different location, so that only a thin sheet is attached to the measurement target, minimizing the effect on the surrounding flow,” said Prof. Motosuke.
A high-speed airflow tunnel was used in the testing environment, the team achieved practical flow measurements with a wide range of airflow speeds from (30 – 170) m/s. The developed sensor demonstrated both high flexibility and scalability. The team estimated the heater output to vary as the one-third power of the wall shear stress. The sensor output comparing the temperature difference between two oppositely placed sensors demonstrated a peculiar sinusoidal oscillation as the flow angle changed.
“Although this sensor is designed for fast airflows, we are currently developing sensors that measure liquid flow and can be attached to humans based on the same principle. Such thin and flexible flow sensors can open up many possibilities,” highlights Prof. Motosuke.
Click here for the Published Research Paper