The energy and transportation sectors often use different types of fluid machinery, including pumps, turbines and aircraft engines, all of which result in high carbon emissions. This is mainly due to inefficiencies in fluid machines caused by flow separation around curved surfaces, which are quite complex in nature.
Therefore, in order to improve the efficiency of the fluid machine, it is necessary to characterize the flow near the upper wall curved surface to prevent this flow separation. The challenge in accomplishing this is many times over. First, conventional flow sensors are not flexible enough to fit into the curved walls of fluid machines. Second, now flexible sensor suitable for curved surfaces where liquid angle (direction of flow) cannot be detected. Furthermore, these sensors are limited to detecting flow separation only at speeds less than 30 m/s.
In a new study, Professor Masahiro Motosuke from 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, took up this challenge. As Professor Motosuke said, “Feel shear stress and its direction on curved surfaces, where flow separation is easy to occur, is particularly difficult to achieve without the use of a new technique. ”
Their work has been published in Micro muscle.
In their research, the team developed a flexible flow sensor based on a polyimide thin film that can be easily installed on curved surfaces without affecting the surrounding airflow, an important requirement. to measure effectiveness. To do this, the sensor is based on microelectromechanical systems (MEMS) technology. More, novel design allows the integration of multiple sensors to simultaneously measure the shear stress of the wall and the yield angle on the wall surface.
To measure shear stress on the walls, the sensor measures heat loss from a micro heater, while the flow angle is estimated using a series of six temperature sensors around the heater to facilitate for omnidirectional measurements. The team conducted numerical simulations of the airflow to optimize the geometry of the heaters and sensor arrays.
Using the high-velocity airflow tunnel as a test medium, the team achieved efficient flow measurements with a wide airflow speed range of (30–170) m/s. The developed sensor exhibits both high flexibility and scalability. “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 plate is attached to the target,” said Professor Motosuke. measurement, minimizing the influence on the surrounding flow”.
The team estimated the heater output would change at one-third of the wall shear stress, while the sensor output comparing the temperature difference between two opposite sensors showed a special sinusoidal oscillations when the flow angle changes.
The developed sensor has the potential for a wide range of applications in industrial-scale fluid machinery that often involves complex flow separations around three-dimensional surfaces. Furthermore, the operating principle used to develop this sensor can be extended beyond high-speed subsonic airflow.
“Although this sensor is designed for fast airflows, we are currently developing sensors that measure liquid flow and can be attached to a person based on the same principle,” said Professor Motosuke. . Such thin and flexible flow sensors could open up many possibilities.”
Taken together, the new MEMS sensor could be a game changer in developing efficient fluid machinery with reduced harmful impacts on our environment.
Koichi Murakami et al., Development of a flexible MEMS sensor for subsonic flow, Micro muscle (In 2022). DOI: 10.3390 / mi13081299
Tokyo University of Science
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