A Novel MEMS-Based Probe for Unsteady Aerodynamic Measurements: A Proof-of-Concept Study

A novel MEMS-based probe is described which is capable of measuring unsteady flow angles, total pressure and velocity. Uniquely, this probe uses shear stress sensors to relate the surface streamline directions on the probe face to the freestream flow angles. The probe has the potential to be miniaturised to around 1mm in diameter and achieve a temporal resolution of up to several 100kHz. A computational study of virtual calibrations is used to understand how to adjust the probe geometry and sensor locations to maximise the sensitivity and range of the device. The most promising configuration was calibrated experimentally using a large-scale probe to demonstrate the feasibility of the concept.

The Effect of Sensor Dimensions on the Performance of Flexible Hot Film Shear Stress Sensors

This paper presents a study to determine the effect of sensor dimensions (length, width, and thickness) on the performance of flexible hot film shear stress sensors. The sensing component of a hot film sensor is nickel thermistor, and the flexible substrate material is polyimide. Several groups of flexible hot film shear stress sensors with different lengths, widths, and thicknesses were studied. The temperature coefficient of resistance (TCR) was measured. The TCR increased slightly with increasing thickness. The frequency response (time constant) of the flexible hot film shear stress sensor was obtained by the square wave, while the sensitivity was tested in a wind tunnel. The study found that as the sensor length was shortened, the frequency response increased, and the sensitivity decreased.

Ultrasonic Measurement of Gas Bubbles Advecting Under a Ship Bottom for Investigating Drag Reduction Performance

Bubbles injected into a turbulent boundary layer have a significant potential to reduce frictional shear stress, but this drag reduction technique has not been optimized yet because of its low and unstable performance. If monitoring and controlling of advective bubbles beneath ships are realized, these provide insight for improving the performance. In this paper, we performed experiments using a model ship with 4 m in length in a towing tank with 80 m in distance. The model ship is fully made of acrylic resin and mounts shear stress sensors and ultrasonic measurement system. The shear stress and bubble information, such as a void fraction and a thickness of liquid film above the bubbles, are obtained at three locations arranged at the front, the middle and the rear of the ship bottom plane. By analyzing these data, it is confirmed that the drag reduction occurs when a thin liquid film exists.