Research on MEMS skin friction measurement technology conformal to a conical model surface

Abstract The precise measurement of skin friction on the surfaces of high-speed vehicle models is fundamental for refining aerodynamic designs and developing effective drag-reduction strategies. However, the compact size of conical models and the complex nature of the surface flows present significant challenges, making it absolutely essential to pursue research into high-precision skin friction measurement that can c adapt to the model’s surface contours. This paper introduces the design of a capacitive MEMS skin friction sensor with a conformal measurement head that matches the surface of a conical model with a 20° half-angle. A key innovation lies in using the same fabrication process for both the conical model and the MEMS sensor, enabling an integrated, co-fabricated package where the sensitive element and its housing are seamlessly merged. This approach successfully tackles the long-standing issue of standard MEMS sensor heads failing to conform to curved model surfaces. Moreover, to cut down on assembly errors that could disturb the flow over the conical surface, we have fine-tuned the sensor’s assembly technique. This optimization ensures that the step height between the sensor’s active area and the surrounding wall is kept under 10 µm—a negligible value compared to the several-100 µm-thick boundary layer, meaning minimal interference with the wall-bounded flow. Following static calibration, the MEMS skin friction sensor performed excellently across a 0–100 Pa range, boasting a repeatability better than 1‰, linearity under 0.5%, and a resolution of 0.2 Pa. The sensor was then put to the test in a wind tunnel under Mach 8 conditions. The test results indicate that the developed conformal MEMS skin friction sensor features conformal integration with the conical model surface, miniaturization, and high sensitivity, having achieved a measurement repeatability of 3.85% at individual test points.