MEMS Skin Friction Sensor

Simultaneous mean and dynamic shear stress measurement will enable NASA ATP facilities to precisely measure wall skin friction, which is currently not possible. Specifically, in the subsonic and the transonic regimes, this sensor will allow NASA ATP to explore skin friction drag reduction technology. This capability provides scientific value and poses significant commercial gain to NASA ATP by means of providing aerodynamic design and testing opportunity to the aviation industry. Furthermore, this technology enables NASA to establish a primary calibration standard for other shear stress measurement techniques, potentially extending this capability to supersonic and hypersonic regimes. Specific NASA ATP facilities that will benefit from precise skin friction instrumentation for aerodynamic performance estimation are: ¿ NASA Glenn Research Center: 9' by 15' low speed wind tunnel ¿ NASA Langley Research Center: 14' by 22' Subsonic Wind Tunnel, 20 Foot Vertical Spin Tunnel, and the 11 ft x 11 ft Transonic Unitary Plan Facility. The silicon micromachining technique inherently minimizes unit cost. Overall, NASA and the aviation industry stand to significantly benefit via better aerodynamic design and higher efficiency/ lower drag at lower cost.

Several research institutes and aviation companies perform routine wind tunnel testing in the subsonic and transonic regimes. Formula 1 cars undergo aerodynamic design changes on a weekly basis and are tested at full scale in wind tunnels. With depleting petroleum reserves, wind turbines are being increasingly utilized, necessitating blade/vane design and material improvements for better efficiency. Wind turbine control is increasingly implemented in wind farms for power regulation using turbine pitch and yaw control techniques where skin friction measurement may serve as a feedback signal. In 2008 alone the wind energy industry attracted over $17 billion indicating substantial amount would be invested in control system, which is a portion of the 34% of the wind turbine cost. Skin friction measurement is extremely important for advancements in all of these applications. Shear stress may also be used to estimate flow rate, which opens the $1.35 billion flow rate sensor market for non-intrusive measurements. For example, remote flow rate monitoring in transcontinental pipelines for transporting natural gas and other hydrocarbon fuels. This sensor may also serve as a platform technology with a potential impact on a broad application spectrum that ranges from fundamental scientific research to industrial process control, biomedical applications, etc.