SBIR-STTR Award

The ability to obtain time-resolved, direct wall shear stress measurement is an important asset to aerodynamic research, flow control and to enhance the fundamental understanding of the turbulent boundary layer. Due to a lack of reliable and affordable skin friction sensors, existing indirect methods are used to measure wall shear stress but their usefulness is limited since prior knowledge of the flow is required for indirect sensing. The proposal will result in an instrument-grade, all-sapphire optical miniature sensor to enable mean and fluctuating wall shear stress measurements in high temperature environments. The device must possess sufficient temporal and spatial resolution to capture the spectrum of turbulent wall shear stress fluctuations. As a result, micromachining techniques are employed to enable the sensor to meet the sensing requirements. The sapphire-based, optical transduction technique allows the sensor to operate in high temperature environments while mitigating susceptibility from electromagnetic interference. The micro-scale structures of the optical sensor are hydraulically smooth to enable non-intrusive wall shear stress measurements.

Benefits:
The benefits of the sapphire-based, optical wall shear stress sensor enable the following

Benefits:
- extend wall shear stress sensing capabilities at extreme temperatures (>1500C) - new high-speed measurement systems - uniform sapphire material sensors for matched thermal expansion - optical transduction scheme for reduce EMI Commercial benefits of the sensor include: - wall shear stress measurements in a high speed flow application - flow separation detection - flow control - feedback sensor.

Keywords:
MEMS, high temperature, wall shear stress, skin-friction, optical fibers, sapphire

The Interdisciplinary Consulting Corporation (IC2), in partnership with the University of Florida (UF) and Innoveering, LLC, proposes to develop an innovative precision micro-scale surface-mountable sensor for measuring local wall shear stress in [a] high speed flow field (approximately 0.8 < M < 5) to enable characterization of critical boundary layer flows in ground and flight tests in response to AF14-AT08: Highly-Resolved Wall-Shear-Stress Measurement in High Speed Flows.The proposed sapphire optical wall shear stress and dynamic pressure sensors will enable characterization of complex hypersonic flow environments in ground and flight test facilities at temperatures up to 1200K. The proposed wall shear stress sensor consists of a miniature floating element sensor possessing optical gratings on a floating element and support wafer that form segments of a moir fringe.The pressure sensor utilizes a single sapphire optical fiber to detect the deflection of a reflective sapphire diaphragm.Optical transduction of the moir fringe and diaphragm deflections are achieved via high-temperature sapphire optical fibers, enabling flush-mounted sensor packages.The high-temperature optical fibers can be several meters long and are attached to a photodiode array on the non-sensing end, allowing for the electronics to be remotely located.The Interdisciplinary Consulting Corporation (IC2), in partnership with the University of Florida (UF) and Innoveering, LLC, proposes to develop an innovative precision micro-scale surface-mountable sensor for measuring local wall shear stress in [a] high speed flow field (approximately 0.8 < M < 5) to enable characterization of critical boundary layer flows in ground and flight tests in response to AF14-AT08: Highly-Resolved Wall-Shear-Stress Measurement in High Speed Flows.The proposed sapphire optical wall shear stress and dynamic pressure sensors will enable characterization of complex hypersonic flow environments in ground and flight test facilities at temperatures up to 1200K. The proposed wall shear stress sensor consists of a miniature floating element sensor possessing optical gratings on a floating element and support wafer that form segments of a moir fringe.The pressure sensor utilizes a single sapphire optical fiber to detect the deflection of a reflective sapphire diaphragm.Optical transduction of the moir fringe and diaphragm deflections are achieved via high-temperature sapphire optical fibers, enabling flush-mounted sensor packages.The high-temperature optical fibers can be several meters long and are attached to a photodiode array on the non-sensing end, allowing for the electronics to be remotely located.