Highly-Resolved Wall-Shear-Stress Measurement in High Speed Flows

ABSTRACT: 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. BENEFIT: 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