Measurement Technologies

Wireless Shear Stress Sensor Array

 


Research Objectives

To develop a wireless shear-stress sensor array to provide three-dimensional, time-resolved, fluctuating skin friction data to aid turbulence model development.

Approach

Each sensor is effectively an LC tank made up of a variable-capacitance floating element and an integrated inductor. The sensing antenna is inductively coupled to the tank and can detect a change in the resonant frequency caused by a displacement of the floating element. An array is realized by designing each sensor to have it’s own unique resonant frequency. Then a single broad spectrum antenna can monitor the entire array.

Broader Impact

The realization of such an array will enable fundamental scientific studies of complex turbulent flows. It could also be implemented into a feedback control system for future air vehicles employing active flow control.

Capacitive Shear Stress Sensors

This project focuses on the development of a non-intrusive, direct, time-resolved wall shear stress sensor system for low-speed applications. The goals of the project include the fabrication and packaging of a 2-D wall-shear stress sensor with backside wire bond contacts to ensure hydraulic smoothness in flow environments. A differential capacitance transduction scheme is utilized with interdigitated comb fingers on each side of a suspended floating element, allowing for measurements to be made in both the positive and negative x- and y-directions.  A synchronous modulation-demodulation circuit is employed to simultaneously capture both mean and fluctuating shear content. Both AC and DC calibrations are performed to determine sensor sensitivity in both directions of transduction. This is the most successful effort of shear sensor development in published literature. 

A Grazing Flow Impedance Facility For Engine Nacelle Acoustic Liners

Acoustic liners remain the standard for providing a method to reduce environmental noise from aircraft engine nacelles. To aid in their development, facilities are required that are capable of accurately educing the acoustic impedance in the presence of mean flow. The Grazing Impedance Tube at NASA LaRC possesses these capabilities and was donated to the University of Florida. Improvements have been made to enable optical flow diagnostics, provide an increased speed range, and reduce turbulence levels. This facility provides a testbed to improve upon current liner impedance eduction methods as well as facilitate development of novel design approaches and studies into fundamental liner flow physics.

Grazing Flow Impedance Tube Profile

Metric Value
Dimensions 2" x 2"

Maximum Mach Number

0.6
Maximum SPL

130 dB @ Ma = 0.5

MEMS-based Optical Sensors for High Temperature Applications

The goal of this research is to develop a pressure sensor and shear stress sensor that are able to provide continuous, time-resolved flow measurements within high temperature environments such as those seen in hypersonic wind tunnels and turbines.  A primary focus of this research is on the micromachining of sapphire using a picosecond laser.  Sapphire’s mechanical and thermal properties make it an ideal material for high temperature measurements.  Each sensor operates by mechanically deflecting under either a pressure or shear stress.  These deflections can then be detected using an opto-mechanical transduction scheme.  The completed sensors will be tested in flow cells and wind tunnels at UF as well as in other transonic and hypersonic facilities.

J-355PS Picosecond Laser Micromachining Workstation from Oxford Lasers

Development of a MEMS Piezoelectric Microphone for Aeroacoustic Applications

Description

Boeing Dreamliner

Passenger expectations for a quiet flight experience [1] coupled with concern about long-term noise exposure of flight crews [2] drive aircraft manufacturers to reduce cabin noise in flight. Cabin noise has traditionally been limited using insulating panels and skin dampers on the fuselage. Unfortunately, these thin panels are not effective at reducing low frequency (long wavelength) noise and cannot be made thicker due to weight concerns [1]. Treating the noise at its source shows potential for reduction of low frequency noise and weight savings compared to insulating panels. With fuel costs rapidly increasing, reduction of excess weight and subsequent maximization of the "revenue-generating payload" [3] is more important than ever.

In order to identify noise sources and assess the impact of noise reduction technologies during the design process, aircraft manufacturers require robust, low cost microphones. Measuring primary sources of cabin noise, such as shockcell noise, is difficult under simulated cruise conditions in test facilities [1] and establishes the need for microphones that can be used in full-scale tests at altitude. Their use on the fuselage exterior requires extremely small packaged sizes, in addition to the ability to withstand moisture and freezing conditions at flight altitudes. Microelectromechanical systems (MEMS) microphones show promise for meeting the stringent performance requirements of aircraft manufacturers at reduced size and cost, made possible using batch fabrication technology [4-9].