Skin friction measurements in short duration high enthalpy flows

Novean, Michael; Schetz, Joseph A.; Hazelton, David; Bowersox, Rodney D. W.

doi:10.2514/6.1995-6109

Cited by 7 publications

(3 citation statements)

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“…Both foil and semi-conductor strain gages have their relative advantages and disadvantages for this application. 45,46,47 Also, current pressure sensor designs are not able to make accurate high-speed measurements in harsh environments, including high temperature, high Mach number flows which can cause ionization of the gas. Currently, measurements in such an environment are made through pressure taps that protect the sensor, but the process greatly reduces the frequency response.…”

Section: Motivation For Employing Fiber Opticsmentioning

confidence: 99%

“…91,92,93,94 Attached to the beam were two Luna EFPI fiber optic strain sensors, as pictured in Figure 97. The concept was to construct a skin friction sensor as close as possible to previously fabricated conventional strain gage designs that have been successful.…”

Section: Version 1 Skin Friction Sensormentioning

confidence: 99%

“…1 In fact, Schetz's research group has produced a series of skin friction sensors based on strain gages mounted to the cantilever beam in a non-nulling arrangement. 21,22,23 As with any sensor, new design concepts take advantage of more sensitive transducing technology as it evolves. In the current study, the sensing technology has moved to fiber optics, allowing a design principle based on deflection instead of strain, which is new in non-nulling cantilever beam designs.…”

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confidence: 99%

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Development of fiber optic aerodynamic sensors for high Reynolds number supersonic flows

Pulliam¹,

Schetz²

2001

39th Aerospace Sciences Meeting and Exhibit

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Aerospace Engineering (ABSTRACT)The purpose of the project was to examine fiber optic sensors for the measurement of pressure, skin friction, temperature, and heat flux in high Reynolds number, supersonic flow. Using a standard fiber optic signal conditioning unit (specifically a broadband interferometric system using spectra), the work centered around determining under what conditions these sensors will work effectively and quantifying the total system limitations.An interferometric-based, fiber optic skin friction sensor was developed for the measurement of wall shear stress in complex, supersonic flows. This sensor type was tested successfully in laminar, incompressible flow, and supersonic flow up to Mach 1.92, Mach 2.4 and 3.0 flow, in which the sensor operated with varying success. A micromachined, fiber optic pressure sensor was also tested in these supersonic conditions, also with varying success. The accurate operation of these sensors was found to be tied to the flow conditions and the fiber optic, signal processing system.A correlation was found to exist between the energy of the flow, either through its dynamic pressure or through external disturbances such as shocks or separation, and the noise in the signals, expressed by the variance of the gap estimate, for the pressure and skin friction sensors in these flows. The energy of the flow couples with the mechanical properties of the sensor reducing the fringe contrast of the signal used by the optical signal processing system to determine a gap estimate. As the energy of the flow is increased and the sensor is excited, the fringe contrast is reduced. A practical limit of a normalized fringe contrast of 0.10 was found for producing accurate gap estimates in real flows. A consequence is that there is a limit to the dynamic pressure of the flow for the sensors to operate accurately, which is demonstrated by the varying success of the supersonic wind tunnel tests. This correlation is sensor specific, meaning that sensors can be designed to operate successfully in any flow. Also, the signal processing system, which forms the other end of the total system, could be improved to allow accurate measurements with the current sensors.iii

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Section: Motivation For Employing Fiber Opticsmentioning

confidence: 99%