Temperature step effects on direct measurement of skin-friction drag

Voisinet, R.

doi:10.2514/6.1978-779

Cited by 8 publications

(5 citation statements)

References 4 publications

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“…This error becomes larger at low shear levels, i.e. high Mach numbers and/or low Reynolds numbers [42]. The temperature difference between the rubber RTV sheet and the sensor complex Finally, it is worth noting that the various measuring techniques used for comparison here predict skin friction to within ± 18%.…”

Section: Flight Test Resultsmentioning

confidence: 85%

Study of rubber damped skin friction gages for transonic flight research

Sang

Schetz²

2002

40th AIAA Aerospace Sciences Meeting &Amp; Exhibit

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A non-intrusive direct-measuring skin friction device with a rubber RTV sheet over the surface of the floating head, gap and housing was developed for application in 3D, unsteady, transonic flight conditions. Design conditions required optimum gage performance at altitudes ranging from 15,000 to 45,000 feet, Mach numbers ranging from 0.6 to 0.99 resulting in shear values of 0.3 to 1.5 psf. under vibration conditions up to 8.0 g rms over a 15 -2,000 Hz frequency range. The gage consisted of a rubber RTV sheetcoated floating element attached to an aluminum cantilevered beam. A dual-axis, full bridge strain gage configuration was used with the application of semi-conductor strain gages to increase instrument sensitivity. The gage was studied with and without a viscous liquid (glycerin) fill in the housing. Vibration verification testing was performed at 1.0 g rms in the Virginia Tech modal analysis lab to ensure adequate damping performance over a 0 -3200 Hz frequency range. Tests revealed that the rubber RTV compound sheet provided adequate viscoelastic damping, with or without viscous liquid fill. Gage performance verification testing was performed on in the Virginia Tech supersonic wind tunnel at shear levels of τ w = 3.9 to 5.3 psf in a Mach 2.4 flow. Skin friction values in good agreement with previous testing and analytical predictions were obtained from the tests with adequate damping in the low vibration environment of the Virginia Tech supersonic wind tunnel. The gage proved robust as it survived repeated runs including the violent start and unstart processes typical of a supersonic, blowdown wind tunnel. Flight tests were performed at NASA Dryden Flight Research Center, with the gage mounted in a plate suspended below an F-15 aircraft. This provided a mildly 3D, turbulent boundary layer on a vibrating surface. The gage was tested without liquid fill in the gage cavity, and it performed satisfactorily in this high vibration environment. The gage demonstrated adequate damping and good robustness, surviving the complete flight test intact and remained fully operational. The sensor measured skin friction values 30%-50% higher than those predicted by indirect methods and analogies generally valid for 2D, steady flows. The gage indicated trends in skin friction values for different flight conditions in good agreement with the other methods. Possible reasons for the differences in numerical values are discussed in detail, including potential uncertainties in the gage output and limitations and uncertainties in the methods used for comparison. Finally, suggestions for further development of such gages are provided for flight test applications.iii ACKNOWLEDGEMENTS

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Section: Flight Test Resultsmentioning

confidence: 85%

Study of rubber damped skin friction gages for transonic flight research

Sang

Schetz²

2002

40th AIAA Aerospace Sciences Meeting &Amp; Exhibit

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“…Through iterations of past designs, sources of error have been identified, controlled, and minimized. These sources include gap-ratio effects, lip-ratio effects, floating element misalignment [6], step-temperature effects [15], pressure gradients [16], etc. Still, it is important to report the magnitudes of these errors, generally in the form of an overall uncertainty, so that a level of confidence may be placed on the measurement data.…”

Section: Uncertainty Analysismentioning

confidence: 99%

Skin Friction Sensor Validation for High-Speed, High-Enthalpy Flow Applications

Meritt

Schetz

2014

30th AIAA Aerodynamic Measurement Technology and Ground Testing Conference

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This investigation concerns the design, build, and testing of a new class of skin friction sensors capable of performing favorably in high-speed, high-enthalpy flow conditions, such as those experienced by atmospheric re-entry vehicles, scramjets, jet engines, material testing, and industrial processes. Fully understanding and optimizing these complex flows requires knowledge of the relevant aerodynamic properties, which, in turn, requires numerical and analytical modeling as well as reliable diagnostic instrumentation. The present skin friction sensor design was founded on a direct-measuring, non-nulling, cantilever beam arrangement. A rigorous, multi-step approach was developed to systematically test the sensor through various facilities, where flow enthalpy and run duration were progressively increased, culminating in simulated scramjet flight conditions at the Air Force Research Laboratory. The first phase of the investigation concerns itself with the validation of the sensor to ensure that the measured wall shear values were within an accurate range of the true values. The validation cycle was conducted through an initial series of calibrations to characterize the sensors' static, dynamic, pressure, and thermal responses. The use of bench test facilities further identified the vibratory response and electromagnetic interference properties of the sensor. The cycle was concluded in the Virginia Tech Hypersonic Tunnel under simple, Mach 3 flow conditions. Flow stagnation temperatures and pressures ranged from 300 to 655 K (540 to 1180 °R) and 750 to 1000 kPa (109 to 145 psia), respectively. Wall shear was experimentally measured between 132 and 248 Pa (2.76 and 5.18 psf) over a skin friction coefficient range from 0.00104 to 0.00192. The experimental measurements demonstrated favorable agreement with independent analyses including flat-plate analytical estimations, numerical turbulence model predictions, and historical direct-measuring skin friction sensor data. The total uncertainty of the present skin friction sensor was determined to be ±8.7% at 95% confidence. NomenclatureCf = coefficient of skin friction P0 = stagnation pressure M = Mach number Re = Reynolds number T0 = stagnation Temperature τw = wall shear stress x = stream-wise flow direction y = cross flow direction ωn = vibrational frequency ζ = damping coefficient Downloaded by UNIVERSITY OF QUEENSLAND on July 30, 2015 | http://arc.aiaa.org |

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“…It was important to match the properties of the floating element to those of the surrounding engine wall as closely as possible, so as to prevent errors due to temperature mismatch between the floating element and the surrounding engine wall. Voisinet's 21 study showed that such a temperature mismatch could lead to significant errors in the measurement of skin friction. By providing a heat flow path as much like the rest of the engine wall as possible, this error can be minimized.…”

Section: General Design Attributesmentioning

confidence: 99%

“…A schematic of his device is shown above in Figure 5. The work that followed, including that of Allen 19,20 , Voisinet 21 , and Roensch and Cadwell…”

mentioning

confidence: 99%

Development and Ground Testing of Direct Measuring Skin Friction Gages for High Enthalpy Supersonic Flight Tests

Smith

2002

22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference

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Aerospace Engineering (ABSTRACT)A series of direct-measuring skin friction gages were developed for a high-speed, high-temperature environment of the turbulent boundary layer in flows such as that in supersonic combustion ramjet (scramjet) engines, with a progression from free-jet ground tests to a design for an actual hypersonic scramjet-integrated flight vehicle. The designs were non-nulling, with a sensing head that was flush with the model wall and surrounded by a small gap. Thus, the shear force due to the flow along the wall deflects the head, inducing a measurable strain. Strain gages were used to detect the strain. The gages were statically calibrated using a direct force method. The designs were verified by testing in a well-documented Mach 2.4 cold flow. Results of the cold-flow tests were repeatable and within 15% of the value of C f estimated from simple theory. The first gage design incorporated a cantilever beam with semiconductor strain gages to sense the shear on the floating head. Cooling water was routed both internally and around the external housing in order to control the temperature of the strain gages. This first gage was installed and tested in a rocket-based-combined-cycle (RBCC) engine model operating in the scramjet mode. The free-jet facility provided a Mach 6.4 flow with P 0 = 1350 psia (9310 kPa) and T 0 = 2800 °R (1555 °K). Local wall temperatures were measured between 850 and 900 °R (472-500 °K). Output from the RBCC scramjet tests was reasonable and repeatable. A second skin friction gage was designed for and tested in a wind tunnel model of the Hyper-X flight vehicle scramjet engine. These unsuccessful tests revealed the need for a radically different skin friction gage design.The third and final skin friction gage was specifically developed to be installed on the Hyper-X flight vehicle. Rather than the cantilever beam and semiconductor strain gages, the third skin friction gage made use of a flexure ring and metal foil strain gages to sense iii the shear. The water-cooling and oil-fill used on the previous skin friction sensors were eliminated. It was qualified for flight through a rigorous series of environmental tests, including pressure, temperature, vibration, and heat flux tests. Finally, the third skin friction gage was tested in the Hyper-X Engine Model (HXEM), a full-scale-partial-width wind tunnel model of the flight vehicle engine. These tests were conducted at Mach 6.5 enthalpy with P 0 = 555 psia (3827 kPa) and h 0 = 900 Btu/lb m in a freejet facility. The successful testing in the wind tunnel scramjet model provided the final verification of the gage before installation in the flight vehicle engine. The development, testing, and results of all three skin friction gages are discussed.

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Temperature step effects on direct measurement of skin-friction drag

Cited by 8 publications

References 4 publications

Study of rubber damped skin friction gages for transonic flight research

Study of rubber damped skin friction gages for transonic flight research

Skin Friction Sensor Validation for High-Speed, High-Enthalpy Flow Applications

Development and Ground Testing of Direct Measuring Skin Friction Gages for High Enthalpy Supersonic Flight Tests

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