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Journal Article•DOI•

A nonintrusive laser interferometer method for measurement of skin friction

D. J. Monson1•
Ames Research Center1
01 Jan 1983-Experiments in Fluids (Springer-Verlag)-Vol. 1, Iss: 1, pp 15-22
TL;DR: In this article, a method is described for monitoring the changing thickness of a thin oil film subject to an aerodynamic shear stress using two focused laser beams, which is then simply analyzed in terms of the surface skin friction of the flow, including the effects of arbitrarily large pressure and skinfriction gradients, gravity, and time-varying oil temperature.
Abstract: A method is described for monitoring the changing thickness of a thin oil film subject to an aerodynamic shear stress using two focused laser beams. The measurement is then simply analyzed in terms of the surface skin friction of the flow. The analysis includes the effects of arbitrarily large pressure and skinfriction gradients, gravity, and time-varying oil temperature. It may also be applied to three-dimensional flows with unknown direction. Applications are presented for a variety of flows including two-dimensional flows, three-dimensional swirling flows, separated flows, supersonic high-Reynolds-number flows, and delta-wing vortical flows.

Summary (1 min read)

Jump to: [2.1 Principle] – [2.2 Instrument] – [3.1 AxisymmetricTwo-DimensionalBoundary-LayerFlow] – [I I] and [4. Conclusions]

2.1 Principle

  • A llne of oll is applied ahead of the front beam, the flow is started, and the oil flows downstream past the two beams.
  • The laser beams measure the time rate of change of the oil film's slope by monitoring the tlme-dependent optical interference as discussed in Section 2.2.
  • This information, in turn, is used to compute the average skin friction during the measurementperiod using the oil-flow theory and data-reductionequationsdiscussedin Section 2.3.

2.2 Instrument

  • The two-beam _nstrument cannot be used if wind-tunnel geometries require angles in the range between 30°and 70°..
  • There, the angles are too near the oil Brewster angle of 54°, where the oil reflects the p-polarization poorly.
  • One method of avoiding this problem is to increase the incidence angle to a value beyond 70°.

3.1 AxisymmetricTwo-DimensionalBoundary-LayerFlow

  • The initial verificationexperimentsfor the two-beam laser interferometer method were performedby Monson and Higuchi (1981) and later repeated by Monson (1983) in a simple two-dimensionalboundary-layerflow with no gradients.
  • The tunnel has a cylinder mounted along its centerlineon which the skin friction was measured.
  • (A section of the cylinder can be rotated to produce a swirling boundary layer, but the cylinderwas stationaryfor these tests.).

I I

  • Large plexlglass side windows allow laser beam access in and out of the tunnel.
  • The error bars on the mean laser interferometerdata representconfidencelimits of 95%.
  • Excellent agreement between the two methods and with theory is observed for the axial components.
  • Monson (1983) finds that shallow flow angles result both in long oil-flow path lengthswhich cause a persistenceof oil surfacewaves, and large errors in measured skin friction caused by small errors in applied oil llne direction.
  • As a result, this angle is probably close to the lower limit for which the present method can accurately measure the transverse skin-friction component in threedimensional flows.

4. Conclusions

  • Limitations to the method occur in flows possessing high dust levels, at very high skin-frlctlon levels, or when measuring transverse skin-frlction components in three-dlmensional flows nearly perpendicular to the local flow direction.
  • In spite of these limitations, this method has been used to successfully measure skin-friction levels between O.1 and 120 N/m 2, and transverse components in three-dimensional flows within 3@ of perpendicular to the local flow direction.

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NASA Technical Memorandum 84300
NASA-TM-84300 19830004123
A NonintrusiveLaserInterferometer
Methodfor Measurementof
SkinFriction
Daryl J. Monson
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October 1982
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Lt,[,'GLEY RESEARCH CENTER
L_L_2?,RY,NASA
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IUANA
NationalAeronauticsand
SpaceAdministration
NASA Technical Memorandum 84300
A NonintrusiveLaserInterferometer
Methodfor Measurementof
SkinFriction
Daryl J. Monson, Ames ResearchCenter, Moffett Field, California
NASA
NationalAeronautics and
SpaceAdministration
Ames ResearchCenter
MoffettField,California94035
_/?j---/,_,.37_#-
• !
Abstract
A method is described for monitoring the changing thickness of a thin oil film
subject to an aerodynamic shear stress using two focused laser beams. The measure-
ment is then simply analyzed in terms of the surface skin friction of the flow.
The analysis includes the effects of arbitrarily large pressure and skin-friction
gradients, gravity, and time-varying oil temperature. It may also be applied to
three-dimensional flows with unknown direction. Applications are presented for a
variety of flows including two-dlmensional flows, three-dimensional swirling flows,
separated flows, supersonic high Reynolds number flows, and delta-wing vortical
flows.
Citations
More filters
Journal Article•DOI•
Empirical mode decomposition and Hilbert transforms for analysis of oil-film interferograms

[...]

Kapil Chauhan1, Henry C.-H. Ng1, Ivan Marusic1•
University of Melbourne1
01 Oct 2010-Measurement Science and Technology
TL;DR: In this paper, the Hilbert transform was used for analyzing oil-film interferograms, and it is shown to be superior for treating amplitude and frequency modulated data, making it robust to wide differences in the quality of interferogram.
Abstract: Oil-film interferometry is rapidly becoming the preferred method for direct measurement of wall shear stress in studies of wall-bounded turbulent flows. Although being widely accepted as the most accurate technique, it does have inherent measurement uncertainties, one of which is associated with determining the fringe spacing. This is the focus of this paper. Conventional analysis methods involve a certain level of user input and thus some subjectivity. In this paper, we consider empirical mode decomposition (EMD) and the Hilbert transform as an alternative tool for analyzing oil-film interferograms. In contrast to the commonly used Fourier-based techniques, this new method is less subjective and, as it is based on the Hilbert transform, is superior for treating amplitude and frequency modulated data. This makes it particularly robust to wide differences in the quality of interferograms.

24 citations

Proceedings Article•DOI•
Laser skin friction measurements and CFD comparison of weak-to-strong swept shock/boundary-layer interactions

[...]

Kwang-Soo Kim1, Yeol Lee1, Farrukh S. Alvi1, Gary S. Settles1, C. C. Horstman2 •
Pennsylvania State University1, Ames Research Center2
01 Jan 1990
TL;DR: In this article, a joint experimental and computational study of skin friction in weak-to-strong swept shock wave/turbulent boundary-layer interactions has been carried out, and the results show a systematic rise in the peak c(f) at the rear part of the interaction, where the separated flow atttaches.
Abstract: A joint experimental and computational study of skin friction in weak-to-strong swept shock wave/turbulent boundary-layer interactions has been carried out. A planar shock wave is generated by a sharp fin at angles of attack alpha = 10 deg and 16 deg at M(infinity) = 3 and 16 and 20 deg at M(infinity) = 4. Measurements are made using the Laser Interferometer Skin Friction meter, which optically detects the rate of thinning of an oil film applied to the test surface. The results show a systematic rise in the peak c(f) at the rear part of the interaction, where the separated flow atttaches. For the stronget case studied, this peak is an order of magnitude higher than the incoming freestream c(f)level.

22 citations

Proceedings Article•DOI•
Modern skin friction measurement techniques - Description, use, and what to do with the data

[...]

Jonathan W. Naughton, Mark Sheplak1•
University of Florida1
19 Jun 2000

21 citations

Proceedings Article•DOI•
An experimental study of a three-dimensional shock wave/turbulent boundary-layer interaction at a hypersonic Mach number

[...]

M. I. Kussoy, K. C. Horstman, K.-S. Kim1•
Ames Research Center1
01 Jun 1991
TL;DR: Experimental data for a series of three-dimensional shock-wave/turbulent boundary-layer interaction flows at Mach 8.2 are presented in this paper, where the test bodies, composed of sharp fins fastened to a flat-plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary layer separation, and turning angle.
Abstract: Experimental data for a series of three-dimensional shock-wave/turbulent-boundary-layer interaction flows at Mach 8.2 are presented. The test bodies, composed of sharp fins fastened to a flat-plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface-pressure, heat-transfer, and skin-friction distributions, as well as limited mean flowfield surveys both in the undisturbed and interaction regimes. The data were obtained for the purpose of validating computational models of these hypersonic interactions.

20 citations

Proceedings Article•DOI•
Skin friction measurements by laser interferometry in swept shock wave/turbulent boundary-layer interactions

[...]

Kwang-Soo Kim1, Gary S. Settles1•
Pennsylvania State University1
01 Jan 1988
TL;DR: In this article, the laser interferometric skin friction meter was used to measure wall shear stress distributions in two interactions of fin-generated swept shock waves with turbulent boundary layers, and the results indicate that such measurements are practical in high-speed interacting flows, and that a repeatability of + or - 6 percent or better is possible.
Abstract: The laser interferometric skin friction meter was used to measure wall shear stress distributions in two interactions of fin-generated swept shock waves with turbulent boundary layers. The basic research configuration was an unswept sharp-leading-edge fin of variable angle mounted on a flatplate. The results indicate that such measurements are practical in high-speed interacting flows, and that a repeatability of + or - 6 percent or better is possible. Marked increases in wall shear were observed in both swept interactions tested.

16 citations

References
More filters
Journal Article•
Describing Uncertainty in Single Sample Experiments

[...]

S. J. Kline
01 Jan 1953-Mechanical Engineering

7,568 citations

Journal Article•DOI•
An outline of the techniques available for the measurement of skin friction in turbulent boundary layers

[...]

K.G. Winter1•
Royal Aircraft Establishment1
01 Jan 1979-Progress in Aerospace Sciences
TL;DR: In this article, the authors discuss force-measurement balances, the use of the velocity profile, pressure measurements by surface pitot tubes or about obstacles, and the analogies of heat transfer, mass transfer or surface oil flow.

337 citations

Journal Article•DOI•
A study of the motion of oil films on surfaces in air flow, with application to the measurement of skin friction

[...]

L H Tanner, L G Blows
01 Mar 1976-Journal of Physics E: Scientific Instruments
TL;DR: In this paper, a simple relation is obtained between the film thickness variation and the skin friction distribution, and the results confirm the theory and show that the method gives reasonably accurate measurements of skin friction distributions in low speed flows.
Abstract: An oil film on a solid surface moves under the action of gravity or of the pressure gradient and skin friction resulting from the flow of air over the oil surface. Such oil flows are studied experimentally and theoretically. If the film is thin enough, the dominant force is the skin friction, and a simple relation is obtained between the film thickness variation and the skin friction distribution. The other forces give a perturbation which may be estimated and which decreases with time. The appropriate film thickness is of the order of 10 mu m and so is conveniently measured by interferometry. Experimental results confirm the theory and show that the method gives reasonably accurate measurements of skin friction distribution in low speed flows.

246 citations

Journal Article•DOI•
A skin friction meter, using the viscosity balance principle, suitable for use with flat or curved metal surfaces (based on thickness measurement)

[...]

L H Tanner
01 Mar 1977-Journal of Physics E: Scientific Instruments
TL;DR: In this paper, a laser beam focused at position x, reflects partly from the oil surface and partly from a metal substrate, and the reflected beams are focused on a photocell and the pen recorder output gives an interferometric record of y against t.
Abstract: An oil film is placed on a surface over which gas is flowing, and moves under the influence of skin friction. The skin friction meter to be described makes use of the fact that, at time t after the start of the flow with skin friction tau , the thickness y of oil of viscosity mu at a point x close downstream of the leading edge is y= mu x/ tau t. A laser beam focused at position x, reflects partly from the oil surface and partly from the metal substrate. The reflected beams are focused on a photocell and the pen recorder output gives an interferometric record of y against t. To permit accurate setting of the position x, a second laser beam is used which is set at the upstream oil edge, x=0. The results obtained show good agreement with theory, repeatability and consistency. The meter can be used with any polished metal surface, whether flat or curved, and provides versatile and potentially accurate method for skin friction measurement.

59 citations

Journal Article•DOI•
Skin Friction Measurements by a Dual-Laser-Beam Interferometer Technique

[...]

Daryl J. Monson1, H. Higuchi•
Ames Research Center1
01 Jun 1981-AIAA Journal
TL;DR: In this article, a portable dual-laser-beam interferometer that nonintrusively measures skin friction by monitoring the thickness change of an oil film subject to shear stress is described.
Abstract: A portable dual-laser-beam interferometer that nonintrusively measures skin friction by monitoring the thickness change of an oil film subject to shear stress is described. The method is an advance over past versions in that the troublesome and error-introducing need to measure the distance to the oil leading edge and the starting time for the oil flow has been eliminated. The validity of the method was verified by measuring oil viscosity in the laboratory, and then using those results to measure skin friction beneath the turbulent boundary layer in a low speed wind tunnel. The dual-laser-beam skin friction measurements are compared with Preston tube measurements, with mean velocity profile data in a "law-of-the-well" coordinate system, and with computations based on turbulent boundary-layer theory. Excellent agreement is found in all cases. (This validation and the aforementioned improvements appear to make the present form of the instrument usable to measure skin friction reliably and nonintrusively in a wide range of flow situations in which previous methods are not practical.)

50 citations

Related Papers (5)
A study of the motion of oil films on surfaces in air flow, with application to the measurement of skin friction

[...]

01 Mar 1976-Journal of Physics E: Scientific Instruments
L H Tanner, L G Blows
An outline of the techniques available for the measurement of skin friction in turbulent boundary layers

[...]

01 Jan 1979-Progress in Aerospace Sciences
K.G. Winter
Skin Friction Measurements by a Dual-Laser-Beam Interferometer Technique

[...]

01 Jun 1981-AIAA Journal
Daryl J. Monson, H. Higuchi
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[...]

01 Jan 1993
Daryl J. Monson, George G. Mateer, Florian R. Menter
A skin friction meter, using the viscosity balance principle, suitable for use with flat or curved metal surfaces (based on thickness measurement)

[...]

01 Mar 1977-Journal of Physics E: Scientific Instruments
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