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GB2272514A - Measuring surface pressure - Google Patents

Measuring surface pressure Download PDF

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Publication number
GB2272514A
GB2272514A GB9223659A GB9223659A GB2272514A GB 2272514 A GB2272514 A GB 2272514A GB 9223659 A GB9223659 A GB 9223659A GB 9223659 A GB9223659 A GB 9223659A GB 2272514 A GB2272514 A GB 2272514A
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GB
United Kingdom
Prior art keywords
light
dye
pulsed
pressure
laser
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9223659A
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GB9223659D0 (en
Inventor
Alan Geraint Davies
Michael Dunleavy
David Jonathan Bedwell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems PLC
Original Assignee
British Aerospace PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Aerospace PLC filed Critical British Aerospace PLC
Priority to GB9223659A priority Critical patent/GB2272514A/en
Publication of GB9223659D0 publication Critical patent/GB9223659D0/en
Publication of GB2272514A publication Critical patent/GB2272514A/en
Withdrawn legal-status Critical Current

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01MTESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M9/00Aerodynamic testing; Arrangements in or on wind tunnels
    • G01M9/06Measuring arrangements specially adapted for aerodynamic testing
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/02Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

Surface pressure is measured on a surface (1) eg. of a model in a wind tunnel (3) by applying or including in the surface a fluorophore dye. Fluid containing oxygen flows over the dyed surface and pulsed or chopped light (4) from a source (5) is directed at the dyed surface (1). The rate of decay of the resulting fluorescence (6) excited by the pulsed or chopped light (4) is measured (7) to indicate directly the surface pressure, which varies with the concentration of oxygen molecules at the surface. The fluorophore dye may be incorporated in a gaspermeable paint with a polymer base, having a preferred composition 0.13% (wt) palladium octaethylporphyrin as the dye, 4.7% (wt) polymethylmethacrylate and the balance tetrahydrofuran. The dye can alternatively be applied in solution or be incorporated in a composite structure comprising an epoxy resin. <IMAGE>

Description

METHOD AND APPARATUS FOR MEASURING SURFACE PRESSURE This invention relates to a method of and apparatus for measuring surface pressure on a surface which is particularly, but not exclusively, suitable for use in measuring surface pressure on a model in a wind tunnel.
Surface pressure measurements on a wind tunnel model are difficult to carry out and can be both expensive and time consuming. Conventionally such measurements are made by way of fine diameter holes or tappings formed in the surface of the model, which holes are connected to electro mechanical pressure transducers. Whilst the accuracy is high using sensitive transducers it is necessary to place the fine diameter holes wherever a pressure measurement needs to be taken with the result that either a great many holes and transducers are necessary or if fewer transducers and holes are utilised pressure readings in some areas of the model surface will be missed. However if a great many transducers and holes are used the model becomes unnecessarily complicated and expensive.As an alternative, pressure transducers are mounted on the actual surface of the model but these are expensive and only give limited spatial resolution.
A further conventional method of measuring surface pressure which is particularly applicable to wind tunnel models is the optical pressure measurement system. This system involves the application of a dye in a gas permeable paint to the surface of the wind tunnel model and the excitation of this dye by a suitable light source to produce fluorescence of the dye at a particular wavelength. The fluorescence is quenched by the presence of oxygen molecules so that a measurement of the fluorescence intensity leads to an indication of the concentration of oxygen molecules at the surface of the model. This concentration can be related to the partial pressure of the oxygen and thus to the surface pressure immediately above the dye and model surface.
Whilst this latter technique has been commercially relatively successful it does have various shortcomings.
In particular pressure measurements which are reasonably accurate on flat surfaces are not accurate with increasing surface curvature, the addition of paint layers, particularly to leading edge areas, locally increases the leading edge radius and thus distorts the aerodynamic characteristics of the model, and tests have to take place in complete darkness. Additionally movement of the model in the wind tunnel air stream causes problems in that the image is continually moving across fluorescence intensity detector areas. This latter problem is exacerbated by the fact that intensity varies with illumination intensity, illumination angle, viewing angle and distance from the illumination source to the model which makes it difficult to calibrate accurately for uniformity of response of individual pixels within a detector which may be a Charge Coupled Device (CCD) camera array.In theory each pixel needs to be separately calibrated and if the model image moves relative to the camera then the calibration is invalid.
There is thus a need for a generally improved method and apparatus for measuring surface pressure which at least minimises the foregoing problems with conventional systems and techniques and which is applicable to testing of models in wind tunnels.
According to one aspect of the present invention there is provided a method of measuring surface pressure on a surface, in which a fluorophore dye is applied to or made to form part of the surface, fluid containing oxygen is flowed or allowed to flow over the dyed surface, pulsed or choppsed light is impinged on the dyed surface and the rate of decay of the resulting fluorescence excited by the pulsed or chopped light is measured to indicate directly the surface pressure as a function of the decay rate which varies with the concentration of oxygen molecules at the surface.
Preferably the fluorophore dye utilised is palladium octaethylporphyrin.
Conveniently the surface is a metal surface having a porous oxide layer to which the dye is applied.
Alternatively the dye is incorporated in the surface which is in the form of a composite structure comprising an expoxy resin.
Advantageously the fluorophore dye is contained in a gas permeable paint which is applied to the surface.
Preferably the dye is contained in a polymer base and more preferably the paint contains, by weight, from 0.001 to 0.13% Palladium Octaethylporphyrin as the dye.
Conveniently the paint utilised contains, by weight, substantially 0.13t Palladium Octaethylporphyrin, substantially 4.7% Polymethylmethacrylate and the balance, apart from impurities and incidental constituents, being tetrahydrofuran.
Alternatively the dye is applied to the surface in a solution of benzene.
Conveniently the light utilised is pulsed laser light, pulsed Xenon flash light or chopped arc light.
Advantageously the length of each light pulse or chop is less than and/or terminates faster than the decay rate of the dye.
Preferably the light is laser light provided by a laser provided by a frequency doubled Nd/YAG laser.
Conveniently the light is provided by a laser operated at a wavelength in the range of from 300 to 7001un, and with a pulse duration in the range of from 1 namosecond to O.1 seconds.
Advantageously the laser wavelength is substantially 532 nanometres, the pulse duration is substantially 13 nanoseconds and the power is substantially 3 millijoules.
Conveniently the surface on which pressure is to be measured is carried on or provided by a model in a wind tunnel.
According to another aspect of the present invention there is provided a paint for use in the foregoing method containing, by weight, substantially 0.13% Palladium Octathylporphyrin, and substantially 4.7* Polymethylmethacrylate with the balance, apart from incidental constituents and impurities being a tetrahydrofuran.
According to a further aspect of the present invention there is provided apparatus for measuring surface pressure on a surface, including a source of pulsed or chopped light for impingement on a fluorophore dye carrying or containing surface whose surface pressure is to be measured, a detector for detecting the intensity of fluorescence produced by the pulsed or chopped light impingement on the surface, and processing means for processing a fluorescence output signal received from the detector and processing the signal to provide a surface pressure value.
Preferably the source of pulsed or chopped light is a Xenon flash unit or arc light, Conveniently the source of pulsed laser light is a frequency doubled Nd/YAG laser.
For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which; Figure 1 is a schematic block diagram of apparatus according to one embodiment of the present invention for measuring surface pressure on a surface.
The method according to the present invention for measuring surface pressure on a surface is suitable for many applications in which it is desired to measure the pressure exerted on a surface by a flow of oxygen containing fluid over the surface. For example it may be used to measure air pressure on the surface of an aircraft in flight, wind pressure on a super structure such as a building or bridge or the pressure exerted on the surface of a vehicle such as a car or train by the air through which it moves. Alternatively the method can be used to measure the surface pressure exerted by a liquid in which a vessel such as a ship or submarine is moving.
However for the sake of convenience the invention will be described in terms of use for measuring the pressure on a surface of a model in a wind tunnel, with reference to the schematic apparatus diagram of Figure 1.
As shown in Figure 1 a fluorophore dye 1 is applied to a surface such as the leading edge of an aircraft wing 2 in a wind tunnel 3. The dye 1 may be applied directly to the surface or incorporated in the surface in any convenient manner. For example the dye may be carried in a paint, or solvent. One suitable dye is palladium octaethylporphyrin.
This may be applied direct to a metal surface such as aluminium, preferably to a porous oxide coated metal surface. The dye may be dissolved in solution in any suitable solvent such as benzene. A suitable solution would be about 1 milligramme of Palladium Octaethylporphyrin in about 10 millilitres of benzene.
Alternatively the dye may be incorporated in the surface for materials such as a composite structure. In this case the dye may be dissolved in the epoxy resin, either in the epoxy or amine constituent. The resin may form the outer layer of the surface or may be a coating thereon.
However the technique preferred is to incorporate the dye in a gas permeable paint which is applied to the surface. A suitable paint contains, by weight, substantially 0.13% palladium octaethylporphyrin, substantially 4.7% polmethylmethacrylate and the balance, apart from impurities and incidental constituents, being tetrahydrofuran.
The light utilised may be pulsed laser light pulsed Xenon flash light or chopped arc light providec by any convenient source or unit. Preferably the length of each light pulse or chop is less than and/or terminates faster than the decay rate of the dye. If the light 4 is provided by a pulsed laser source 5, as is preferred and as is shwn in Figure 1, the laser wavelength should preferably be in a range which shows strong dye absorption and subsequent fluorescence. The laser energy should preferably be sufficient to allow the decay sigals to be analysed accurately.
In the illustrated embodiment pulsed laser light 4 from the source 5 is impinged on the dyed surface 1 and the rate of decay of the resulting fluorescence 6 excited by the laser light is detected by a detector 7 and measured in processing means 8, which may incorporate a storage oscilloscope, to indicate directly the surface pressure as a function of the decay rate which varies with the concentration of oxygen molecules at the surface on which the dye/paint 1 is applied. A filter 9 in the laser light beam 4 removes unwanted radiation but allows the surrounding area to be illuminated in the normal way from ambient light. On the output side a filter 10 in the fluorescence beam 6 removed all radiation at the laser wave length but allowed the fluorescence wave length to pass through.The beams 4 and 6 entered and left the wind tunnel 3 via optical windows 11 which also allowed ambient light to enter the wind tunnel 3. The detector 7 was not screened from the ambient light. Thus it is, with the apparatus and method of the present invention, unnecessary to carry out the method in total darkness as is usual in the earlier described conventional systems.
The response of the detector 7 is recorded on a storage oscilloscope in the processing means 8 and the readings processed. It has been found that the pressure is directly proportional to the rate of decay of the fluorescence 6 so that the plot of the inverse of the decay time constant against pressure is substantially a straight line. The decay time constant varies with pressure and the decay time constant at a constant pressure is independent of illumination intensity. Thus the presence of oxygen not only reduces the intensity of fluorescence but also increases the rate of decay of the fluorescence 6 if the excitation illumination laser light beam 4 is removed. The temporal response of the fluorophore dye/paint in the paint 1 to the pulsed or chopped light 4 gives a direct reading of the surface pressure on the surface 2.
As the measurement of decay rate is independent of illumination or fluorescence absolute intensity the application of the method to curved surfaces such as the wing 2 does not create any problems as a result of varying intensity. Also since the dye may be absorbed into the oxide layer or an aluminium substrate, no dimensional changes are caused in aerodynamically critical areas. There is no requirement to calibrate each pixel in a CCD image recording camera if used as the detector 7 and, as typical decay times are of the order of microseconds movement of the wind tunnel model is very little. As measurement times are short dynamic measurements are feasible.
Preferably the laser light beam 4 is provided by a frequency doubled Nd/YAG laser 5 having a frequency of substantially 532 nanometres with a pulse length of substantially 13 nanoseconds and a power of substantially 3 millijoules. For steady state pressure measurement, pulse repetion of 20 Hz is suitable. More generally the laser should be operated at a wavelength in the range of from 300 to 600 mn to cause the dye to fluoresce, and at an intensity level commensurate with the viewing or analysing optics and detectors. The pulse duration should preferably be in the range of from 1 nanosecond to 0.1 seconds depending upon the application and timescale of pressure fluctuations.

Claims (21)

1. A method of measuring surface pressure on a surface, in which a fluorophore dye is applied to or made to form part of the surface, fluid containing oxygen is flowed or allowed to flow over the dyed surface, pulsed or chopped light is impinged on the dyed surface and the rate of decay of the resulting fluorescence excited by the pulsed or chopped light is measured to indicate directly the surface pressure as a function of the decay rate which varies with the concentration of oxygen molecules at the surface.
2. A method according to claim 1, in which the fluorophore dye utilised is palladium octaethylporphyrin.
3. A method according to claim 1 or claim 2, in which the surface is a metal surface having a porous oxide layer to which the dye is applied.
4. A method according to claim 1 or claim 2, in which the dye is incorporated in the surface which is in the form of a composite structure comprising an expoxy resin.
5. A method according to any one of claims 1 to 4, in which the fluorophore dye is contained in a gas permeable paint which is applied to the surface.
6. A method according to claim 5, in which the dye is contained in a polymer base.
7. A method according to claim 5 or claim 6, in which the paint contains, by weight, from 0.001 to 0.13% Palladium Octaethylporphyrin as the dye.
8. A method according to claim 6, or claim 7, in which the paint utilised contains, by weight, substantially 0.13t Palladium Octaethylporphyrin, substantially 4.7% Polymethylmethacrylate and the balance, apart from impurities and incidental constituents, being tetrahydrofuran.
9. A method according to any one of claims 1 to 3, in which the dye is applied to the surface in a solution of benzene.
10. A method according to any one of claims 1 to 9 in which the light utilise is pulsed laser light pulsed Xenon flash light or chopped arc light.
11. A method according to claim 10, in which the length of each light pulse or chop is less than and/or terminates faster than the decay rate of the dye.
12. A method according to claim 10 or claim 11, in which the light is laser light provided by a frequency doubled Nd/YAG laser.
13. A method according to claim 4, in which the light is provided by a laser, is operated at a wave length in the range of from 300 to 700 > m and with a pulse duration in the range of from 1 nanosecond to 0.1 seconds.
14. A method according to claim 13, in which the laser frequency is substantially 532 nanometres, the pulse length is substantially 13 nanoseconds and the power is substantially 3 millijoules.
15. A method according to any one of claims 1 to 14, in which the surface on which pressure is to be measured is carried on or provided by a model in a wind tunnel.
16. A method of measuring surface pressure on a surface, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
17. A paint for use in the method of any one of claims 1 to 16, containing, by weight, substantially 0.13% Palladium Octaethylporphyrin, and substantially 4.7* Polymethylmethacrylate with the balance, apart from incidental constituents and impurities, being tetrahydrofuran.
18. Apparatus for measuring surface pressure on a surface, including a source of pulsed or chopped light for impingement on a fluorophore dye carrying or containing surface whose surface pressure is to be measured, a detector for detecting the intensity of fluorescence produced by the pulsed or chopped light impingement on the surface and processing means for processing a fluorescence output signal received from the detector and processing the signal to provide a surface pressure value.
19. Apparatus according to claim 18, wherein the source of pulsed or chopped light is a laser, Xenon flash unit or arc light.
20. Apparatus according to claim 19, wherein the source of pulsed laser light is a frequency doubled Nd/YAG laser.
21. Apparatus for measuring surface pressure on a surface, substantially as hereinbefore described and as illustrated in Figure 1 of the accompanying drawings.
GB9223659A 1992-11-11 1992-11-11 Measuring surface pressure Withdrawn GB2272514A (en)

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Application Number Priority Date Filing Date Title
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Application Number Priority Date Filing Date Title
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GB2272514A true GB2272514A (en) 1994-05-18

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0990130A4 (en) * 1996-04-12 2000-04-05 Mc Donnell Douglas Corp PRESSURE DETERMINATION METHOD
US7176272B2 (en) 2002-11-08 2007-02-13 Leatech, Llc Pressure sensitive material
CN109990755A (en) * 2019-04-02 2019-07-09 石家庄铁道大学 Vehicle-curved bridge coupling system dynamic experiment equipment and method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112067244B (en) * 2020-09-07 2023-09-05 中国航空工业集团公司沈阳空气动力研究所 Bi-component fluorescent oil film formula suitable for subsonic temporary flushing wind tunnel and using method
CN116046744A (en) * 2023-02-27 2023-05-02 同济大学 Application of fluorescent dyes in judging the pore pressure of cement-based materials in different environments
CN119390225B (en) * 2024-10-30 2025-09-19 上海交通大学 Preparation method of high-altitude water for icing wind tunnel simulation

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0029653A1 (en) * 1979-11-21 1981-06-03 THE GENERAL ELECTRIC COMPANY, p.l.c. Optical systems for sensing and measuring physical quantities
WO1987000023A1 (en) * 1985-07-03 1987-01-15 International Biomedics, Inc. Methods of measuring oxygen concentration
EP0252578A2 (en) * 1986-07-02 1988-01-13 John E. Shulze Sensor system using fluorometric decay measurements
EP0329297A2 (en) * 1988-02-16 1989-08-23 Medex, Inc. Method and apparatus for measuring partial pressure of oxygen in a fluid
EP0472243A2 (en) * 1990-08-20 1992-02-26 The Board Of Regents Of The University Of Washington Surface pressure measurement by oxygen quenching of luminescence

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0029653A1 (en) * 1979-11-21 1981-06-03 THE GENERAL ELECTRIC COMPANY, p.l.c. Optical systems for sensing and measuring physical quantities
WO1987000023A1 (en) * 1985-07-03 1987-01-15 International Biomedics, Inc. Methods of measuring oxygen concentration
EP0252578A2 (en) * 1986-07-02 1988-01-13 John E. Shulze Sensor system using fluorometric decay measurements
EP0329297A2 (en) * 1988-02-16 1989-08-23 Medex, Inc. Method and apparatus for measuring partial pressure of oxygen in a fluid
EP0472243A2 (en) * 1990-08-20 1992-02-26 The Board Of Regents Of The University Of Washington Surface pressure measurement by oxygen quenching of luminescence

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0990130A4 (en) * 1996-04-12 2000-04-05 Mc Donnell Douglas Corp PRESSURE DETERMINATION METHOD
US7176272B2 (en) 2002-11-08 2007-02-13 Leatech, Llc Pressure sensitive material
CN109990755A (en) * 2019-04-02 2019-07-09 石家庄铁道大学 Vehicle-curved bridge coupling system dynamic experiment equipment and method

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Publication number Publication date
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