PRESSURE SENSITIVE PAINTS

VEERESHGOUDA S. N.12GAMB4017

M.E. AMTDept. of Mechanical Engineering

UVCE, BangaloreA one-eighteenth scale model of an Air Force tailless aircraft recently underwent aerodynamic testing in Arnold Engineering Development Center’s four-foot transonic wind tunnel. The test was a technology demonstration entry in which conventional methods and Pressure Sensitive Paint were used to compare the effectiveness of a jet effects spoiler with a solid spoiler in yaw and roll control and stability of the aircraft. (Photos by Rick Goodfriend) “http://www.arnold.af.mil/shared/media/photodb/photos/080401-F-9114G-010.jpg”

Contents

• Conventional Technique• Pressure Sensitive Paints (PSP) basics• About Fluorescence• Anatomy of PSP• Materials for PSP• Setup and Data Acquisition

– Hardware and software requirements• Advantages• Disadvantages and Conclusion

A light Humour before we proceed

“If I could explain it to

the average person, I

wouldn't have been

worth the Nobel Prize.”-People (22 July 1985) Richard P. FeynmanThe Nobel Prize in Physics 1965

Before PSPPressure taps were used- Extensive construction time while producing data with limited spatial resolution

http://www.grc.nasa.gov/WWW/k-12/airplane/tunpsm.html

PSP Basics• The PSP method is based on the sensitivity of certain luminescent

molecules to the presence of oxygen.

• A typical PSP is comprised of two main parts (Fig 1),– an oxygen-sensitive fluorescent molecule( luminophore ), and – an oxygen-permeable binder.

• Pressure sensitivity of the luminescent molecules: excited luminophore interacts with an oxygen molecule and transfers some of the excited state energy to a vibrational mode of the oxygen molecule. – The resulting transition to the ground state is radiation less, this process is

known as oxygen quenching.

The rate at which these two processes compete is dependent on the partial pressure of oxygen present, a higher oxygen concentration causing additional quenching of the molecule, resulting in a lower light intensity

This relation between the energy and frequency is called the Planck relation: Since the frequency , wavelength λ, and speed of light c are related by λν = c, the Planck relation for a photon can also be expressed as

N2-laser operating in a

quasi-continuous mode (1000 Hz) in combination with fiber-optic illumination system

337 nm

About Luminescence • Luminescence is emission of light by a substance not resulting from heat; it is thus

a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal.

• Radium dials: Phosphorous doped with ZnS:Cu give light greenTYPES: Chemiluminescence, -chemical reaction

Bioluminescence, - biochemical reaction by a living organism, Haemoglobin Electrochemiluminescence, - electrochemical reaction

Crystalloluminescence, produced during crystallization Electroluminescence, a result of an electric current passed through a substance

Cathodoluminescence, luminescent material being struck by the electrons Mechanoluminescence, mechanical action on a solid

Triboluminescence -bonds in a material are broken when that material is scratched, crushed, or rubbed Fractoluminescence, generated when bonds in certain crystals are broken by fractures Piezoluminescence, produced by the action of pressure on certain solids[3]

Sonoluminescence, a result of imploding bubbles in a liquid when excited by sound

Photoluminescence, a result of absorption of photons Fluorescence, photoluminescence as a result of singlet–singlet

electronic relaxation (typical lifetime: nanoseconds) Phosphorescence, photoluminescence as a result of triplet–singlet

electronic relaxation (typical lifetime: milliseconds to hours) Radioluminescence, -bombardment by ionizing radiation Thermoluminescence, -the re-emission of absorbed light when a substance is heated

• A temperature sensitivity occurs when the binder for the pressure-sensitive luminescent molecule has oxygen permeability that is a function of temperature

Oxygen permeable binder ~ 10μm(polymer, silicone rubber orporous solid)

Luminescent Molecules (Ruthenium complexes, Metal porphrins)

Undercoat scattering layer ~15μm

http://www.chem.ufl.edu/~kschanze/Dissertations/kose.pdf

Materials for Paint

• Luminophore- platinum tetra(pentafluorophenyl)porphine (PtTFPP)– should possess high luminescence quantum yield, long

emission lifetime, large Stokes shift, and excellent photostability.

– It is also desired that their excitation and emission fall into visible region of the spectrum.

• Binders- Polymers-(fluoro/isopropyl/butyl)acrylic (FIB) – high sensitivity to oxygen concentration with a low

temperature dependence of

Coatings• PSP coatings used at NASA

• Boeing PF2B – ruthenium bathophenanthroline in silicone rubber binder (soft paint, chlorinated solvent)• UW (ISSI) FIB – PtTFPP in FIB copolymer binder (hard, good steady state paint)• NASA Langley – PtTFPP in FEM (very hard, very smooth finish)• ISSI sol-gel – Ru(ph2-phen) and PtTFPP on sol-gels (higher frequency response)•Anodized aluminum – dip coated Ru(ph2-phen) on anodized surface (very high freq. response)• UW PtOEP in MAX acrylic copolymer (ice paint)

Table-Photophysical properties of pressure sensitive luminophores. Shaded luminophores are also used for temperature sensing

http://www.chem.ufl.edu/~kschanze/Dissertations/kose.pdf

• The intensity of emitted light is inversely proportional to the partial pressure of oxygen (oxygen quenching)and thus to the air pressure in wind tunnel

Data Acquisition

Long- pass filterShort-pass filter

Hardware requirements

Charge-coupled device (CCD)camera

Pulse/Delay Generator

2-inch Air-Cooled LED Lamp

Parabolic LED Reflector

Software requirements

• OMS Acquire and OMS-Lite Software• ProImage

Why use PSP?

• Dynamic and real-time measurements possible.

• Low-cost, non-intrusive, full-field surface pressure and temperature measurements in Transonic Wind-tunnel testing.

• Provides virtually limitless spatial resolution hence high accuracy.

• To make comparison with computational-fluid-dynamics models

Applications

• Low-Speed Measurements: Flow velocity - 36m/s; wheel rotation velocity –72 RPS.Subsonic Measurements

• Transonic Measurements Mach numbers between 0.8 and 1.2• Supersonic Measurements• TSP Measurements• Investigation of Internal FlowsFlow-Field Visualization• Interaction with CFD Approaches

“http://www.innssi.com/PSPApplications.html”

Lifetime PSP F16 Test at ARCPioneer Rocketplane

Rotating blades PSP

http://www.grc.nasa.gov/WWW/OptInstr/LC/PSP_TSP_examples.pdf

Applications contd..

CONCLUSION

• Pressure sensitive paint is a powerful tool for the aerodynamic community to acquire full field pressure distributions on aerodynamic models.

• pressure sensitive paints exhibit undesirable sensitivity to variations in temperature and illumination– A solution is to have a reference Luminophore

“Binary pressure sensitive paint” has been developed

1) T. Liu.,M. Guille, J.P. Sullivan, “Accuracy of Pressure Sensitive Paint”, AIAA Journal, vol. 39, n 1, pp. 103-112,(2001)2) Gouin, S., Gouterman, M., “Ideality of Pressure-Sensitive Paint. I. Platinum Tetra(pentafluorophenyl) porphine inFluoroacrylic Polymer”, Journal of Applied Polymer Science, Vol. 77, pp. 2795 – 2804, (2000)

REFERENCES• Chris D. Geddes, Joseph R. Lakowicz “Advanced Concepts in Fluorescence Sensing, Part”• http://www.innssi.com/ (or) http://psp-tsp.com/• http://www.grc.nasa.gov/WWW/k-12/airplane/tunpsm.html• http://en.wikipedia.org/wiki/Pressure-sensitive_paint• http://www.psp-tsp.com/pdfs/Accuracy%20of%20PSP.pdf• http://www.optrod.com/

• Yumi Takeuchi · Yutaka Amao “Materials for Luminescent Pressure-Sensitive Paint” Springer Ser Chem Sens Biosens (2005) 000: 303–322 DOI 10.1007/5346_010

“Thank-you”

“The first principle is that you must not fool yourself, and you are the easiest person to fool”

-Richard P. Feynman

May 11, 1918 – February 15, 1988