Sensors and Actuators B 97 (2004) 13–21 Dual-luminophor pressure-sensitive paint I. Ratio of reference to sensor giving a small temperature dependency Gamal E. Khalil b,∗ , Colin Costin b , Jim Crafton 1 , Grant Jones a,1 , Severin Grenoble b , Martin Gouterman b , James B. Callis b , Larry R. Dalton b a Innovative Scientific Solution Inc. (ISSI), 2766 Indian Ripple Road, Dayton, OH 45440-3638, USA b Department of Chemistry, The University of Washington, Seattle, WA 98195, USA Received 6 September 2002; received in revised form 10 March 2003; accepted 13 May 2003 Abstract Pressure-sensitive paint (PSP) is playing an important role in aerodynamic testing. Its use provides a number of advantages over discrete pressure taps traditionally used on conventional wind tunnel models: (i) obtaining continuous quantitative pressure distributions over a surface; (ii) visualizing dynamic flow processes that measure areas not possible with conventional pressure taps (e.g. thin trailing edges); and (iii) real time modeling. The result is better integration of experimental and computational fluid dynamics leading to significant reductions in time for prototyping of new designs. The use of PSP relies on accurate measurement of changes in the paint’s luminescent intensity as a function of pressure change, which in turn requires careful monitoring and placement of light sources and pre-calibration of the PSP covered surface in “wind-off” conditions. Paint in-homogeneity and inconsistent surface illumination require exact registration of the calibration ‘wind-off’ image with subsequent ‘wind-on’ images for intensity change calculations to be meaningful. Model motion between ‘wind-on’ and ‘wind-off’ images leads to systematic errors that are hard to quantify. A dual-luminophor paint containing both a sensor and a reference luminophor molecule should alleviate these technical problems. This paper introduces such a dual-luminophor PSP made from our newly developed oxygen-sensitive molecule platinum tetra(pentafluorophenyl)porpholactone (PtTFPL), which provides I sen , and magnesium tetra(pentafluorophenyl)porphine (MgTFPP), which provides I ref as the pressure-independent reference. The ratio I ref /I sen in the FIB polymer produced ideal PSP measurements with a temperature dependency of -0.1%/ ◦ C. © 2003 Elsevier B.V. All rights reserved. Keywords: Porphyrin; Porpholactone; PSP (pressure-sensitive paint); Dual-luminophor paint; Referenced pressure-sensitive paint 1. Background Quantitative pressure measurements in a wind tunnel environment utilizing digital video imaging began with our group in 1987 [1]. The system consisted of a luminescent molecule incorporated into a paint matrix that is permeable to oxygen. The luminescence is quenched by oxygen and this quenching can determine the pressure through the Stern– Volmer equation [1,2]. By calculating the ratio of intensi- ties of a pressure-sensitive luminescent probe taken during wind-off and wind-on conditions, we were able to quantita- tively map a continuous two-dimensional pressure field onto the aerodynamic surface being studied. However, there were several serious problems. In particular, photo degradation, response time, and temperature dependency. In addition, displacement of the model due to aerodynamic loading that ∗ Corresponding author. Tel.: +1-206-543-5579; fax: +1-206-685-8665. E-mail address: gkhalil@u.washington.edu (G.E. Khalil). 1 Tel.: +1-937-429-4980; http://www.innssi.com. commonly occurs during wind tunnel testing resulted in a mismatch of the wind-off and wind-on images. Errors re- sulting from model displacement can be partially resolved using image registration techniques to align the wind-off and wind-on. However, this does not correct for the changes in illumination intensity that result from the model movement. From the initial studies of pressure-sensitive paint (PSP) at the University of Washington [1], it was clear that PSP accuracy requires temperature correction. More recently, Liu et al. reviews [3] also stressed the importance of temperature correction for accuracy. Brown, in his Ph.D. [4] thesis on PSP studies at low wind velocities, and recently by Mebarki and Cooper [5] both showed that even with small pressure changes temperature correction remains important. Schanze research group at the University of Florida has been very active studying and evaluating the temperature sensitivity of PSP [6]. Harris [7], of our group, investigated the incorporation of a reference solid inorganic phosphor that is temperature and pressure insensitive to replace the wind-off (I wind-off ) image 0925-4005/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-4005(03)00484-2