Yoshimi Iijima

Novel Pressure-Sensitive Paint for Cryogenic and Unsteady Wind-Tunnel Testing

A novel pressure-sensitive paint (PSP) formulation suitable for use in cryogenic and unsteady wind-tunnel testing has been developed. This new PSP uses poly [1-(trimethylsilyl)-1-propyne] [poly(TMSP)] as a binder. Poly(TMSP) is a glassy polymer having extremely high gas permeability. Unlike the conventional polymer-based paints, PSP based on poly(TMSP) maintains oxygen sensitivity even at cryogenic temperatures and exhibits fast response time. This paint is sprayable on any model surface including stainless steel and ceramics. These capabilities allow us to apply this PSP to a cryogenic wind tunnel and a short-duration shock tunnel. To demonstrate the capability of poly(TMSP)-PSP for pressure measurements in a cryogenic wind tunnel, a circular-arc bump model and a delta wing model were tested in the National Aerospace Laboratory 0.1-m Cryogenic Wind Tunnel at 100 K. It has been verified that poly(TMSP)-PSP can provide high SIN pressure distribution data at high O 2 concentration. A comparison of the measured intensity data with the pressure tap measurements has suggested that the in situ calibration can be used to obtain quantitative pressure data

Optimization of temperature-sensitive paint formulation for large-scale cryogenic wind tunnels

In this paper, a new temperature-sensitive paint (TSP) technique for boundary-layer transition detection in a production-type large cryogenic wind tunnel is present. The formulation of Ru(trpy) based TSP system has been optimized in terms of luminescence intensity and robustness. The optimum dye-binder-solvent combination has been determined through systematic sample tests. A new binder has been introduced and the resulting coating was found free from cracking at cryogenic temperatures. This is contrary to the silicone-based pervious cryogenic TSP that are subject to micro cracks at reduced temperatures. The new TSP can meet the root-mean-square roughness requirement less than 0.15 /spl mu/m. Experiments in the NAL 0.1-m transonic cryogenic wind tunnel have shown that transition occurs earlier on the unpolished surface than the polished surface, although the roughness value itself increasing by polishing. This suggests that the waviness of the coating could affect on the growth of instability in boundary layers.

Cryogenic pressure sensitive fluorescent paint systems

In recent experiments, we demonstrated the feasibility of using luminescent coatings for surface pressure measurement in a cryogenic wind tunnel. Numerous PSP samples were calibrated and a new coating technology in which luminescent molecules are directly deposited onto an anodized aluminum model surface was developed. The resulting coating has an extremely high oxygen sensitivity for mole fractions of oxygen less than 0.1%. Cryogenic pressure calibration techniques are discussed and calibration curves presented. To demonstrate this technology, a 14%thick bump model was tested in the 0.1-m Transonic Cryogenic Wind Tunnel at NAL. Mach number was changed from 0.4 to 0.84 whereas temperature was maintained at 100 K. A small amount of oxygen was injected into the tunnel and the mole fraction of oxygen ( 250 PPM )in the test gas was kept constant. The results using an in situ calibration for the paintderived pressure distributions are in good agreement with pressure tap measurements.

Open-system pressure sensitive paint for surface pressure measurements in a cryogenic wind tunnel

Pyrene-, ruthenium-, and porphyrin-based, anodized aluminum pressure sensitive paint (AA-PSP) is developed for surface pressure measurements in a cryogenic wind tunnel. These AA-PSPs were calibrated to determine the pressure sensitivity by injecting a small amount of oxygen in the test gas. The mole fraction of oxygen was varied from 4 ppm up to 2000 ppm. The calibration tests were conducted in the 0.1 m Transonic Cryogenic Wind Tunnel (TCWT) at National Aerospace Laboratory, Japan. Luminophore choice affected the pressure sensitivity with a pyrene-based AA-PSP having the best sensitivity. These AA-PSPs were applied for surface pressure measurements on a 14% thick circular arc-bump model in the TCWT. The results of pyrene- and ruthenium-based AA-PSPs showed good agreement with pressure taps. Pressure sensitivity, signal level, and uniformity of luminescent coating affected the pressure measurements.

EVALUATION OF SEVERAL CALIBRATION TECHNIQUES FOR PRESSURE SENSITIVE PAINT IN TRANSONIC TESTING

A pressure sensitive paint (PSP) was applied to a large transonic wind tunnel testing of a rocket fairing model at M=0.9 and three paint calibration techniques were evaluated by comparing the paint data with intensive pressure tap measurements. A temperature sensitive paint (TSP) was also applied in a separate run to compensate for temperature dependency of the PSP. The test results showed an advantage of the in situ calibration with five pressure tap data because the taps covered a whole pressure and temperature range on the paint surface in this particular experiment. The simple a priori calibration was found to be unsuitable due to a temperature distribution at transonic regime. A newly proposed PSP/TSP combined calibration which used both the PSP and TSP measurements also showed good agreement with the pressure tap data without using any pressure tap data. This method would be useful in a blowdown tunnel application and a pressure measurement with an existing model with no pressure tap. However, further evaluation is necessary by taking both PSP and TSP images simultaneously. Finally, a linear affine transformation was applied to extract pressure data at an arbitrary point on the model and showed possibility of a future multi-camera application.

Development of electroluminescence based pressure-sensitive paint system

We introduce a pressure-sensitive paint (PSP) measurement system based on an electroluminescence (EL) as a surface illumination. This consists of an inorganic EL as the illumination, a short-pass filter, and a platinum-porphyrin based PSP. The short-pass filter, which passes below 500 nm, was used to separate an overlay of the EL illumination and the PSP emission. The EL shows an opposite temperature dependency to that of the PSP. It gives a uniform illumination compared to that of a point illumination source such as a xenon lamp. Under atmospheric conditions, the resultant EL-PSP system reduces the temperature dependency by 54% compared to that of a conventional PSP system. An application of the EL-PSP system to a sonic jet impingement shows that the system demonstrated its reduction of the temperature dependency by 75% in a pressure measurement and reduces an image misalignment error.

Visualization of the quiet test region in a supersonic wind tunnel using luminescent paint

A temperature-sensitive luminescent paint technique has been used to visualize boundary-layer transition on a 10-degree cone model in the 0.2-m Supersonic Wind Tunnel at National Aerospace Laboratory. A luminescent paint based on EuTTA was applied on the model surface using airbrush. The paint coating was excited by a Xenon light and the luminescence image was acquired using a high resolution cooled-CCD camera. To enhance thermal signature across transition, tunnel flow was heated by a sudden shutdown of cooling water supply to heat exchanger. Two images were taken for each condition, one is transient image taken in heating process and the other is reference image taken in steady condition. By ratioing these two images, global transition patterns on the cone have been visualized as the edges of brightness. From transition images at various model locations in the test section, it was found that transition remains at a fixed spatial location with respect to the tunnel. This indicates that the cone transition is induced by radiated noise propagating from turbulent boundary layers on the tunnel walls. Effects of the stagnation pressure were also studied over the range from 55 to 150 kPa. The extent of quiet test region was found to be strongly sensitive to the pressure or unit Reynolds number. At the NAL 0.2-m SWT, natural transition did not occur on the cone at lower values of unit Reynolds number.

Global Pressure and Temperature Measurements of Ballistic-Range Testing by PSP and TSP Techniques

A ballistic-range testing gives great insights into a free-flight aerodynamics. It can be seen in a wide flow regime such as from a high-speed flow (ex. a capsule re-entry test and a debris test) to a low-speed flow (ex. a baseball trajectory test and a soccer-ball trajectory test). The surface pressure and temperature are two important factors to determine the motion of the free-flight object. However, there are limited experimental tools available to capture the surface information. We are developing the pressureand temperature-sensitive paint techniques to capture the surface pressure and temperature of a free-flight object. Two approaches are described in this paper. One is a motion-capturing PSP/TSP system that extracts global pressure or temperature information of a free-flight object. The other is an electro-luminescence PSP/TSP system that combines the illumination source on a free-flight object.

Quantum Dots as Global Temperature Measurements

ZnS-capped CdSe semiconductor nanocrystals (quantum-dots, QDs) provide size-tunable optical properties. QDs show shifted luminescent peaks due to crystal size. They exhibit strong and stable luminescence with a 50 % quantum yield at room temperature [1]. Walker et al. used QDs as a global temperature probe [2]. They used a polymer support of poly(lauryl methacrylate) to create a global temperature sensor. This type of sensor, called a temperature-sensitive paint (TSP), has been widely used in aerospace measurements [3]. Conventional TSP uses a phosphorescent molecule as a temperature probe. This type of molecule has a relatively wide FWHM (full width at half maximum), which is roughly 100 nm. When applying a QD as a temperature probe, the FWHM is narrower than that of phosphorescent probes and is roughly 40 nm [1]. A low FWHM will widen the selection of probe molecules to prepare multi-color sensors in the visible wavelength range. In addition, a high quantum yield of QDs can be beneficial as an optical temperature sensing probe to increase the signal-to-noise ratio.

Development of Luminophore-Pendant Temperature-Sensitive Paint and its Application to Pressure-Sensitive Paint for Aerodynamic Measurements

In this paper, current status of the development of luminophore-pendant temperature-sensitive paint of poly[l-(trimetylsilyl)phenyl-2-phenylacetylene] (PTMST) is discussed. PTMST uses poly(l-trimethylsilyl-l-propyne) (PTMSP) based polymer, which is known as one of the highest gas permeable polymers. Because of its high gas permeability and single luminescent compound, we can expect fast response of PTMST to the change in temperature and pressure of the test gas. We can also create PTMST-based two-color PSP for temperature-compensated pressure sensor by simply mixing pressure-sensitive luminophore in PTMST. In this paper, we mix platinum tetrakis (pentafluorophenyl) porphyrin (PtTFPP) as a pressure-sensitive luminophore to create PTMST-based two-color PSP (PtTFPP-PTMST). Spectral analysis shows that PtTFPP-PTMST provides temperature sensitive peak of PTMST (around 540 nm) and pressure sensitive peak of PtTFPP (around 650 nm), which can be separated by band-pass filters. We have calibrated PTMST from 100 K to 373 K as well as PtTFPP-PTMST from 120 K to 333 K to study the static characteristics of these sensors. PTMST provides the temperature sensitivity over the calibrated range, giving the maximum value of 2.72%/K at 100 K. PTMST itself is almost pressure independent. Pressure sensitivity of PtTFPP-PTMST is 0.26%/kPa at 293 K. PtTFPP-PTMST shows pressure sensitivity of 0.66%/kPa even at cryogenic temperature of 120 K. The unsteady characteristic of PtTFPP-PTMST is determined using a step response to a pressure change caused by a shock tube. The response time of PtTFPP-PTMST is on the order of milliseconds. A demonstration of PTMST at cryogenic measurement is shown by transition detection of PTMST-coated NACA64A012 model in JAXA 0.1m Transonic Cryogenic Wind Tunnel. PTMST detects a natural transition as well as a forced transition induced by a roughness at the leading edge at Mach 0.4, total temperature 200 K, and total pressure 120 kPa.