Yasuhiro Egami

Application of pressure-sensitive paints to low-pressure range

The pressure-sensitive paint (PSP) technique has potential as a powerful diagnostic tool for measurements in the high Knudsen number regime because it is based on luminescence of molecules. Three types of PSP [two composed of organic dye and polymer (luminophore/binder), platinum octaethylporphyrin (PtOEP)/silicone polymer (GP197) and platinumtetrakis (pentafluorophenyl) porphyrin (PtTFPP)/poly[1-(trimethylsilyl)-propyne] [poly(TMSP)], and the other ruthenium II tris (4,7-diphenyl-1, 10-phenanthrolin chloride (Bath-Ru) adsorbed on anodized aluminum] are applied to the rarefied gas flow mainly lower than 150 Pa (about 1 torr) to examine fundamental properties, such as pressure/temperature sensitivity, time response of luminescence, and so on

Development of Lifetime Imaging System for Pressure-Sensitive Paint

We developed a lifetime imaging system to simultaneously measure pressure and temperature from the luminescent decay of PtTFPP. Analysis of PtTFPP-PSP by a streak camera showed that this PSP exhibited a transient behavior after pulsed excitation, similar to that suggested by Smoluchowski. Utilizing this characteristic, one could determine pressure and temperature by taking three images with different gated times. We built a lifetime imaging system composed of a pulsed laser and an intensified CCD (ICCD) camera. The three gated times of the ICCD were determined referring to the streak camera data. The performance of this system was evaluated over the wide range of pressure and temperature using a PSP-coated flat plate as a test article. As a result, we found that we could fit the ratios of the gated images with a smooth function of pressure and temperature. This allowed us to reconstruct pressure and pressure fields from the measured images. The accuracy of the lifetime imaging system was determined for various pressures and temperatures, and, as a verification test, pressure and temperature patterns induced by a sonic impingement flow were visualized by using this system.

High Reynolds number transition detection by means of temperature sensitive paint

Simulating true flight Reynolds numbers with scaled models requires the use of cryogenic wind tunnels. Transition detection in ‘warm’ wind tunnels can be realized using commercially available IR cameras. In cryogenic testing, IR imaging becomes more difficult because of the reduction in radiated energy and the shift to longer wavelengths. Therefore, the temperature sensitive paint method has become a promising alternative here. Transition detection measurements were carried out using different models in several cryogenic wind tunnels, namely the European Transonic Windtunnel, the pilot facility of the European Transonic Windtunnel, the cryogenic wind tunnel in cologne and the cryogenic Ludwieg Tube facility of in Gottingen. With the temperature sensitive paint method, similar information can be obtained as for IR imaging in warm wind tunnels, but with higher spatial resolution. This means, that one can determine the instability leading to transition, namely Tollmien-Schlichting or crossflow instabiltiy, observe laminar separation bubbles (and turbulent reattachment), detect flow separation and locate shocks as well as vortex signatures.

Complementary Numerical and Experimental Data Analysis of the ETW Telfona Pathfinder Wing Transition Tests

Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Results of pre-test numerical analysis demonstrated that the Pathfinder wing pressure distribution was adequate for providing calibration test points. The ETW tests provided pressure distribution data while transition positions were determined from images using the Cryogenic Temperature Sensitive Paint Method (cryoTSP). The evaluation of this data with several transition prediction tools was used to establish the transition N-factor values for ETW. In this work, after-test CFD solutions are obtained using numerical Navier-Stokes solutions. In the first part of this work, numerical results are given which verify the requirements of the Pathfinder wing as a calibration model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental and numerical data. In the third part the correlation of experimental transition locations to critical N-factors is summarized for ETW Test Phases I and II. In the fourth part numerical analysis and experimental data are used complementarily.

Application of Pressure-Sensitive Paint for Determination of Dynamic Surface Pressures on a Rotating 65° Delta Wing and an Oscillating 2D profile in Transonic Flow

Visualization and measurements of aerodynamic effects on a delta-wing model and a 2D-wing-profile model were conducted using an optical pressure measurement system, based on the pressure-sensitive paint (PSP) technique. The PSP technique can be used to obtain absolute pressure measurements on the surface of a model and in addition to evaluate quantitative aerodynamic flow phenomena by using scientific grade cameras and image processing techniques. The PSP technique has been used here for investigations of periodic and unsteady flows: first, a 65deg delta wing was tested in the transonic wind tunnel DNW-TWG in Gottingen. A specially designed roll apparatus enabled roll rates up to 10 Hz. The experiments were carried out at angles-of-attack up to alpha = 17deg at Ma = 0.8. Since the rotation of the delta wing is a periodic motion, the phase-locked unsteady PSP technique can be applied. In a second wind tunnel campaign in the DNW-TWG in collaboration with the DLR Institute of Aeroelasticity, a 2D-wing-profile model, which is pitch oscillating at up to 30 Hz, was investigated. The experiments were performed at angles-of-attack alpha = 1.12deg plusmn 0.6deg at Ma = 0.72. For these experiments pressure measurements were carried out in one wind tunnel entry by means of both phase-locked unsteady as well as unsteady PSP techniques.

Advanced Measurement Techniques for High Reynolds Number Testing in Cryogenic Wind Tunnels

The present paper addresses the development, qualification trials and application of some non-intrusive measurement techniques suitable for operation in industry-scale, pressurised cryogenic wind tunnels. The application of cryogenic Temperature-Sensitive Paint (cryoTSP) as a tool for transition detection is described as well as the implementation of the Image Pattern Correlation Technique (IPCT) and the Backward Oriented Schlieren method (BOS) in the European Transonic Windtunnel (ETW). Progress on the development of cryogenic Pressure-Sensitive Paint (cryoPSP) is shown, and considerations for the establishment of a Particle Image Velocimetry system suited for low temperatures (cryoPIV) are presented. Furthermore, the state of adaptation of the microphone array technique

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.

Using cryoTSP as a tool for transition detection and instability examination at high Reynolds numbers

The method of temperature-sensitive paint (TSP) adapted to cryogenic wind tunnels, i.e. cryoTSP is used to detect the natural laminar-turbulent transition of boundary layers in high speed flows. Besides pure transition detection, cryoTSP images provide information on the transition zone, the characteristics of transition, and on the type of instability. A method is proposed to determine the transition zone out of cryoTSP result images for 2D-wings, where the transition process is caused by Tollmien-Schlichting instabilities.

Organic Electroluminescent Sensor for Pressure Measurement

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygen molecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence.

Development of new two-component temperature-sensitive paint (TSP) for cryogenic testing

Two-component temperature-sensitive paint (TSP) for cryogenic wind tunnels has been newly developed to extend the highest working temperature up to 320 K, whereas a conventional single-component cryoTSP operates in the temperature range from 100 to 240 K. The two-component cryoTSP includes two luminophores: a ruthenium complex (Ru(trpy)2) and a europium complex, which are very temperature sensitive in the range of 100–240 K and 220–320 K, respectively. The ruthenium complex is excited by blue light while the europium complex requires UV light. One can thence operate the two luminophores independently by illuminating the paint at different wavelengths. Both luminophores emit red light, so that it is possible to use a single camera filter to observe both luminophores. Verification tests at different cryogenic wind tunnels proved that the two-component cryoTSP could detect a boundary layer transition line even up to room temperatures with only a single coating. This means that it is neither necessary to apply a different TSP coating to a model nor use an infrared camera when the wind tunnel is operated at room temperatures. As a result, the two-component cryoTSP enables one to save time and money in cryogenic testing.