Development of a pressure sensitive paint technique for low-speed flows and its application

Pressure sensitive paint (PSP) techniques have been used to measure the pressure distribution on a model surface in high-speed flows. In this study, we developed a PSP technique that can be applied to low-speed flows. Four PSP formulations, each comprised of a porphyrin (PtOEP or PtTFPP) and a polymer (Poly(TMSP) or RTV-118), were tested and the performance of each combination was evaluated. In the static calibration, the luminescence intensity of the PSP coatings was measured from 0 kPa to 11 kPa with 0.5, 1, and 2 kPa increments. Among the four PSP formulations tested, the combination of PtOEP and RTV-118 (PSP-3) showed the best performance. In this study, the low-pressure PSP technique using PSP-3 was applied to an oblique impinging subsonic jet to measure pressure field distributions on the impingement plate at various angles of the oblique jet. For comparison, the flow over the impingement plate was visualized using an oil-film method.     

Automotive testing using pressure-sensitive paint

Measurements of the surface pressure on a simplified automobile model have been performed using pressure-sensitive paint (PSP). The program was undertaken to investigate the use of commercial and in-house PSP at low speed (between 11 m/s and 92 m/s) and to find techniques to improve the measurement accuracy. A comparison ofa priori andin situ calibration methods was also conducted. A linearin situ calibration ora priori methods combined with one tap pressure, correcting for bias errors, were found to provide the best accuracy.     

PSP visualization studies on a convergent nozzle with an

An in-house Pressure Sensitive Paint (PSP) formulation has been developed at the Aero-Physics Laboratory at the University of Manchester. The PSP uses Bathophenanthroline Ruthenium as the luminophore molecule and is incorporated in a sol-gel matrix. Excitation occurs at400–500 nm and emission at550–650 nm. The Stern-Volmer plot of the PSP reveals small temperature dependence, which has always been an intrinsic drawback of PSPs. As a baseline experiment the PSP has been applied to examine the side-wall pressure field of the flow through a convergent nozzle with an ejector, at fully expanded Mach numbers in the rangeM _j =0.52–1.36. Simultaneous static pressure measurements were also conducted to ascertain the accuracy of the PSP results. The paint has demonstrated satisfactory capabilities in not only measuring static pressures but also in visualizing key physical elements of the flow, such as the location of the expansion and oblique shock waves present in such flows.     

Quantitative wind tunnel studies using pressure- and temperature sensitive paints

The pressure sensitive paint (PSP) intensity and lifetime system is an optical measurement technique to investigate absolute pressure fields on model surfaces for basic research in laboratories, industrial wind tunnels or high speed rotating turbo machines. Detailed qualitative and quantitative information and understanding of flow phenomena can be obtained in speed ranges from U_∞=20 m/s up to Ma=5.0. A number of projects of industrial interest has been investigated in different wind tunnels covering low speed, transonic, trisonic and cryogenic facilities. The influence of the main error sources for the components of the PSP system have been checked. Comparison of experimental pressure fields obtained by means of PSP and the results of numerical calculations have been carried out. Different wind tunnel models ranging from basic configurations such as a cropped delta wing to a complex half model of a large propeller-driven transport aircraft with all flaps, rudders and shrouds, and rotating or oscillating models as well as Reynolds number effects on models have been investigated.     

PSP measurement of flow fields in a supersonic combustor with a backward-facing step

The mixing fields within a SCRAM-jet combustion chamber are visualized using pressuresensitive paint (PSP) as an oxygen sensor. The experiments are performed in a small supersonic wind tunnel at the National Aerospace Laboratory — Kakuda Research Center (NAL-KRC). The main stream Mach number is 2.4, and the dynamic pressure ratios between the injected gas and the main flow are 0.3, 0.7, 1.1 and 1.5. Three fuel injection nozzles are used; oxygen is injected from the central nozzle and air from the two nozzles at either side. The spread of the injected gas is measured to observe the effects of placing the nozzles in different positions. The results show that the jet has its own independent flow structure, and that little mixing of gases occurs between the flow structures created by each nozzle. When the injection dynamic pressure ratio is increased, the oxygen fraction rises in the recirculation zone and falls in the separation zone downstream of the injection.     

Visualization of jet mixing in a fluidic oscillator

The fluidic oscillator is a device that generates an oscillating jet when supplied with fluid at pressure. The oscillator has no moving parts — the creation of the unsteady jet is based solely on fluid-dynamic interactions. Fluidic oscillators can operate at frequencies ranging up to 20 kHz, and are useful for flow control applications. The fluidic oscillator evaluated in the current study is comprised of two fluid jets that interact in an internal mixing chamber, producing the oscillating jet at the exit. Both porous pressure-sensitive paint (PSP) and dye-colored water flow are used to visualize the internal and external fluid dynamics of the oscillator. Porous PSP formulations have been shown to have frequency responses on the order of 100 kHz, which is more than adequate for visualizing the fluidic oscillations. In order to provide high-contrast PSP data in these tests, one of the internal jets of the fluidic oscillator is supplied with oxygen, and the other with nitrogen. Results indicate that two counter-rotating vortices within the mixing chamber drive the oscillations. It is also shown that the fluidic oscillator possesses excellent mixing characteristics.     

Quantitative visualization of the leading-edge vortices on a delta wing by using pressure-sensitive paint

Leading-edge vortices on a simple delta wing were visualized by using pressure-sensitive paint (PSP). PSP is an optical pressure measurement technique based on oxygen quenching of luminescent molecules. In the present study, we used PSP composed of platinum octaethylporphyrine (PtOEP) and fluoropolymer (poly-IBM-co-TFEM [Poly (isobutylmethacrtlate-co-trifluoroethylate)]). This new paint has higher sensitivity to pressure and lower sensitivity to temperature than previous ones, reducing an error due to temperature variation during a wind tunnel test. A thin coating of PSP was applied to a delta wing model with 70-degree leading-edge sweep. The coating was excited by Xenon light and emission from the coating was detected by a high-resolution CCD camera. Tests were done at subsonic speeds in the 0.2-m Supersonic Wind Tunnel at the National Aerospace Laboratory in Japan. Complicated flow structures on the delta wing including primary and secondary vortices were clearly visualized using pressure-sensitive paint. An a priori calibration technique was used to convert measured luminescent intensity into pressure. The obtained pressure distributions were in good agreement with pressure tap data. Pressure maps were obtained for various Mach numbers, Reynolds numbers and angles of attack. It was found that an increase in Mach number delayed vortex breakdown while Reynolds number had little effect on the vortex formation.     

Visualization of aerodynamic effects on a double-delta wing aircraft model using Pressure Sensitive Paint (PSP) technique

Visualization of aerodynamic effects on a three-dimensional double-delta wing aircraft model was conducted using an optical pressure measurement system, based on the Pressure Sensitive Paint (PSP) technique, and in addition a laser-light sheet method. The combination of PSP technology with the laser-light sheet method, provides a good understanding of the flow around the wind tunnel model. In recent years, this novel PSP-technology has attracted considerable attention in the aerospace community. The PSP technique can be used to realize absolute pressure measurements on a surface of a model and in addition to evaluate quantitative aerodynamic flow phenomena using a scientific grade camera and image processing techniques. The PSP system was tested in the Transonic Wind Tunnel of the German Aerospace Center in Göttingen (TWG) under real flow conditions. Instantaneous pressure distributions are recorded in almost real-time so that the recognition and analysis of the vortex dynamics on the model surface is possible. Even the vortex breakdown process, as well as the fine structured Kelvin-Helmholtz instabilities and secondary vortex structures, can be detected by this measurement technique.     

Unsteady surface signature of a pulsed vortex generator jet

Abstract  

Porous pressure-sensitive paint (PSP) is employed as a visualization technique for unsteady flow features on a low-pressure turbine blade. Recognizing that the measurement of high-frequency pressure fluctuations in unsteady flows—especially in turbomachinery—has proven to be difficult, recent advancements in the development of porous PSP have enabled the high-resolution measurement of pressure fields with frequency content of at least 20 kHz. In this work, PSP is applied to an L1A low-pressure turbine blade section (Re = 20,000 based on axial chord) to visualize the surface dynamics of a vortex generator jet (VGJ) pulsed at 10.6 Hz with nitrogen gas. Intensity-based, time-resolved PSP measurements reveal the development and the surface structure of the VGJ as well as the spanwise variation in the blowing profile.     

High hydrostatic pressure equipment for neutron scattering studies of samples in solutions

The design of new high pressure equipment for structural and dynamical studies on samples in solution is described. We present two sample cells for applying pressures up to 150 and 700 MPa (i.e. 1.5 and 7 kbar), respectively. These cells are mounted on special sticks and inserted into the calorimeter of a cryostat to regulate the temperature. Different parts of the equipment – the pressure controller, the sticks and the cells – are described. In addition, radiography tests which were performed with neutrons in situ at the Institut Laue Langevin to verify the tightness of the cells and the hydrostatic transmission of the pressure to the sample are presented. First results on model lipids are in agreement with former results by R. Winter et al. [Towards an understanding of the temperature/pressure configurational and free-energy landscape of biomolecules, J. Non-Equilib. Thermodyn. 32 (2007), pp. 41–97].     

Pressure-sensitive paint measurement on co-rotating disks in a hard disk drive

There is much demand for improvement in the performance of a hard disk drive (HDD) along with recent rapid developments of information technology. While high-speed disk rotation of a HDD is necessary to accommodate such needs, it causes disk flutter induced by pressure fluctuation on disks and degrades reliability of a HDD. In order to understand the mechanism of the fluttering phenomenon, it is important to know pressure field on the rotating disk. However, it is impossible to measure the pressure by ordinary methods such as pressure taps. Pressure-sensitive paint (PSP) is a pressure measurement technique based on the oxygen quenching of luminescence and enables us to measure the pressure non-invasively. In general, however, the temperature sensitivity of PSP makes it difficult to measure the precise pressure on the surface with temperature distribution. We measured the time-averaged pressure on the disk rotating at 10 000-20 000 rpm for the first time by adopting a temperature-insensitive PSP composed of pyrene sulfonic acid (PySO₃H) as a luminophore. It was found that the pressure forms a concentric circular distribution and decreases toward the center of the disk. Additionally, we elucidate how disk rotational speed and spacing between co-rotating disks influence on the pressure field.     

Pressure-Sensitive Paint measurement of the flow around a simplified car model

In applying Pressure-Sensitive Paint (PSP) to low-speed flow wind tunnel testing, it is important to minimize any measurement uncertainties. There are various error sources such as camera noise, misalignment of images due to model displacement and temperature distribution over the model. Among these factors, the effects of temperature distribution change during tests on pressure measurement accuracies were studied in the present paper. Pressure and temperature distributions over a simplified car model (1/10 scale Ahmed model) were measured using PSP and Temperature-Sensitive Paint (TSP). Sequential images were acquired at the same intervals over the entire test period, including for the conditions before and after the tunnel run. As a result, it was found that the measurement error caused by temperature distribution over the model could be reduced using a single-point temperature measurement. In addition, by measuring surface temperature distributions on the model using TSP, it was proved that the most accurate pressure measurement could be made by rationing the wind-off image acquired immediately after shutting down the tunnel to the wind-on image acquired immediately before shutting down the tunnel. Using the present measurement technique, complicated pressure fields over the Ahmed model were successfully visualized.     

A-priori evaluations of subgrid-scale terms for large-eddy simulation of compressible turbulent flows

The subgrid-scale terms for different formulations of the energy equation are evaluated from a-priori tests using the direct numerical simulation (DNS) data of a compressible mixing layer at a moderate Mach number of M = 0.65. To extend the generality of the results, the simulations were performed with three different initial conditions for the velocity fields. To examine the impact of strong temperature variations on the subgrid scales, a non-isothermal mixing layer with lower to upper free-stream temperature ratio of 3 is also considered. For cold simulations, with equal free-stream temperatures, the total energy equation is shown to be the best choice in view of the accuracy and the subgrid-scale modelling requirements. For hot simulations, with the free-stream temperature ratio equal to 3, the total enthalpy equation is found to be the best formulation for the energy equation. Furthermore, it is shown that the subgrid-scale pressure dilatation term, which has been largely neglected so far, is of the same order of the subgrid-scale heat flux. Based on the present results, the contribution of the subgrid-scale pressure dilatation can be up to 46% of the total sugbrid-scale activity. Moreover, the time evolutions of the volume-average mean kinetic energy, turbulent kinetic energy, production, dissipation, and pressure dilatation terms are considered. Unlike the subgrid-scale pressure dilatation term, the volume-average pressure dilatation terms are negligible, and compressibility does not affect the large-scale evolutions of the mean and turbulent kinetic energies.     

表面粗糙度的分形特征及其对微通道内层流流动的影响

基于分形几何学,研究了表面粗糙度的分形特征.采用Weierstrass- Mandelbrot函数对多尺度自仿射的表面粗糙度进行了描述;建立了微通道内层流流动的三维模型并对表面粗糙度的影响进行了数值模拟,分析了雷诺数、相对粗糙度和分形维数对流动阻力特性的影响.研究结果表明,与常规尺度通道不同,粗糙微通道的Poiseuille数不再是常数,而是随雷诺数近似线性增加;相对粗糙度越大,流动产生的回流和分离所导致的流动压降越明显.在相同的相对粗糙度下,粗糙表面的分形维数越大,表面轮廓变化就越频繁,这也将导致流动阻 关键词： 粗糙度 层流阻力系数 微通道 分形     

Application of PSP to low density gas flows

Recently optical pressure measurement systems using pressure sensitive paints (PSP) have actively developed to measure continuous pressure distributions on solid surfaces. However, the pressure range has been almost limited above 130 Pa (about 1 Torr) and there is no application to lower pressure range because the pressure sensitivity seems to be not so high in that range. In this study, we have applied three types of PSP [two types are composed by organic dye and polymer (luminophore/binder); PtOEP/GP197 and PtTFPP/poly(TMSP), and another one is Bath-Ru adsorbed on anodized aluminum] to the rarefied gas flow mainly lower than 130 Pa and examine those fundamental properties such as pressure sensitivity, leading to selection of the most suitable PSP among them for the low-pressure range. Since PtTFPP/poly(TMSP) has the highest sensitivity, it is applied successfully to the measurement of the two-dimensional pressure distribution on the surface interacting with a low density supersonic free jet.     

用于叶轮机内流测量的压力敏感涂料校准实验

本文介绍了用于叶轮机械内部流动测量的PSP技术校准系统的组成及校准实验结果。通过对所采集实验图像数据的计算处理,得到了校准特性曲线,与文献的结论基本吻合.同时还对特性曲线的影响因素进行了分析.     

Application of pressure sensitive paint measurement to a low-solidity cascade diffuser of a transonic centrifugal compressor

A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thinlayer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present.     

PSP技术在叶栅叶片表面压力测量中的应用

PSP(Pressure Sensitive Paint)测量技术以不改变叶片表面结构及可以进行全域压力测量的独特优势而受到广泛关注,但是受到几何结构的限制,有关内流场的PSP测量实验难度非常大.本文对ISSI公司所生产PSP测量系统开展了校准试验,完成了三个来流马赫数下叶栅叶片吸力面上静压分布的测量,并与传统压力扫描...     

On the use of multiple interpolation series in scaled particle theory: improved predictions and limitations

We propose further modifications to recent formulations of the scaled particle theory (SPT) of hard particle fluids. In any formulation of SPT, a number of conditions are applied to the central function G. As the exact form of G is unknown, a form must be assumed. Representing G with more than one series has recently been shown (Siderius and Corti, J. Chem. Phys. 127, 144502, 2007) to lead to improved planar surface tension predictions with little change in the already accurate pressure, excess chemical potential and fluid structure predictions. Another condition on G that includes the curvature of the radial distribution at contact was not, however, invoked in this previous work. We incorporate here this additional condition into the multiple series approach, resulting in further improvements to the SPT predictions. We also consider a number of permutations of the multiple interpolation series to explore the limitations of this approach and again find that increasing the number of series will not by itself lead to better predictions of the properties of the hard sphere fluid.     

The pressure and temperature dependence of electron energy-gaps in semiconductor alloys

The pressure and temperature dependences of the direct energy gaps of semiconductor alloys are calculated using the theory of energy gap bowing of Hill. No adjustable parameters are used, and the pressure and temperature coefficients of the bowing parameter are related to the bulk compressibilities and thermal expansion coefficients respectively. The agreement with the rather small number of experimental results is quite good.The non-linear composition dependence of the pressure coefficients of semiconductor alloys suggests that there are inconsistencies in present formulations of dielectric model theories of alloys.