Porous Pressure-sensitive Paint Research Articles

Dynamic stall characteristics of unswept pitching wing

An experimental investigation of dynamic stall on upswept pitching wing was conducted using Particle Image Velocimetry (PIV) and Pressure Sensitive Paint (PSP) techniques. The wing had an aspect ratio AR = 4 and a NACA 0012 airfoil section profile assembled with a round-tip. The wing motion of interest in this study is pitching at a certain angle of attack range and the wing was robustly designed and machined out of Aluminum to minimize elasticity and tip flapping motions. The freestream Mach number, M∞ = 0.1, and the Reynolds number based on chord length, Rec = 2 × 105, were considered as flow parameters for observing dynamic stall phenomena and for comparison with available numerical simulations from literature. The pitching motion of the wing is sinusoidal with a reduced frequency k = πfc/U∞ = 0.1, and the minimum and maximum angle of attack of the pitching motion were 4° and 22°, respectively. Details of flow structures during pitching at various phase angles were captured using planar two-dimensional (2D) PIV at three spans, x/c = 0.5, 0.75, and 1.0 and the pressure imprint on the surface of the wing was captured by a single shot lifetime method using fast porous pressure-sensitive paint. The initial results show the formation of a separation bubble at a small incident angle and the emergence of a dynamic stall vortex (DSV) after the bursting of the separation bubble. The DSV propagates towards the trailing edge of the wing with its integral scale varying across the three spans of the wing revealing three-dimensionality. The PSP results show a uniform build of suction pressure at low angle of attack which later intensifies in a non-uniform manner due to a circulatory motion of the flow during pitching. After the end of the upstroke phase, the flow starts to reattach to the surface of the wing while the DSV grows and moves away from the surface as it travels downstream along the chord until sheds beyond the trailing edge. The PSP results also capture the tip unloading period during the pitching motion.

Global flow visualization of transonic cavity flow with various yaw angles

This study experimentally investigated transonic cavity flows with different length-to-depth ( L/ h) ratios and yaw angles. Two rectangular models with L/ h = 6.14 and 21.5 were examined with yaw angles of 10°, 30°, and 45° under a flow of Mach 0.83. The flow was visualized using pressure-sensitive paint (PSP) to obtain the detailed pressure distribution inside the cavity models. The acquired PSP data were compared with experimental data measured using Kulite transducers, and these data showed favorable agreement. Gradual pressure increases inside the cavity model with L/ h = 6.14 were observed from the PSP measurements as open cavity flow. The flow impingement at the bottom of the cavity and the significant pressure rise inside the cavity model with L/ h = 21.5 were observed as closed cavity flow. The present study quantitatively visualized the evolution of the pressure distribution from symmetric to asymmetric for different yaw angles using porous PSP sensors.

Investigation of transverse jet injections in a supersonic crossflow using fast-responding pressure-sensitive paint

Traditional pressure-sensitive paint (PSP) systems can provide data with high spatial resolution; however, the bandwidth is limited to a few Hz by the response time of the paint. Fast-responding paints have demonstrated response times of up to 100 kHz. Ultra-bright LEDs and fast-framing cameras combined with a porous polymer PSP can be used to produce a system capable of both high spatial resolution and high temporal bandwidth. Measurements of mean and unsteady pressure have been acquired on an experimental setup composed of a Mach-2 channel flow with transverse jet injection. The unsteady pressure data clearly resolve structures not present in the mean pressure data, including multiple lambda shocks upstream of a strong bow shock, high-frequency perturbations in the location of these shocks, and significant deformations of the bow shock structure. Time series of data can be extracted at each pixel, and the spectral content and phase relationship of the flow can be presented as maps of pressure fluctuations at specific frequencies or as correlation coefficients between a control point and the remaining flow. This type of map can be created using arrays of fast pressure transducers; here, we present data representing an array of over 26,000 fast pressure transducers.

1009 感圧塗料を用いたターボファン内部における非定常圧力場の計測技術

Porous pressure sensitive paint (PSP) having fast response and high pressure sensitivity will be a powerful measurement tool to diagnose flow properties in consumer turbomachinery. We have composed test facilities of a turbofan with a transparent casing, to apply a fast-response PSP to measurement of nonstationary pressure distribution on the casing surface of the turbofan. However, luminescent intensity of the PSP without a white undercoat acting as a screen layer is relatively low, which results in low signal-to-noise ratio for pressure measurement. In this study, we have examined the effect of white overcoat with high oxygen permeability made of boron nitrate (BN) nanoparticles, which functions as a screen layer to enhance the luminescence intensity of the PSP through a transparent surface. We have clarified that the BN overcoat can enhance the luminescence intensity and SN ratio of PSP without affecting the time response.

Humidity effects in the response of a porous pressure-sensitive paint

Fast-responding pressure-sensitive paints (PSP) based on luminescent oxygen sensor have porous structure in order to improve diffusive oxygen permeation into paint layer. This porous structure inevitably works as an absorbent of moisture in air, which has considerable influences on the response of the paint. The response of anodized alumina pressure-sensitive paint (AA-PSP), which is one of common fast-responding PSPs, was characterized in moist air. Tris(4,7-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride was used as luminophore. Hydrophobic coating was applied to reduce the moisture adsorption. Emission characteristics of the PSP sample were measured using a calibration apparatus, in which pressure, temperature and humidity can be controlled independently. Moisture sorption isotherm of the PSP sample was measured by volumetric gas adsorption method. The experimental results show that the emission intensity of PSP increases in proportion to the relative humidity at a constant temperature and a pressure. This humidity sensitivity remains a constant value under various temperature conditions. The pressure sensitivity has a constant value irrespective of temperature and relative humidity. Moisture adsorption isotherm of the AA-PSP exhibits that the amount of water slowly increases in proportion to the relative humidity in the range from 20% to 80%. This implies that, within this range, water molecules are adsorbed and diffuse into the pore sidewalls to form thin water layer on the pore surface, which may play a major role in humidity sensitivity of the PSP.

Super-hydrophobic porous pressure-sensitive paint for global unsteady flow measurements

Super-hydrophobic porous pressure-sensitive paint (hydrophobic PSP) is developed based on polytetrafluorethylene (PTFE) particle and platinum (II) meso-tetra(pentafluorophenyl) porphine. The former functions as the water repellent surface, and the latter gives luminescent output related to the pressures. From the luminescent image, global pressure measurements can be achieved in aerodynamic applications. The developed PSP is resistant to the change in the humidity of the test gas, which is one of the major issues for a PSP application in a practical use. The developed PSP shows contact angle more than 150° by the PTFE particle and a porous structure, which describes that the PSP surface is super-hydrophobic. It can be sprayed onto a testing object to open its applications for aerodynamic measurements. The change in the luminescent intensity by the relative humidity of 80% is 6%, and the change by the relative humidity of 60% is only 2% above the pressure at 40kPa. The pressure sensitivity as well as the response time is independent of the humidity.

Pressure-Sensitive Paint Measurements of Transient Shock Phenomena

Measurements of the global pressure field created by shock wave diffraction have been captured optically using a porous pressure-sensitive paint. The pressure field created by a diffracting shock wave shows large increases and decreases in pressure and can be reasonably accurately captured using CFD. The substrate, a thin-layer chromatography (TLC) plate, has been dipped in a luminophore solution. TLC plates are readily available and easy to prepare. Illumination comes from two high-intensity broadband Xenon arc light sources with short-pass filters. The sample is imaged at 100 kHz using a Vision Research Phantom V710 in conjunction with a pair of long and short pass filters, creating a band. The PSP results are compared with numerical simulations of the flow using the commercial CFD package Fluent as part of ANSYS 13 for two Mach numbers.

Unsteady surface signature of a pulsed vortex generator jet

AbstractPorous 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.Graphical Abstract[IMAGE]

A review of pressure-sensitive paint for high-speed and unsteady aerodynamics

The current paper describes the development of pressure-sensitive paint (PSP) technology as an advanced measurement technique for unsteady flow fields and short-duration wind tunnels. Newly developed paint formulations have step response times approaching 1 μs, making them suitable for a wide range of unsteady testing. Developments in binder technology are discussed, which have resulted in new binder formulations such as anodized aluminium, thin-layer chromatography plate, polymer/ceramic, and poly(TMSP) PSP. The current paper also details modeling work done to describe the gas diffusion properties within the paint binder and understand the limitations of the paint response characteristics. Various dynamic calibration techniques for PSP are discussed, along with summaries of typical response times. A review of unsteady and high-speed PSP applications is presented, including experiments with shock tubes, hypersonic tunnels, unsteady delta wing aerodynamics, fluidic oscillator flows, Hartmann tube oscillations, acoustics, and turbomachinery. Flowfields with fundamental frequencies as high as 21 kHz have been successfully measured with porous PSP formulations.

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.

High frame-rate imaging of surface pressure distribution using a porous pressure-sensitive paint

The aim of the present work is to demonstrate the feasibility of a porous pressure-sensitive paint (PSP) for time-resolved surface pressure measurements in unsteady high-speed flows. The porous PSP was composed of bathophenanthroline ruthenium(II) complex, Ru(Ph2-phen) and a silica-gel thin-layer chromatography aluminium plate. The dynamic response of the porous PSP was characterized by a point-wise luminescence intensity measurement conducted in a shock tube facility. The result showed that the time constant of the porous PSP was 13.6 µs. The porous PSP was then applied to the surface pressure distribution imaging of an unsteady flow induced in a two-dimensional Laval nozzle by using a fast-framing complementary metal oxide semiconductor camera. It was clearly shown that the porous PSP well captured the shock-wave motion of the order of kilohertz during the starting process of the supersonic nozzle in a qualitative manner.

C114 PSPによる非定常表面圧力分布計測

Pressure sensitive paint (PSP) is a novel measurement system developed to obtain surface pressure distribution on wind-tunnel testing models. The objective of the present work is to examine the feasibility of this novel surface pressure mapping technique for truly unsteady supersonic flow testing. Using a fast-responding porous PSP and a fast-framing complementary metal oxide semiconductor (CMOS) camera, we have measured unsteady flows induced in a two-dimensional Laval nozzle of a blow-down supersonic wind tunnel. The PSP used in this study was composed of a dye (bathophenanthroline ruthenium(II) complex, Ru(Ph 2-phen) and a silica-gel thin layer chromatography (TLC) plate, on which the dyes were absorbed. The PSP was illuminated by light-emitting-diode (LED) lamps. The results obtained by the present measurement system shows the starting process of supersonic wind tunnel at 5kHz frame rate.

Optical measurements of high-frequency pressure fluctuations using apressure-sensitive paint and Cassegrain optics

Optical measurements of high-frequency pressure fluctuations have been performedto examine the dynamic response of a fast-responding porous pressure-sensitivepaint (PSP). The PSP was composed of meso-tetra(pentafluorophenyl) porphineand a commercial silica-gel thin-layer chromatography plate. Pressure fluctuationsat frequencies on the order of kilohertz were produced on a flat plate by choppingan underexpanded air-jet and then measured by using a newly developed,optical pressure measurement system (OPMS) with a Cassegrain-typeoptical probe. Pressure traces obtained by the present OPMS and theiramplitude spectra were compared with those obtained by a piezo-resistivepressure transducer. The present results demonstrate the feasibility of thepresent OPMS for measuring high-frequency pressure fluctuations witha high spatial resolution and reveal that the present porous PSP canfollow pressure fluctuations at frequencies of several kilohertz at least.

Porous Pressure-Sensitive Paint for Characterizing Unsteady Flowfields

The fast response time characteristics of porous pressure-sensitive paint (porous PSP) are applied to unsteady flowfield measurements. The unsteady flowfield of a fluidic oscillator is investigated by using anodized aluminum (AA), thin-layer chromatography (TLC), and polymer/ceramic (PC) as porous supporting matrices. The frequency response of these PSPs is measured using a shock tube, showing responses of 12.2, 11.4, and 3.95 kHz for AA-PSP, TLC-PSP, and PC-PSP, respectively. Flow oscillations of various phases are captured with these porous PSPs in the fluidic oscillator tests, with AA-PSP giving the sharpest images

Porous pressure-sensitive paint for characterizing unsteady flowfields

Porous pressure-sensitive paint for characterizing unsteady flowfields

Diffusion timescale of porous pressure-sensitive paint

Diffusion timescale of porous pressure-sensitive paint