Pressure-sensitive paint measurements for microscale supersonic flow with wedge models

In the current work, pressure distribution on the surface of blade and endwall is investigated experimentally in a compressor cascade for capturing some flow features by analyzing pressure profile aerodynamics. Pressure is measured using pressure sensitive paint (PSP) technique. Before the tests, some system errors including temperature-dependence of paint, in-situ calibration, and Self-illumination among neighboring structure are studied in details. In addition, the spatial layout scheme of LEDs and CCDs for each test is designed by self-developing optical theoretical method that based on the LTS (light Tracing Simulation). In the post-processing, an in-situ calibration is conducted to convert the intensity of luminescence to pressure, and each test uses independent calibration equation. Finally, discrete pressure is also measured by pressure taps to compare with PSP. All of the tests are performed at the AOA (Attack of Angle) of −2.5°∼10°, and Mach number of 0.4∼0.8. The results show that the pressure distribution at low Mach number presents a good PSP performance in terms of signal-to-noise-ratio, and apparent pressure step gradient is captured at high Mach number. Meanwhile, the pressure distribution at high incidence reveals the unsteady of separated flow. By combining the end-wall plot with profile plot, the influence of corner-flow on main flow in the passage is obtained.

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.

A first time-resolved pressure-sensitive paint (PSP) test campaign at the European Transonic Wind Tunnel (ETW) was conducted within the research initiative “Unsteady flow and interaction phenomena at High Speed Stall conditions”. One of the objectives of this wind tunnel campaign was to resolve time-series of surface pressure distributions caused by complex 3-D buffet phenomena on a full-span airplane model XRF-1 transport aircraft configuration. At higher angle-of-attack and high Mach number, pressure fluctuations with a frequency of several hundred Hertz are expected to occur on the main wing and the horizontal tail plane (HTP) caused by the buffet effect. To capture the expected buffet phenomena by PSP, the German Aerospace Center developed a time-resolved PSP measurement and data acquisition system as well as a post-processing method for measurements in ETW. The measurements were conducted on the main wing and HTP simultaneously, with a camera frame rate of up to 2 kHz. The transonic buffet phenomena were observed at the flight relevant Reynolds number Re = 12.9 × 106 and Re = 25.0 × 106. The time-varying surface pressure distribution on the model was successfully captured by PSP. The time-series and spectra of both PSP and pressure transducer data match very well.

Pressure-Sensitive Paint (PSP) technique has been applied to measure pressure distribution on airfoil models at low Reynolds number (Re = 4.1x10 4.3x10) in the Mars Wind Tunnel (MWT) at Tohoku University. In this study, the capability of PSP for pressure measurement was evaluated with a particular emphasis on its applications to thin airfoil models. The obtained results show that PSP can clearly visualize pressure distributions on the airfoils, allowing us to analyze a behavior of the separated shear layer on the airfoil including laminar-to-turbulent transition and reattachment. A comparison between the PSP and balance measurements indicates that the evolution of a laminar separation bubble over the airfoil surface has a strong effect on the lift and drag characteristics. It has been also verified by this experiment that, using the proposed method for temperature correction, pressure distribution can be obtained quantitatively even on thin airfoils.

The videogrammetric model deformation (VMD) measurement technique is developed, which is integrated with fast-responding pressure sensitive paint (PSP) to measure simultaneously unsteady aeroelastic deformation and pressure field of a wing in transonic and supersonic wind tunnels. The measurement system and data processing are described. The method of generating a deformed wing surface based on VMD measurements for PSP data mapping on the surface is developed and evaluated through simulation. Simultaneous VMD and PSP measurements on an oscillating airfoil section have been conducted in a transonic wind tunnel, and VMD data are obtained from the registration targets in PSP images. Furthermore, dynamic aeroelastic deformation of a thin flexible rectangular wing is measured by using a single-camera VMD system in a low-speed wind tunnel, and the vibration modes are extracted at different angles of attack and freestream velocities.

The fast response Pressure Sensitive Paint (PSP) was studied to develop the capability of making global pressure measurements in unsteady and short duration flow conditions. In this work, the response times of porous PSP were characterized from two dynamic calibration device. Visualization and measurements of aerodynamic effects on a Cylinder/flat plate configuration were conducted in a hypersonic wind tunnel of CAAA using the fast response PSP technique. Unsteady PSP measurement results of Ma=5 were described in this paper. PSP was sprayed on the flat plate surface and it was illuminated by a high power UV light. The luminescence was measured by a high-speed camera. After image processing, the time series absolute pressure distributions on the surface were obtained. Comparison between the PSP result and pressure transducers were also described.

There appears fluttering phenomena in a hard disk drive system with high-speed disks rotating inside a closed space, leading to degrade of reading and writing performance. The precise pressure distribution on the disk may improve the performance, but there has been no report because it is very hard to measure the surface pressure using conventional techniques, such as pressure taps. While pressure sensitive paint (PSP) seems to be suitable for the pressure measurement on the disk, we have to compensate its highly temperature-sensitive characteristics of PSP, because the temperature distribution on the disk is not assumed to be uniform. We employed PySO3H based PSP, which has small temperature sensitivity, and have obtained the pressure distribution on the disk rotated at various speeds (10000–20000 rpm) successfully. The result showed that the pressure is higher at the disk outside than at the center, and forms a concentric circle distribution. Moreover, we found that the pressure difference between the inner and outer region of the disk increases as a square of disk rotation speed.

Polymer/ceramic pressure-sensitive paints with reduced surface roughness were developed for measuring unsteady pressure fields in transonic flow. Four types of polymer/ceramic pressure-sensitive paints, each having different properties (such as particle size, mass content, and solvent), were formulated and applied to transonic wind-tunnel tests of a supercritical airfoil. The effects of surface roughness on the unsteady transonic flow on the airfoil were evaluated at Mach 0.74 at a Reynolds number of . It was found that all four polymer/ceramic pressure-sensitive paints could be used to measure time-series pressure distributions, but the location of the shock wave and the root-mean-square pressure fluctuations differed, depending on the type of polymer/ceramic pressure-sensitive paint. Among the tested polymer/ceramic pressure-sensitive paints, having an arithmetic surface roughness of and a cutoff frequency of 3 kHz yielded practically the same data as a clean airfoil. Using this polymer/ceramic pressure-sensitive paint, propagation of pressure waves and oscillation of shock waves on the airfoil were clearly captured. A spectral analysis revealed that the fundamental frequency of shock-wave oscillation agreed very well with that calculated based on the mechanism proposed in previous studies. These results showed that the selected polymer/ceramic pressure-sensitive paint is an effective means by which to study transonic buffeting on airfoils and three-dimensional wings.

The capability of a lifetime-based Pressure-Sensitive Paint (PSP) method for application in cryogenic wind tunnels was investigated. The relevant experiments were conducted in the Pilot-European Transonic Windtunnel (PETW). The 2D airfoil model (CAST10-II) was painted with PtTFPP/PTMSP paint and tested in a nitrogen atmosphere at 150 K. PSP and pressure tap data were acquired at Mach 0.78 at a total pressure of 160 kPa. The oxygen concentration of the flow was set to 1000 ppm by continuously supplying dry air. As a result, the lifetime-based PSP method successfully visualized the pressure distribution on the airfoil model under cryogenic conditions. The quantitative agreement of PSP and pressure tap data was obtained and the difference in both data came out to be 0.05 in the pressure coefficient Cp. The accuracy of PSP data is comparable to results achievable at ambient conditions. Therefore, it may be concluded that the lifetime-based method was successfully applied under cryogenic conditions. In addition to the lifetime-based method, the intensity-based method was also conducted as a comparison. Furthermore the applicability of the lifetimebased method to tests with model deformation was evaluated.

The current status of pressure sensitive paint (PSP) and temperature-sensitive paint (TSP) has been presented in this paper. PSP and TSP are molecular imaging techniques and enable to measure global pressure and temperature distribution on a model surface. PSP has been achieving a remarkable improvement in responsiveness and detecting resolution of pressure. TSP is used to measure not only temperature distribution but also heat flux and to detect boundary-layer transition.

Pressure-sensitive paint (PSP) is an optical measurement technique based on the photo-chemical reaction between oxygen and luminescent molecules, and has potential as a diagnostic tool for pressure measurement in the high Knudsen number regime. However, the application of PSP to micro flow measurement is not straightforward, because conventional PSPs are too thick owing to their polymer binder. In our previous work, we fabricated pressure-sensitive molecular film (PSMF) by using the Langmuir-Blodgett (LB) technique. In this study, we investigated the temperature dependency of Pt(II) Mesoporphyrin IX (PtMP) based PSMF, and found that the temperature dependency of the pressure sensitivity is very small. Moreover, we have applied PSMF to the pressure measurement of micro gas flows through the 170μm width micro channel and the 100μm width micro nozzle, and the pressure distributions were successfully obtained.

A flexible nanofiber membrane containing dendritic oxygen probe for visual monitoring pressure distribution

To clarify the unsteady pressure distributions on the rotor blades of an axial fan, a pressure-sensitive paint (PSP) technique was used. To capture the image of the rotating fan as a static image, an optical derotator method with a dove prism was adopted. It was confirmed by preliminary experiments with a resonator and a speaker that the pressure fluctuations with 347 Hz can be measured by the present PSP. The measured mean pressure distributions were compared with the predicted results based on large-eddy simulations. The measured instantaneous surface pressure is instrumental to identify acoustic source of fan noise in the design stage.

Unsteady pressure distributions at the wind tunnel model of a pitching Lambda wing with development of vortical flow

The pressure-sensitive paint (PSP) method and the shear-sensitive liquid crystal coating (LCC) method were separately applied to measure the areal pressure and shear stress vector distributions on a planar test surface beneath an inclined, axisymmetric, turbulent impinging jet. The combined results provide the first-ever consolidated measurements of the continuous normal and tangential force distributions beneath a fundamental flow field. Present results indicate that the PSP method can be extended to the measurement of small pressure differences (<~0.1 psig) encountered in low-speed flows. Further, these results provide the first demonstration of the capability of the LCC method to measure continuous surface shear stress vector distributions on planar surfaces where shear vectors of all possible orientations are present.