Yoshitaka Sakamura

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.

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

Optical measurements of high-frequency pressure fluctuations have been performed to examine the dynamic response of a fast-responding porous pressure-sensitive paint (PSP). The PSP was composed of meso-tetra(pentafluorophenyl) porphine and a commercial silica-gel thin-layer chromatography plate. Pressure fluctuations at frequencies on the order of kilohertz were produced on a flat plate by chopping an underexpanded air-jet and then measured by using a newly developed, optical pressure measurement system (OPMS) with a Cassegrain-type optical probe. Pressure traces obtained by the present OPMS and their amplitude spectra were compared with those obtained by a piezo-resistive pressure transducer. The present results demonstrate the feasibility of the present OPMS for measuring high-frequency pressure fluctuations with a high spatial resolution and reveal that the present porous PSP can follow pressure fluctuations at frequencies of several kilohertz at least.

Surface pressure distribution imaging at frame rates over 1 kHz using 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 flows. The porous PSP was composed of bathophenanthroline ruthenium(II) complex, Ru(Ph/sub 2/-phen), and a silica-gel thin-layer chromatography (TLC) aluminum plate. The dynamic response of the porous PSP was characterized by applying it to rapid pressure changes generated by a shock wave and a pulse-jet. The porous PSP was then applied to the transient starting process of flow in a two-dimensional Laval nozzle with a fast-framing complementary metal oxide semiconductor (CMOS) camera. It has been shown that the present imaging system can well capture a rapid flow evolution on the order of kilohertz such as shock wave motion in the nozzle during its starting process.

Development and characterization of a pressure-sensitive luminescent coating based on Pt(II)-porphyrin self-assembled monolayers

A pressure-sensitive luminescent coating (PSLC) applicable to the visualization of pressure distributions in micro-scale flow devices was developed. Pt(II)-porphyrin was synthesized and covalently attached to the surface of indium tin oxide (ITO) glass plates by a self-assembled monolayer (SAM) process. The UV-visible absorption spectrum, pressure and temperature sensitivities and photostability of the PSLC were then measured to characterize the developed PSLC. It was found that (a) the chemisorption of the porphyrin did not greatly perturb the molecular orbitals of the porphyrin responsible for its photophysics, (b) the pressure dependency of the luminescent intensity of the PSLC obeyed a power function curve and the pressure sensitivities at 273, 293, 313 and 333 K were obtained in the pressure range from 5 to 120 kPa, (c) the luminescent intensity of the PSLC almost linearly decreased with temperature and the temperature sensitivities at 5, 40, 100 and 120 kPa evaluated in the temperature range from 273 to 333 K were −0.67, −0.72, −0.75 and −0.78%/K, respectively and (d) the decrease in the luminescent intensity of the PSLC after a 30 min exposure to an excitation light was 1.23% of its initial intensity and much smaller than that of Pt(II)-porphyrin absorbed on a TLC (thin-layer chromatography) sheet.

A Novel Pressure-Sensitive Luminescent Coating for Microscale Flow Visualization

A novel pressure-sensitive luminescent coating of Pt(II) porphyrin has been developed for microscale flow visualization. A Pt(II) porphyrin with activated pentafluorophenyl esters in the side chains was synthesized and then covalently attached to indium tin oxide glass by the self-assembled monolayer technique to make the pressure-sensitive luminescent coating. Its pressure sensitivity was measured with a calibration chamber in a pressure range from 1 to 100 kPa. It is found that the current coating is more sensitive than that of the coating previously developed by Sakamura et al. (Meas. Sci. Technol. 26, 064002, 2015).

Shock Wave Interaction with a Solid Body Floating in the Air

A new shock tube system for the study of shock wave interaction with a solid body floating in the air has been developed. The system consists of a horizontally placed shock tube and a solid-body injecting device, which is mounted on the floor of the test section of the shock tube. A solid body initially placed on the shock tube floor was tossed into the air with the injecting device and then collided with a planar shock wave, which is generated by rapturing the diaphragm between the driver and the driven sections of the shock tube. By tuning the rapturing time of the diaphragm, we can make the shock wave interact with the solid body when it reaches the top of its trajectory almost at rest. In order to demonstrate the applicability of the present system, the shock-induced motion of a hexahedral solid body and the flow field around it were recorded using the shadowgraph technique coupled with a high-speed video camera. Representative results from the present experiments are reported in this paper.

Visualization of Surface Pressure Distributions on a Rotating Model Using a Pressure-Sensitive Paint

The objective of the present work is to study the feasibility of the pressure-sensitive paint (PSP) technique for pressure measurements on rotating objects. The PSP used was composed of a porphyrin derivative (H 2TFPP) and a silica-gel thin-layer chromatography plate. The illumination sources were arrays of blue LED, and the detecter was a CCD camera with 12 bit intensity resolution. In the experiments, the shutter of the CCD camera was left open and a rotating model was flashed repeatedly as it came into position, building up a phase-averaged image on the CCD camera. The present preliminary experiments show that the deformation of the model under air loads seriously affects the PSP measurements on rotating bodies.

Optical measurements of high-frequency pressure fluctuations using PSP and Cassegrain optics

The dynamic response of a pressure-sensitive paint (PSP) to high-frequency pressure fluctuations was studied experimentally. The PSP was composed of meso-tetra(pentafluorophenyl) porphine and a commercial silica-gel thin-layer chromatography plate. Pressure fluctuations at frequencies on the order of kilohertz were produced on a flat plate by chopping an underexpanded air-jet issuing from a converging nozzle with an exit diameter of 2 mm and then measured by using a newly developed, optical pressure measurement system (OPMS) with Cassegrain optics. Pressure traces obtained by the OPMS and their amplitude spectra are compared with those obtained by a conventional pressure transducer. The results reveal that the present OPMS are feasible for measuring periodic high-frequency pressure fluctuations with a high spatial resolution, and that the present PSP can follow pressure fluctuations at frequencies of several kilohertz at least.