Tateyuki Suzuki

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.

An experimental analysis of oblique shock reflection over a two-dimensional multi-guttered wedge

The oblique shock reflection over a multi-guttered model wedge is investigated at constant Mach number. The experimental parameters were the reflecting wedge angle and the depth of the gutter. It is found that, unlike the case of a smooth surface, the wave structure is not self-similar but similar with respect to the coordinate system made dimensionless by the depth when the wedges are geometrically similar (regardless of Reynolds number based on the depth). Again, unlike the smooth surface, the wave structure is essentially unsteady, and the entire body of waves reflected from the bottom of the gutters play a key role in the configuration of a precursory reflected wave as well as in the behavior of the triple point. The slope of the triple point trajectory suggests that it approaches asymptotically that for a smooth surface.

Non-self-similar behavior of the von Neumann reflection

The purpose of the present paper is to consider the von Neumann reflection (vNR) which takes place for a small incident shock Mach number and a small wedge angle. A series of experiments has been performed with ordinary smooth straight wedges and step-like wedges that simulate the former. The reflection configuration over the step-like wedge has suggested unsteady characteristics of the vNR. Contrary to the established notion of shock reflection phenomena over straight wedges, while the triple point trajectory was approximately a straight line through the apex of the wedge, the vNR showed unsteadiness in the relation between angles of incidence and reflection (ωi,ωr), and thus the flow-field proved to be non-self-similar near the triple point. Based on the measured values, the incident angle for the reflected wave and the Mach number of the flow ahead of the reflected wave were estimated. These values show that the reflected wave is not a Mach wave, but it moves on the (ωi,ωr)-plane almost along a trivial...

Regular Reflection of a Shock Wave Over a Porous Layer: Theory and Experiment

The regular reflection of a shock wave over a porous layer has been investigated both theoretically and experimentally. Two model types are considered. One may be called a simple sink theory, in which the deflection angle is the only parameter taking the sink effect of the porous layer into consideration and the detail of the flow in the porous layer is not taken into account. The other model is a more realistic one, in which the pressure wave and the gas flow in the porous phase are considered as well as in the gas phase. In the former, by assuming the deflection angle, the results are compared with the experiment. In the latter, however, since the coupled problem for both phases is too complicated to analyze theoretically, we analyzed two limiting cases and showed in a physical plane the domain where the solution of the coupled problem is possible.

An experimental analysis on shock reflection over the two‐dimensional model of a dust layer

The shock reflection over a multi‐guttered wedge is investigated. The result is compared with the case with a dusty surface. It is found the wave structure is not self‐similiar but similar with respect to a nondimensional coordinate based on the pitch of gutters. The wave structure is essentially unsteady and the entire waves reflected from the bottoms of gutters play a key role to the configuration of reflected wave.

Examination of the von Neumann paradox for a weak shock wave

Oblique reflections of a weak shock wave have been investigated both theoretically and experimentally. A modified three-shock theory is introduced to explain the well-known von Neumann paradox for weak Mach reflection. As a physical reality, the triple point is not a mathematical point and the slipstream has a finite thickness. Consequently, the effect of the slipstream divergence behind the triple point and the minute pressure differences on both sides of the slipstream are taken into account, and both these effects are examined numerically. The angle of divergence is given parametrically in order to calculate some characteristics around the triple point, e.g., the angle of reflection. Numerical results are compared with measurements, and characteristics of solutions are examined. It is found that for weak Mach reflection the modified three-shock theory gives physically realistic solutions, even when von Neumanns three-shock theory has no solution. It is also found that the divergence effect of the slipstream is predominant over the pressure difference. All the experimental data are found to exist in the domain bounded by von Neumanns classical theories and the modified three-shock theory proposed here. The experimental evidence of slipstream divergence is presented.

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.

The von Neumann paradox for strong shock waves

Up to the present, the von Neumann paradox has been mentioned only for weak shock waves, and the classical theories have been considered to be valid for strong shock waves. In the present paper, we discovered experimentally that the paradox also occurs in strong shock waves for the same reason as in weak shock waves. We also explain why it has not been observed so far and demonstrate that the essence of the problem lies in the transport properties of the fluid.

Unsteady behavior of Mach reflection over a particulate layer

Abstract Results of oblique shock reflection over a particulate layer are reported. A variable parameter was the reflecting wedge angle. Other parameters such as an incident shock Mach number and a mean diameter of particles deposited on the wedge were fixed at 1.41 and 30mm, respectively. The wave structure is compared with that for a two-dimensional rough surface model, and their qualitative resemblance reveals that, although the structure is more complicated than the two-dimensional case, the physical phenomenon which plays an essential part (sink effect) is the same in both cases. It is clearly ascertained that the behavior of the triple point is unsteady and self-similarity of wave structure no longer holds.