Response Of Pressure-sensitive Paint Research Articles

Measurement of pressure fluctuation distribution on a flat wall behind supported square cylinder with pressure-sensitive paint

The pressure fluctuation distribution on the floor surface behind a supported square cylinder in a turbulent boundary layer was measured by using pressure-sensitive paint (PSP). Specifically, the accuracy and frequency response of PSP at a Mach number around M = 0.3 were examined. Four square cylinders with different dimensions were investigated in the same turbulent boundary layer, and the detailed relationship between these conditions and Kármán vortex shedding structures was discussed. The values measured with PSP had a similar trend to those measured with a pressure transducer at up to 5 kHz. The peak power spectral density (PSD) of the pressure fluctuations due to Kármán vortex shedding was observed within an error of approximately 30 % at up to frequencies greater than 3 kHz. Moreover, the peak frequency of Kármán vortex shedding was found to decrease with the cylinder height in a manner similar to a previous empirical equation for the Strouhal number. The peak PSD value for the shortest square cylinder (h/w = 3.5, h/δ = 1.1) was twice as high as that for the other cylinders; also, the high-pressure fluctuation area in this case did not spread downstream, which suggests that the flow from the top of the cylinder affected the Kármán vortex shedding generated from the cylinder’s sides. One contour of the two main modes extracted for the highest PSD via the right singular vector vi at the Kármán vortex frequency had an asymmetric distribution behind the supported taller square cylinders (h/w ≥ 7.0, h/δ ≥ 2.3). This result is considered to be derived from the Kármán vortex shedding being mainly generated from the mainstream rather than the boundary-layer flow.

Evaluation of Frequency Response of Pressure-Sensitive Paint to Sound Pressure Fluctuation

Evaluation of Frequency Response of Pressure-Sensitive Paint to Sound Pressure Fluctuation

Dynamic Mode Decomposition of Fast Pressure Sensitive Paint Data.

Fast-response pressure sensitive paint (PSP) is used in this work to measure and analyze the acoustic pressure field in a rectangular cavity. The high spatial resolution and fast frequency response of PSP effectively captures the spatial and temporal detail of surface pressure resulting in the acoustic pressure field. In this work, a high-speed camera is used to generate a continuous time record of the acoustic pressure fluctuations with PSP. Since the level of the acoustic pressure is near the resolution limit of the sensor system, advanced analysis techniques are used to extract the spatial modes of the pressure field. Both dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) are compared with phase averaging for data analysis. While all three techniques effectively extract the pressure field and reduce the impact of sensor noise, DMD and POD are more robust techniques that can be applied to aperiodic or multi-frequency signals. Furthermore, DMD is better than POD at suppressing noise in particular regions of the spectrum and at effectively separating spectral energy when multiple acoustic excitation frequencies are present.

Ultrafast pressure-sensitive paint for shock compression spectroscopy

A pressure-sensitive paint (PSP) consisting of rhodamine 6G (R6G) dye in poly-methylacryate (PMMA) polymer is studied during nanosecond GPa shock compression created by km s−1 laser-launched layer plates. In contrast with conventional PSP, whose response time is limited to microseconds by diffusion of O2 in porous materials, the response time of this PSP is limited to ∼10 ns by fundamental photophysical processes. The mechanism of shock-induced PSP intensity loss is shown to be shock-enhanced intersystem crossing, which transfers some R6G population from the emissive S1 state to the dark T1 state. Simulations of dye photophysics and comparisons to experiment show that the PSP is sensitive to the complicated time-dependent density profiles produced in PMMA by different duration shocks. The risetime of the PSP response is limited by the S1 lifetime under shock compression. The fall time is limited by the T1 lifetime, which can be decreased by adding triplet quenchers. The PSP can function in two modes. When dissolved O2 (a triplet quencher) was eliminated, the fall time became relatively slow (microseconds), and the PSP sampled the peak shock pressure and held that value for a long time. When dissolved O2 was present, the intensity loss recovery became faster, so the PSP could function as a transient recorder of the shock-induced time-dependent density profile.

GS32 ポリマー型感圧塗料を用いた低速流れ場における非定常圧力計測技術

Pressure sensitive paint (PSP) is a useful noncontact measurement technique to obtain continuous pressure distribution on solid surfaces. The application of PSP to low speed flows in mechanical engineering fields, including unsteady flow measurement related to analysis of aerodynamic noise, is highly demanded. Polymer-based PSP has high pressure sensitivity for low-speed flow field, but the unsteady response of the polymer-based PSP is not examined enough. In this study, we investigate the unsteady response of the polymer-based PSP, to evaluate the feasibility of the polymer-based PSP as a measurement tool for unsteady low-speed flows. We have applied the polymer-based PSP in low-speed flow to measurement of unsteady pressure distribution around a circular cylinder, and compared the amplitude spectra of PSP and that of pressure probe, which are obtained by FFT analysis. Furthermore we have visualized the distribution of the integrated intensity of the PSP amplitude spectrum around the peak, to visualize the area with large pressure fluctuation on the cylinder.

Luminescence Lifetime Response of Pressure-Sensitive Paint to a Pressure Transient

Pressure-sensitive paint (PSP) is used to acquire high-fidelity images of steads pressure distributions across surfaces. The PSP luminescence emission response to excitation light depends in a straightforward way on the oxygen concentration (hence air pressure) and the irradiance incident on the PSP lumiphores. Often, however, the phenomenon of interest is unsteady. During a rapid change in pressure. the oxygen concentration within a PSP layer varies with depth. Moreover, the excitation irradiance varies with depth as a result of attenuation, and this affects signal generation when the spatial distribution of oxygen is also changing. Prior studies have been reported on the transient response of PSP using the radiometric technique to detect pressure, we have extended the study by applying a luminescence lifetime technique. Oxygen concentration as a function of time and depth are obtained by solving the mass diffusion equation. with appropriate initial and boundary conditions. We develop a luminescence emission model that takes the spatially varying oxygen concentration and excitation absorption profile into account and relate pressure to the lifetime of the luminescence emission. Oxygen concentration is governed by mass diffusion of oxygen through a PSP layer during a rapid change in pressure, and the absorption of excitation light is governed by Beer's law. The significance of both the mass diffusivity and the optical depth of PSP are assessed. A numerical method was used to solve the mass diffusion equation that allows modeling of the oxygen concentration within the PSP given an arbitrary pressure function. We have used a double-image digital camera to acquire PSP emission lifetime data from several paint thicknesses during a rapid change in pressure. These data were compared to the results predicted by the model.

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 thin-layer 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.

Diffusion Timescale of Porous Pressure-Sensitive Paint

Pressure-sensitive paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic flows require fast time response of the paint. There are two characteristic time-scales that are related to the time response of PSP. One is the luminescent lifetime representing an intrinsic physical limit for the achievable temporal resolution of PSP. Another is the time-scale of oxygen diffusion across the PSP layer. When the time-scale of oxygen diffusion is much larger than the luminescent lifetime, the time response of PSP is controlled by oxygen diffusion. In a thin homogenous polymer layer where diffusion is Fickian, the oxygen concentration 1021 can be described by the diffusion equation in one-dimension.

Accuracy of Pressure-Sensitive Paint

Uncertainty in pressure sensitive paint (PSP) measurement is investigated from a standpoint of system modeling. A functional relation between the imaging system output and luminescent emission from PSP is obtained based on studies of radiative energy transports in PSP and photodetector response to luminescence. This relation provides insights into physical origins of various elemental error sources and allows estimate of the total PSP measurement uncertainty contributed by the elemental errors. The elemental errors and their sensitivity coefficients in the error propagation equation are evaluated. Useful formulas are given for the minimum pressure uncertainty that PSP can possibly achieve and the upper bounds of the elemental errors to meet required pressure accuracy. An instructive example of a Joukowsky airfoil in subsonic flows is given to illustrate uncertainty estimates in PSP measurements.

Step response of pressure-sensitive paints

An experimental and analytical characterization of the response of three typical pressure-sensitive paint (PSP) formulations to a step change in pressure is presented. The three PSP formulations tested have all been previously used in wind-tunnel experiments and have been shown to have acceptable aerodynamic surface properties and mechanical durability. The time response of the PSP coatings is dependent on the diffusion of oxygen through the PSP binder material with typical time constants ranging from 0.05 to 2.5 s. The PSP response is best characterized by a two-term exponential decay function representing a complex first-order dynamic system. In contrast, a standard pressure transducer responds as a second-order dynamic system. The two-exponential curvefit provides a convenient way to compare the time response of different PSP formulations. A mass diffusion model of the PSP response is also presented that is capable of predicting the time response of PSP layers. Nomenclature Aj = constant in mass diffusion solution, Eq. (7) a = binder layer thickness B = constant in two-exponential curvefit, Eq. (10) Ci, C2 = constants in two-exponential curvefit, Eq. (10) Dm = mass diffusivity, Eq. (5) /i, /2 = functional relationships / = light intensity N, n = mass concentration in the binder layer P = pressure R = calibration constant, Eq. (1) S = calibration constant, Eq. (1) x = distant above the substrate e}, e2 = exponential decay terms, Eq. (10) X = wavelength A./ = eigenvalues in mass diffusion solution, Eq. (7) a = Henry's constant, Eq. (2) TI , T2 = time constants, Eq. (10) r = time constant, Eq. (8) Subscripts