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In this paper, a fast-PSP measurement system using the intensity method is constructed to capture the fluctuating pressure field generated by the vertical supersonic (Ma = 1.2) jet impingement on a plate at different impingement distances. The paint formulation is optimized by adding a specific proportion of epoxy resin binder to PC-PSP primer, resulting in no significant peeling even after approximately 100 jet impingements. The light intensity decreased by 12.75% over 35 jet impingements (Ma = 0.7–1.2) without adjusting the light source power. The paint is calibrated and found to have a response time of 83 μs, a pressure sensitivity of 0.5833%/kPa, and a temperature sensitivity of 1.9%/K at 20 °C. The experiment is conducted in an anechoic chamber to investigate the effect of vertical jet impingement on a flat plate with impingement distances (L/d) ranging from 2 to 5. The PSP system captured dynamic pressure signals with a frequency of up to 9212 Hz (L/d = 2). Analysis of the surface pressure distribution in a period showed that an alternating axisymmetrical ring structure is formed in the periphery due to the interaction of expansion and compression waves at the impingement center. The evolving radius of the ring structure over time indicated that its outward expansion speed initially increases and then decreases. The proposed PSP measurement system provides technical assistance for investigating noise mechanisms in close-range vertical jet impingement. [ABSTRACT FROM AUTHOR]

The back pressure rise in a supersonic air intake could affect the engine performance and, in extreme conditions, result in a catastrophic unstart phenomenon. The present study compares different back pressure states that occur during an unstart of a mixed-compression air intake at Mach 3 using a fast-response pressure-sensitive paint, with an emphasis on the isolator flow. At low back pressure, the isolator dynamics is strongly correlated with the unsteadiness around the external compression corner. At high back pressure, a normal shock train dictates the isolator flowfield from its leading shock foot downstream. At the onset of unstart, an oblique shock train transpires involving large-scale flow separation, boundary layer thickening, and mitigated unsteadiness at the isolator floor. Like in previous studies, the prominence of low-frequency unsteadiness and upstream wave propagation is observed at high back pressure. However, in addition, the present study shows strong upstream communication of back pressure in a narrow frequency band through acoustic mechanisms, that eventually leads to the intake unstart. At the onset of unstart, the prominent frequency varies linearly along the isolator length, matching closely with the half-wave resonator model. Suppressing the oscillations at the preferred frequencies could be a promising control strategy to mitigate or delay intake unstart. When the intake unstarts, a 3D bifurcated shock stands at the inlet and the unsteady flow spillage takes place around oblique shocks off the sidewalls at low frequencies. [ABSTRACT FROM AUTHOR]

The surface pressure field generated by a supersonic impinging jet on a vertical flat plate was measured using a pressure-sensitive paint (PSP) and a double-pulsed laser. The Mach number of the jet was M j = 1.23 and the position of the flat plate was h/D = 4.5. A significant peak at St = 0.41 (15.2 kHz) was observed in the spectra measured by a microphone, and unsteady pressure transducers. The feedback loop involved in the acoustic loading occurred at this frequency. Coherent structures of the flow were extracted by applying the azimuthal Fourier decomposition and the dynamic mode decomposition (DMD) to PSP images on the impingement plate. Axisymmetric modes expanding outward from the impingement point of the jet were observed for the azimuthal mode m = 0. Two helical modes related to the feedback loop were identified for |m| = 1. It was confirmed that the RMS values of the amplitudes of these DMD modes were larger than the other modes. The frequencies of these DMD modes were St = 0.39 (14.3 kHz) and St = 0.37 (13.7 kHz), respectively. Coherent structures associated with phenomena faster than 10 kHz were successfully extracted from PSP measurement data. [ABSTRACT FROM AUTHOR]

This study experimentally determines high-frequency aeroacoustic noises of the high-speed dual-impinging jet, focusing on the generation and evolution mechanism between impingement tones modes and far-field acoustic spectra. The variables of the high-speed impinging jet are Mach number (Ma = 0.9 and 1.1), fixed diameter (D) of nozzle, nozzle spacing (3.5D), and impingement distance (4D). A novel fast-responding pressure-sensitive paint (fast-PSP) with a significantly extended frequency response ability was designed to develop an accurate phase-resolving propagation process of aeroacoustic noises and handle high impingement momentum challenges posed by the high-speed impinging jet. The PSP raw data were enhanced by calibration, image restoration, and proper orthogonal decomposition filtering. Two distinct far-field spectral characteristics were identified based on synchronized acoustic measurements. The existence of the stagnation region affected by the fountain effect in the dual-impinging jet was determined using spatial–temporal cross-correlation analysis. Subsequently, the concurrent axisymmetric dual annulus mode and its coupling behavior at Ma = 0.9 and the non-axisymmetric helical mode and its periodic fragmentation-reconstruction patterns at Ma = 1.1 were identified by spectral proper orthogonal decomposition. Finally, the spatial–temporal evolution of the phase-locked first-order mode was extracted, and the transient variations of coherent structures and their mechanisms for discrete tone noise generation were quantitatively investigated. The expansion and coupling of the dual annulus modes promoted the dominance of single-tone peaks across the entire acoustic spectrum. The helical mode, exhibiting both rotational and expansion behaviors, enhanced the coherent vorticity at the periphery of the coherent structures, resulting in intense impingement tones sound sources. [ABSTRACT FROM AUTHOR]

The shock/boundary-layer interaction induced by a 20° compression ramp in a Mach 2 flow was investigated using fast pressure-sensitive paint with a bandwidth of about 10 kHz. The mean separated flow length-scale is about two upstream boundary layer thicknesses, which indicates the interaction is weak. The primary analysis consists of cross-correlations, coherence, and time-domain filtering. Two different frequency bands were investigated: low-frequency (f < 2000 Hz; StL < 0.1) and mid-frequency (0.1 < StL < 0.26). The low-frequency band time sequences and coherence reveal the shock-foot motion is mainly correlated with the reattachment region, which is indicative of the well-established breathing motion of the separation bubble. The breathing motion is observed to occur locally and globally (spanwise-averaged). Furthermore, in the low-frequency band, fluctuations in the upstream boundary layer are moderately correlated with the reattachment region fluctuations, but show no correlation with the intermittent region fluctuations. In the mid-frequency band, the intermittent region, separation bubble and reattachment region all exhibit significant correlation with the upstream boundary layer fluctuations, with the upstream fluctuations leading. The time-sequences in this frequency band reveal broad regions of pressure fluctuations that sweep through the interaction and affect the entire interaction. There is no known turbulent source for such large-scale fluctuations and they are believed to be due to a wind tunnel phenomenon. It is concluded that the dominant low-frequency breathing motion follows an oscillator model, but there remain significant correlations to upstream fluctuations that are not tied to the dominant breathing motion and seem to follow an amplifier model. [ABSTRACT FROM AUTHOR]

Image registration is an essential step in the data processing of pressure-sensitive paint (PSP) measurements. As PSP technology is gradually expanded to increasingly harsh environments, it faces challenges such as severe image misalignment due to model deformations/motions, which pose difficulties to traditional feature-based registration algorithms. To improve registration accuracy and efficiency, we propose an end-to-end image registration method based on deep learning. Initially, a PSP dataset based on PSP images is constructed through data augmentation. Three types of residual network and three training strategies are then adopted to prepare the deep-learning model for automatic image registration. The optimal combination of the residual network and training strategy is selected for validation using fabricated PSP images and outperforms two traditional algorithms (i.e., the Sift and Watershed methods). Finally, the performance of the deep-learning method is compared with that of traditional algorithms adopting a new metric of the overlapping rate for assessing the registration accuracy on experimental PSP images. The results show that the deep learning method outperforms the traditional algorithms in terms of registration accuracy and robustness. [ABSTRACT FROM AUTHOR]

Additive manufacturing technologies increasingly revolutionize current production techniques for object manufacturing. Particularly, fused deposition modeling (FDM) strongly impacts production processes by enabling the cost‐effective and efficient creation of structures with complex designs and innovative geometries. The use of conductive filaments in FDM printing is paving the way for the advancement of entirely printed sensors and circuits, although this domain is still in its early stages. In this article, the design and production of bilayer deformable pressure sensors fabricated using conductive thermoplastic polyurethane are investigated. The potential to vary the mechanical and electrical characteristics of FDM‐printed components by adjusting printing parameters is explored. The influence of different levels of material infill (20%, 50%, and 100%) and different contact geometries between layers (domes, pyramids, and cylinders) is studied. Electromechanical tests are carried out to characterize the sensor, applying pressures up to 22 kPa. The 3D‐printed pressure sensors demonstrate tunable mechanical and electrical sensitivities at different infill values, with the highest value of −6.3 kPa−1 achieved by using a pyramid layer at 100% infill. Sensor outputs registered during cyclic tests show reproducible responses with a wide range of sensitivity, paving the way for applicability in recording both static and periodic pressure changes. [ABSTRACT FROM AUTHOR]

Fast pressure-sensitive paint (PSP) was applied to an inlet/isolator designed using the Osculating Internal Waverider Inlet with Parallel Streamlines (OIWPS) method. The dorsal isolator surface pressure was measured using anodized-aluminum PSP through transparent cast acrylic that makes up the ventral portion of the isolator. Temperature-sensitive paint was utilized to correct for the PSP's temperature sensitivity. The model was tested under Mach 5.7 flow at Re = 8.5 × 10 6 /m and 10.2 × 10 6 /m in the AFOSR–Notre Dame Large Mach-6 Quiet Tunnel (ANDLM6QT) under conventional noise conditions. Flow phenomena, such as shocks originating in the inlet and flow separation at the throat, were visualized with high spatial resolution. The dynamics measured by the PSP and pressure transducers matched well where the spectral signal-to-noise ratio was above unity. Power spectral densities showed significant frequency content at ≈ 1 kHz in the shock-wave/boundary-layer interaction (SWBLI) regions. Coherence analysis showed a linear relationship between the unsteady pressures at locations underneath different SWBLI in the isolator, with the exception of the Busemann throat shock. Temporal correlation of shock positions indicated that disturbances propagated downstream at 114% of the core-flow velocity; however, improved calculations of the core-flow velocity are needed to refine this assessment. The surface pressure fields at Re = 8.5 × 10 6 /m and 10.2 × 10 6 /m were quantitatively very similar, and the results in the ANDLM6QT were qualitatively similar to previous studies in the Boeing/AFOSR Mach-6 Quiet Tunnel under noisy flow. [ABSTRACT FROM AUTHOR]

Pressure-sensitive paint (PSP) was applied to the surface of a NACA0012 airfoil to investigate pressure fluctuations associated with trailing edge (TE) noise under low-velocity flow conditions. The primary focus is to assess the feasibility of employing laser pulses exposed at the airfoil surface to mitigate TE noise. However, the weak pressure fluctuations accompanying TE noise pose a challenge, as they are overshadowed by image sensor noise in high-speed cameras capturing PSP emission changes. To address this issue, a novel time-resolved phase-locking technique was introduced, utilizing the signal from a semiconductor pressure transducer at the trailing edge as a phase-lock trigger source. By repetitively conducting phase-locked measurements (1150 times), time series ensemble averaged data based on PSP emission images were obtained, enabling the capture of these subtle pressure fluctuations. Quantitatively, fluctuations with a dominant frequency of 679 Hz and an amplitude of 50 Pa are resolved within an accuracy of about 15 Pa, achieved at a recording rate of 19.2 kHz. Both the suppression and subsequent redevelopment of the pressure field with the TE noise offer valuable insights into the dynamics of TE noise and open avenues for targeted noise reduction strategies in aerodynamic applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a photodegradation correction method for the dual-luminophore pressure-sensitive paint (PSP) measurement using lifetime-based imaging, which was proposed for correction of the temperature-induced error but has suffered from photodegradation in the previous studies. We introduced a parameter that characterizes the photodegradation of a dual-luminophore PSP as the intensity ratio between the two luminophores. The changes in the calibration coefficients for the pressure and the temperature due to photodegradation were corrected based on this parameter. In this study, a coupon-based calibration test was performed, and the luminescence characteristics of the dual-luminophore PSP including photodegradation were investigated. Then, the proposed method was applied to a coupon-based validation test and a jet impingement test, and the effectiveness of the method was evaluated by comparing results with and without correction. The pressure measurement accuracy was significantly improved by photodegradation correction. [ABSTRACT FROM AUTHOR]

This study investigated unsteady pressure measurements on a pitching OA309 airfoil at a Mach number of 0.1 using a fast-responding pressure-sensitive paint (fast PSP). Two commonly used data acquisition methods applicable to fast PSPs, namely the real-time intensity-based method and the single-shot lifetime-based method, were separately used to obtain the pressure distributions on the upper surface at a reduced pitching frequency (k = πfc/U∞) of 0.074. The signal-to-noise ratio, influences of model motion, and temperature-induced errors associated with the two methods were compared to explore the advantages and disadvantages of the methods. The real-time intensity-based method outperformed the single-shot lifetime-based method in pressure measurements on moving models with very low speeds. Flow separation and reattachment were identified according to the temporal- and spatial-resolved pressure fields obtained through the real-time intensity-based method; finally, the effects of the pitching amplitude and the leading-edge vortex generators were studied. The results showed that flow separation was postponed as the pitching amplitude increased, while flow reattachment occurred earlier on the airfoil equipped with leading-edge vortex generators. [ABSTRACT FROM AUTHOR]

Roughness, in various distributions and on various scales, is widely encountered in turbine modules and has a complex modulating effect on the distribution of film cooling effectiveness. In this study, the fast-response pressure-sensitive paint technique was utilized to analyze the steady and unsteady behaviors of film cooling effectiveness under various roughness conditions. Two roughness conditions (upstream roughness and the combination of upstream and downstream roughness) were examined at three roughness scales (ks/D = 0.016, 0.129, and 0.782) and three blowing ratios (M = 0.5, 1.0, and 1.5). Comparisons of the steady behaviors of cooling effectiveness revealed that upstream roughness was the primary factor influencing cooling effectiveness for the adequate film attachment (M = 0.5 and 1.0) and that the cooling effectiveness deteriorated with rising ks/D. Downstream roughness improved the cooling effectiveness in cases with poor film attachment (M = 1.5). Considering that the distribution of film cooling effectiveness is modulated by the vortical structures of jet in crossflow, the unsteady behaviors of roughness-affected cooling effectiveness were analyzed through proper orthogonal decomposition. Upstream roughness influenced the counter-rotating vortex pair and horseshoe vortex (HV) signatures by separately widening and shortening the patterns in the lateral and streamwise directions, a trend that became more pronounced with increasing ks/D values. Moreover, larger roughness scales at lower blowing ratios caused asymmetry in the signatures. Downstream roughness primarily affected the signatures through local morphological variations, inducing oscillations in modal patterns. For attached films, downstream roughness had a nonsignificant impact, while for detached films, disturbances caused by downstream roughness resulted in vague and asymmetric modal patterns. Evaluation of the reconstructed cooling effectiveness revealed that roughness tended to affect the unsteady behavior of HV-modulated cooling effectiveness at high frequencies. These clarified steady and unsteady behaviors across various roughness conditions provide references for improving film-cooling structures to accommodate diversely roughened turbine modules. [ABSTRACT FROM AUTHOR]

In addressing the broad spectrum of applications for optical pressure sensors, their predominant drawback lies in their limited sensitivity to pressure fluctuations. To overcome these constraints, this study introduces a luminescent manometer harnessing the emission properties of Cr3+ ions in Li3Sc2(PO4)3, operational in three distinct reading modes: spectral shift, ratiometric, and lifetime‐based. Notably, the conducted research establishes this luminescent manometer as the most sensitive reported to date in both spectra shift (λ/dp = 23.9 nm/GPa) and lifetime‐based (SR = 93.56%/GPa) modes. A departure from conventional lifetime‐based luminescent pressure gauges, Li3Sc2(PO4)3:Cr3+ exhibits a prolongation of lifetime of the 4T2 state correlated with increasing pressure. The advantages extend beyond sensitivity, encompassing a three‐fold surge in emission intensity with pressure escalation from ambient to 3 GPa, coupled with minimal susceptibility to temperature‐induced fluctuations. Unquestionably, Li3Sc2(PO4)3:Cr3+ showcases remarkable manometric performance, validating its significant application potential in diverse scenarios within the realm of optical pressure sensors. [ABSTRACT FROM AUTHOR]

Three-dimensional effects of sidewalls on the low-frequency unsteadiness of the shock-wave/boundary-layer interaction (SBLI) are of academic and practical importance but not yet well understood. Considerable attention has been paid to the viscous effect of sidewalls, whereas the potential inviscid confinement effect of sidewalls has received little attention. The present work provides experimental evidence of multiscale spanwise travelling waves crossing the separation front under the confinement of sidewalls. Global pressure measurements were made for a sidewall-confined 24? compression ramp interaction in Mach-2.83 flow using fast-responding pressure-sensitive paint. The unsteady pressure in a statistically two-dimensional intermittent region suggests that in addition to the canonical streamwise oscillation, the separation front exhibits significant low-frequency, multiscale spanwise distortion. Modal analysis further reveals that multiscale spanwise unsteadiness has higher intensity and frequency than the streamwise oscillation. Such strong spanwise unsteadiness calls attention to the low-frequency unsteadiness in previous sidewall-confined SBLI experiments and encourages further study on the mechanism of the confinement effect. [ABSTRACT FROM AUTHOR]

Unsteady pressure-sensitive paint (i-PSP) measurements were performed at a sampling rate of 30 kHz to investigate the near-endwall blade suction surface flow inside a low-pressure turbine cascade operating at engine-relevant high-speed and low-Re conditions. The investigation focuses on the interaction of periodically incoming bar wakes at 500 Hz with the secondary flow and the blade suction surface. The results build on extensive PIV measurements presented in the first part of this two-part publication, which captured the 'negative-jet-effect' of the wakes throughout the blade passage. The surface pressure distributions are combined with CFD to analyze the flow topology, such as the passage vortex separation line. By analyzing data from phase-locked PIV and PSP measurements, a wake-induced moving pressure gradient negative in space and positive in time is found, which is intensified in the secondary flow region by 33% with respect to midspan. Furthermore, two methods of frequency-filtering based on FFT and SPOD are compared and utilized to associate a pressure fluctuation peak around 678 Hz with separation bubble oscillation. [ABSTRACT FROM AUTHOR]

Particle image velocimetry (PIV) measurements were performed inside a low-pressure turbine cascade operating at engine-relevant high-speed and low-Re conditions to investigate the near-endwall flow. Of particular research interest was the dominant periodic disturbance of the flow field by incoming wakes, which were generated by moving cylindrical bars at a frequency of 500 Hz. Two PIV setups were utilized to resolve both (1) a large blade-to-blade plane close to the endwall as well as midspan and (2) the wake effects in an axial flow field downstream of the blade passage. The measurements were performed using a phase-locked approach in order to align and compare the results with comprehensive CFD data that are also available for this test case. The experimental results not only support a better understanding and even a quantification of the wake-induced over/under-turning inside and downstream of the passage, they also enable the tracing of the 'negative-jet-effect', which is widely known in the CFD branch of the turbomachinery community but is seldom visualized in experiments. The results also reveal that the bar wake periodically widens the blade wake by up to 165%, while the secondary flow is less affected and exhibits a phase lag with respect to the 2D-flow effects. The results presented here are an essential basis for the subsequent investigation of the near-endwall blade suction surface effects using unsteady pressure-sensitive paint in the second part of this two-part publication. [ABSTRACT FROM AUTHOR]

What will the low-carbon cities of tomorrow be made from? We see an unexpected answer today in the return of 'premodern'/'preindustrial' materials to central cities and skylines. Champions of new mass timber materials have driven a race on iconic 'plyscrapers' and, increasingly, novel systems of industrial prefabrication. Drawing on the notion of sociotechnical imaginaries, we explore how advocates attempt to 'fix' desirable future cities and urban bioeconomies through this biomaterial. In doing so, we suggest that mass timber's emergent sociotechnical imaginary embodies a distinct kind of futuring, which we label 'nostalgic futurism', conjoining 'technofuturist' and 'nostalgic-reparative' visions. We find that, on the one hand, mass timber proponents embrace competitive novelty, uniting drives for architectural distinction and high-tech disruption. On the other hand, aesthetic advocates put forward visions around the material's more traditional premodern/preindustrial associations, in narratives of biophilic design which claim therapeutic benefits of contact with visible nature in buildings. These conjoined forward- and backward-looking compulsions pose tensions and internal contradictions. Nostalgic-reparative visions risk greenwashing and reproducing unequal access to environmental amenities, while reinscribing regressive appeals to an imagined past. Meanwhile, technofuturist drives extend late capitalist growth imperatives and pressures for accelerated material churn in both forests and urban centres—while obscuring tough questions about mass timber buildings' expected lifetimes and claims for long-term carbon sequestration. Conversely, a reimagined mass timber project might support more progressive movements for climate restoration, repair, and reparations. [ABSTRACT FROM AUTHOR]

Maintaining high levels of patient motivation and enjoyment during physical rehabilitation is crucial for achieving optimum therapy outcomes. However, the prolonged and repetitive nature of postural control rehabilitation in children with Developmental Coordination Disorder (DCD) often leads to a rapid decrease in motivation levels. Digital therapy devices and exergames offer valuable solutions to this problem by providing therapists with the ability to incorporate objective outcome measures into their practice. Adjustable Tangible User Interfaces (TUI) are ideal for implementing digital innovation into physiotherapy clinical settings. Therefore, this study aimed to discuss the development rationale and iterative co-creation process of Matti, a pressure-sensitive, adaptable TUI for rehabilitation purposes. A structured overview of TUI requirements within a clinical setting was provided for future developers. The results showed that the Matti device can be used as a viable tool for exergaming rehabilitation. Future investigations on the measurement capabilities are required to enable the reliable adoption of objective outcome measures. The impact of TUI and gamified postural control assessment on patients’ motivation and therapy outcomes should also be evaluated. [ABSTRACT FROM AUTHOR]

An experimental investigation was carried out to study the fluid–structure interactions on a compliant panel subjected to an impinging shock wave and an incoming turbulent boundary layer. These experiments were aimed at understanding the time-averaged and unsteady characteristics of fluid–structure interaction at Mach 2. Two shock impingement locations on the panel (aspect ratio of 2.82), namely the central and three-fourths of the panel length, were tested. The shock boundary layer interactions on a rigid flat plate served as a baseline case. Measurements include shadowgraph and surface oil flow visualizations, panel deflections using a capacitance probe, cavity acoustics using a pressure sensor, surface pressures using discrete pressure sensors, and pressure-sensitive paints. Results show that the interaction on the compliant panel is relatively three-dimensional as compared to a rigid plate with a nominally two-dimensional interaction. Pressure fluctuations on the compliant panel are significantly higher than on the rigid plate, and the fluctuation spectra are multi-modal. Strong coupling at some frequencies was observed between the shock and the panel for both shock impingement locations. The present study suggests that for a compliant panel, the shape of pressure spectra is sensitive to the measurement location on the panel, the panel modifies the pressure distribution around the interaction, and the energy in dominant modes depends on the shock impingement location. [ABSTRACT FROM AUTHOR]

The flow field in a cavity depends on the properties of the upstream boundary layer and the cavity geometry. Comprehensive studies for rectangular cavities have been conducted. This experimental study determines the global surface pressure pattern for elliptical cavities (eccentricities of 0, 0.66 and 0.87) in a naturally developed turbulent boundary layer using pressure-sensitive paint. The ratio between the length (major axis) and the depth is 4.43–21.5, and the freestream Mach number is 0.83. The mean surface pressure distribution of an elliptical cavity resembles that of a rectangular cavity. A change in the value of eccentricity (wall curvature) affects the region for an adverse pressure gradient in an open cavity, an extension of the plateau in a transitional–closed cavity and flow expansion near the front and rear edges. The boundaries between an open, transitional and closed cavities vary. [ABSTRACT FROM AUTHOR]

The effects of the burnt-to-unburnt temperature ratio (T b / T u) (reciprocal density ratio) on thermoacoustic combustion instability were investigated in a hydrogen-rich ram combustor by controlling the inlet air temperature under cruising conditions. Steady and unsteady combustion dynamics were investigated with the simultaneous measurement of combustion pressure and near-infrared (NIR) emissions. Time-resolved NIR images were analyzed using dynamic mode decomposition (DMD) to extract modes of the combustion instability, which show two oscillation modes: longitudinal (500 Hz) and flame-vortex interaction modes (2000 Hz) with a Strouhal number of approximately 0.5. The thermoacoustic combustion instability was not excited at T b / T u = 3.3, but was excited at T b / T u = 2.6 and 2.9. The DMD modes show that the structure of the vortex mode is similar to that of the fourth longitudinal mode at T b / T u = 2.6 and 2.9, indicating that the coupling of the vortex and the fourth longitudinal modes excited the thermoacoustic combustion instability. • The burnt-to-unburnt temperature ratio T b / T u influenced thermoacoustic instability (TI) in a hydrogen-rich combustor. • Dynamic mode decomposition analysis extracted a longitudinal mode (500 Hz) and a vortex mode (2000 Hz). • At low T b / T u , TI was excited owing to the similar structures of the vortex and fourth longitudinal modes. • Vortex mode was changed by the enhanced vortex formation near the injectors at high T b / T u. • At high T b / T u , TI was not excited owing to the low correlation between the vortex and fourth longitudinal modes. [ABSTRACT FROM AUTHOR]

Base pressure fluctuations associated with the large-scale wake structures behind a freestream-aligned circular cylinder and aerodynamic force fluctuations related to them are experimentally investigated in the wind tunnel tests. Measurements at R e D = 6.97 × 10 4 and 1.04 × 10 5 were conducted using pressure-sensitive paint (PSP) and a magnetic suspension and balance system (MSBS) for creating a supportless condition. The obtained pressure fields were mainly analyzed by a modal decomposition combining azimuthal Fourier decomposition and proper orthogonal decomposition (POD). The pressure fluctuations caused by large-scale vortex shedding were observed from the results of frequency analysis for mode coefficients. The states of the fluctuations were classified into three patterns, which are anticlockwise/clockwise circular and flapping patterns. These patterns have been observed in the previous studies for velocity fluctuations in the wake of a freestream-aligned circular cylinder. The conditional sampling analysis revealed that the trend in the amplitude of the pressure fluctuations is different by the state, and the flapping pattern causes a large pressure difference across the cylinder axis. Furthermore, the relationship between the antisymmetric pressure fluctuations and lift fluctuations, which act in the lateral direction of the cylinder, is confirmed. [ABSTRACT FROM AUTHOR]

During the practical operation of gas turbines, relatively cooled air from the compressor and the rim seal is applied in order to prevent mainstream ingestion into the space between the rotor and stator disc cavities, which can prolong the service life of hot components. On the one hand, the purge flow from the rim seal will inevitably interact with the mainstream and result in secondary flow on the endwall. On the other hand, it can also provide an additional cooling effect. In this paper, four rim seal structures, including an original single-tooth seal (ORI), a double-tooth seal (DS), a single-tooth seal with an adverse direction of the coolant purge flow and mainstream (AS) and a double-tooth seal with an adverse direction of the coolant purge flow and mainstream (ASDS), are experimentally and numerically investigated with mass flow ratios of 0.5%, 1.0% and 1.5%. The flow orientation of the coolant from the rim seal is considered as one of the main factors. The pressure-sensitive paint technique is used to experimentally measure the film cooling effectiveness on the endwall, and flow field analysis is conducted via numerical simulations. The results show that the cooling effect decreases in the cases of DS and ASDS. AS and ASDS can achieve a better film cooling performance, especially under a higher mass flow ratio. Furthermore, the structural changes in the rim seal have little impact on the aerodynamic performance. AS and ASDS can both achieve a better aerodynamic and film cooling performance. [ABSTRACT FROM AUTHOR]

Pressure-sensitive paint (PSP) has received significant attention for capturing surface pressure in recent years. One major source of uncertainty in PSP measurements, temperature dependency, stems from the fundamental photophysical process that allows PSP to extract pressure information. The motion-capturing PSP method, which involves two luminophores, is introduced as a method to reduce the measurement uncertainty due to temperature dependency. A theoretical model for the pressure uncertainty due to temperature dependency is proposed and demonstrated using a static pressure measurement with an applied temperature gradient. The experimental validation of the proposed model shows that the motion-capturing PSP method reduces the temperature dependency by 37.7% compared to the conventional PSP method. The proposed model also proves that a PSP with zero temperature dependency is theoretically possible. [ABSTRACT FROM AUTHOR]

Modern gas turbines have evolved by increasing the turbine inlet temperature (TIT) to improve performance. This development has led to a demand for cooling techniques. Among these, the film cooling, which involves injecting compressed air through holes on the turbine surface, is a prominent cooling technique used to protect the turbine surface. In this study, a comparative analysis is conducted between the conventional fan-shaped film cooling hole, primarily used in film cooling techniques, and modified shapes achieved by altering the geometry of the film cooling hole based on a fan-shaped hole to assess and compare the cooling performance on a flat plate surface. The adiabatic film cooling effectiveness was measured for three film cooling holes, the Baseline of a 7-7-7 fan-shaped film cooling hole, namely, Staircase, which had a double-step at the hole exit, and Compound Expansion, which had an additional expanded flow path at the hole leading edge. The used measurement technique was the pressure-sensitive paint (PSP) technique, using nitrogen gas as the foreign gas, and experiments were conducted at a density ratio of 1.0 and blowing ratios ranging from 0.5 to 2.0. The results reveal that the modified holes featured wider lateral expansion at the hole exits, resulting in a broader distribution of the cooling effectiveness in the lateral direction compared to the Baseline. The Staircase shows a better performance, although an overall cooling effectiveness trend similar to that of the Baseline. Furthermore, the Compound Expansion demonstrates an enhancement in the cooling performance with an increased blowing ratio, notably achieving nearly double the cooling effectiveness compared to that of the Baseline at a blowing ratio of 2.0. [ABSTRACT FROM AUTHOR]

Several studies have previously been conducted to improve the cooling performance of film cooling. However, most of the research has conducted experiments with film cooling holes on flat plates, and thus, the results of these studies do not encompass the influence of the complex mainstream behavior within the turbine passage on film cooling. In this study, three different film cooling hole configurations were installed on the endwall of a turbine linear cascade to measure adiabatic film cooling effectiveness and evaluate cooling performance. The film cooling holes compared in the experiment for film cooling effectiveness were a 7-7-7 fan-shaped hole (Baseline), a Baseline with a double-step structure at the hole exit (Staircase), and a Baseline with an additional expanded passage at the hole leading edge (Compound Expansion). A total of nine holes were manufactured on the turbine endwall to assess film cooling performance, as various factors, such as mainstream acceleration, secondary flow within the turbine passage, and so on, can influence film cooling. Adiabatic film cooling effectiveness was measured using the pressure-sensitive paint (PSP) technique. Mass flow ratios ranging from 0.25% to 1.25% of the mass flow rate of a single turbine passage were supplied to the plenum chamber within the test rig. As a result, all experimental results confirmed the impact of secondary flow within the turbine passage on film cooling. In the case of the Staircase, it exhibits an overall cooling trend similar to the Baseline. It shows small cooling performance degradation compared with Baseline due to lift-off, and its double-step structure laterally expanding results in better cooling performance at high mass flow ratio (MFR) conditions. For the Compound Expansion, at low MFR, the momentum of the coolant is lower compared with other configurations, leading to lower cooling performance due to the influence of secondary flow. However, at high MFR, the Compound Expansion provides wider protection compared with other hole geometries and shows high cooling performance. [ABSTRACT FROM AUTHOR]

During its life cycle, packaging comes into contact with various substances and even those it protects. Thus, for example, oil, water, and alcohol, if spilled on the packaging, can damage its functionality. In addition to exposure to chemicals, graphic products (packaging) can be exposed to moisture and UV radiation, which can negatively affect their stability during transport, storage, and handling. The choice of printing substrate can directly affect the stability of prints against different degrading influences. This paper explores the stability of thermochromic (TC) and conventional offset printing inks printed on environmentally friendly printing substrates intended for packaging applications (labelling). Results have confirmed that used printing substrates and printing inks give prints good rub resistance, but somewhat lower stability in terms of ethanol, water, and UV radiation. The choice of printing substrate can directly affect the stability of prints against different degrading influences. The resistance of prints to oil cannot be clearly defined since the samples were altered with the coloration of the oil. It can only be stated that oil reduced the functionality of the TC prints given that the samples were colored by the oil itself. [ABSTRACT FROM AUTHOR]

This paper describes a theoretical method for reconstruction of the skin friction topology in complex separated flows, which is developed based on the exact relation between skin friction and surface pressure through the boundary enstrophy flux (BEF). The key of this method is that a skin friction field is reconstructed from a surface pressure field as an inverse problem by applying a variational method. For applications, the approximate method is proposed, where the composite surface pressure field is given by a linear superposition of the base-flow surface pressure field and the surface pressure variation field and the base-flow BEF field is used as the first-order approximation. This approximate method is constructive in a mathematical sense since a complex skin friction field in separated flows can be reconstructed from some elemental skin friction structures (skin friction source/sink, vortex and their combinations) by a linear superposition of some simple surface pressure structures. The distinct topological features, such as critical points, separation lines and attachment lines, naturally occur as a result of such reconstruction. As examples, some elemental skin friction structures in separated flows are reconstructed in simulations, and the skin friction fields in shock-wave/boundary-layer interactions (SWBLIs) are reconstructed from pressure sensitive paint (PSP) images obtained in wind tunnel experiments. [ABSTRACT FROM AUTHOR]

A novel turbulated cutback structure is designed for trailing-edge cooling, which has smooth-transition protrusions on the cutback surface. Experimental investigations are carried out on the effects of the protrusion configuration and the blowing ratio M on adiabatic cooling effectiveness and convective heat transfer coefficient of the cutback surface using transient thermochromic liquid crystal technology and steady pressure-sensitive paint technology as measuring methods. As M increases, the comprehensive heat transfer performance (heat flux ratio) first increases and then decreases, reaching a peak at M = 1.00. The smooth-transition protrusions effectively enhance the comprehensive heat transfer performance by 12.4 ~ 36.8% of the cutback surface. [ABSTRACT FROM AUTHOR]

All‐solid‐state lithium batteries (ASSLBs) based on sulfide solid electrolytes (SEs) are one of the most promising strategies for next‐generation energy storage systems and electronic devices. However, the poor chemical/electrochemical stability of sulfide SEs with oxide cathode materials and high interfacial impedance, particularly due to physical contact failure, are the major limiting factors to the development of sulfide SEs in ASSLBs. Herein, the composite cathode of MOF‐derived Fe7S8@C and Li6PS5Br fabricated by an infiltration method (IN–Fe7S8) with dissoluble sulfide electrolyte (dissoluble SE) is reported. Dissoluble SE can easily infiltrate the porous sheet‐type Fe7S8@C cathode to homogeneously contact with Fe7S8 nanoparticles that are embedded in the surrounding carbon matrixes and form a fast ionic transport network. Benefiting from applying dissoluble SE and Fe7S8@C, the IN‐Fe7S8‐based cells displayed a reversible capacity of 510 mAh g−1 after 180 cycles at 0.045 mA cm−2 at 30 °C. This work demonstrates a novel and practical method for the development of high‐performance all‐sulfide‐based solid state batteries. [ABSTRACT FROM AUTHOR]

The superposition effect of optimized laidback fan-shaped film cooling holes on a vane was experimentally investigated. The film cooling experiments were conducted using a linear cascade with five vanes and the blow-down cascade facility of the Korea Aerospace University. The Reynolds number calculated using the velocity of cascade exit and chord length of vane was 1.1×106. The film cooling effectiveness (FCE) was investigated by applying a pressure sensitive paint technique with a density ratio of 1.5 (DR) and four different blowing ratios (BR). To focus the superposition of the coolant, each coolant cavity had only a single-row holes and the flow rate for each cavity was separately controlled. Also, test vanes were designed so that the flow disturbance by the upstream non-injecting holes was excluded. The dimensions of the laidback fan-shaped (LBF) hole installed on the vane was derived from a series of experimental optimization processes using a flat plate test section at the DR of 1.5 and BR of 2.0 conditions. The cascade test results presented that FCE of the optimized LBF hole increased as the BR increased and FCE of suction side (SS) showed superior film cooling performance compared to the pressure side (PS). Generally, the FCE obtained by superposing the single-row injection case was well-matched with FCE of multi-row injection cases. The difference between the two results enlarged toward downstream, however, the maximum difference was only 0.03 units. [ABSTRACT FROM AUTHOR]

Highly maneuverable aircraft configurations can be subjected to tail buffeting phenomena at moderate subsonic speeds and medium to high angles of attack. Detailed measurement of the aerodynamic surface pressure fluctuations and the corresponding vibrations is of great importance to investigate these buffeting effects. Fast-response pressure sensitive paint (iPSP) was developed at the German Aerospace Center (DLR) to measure unsteady pressure fluctuation effects in a setup with high-speed cameras. The setup allows a high spatio-temporal resolution of the unsteady surface pressures. In the present paper the iPSP method is applied to a mixed-material, flexible aircraft wind tunnel model with double-delta wing and horizontal tail plane in these flow conditions. The low-speed buffeting effects on the configuration are measured using a synchronized system of five connected high-speed cameras to simultaneously record the unsteady surface pressures with iPSP and the dynamic three-dimensional structural deformation. The present application case is particularly challenging due to low levels of pressure fluctuation in the low-speed regime, multi-frequency aeroelastic phenomena on the model, a long distance between the cameras and the model, as well as the combination of synchronized measurement of unsteady surface pressure and structural deformation. Advanced data analysis methods are applied in a post-processing tool chain to cope with these challenges. The focus of the present paper is the setup of the synchronized measurement chain as well as the data analysis tools. First results are evaluated with respect to iPSP unsteady surface pressures. The root-mean square surface pressures show good agreement with high-fidelity CFD results for the flow conditions of interest. Particular focus of the analysis is on the lessons learned regarding the UV illumination setup, the camera arrangement as well as post-processing tools. [ABSTRACT FROM AUTHOR]

Global surface pressure measurements of a 5.7% scale AFRL Initial Concept 3.X vehicle (IC3X) were obtained using a fast-responding ruthenium-based pressure-sensitive paint (PSP) at the UTSA Mach 7 Ludwieg Tube Wind Tunnel at two different angles of attack, 0° and 2.5°. Static calibration of the paint was performed over a range of 0.386 kPa to 82.7 kPa to relate luminescent intensity to pressure. Details on the facility, paint preparation, application, calibration, and image processing techniques are provided in the manuscript. The results from statistical, spectral, and proper orthogonal decomposition (POD) analyses are presented to characterize the pressure field observed on the model. The experimental results qualitatively follow the expected trends and correspond to the occurrence of shock waves and expansion fans, which were visualized via Schlieren imaging. The theoretical pressure range obtained from conical shock analysis for 0° agrees with the experimentally derived pressure range for the model, and the outliers are attributed to errors in image registration. This study presents preliminary pressure measurements that pave the way for obtaining time-resolved global PSP measurements to train and validate aerothermodynamic machine learning models. [ABSTRACT FROM AUTHOR]

Unsteady pressure-sensitive paint (i-PSP) measurements were performed at a sampling rate of 30 kHz to investigate the near-endwall blade suction surface flow inside a low-pressure turbine cascade operating at engine-relevant high-speed and low-Re conditions. The investigation focuses on the interaction of periodically incoming bar wakes at 500 Hz with the secondary flow and the blade suction surface. The results build on extensive PIV measurements presented in the first part of this two-part publication, which captured the ’negative-jet-effect’ of the wakes throughout the blade passage. The surface pressure distributions are combined with CFD to analyze the flow topology, such as the passage vortex separation line. By analyzing data from phase-locked PIV and PSP measurements, a wake-induced moving pressure gradient negative in space and positive in time is found, which is intensified in the secondary flow region by 33% with respect to midspan. Furthermore, two methods of frequency-filtering based on FFT and SPOD are compared and utilized to associate a pressure fluctuation peak around 678 Hz with separation bubble oscillation.

Luminescent imaging is an area of active research for obtaining physical and chemical properties of a flow. Oxygen-sensitive luminescent probes are used as pressure-sensitive paints to capture unsteady flow over a fluid dynamic surface. The luminescent output is acquired by a photo-sensitive imaging chip, such as CCD and CMOS. Because these imaging chips acquire a digital signal, luminescent imaging is a poor technique for the measurement of small changes in the signal, which is equivalent to or lower than the noise level. A differential luminescent imaging method is studied to capture small fluctuations in a signal level. A theoretical model to describe the differential method is introduced and validated by experiments. Based on the static characterization, it is shown that the differential method possessed its sensitivity to capture fluctuations as small as 0.002% of the mean signal, which is an improvement in sensitivity by a factor of 81 as compared to the conventional luminescent imaging method. [ABSTRACT FROM AUTHOR]

The motivation of this article is to address the ambivalent position of policy analysis when it intervenes in the real-world policy process through policy evaluation. It tackles the underresearched question of the challenges faced by policy analysis in relation to applied research mandates. It argues that policy analysis is constantly at risk of instrumentalisation by politico-administrative players. The article is based on the evaluation of the medical cannabis policy in Switzerland as a case study. The results point out four specific challenges faced by applied policy analysis: political pressure, scientific integrity, access to sensitive data, and epistemic legitimacy. However, applied policy analysis can contribute to de-escalating controversies by presenting a bigger and contextualised picture of the considered political issues. Policy evaluation can identify deficient implementation processes, but also wider mismatches among legislative and societal processes. Hence, although evidence is subordinated to other factors in the decision-making process, evaluations provide an outside perspective, which can help solving controversies around policies. The article contributes to the literature on the politics of policy analysis by showing that confronting policy analysis with practical problems brings both scientific and policy benefits. [ABSTRACT FROM AUTHOR]

This study aimed to develop a two-color pressure-sensitive paint (PSP) that has both high pressure sensitivity and high temperature sensitivity. Different nitrobenzoxadiazole (NBD) derivatives were used as the temperature probe. Among them, NBD-ZY37 demonstrated favorable stability against photodegradation, and its temperature sensitivity in an RTV118-based two-color PSP was −1.4%/°C. Moreover, temperature sensitivity was independent of pressure in the tested temperature range. PtTFPP was used, and its pressure sensitivity was measured to be 0.5% per kPa. The two-color PSP paint underwent further examination in jet impingement experiments. The experimental results indicated that the pressure fluctuation introduced by the shock waves occurred earlier at higher impingement angles. Specifically, when the pressure ratio was 2.38, increasing the impinging angle from 15° to 30° caused the location of the pressure wave to move from s/D at 0.8 to the exit of the nozzle. Simultaneously, the shape of the maximum pressure zone changed from a fan shape to a round shape. Additionally, the jet region expanded when the pressure ratio was increased. [ABSTRACT FROM AUTHOR]

The temperature-sensitive paint (TSP) method, an optical measurement technique, is used for qualitative skin friction visualizations in a wide variety of aerodynamic applications. One such application is the visualization of the laminar–turbulent boundary-layer transition. Optical access to the surface of interest is mandatory for the measurement system, which consists of scientific cameras and LEDs. But the optical access to the area of interest is often impeded by the available windows of the wind tunnel and the wind tunnel model itself, reducing the field of view and the spatial resolution. In some cases, it is of interest to increase the flexibility of the installation of the optical measurement system by reducing its physical dimensions and placing the installation inside the plenum. The DLR Swept flat PlatE Cross-flow TRAnsition (SPECTRA-A) configuration was selected to investigate the influence of two-dimensional steps on the cross-flow-induced boundary layer transition by means of TSP, as part of the EU project Clean Sky 2. The SPECTRA-A configuration consists of two main elements: a flat plate and a displacement body mounted within a very close distance of each other, creating a narrow gap between the two elements. The surface of interest is the area on the flat plate facing the displacement body. The narrow gap limits the utilization of an external camera setup due to poor optical access. A new optical setup consisting of four miniature CMOS machine-vision cameras and five miniature high-power LEDs was integrated into the displacement body. The characteristics of the camera system were analyzed in laboratory tests, establishing that the miniature CMOS machine-vision cameras are suitable for qualitative TSP skin friction visualizations. This was confirmed by successfully measuring the laminar–turbulent boundary-layer transition on the SPECTRA-A configuration. The integrated TSP system is capable of resolving even small variations of the transition location caused by changing the amplitude of the stationary cross-flow instability. The quality of the TSP visualization with the integrated optical system allows for the measurement of the transition location and the wavelength of the stationary cross-flow instability. Overall, a cost-effective TSP visualization system with small space requirements was developed and tested for future applications in wind tunnel models, model support, or side walls of wind tunnels. [ABSTRACT FROM AUTHOR]

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The deterioration of cadmium yellow paints in artworks by Joan Miró (1893–1983) and in painting materials from his studios in Mallorca (Spain) was investigated. Analysis of samples from Miró's paintings and from paint tubes and palettes showed that degraded paints are composed of poorly crystalline cadmium sulfide/zinc cadmium sulfide (CdS/Cd1−xZnxS) with a low percentage of zinc, in an oil binding medium. Cadmium sulfates were identified as the main deterioration products, forming superficial white crusts detected using SR µXANES and µXRD techniques. Time-resolved photoluminescence measurements demonstrated that highly degraded samples display a pink/orange emission from the paint surface with a microsecond lifetime, a phenomenon observed in other degraded cadmium yellow paints. In agreement with recent studies on altered cadmium paints, these results suggest that the stability of the paint is related to its manufacturing method, which affects the degree of crystallinity of the resulting pigment. This, together with the environmental conditions in which artworks have been exposed, have induced the degradation of yellow paints in Miró's artworks. It was finally noted that the paints exhibiting alteration in the analysed Miró artworks have a chemical composition that is very similar to the tube paint 'Cadmium Yellow Lemon No. 1' produced by Lucien Lefebvre-Foinet. Indeed, paint tubes from this brand were found in the studio, linking the use of this product with Miro's degraded artworks. [ABSTRACT FROM AUTHOR]

Pressure‐sensitive paints (PSPs) have been demonstrated to be very important for aerodynamics research. In order to improve the pressure sensitivity and adhesion ability of PSP, herein, a series of fluorine‐containing copolymers compositing of an oxygen and pressure‐responsive probe derived from platinum(II)‐5,10,15,20‐tetrakis‐(2,3,4,5,6‐pentafluorophenyl)‐porphyrin (PtTFPP) named as poly[(tBs)a‐co‐(TFEM)b‐co‐(PtTFPP‐1MA)c] were synthesized and investigated as PSPs. These PSPs were constructed with different fluorine ratios for the investigation of the effect of fluorine contents on PSPs. Especially, PSP (F0.33) with the trifluoroethyl methacrylate (TFEM) molar ratio of 33% in the copolymers could adhere well to the surface of an aircraft model. F0.33 showed high oxygen sensitivity (I0/I100 = 32.87), reasonable response time to oxygen (44 s), high pressure sensitivity (SP = 0.75%/kPa at 20°C) and low temperature response (ST = −0.77%/°C at 100 kPa). F0.33 was further sprayed on the surface of a delta wing of an aircraft model and its pressure response was verified in a wind tunnel. The data from F0.33 film at the same wind speed and position were close to the pressure data measured by using traditional method using open pressure holes, showing the potential application of these PSPs. [ABSTRACT FROM AUTHOR]

The spray painting is widely used in automobile industries, marines and navy, etc. Extensive development of research is going in Robotics for painting application. In which it gives the best quality and productivity but also reduces paint consumption during painting. This study will help in identifying the factors affecting the spray coating, environmental and chemical properties. The input factors which directly affects the output are spray gun design, nozzle sizes, the distance between substrate and gun, paint pressure flow, viscosity, flash point, pour point, robot speed, temperature, size of droplets, spray time, overspray. The output factors which we want to minimise are surface roughness, thickness, over-spray, the quantity of spray, operation time, heat transfer, corrosion, cracks, peeling and maximise the film adhesive, and the life span of the substrate. To enhance the quality of substrate, the carbon nanotubes (CNTs), like Multiwall Carbon Nanotubes (MWCNTs), are infused in paint by ultrasonication and magnetic stirrer process while preparing the nanopaint. The nanopaint has mechanical, thermal, electrical, chemical and physical properties. Nanopaint acts as a coolant, anti-corrosion, self-healing, and has less viscosity in nature with high young's modulus. The formation of pores, debris and layers are very less in robot nanospray painting. [ABSTRACT FROM AUTHOR]

The turbine blades of aircrafts must be properly cooled to prevent engine failure. Thus, to investigate the influence of the tip structure on the film cooling effect, pressure-sensitive paint test technology was used to determine the adiabatic film cooling effectiveness in this study. The experiment was completed in a cascade comprising three straight blades. The effects of the blowing ratio, density ratio, tip clearance, and tip structure on film cooling efficiency were analyzed. The experimental results demonstrated that, as the blowing ratio increased, the film coverage area and film cooling efficiency increased under most experimental conditions. However, the film cooling efficiency was found to initially increase, and subsequently decrease, as the blowing ratio increased. The respective influences of the density ratio and tip clearance on the film cooling efficiency were found to be significant. The density ratio experiments revealed that a high-density ratio can result in better film coverage than the low-density-ratio air. The tip clearance experimental results indicated that a small tip clearance promotes an increase in film cooling efficiency; this is because the small tip clearance negatively affects the main stream leakage flow, which can reduce the film coverage area. Under the conditions of the Base case 2 configuration, a blowing ratio of 2.1, and a tip clearance of 0.6%h, the average film cooling efficiency of the blade tip was 0.22. Among the three blade tip structures applied in this study, Base case 2 demonstrated higher film cooling efficiency than the other two blade tip structures under the conditions of the same blowing ratio, tip clearance, and density ratio. [ABSTRACT FROM AUTHOR]

The evolution of pressure-sensitive paint (PSP)-based surface pressure measurement technology for rotating machinery is significant for flow mechanism analysis and blade design. Considering the challenges of reducing motion blur and improving signal-to-noise ratio (SNR) in the application of PSP technology for the rotating machinery, an accumulated imaging method with phase-locking based on the periodic characteristics of the rotor flow field has been proposed in this study, which is capable of capturing the phase-averaging pressure on the rotor blade surface. The motion blur is reduced by pulse acquisition of PSP luminescent, and the SNR is improved by accumulating luminescent signals of the same phase multiple times, which can address the challenge. Single PSP luminescence acquisition time and accumulation number are the two most crucial parameters for measurement accuracy, and the constraints of the parameters are discussed in detail according to the principle of PSP. The PSP measurement system for rotating machinery based on the proposed method has been established, and the method is successfully applied to the rotating blade surface pressure measurement of a transonic axial fan. Besides, the proposed method can also be applied to the temperature measurement of the rotating blades based on temperature-sensitive paint. The results offer a technical foundation for the pressure measurement of rotating machinery. [ABSTRACT FROM AUTHOR]

Microscopic particles of transparent colourless silicate glass have been found in numerous oil paintings dating from the fifteenth and sixteenth centuries. The widespread occurrence of such powdered glass has been demonstrated in combination with various pigments and within different pictorial layers in works by artists belonging to the Italian, German, Netherlandish, French, Spanish and Portuguese schools. The aims of this paper are to evaluate the multiple current hypotheses for its use, which include modification of transparency, siccative effects and rheology, and through reconstruction experiments, to gain a better understanding of the modifications of the physical and chemical properties of the paint induced by the addition of glass powder. Experimental works have been carried out using lead white based oil paint mixtures, since this pigment is one of those most frequently mixed with crushed glass in Italian paintings. Optical (reflectance and transmittance), rheological and Fourier transform infrared spectroscopy measurements were carried out on pure lead white paint as well as on paint mixtures containing varying amounts of crushed glass. These experiments indicated that the addition of crushed glass increases the transparency and siccative effect of paint films, without significantly altering rheological properties. [ABSTRACT FROM AUTHOR]

Pressure-sensitive paint (PSP) measurement for turbine blades and vanes is often limited by the optical window and occlusion of the complex blade structure. Endoscopic PSP imaging systems have been designed for the pressure measurement of integrated inter-turbine duct (IITD) guide vanes. Notably, the objective lens of the endoscope leads to severe and dynamic image distortion. The classical direct linear transformation (DLT) algorithm does not consider nonlinear distortion, which reduces the accuracy of three-dimensional (3D) pressure field reconstruction. Therefore, in this study, a dynamic distortion correction endoscopic (DDCE) PSP technique is proposed. Real-time endoscopic images are registered to the post-calibration images through affine transform. Next, the distortion was compensated using the post-calibrated distortion and intrinsic matrix, and the relationship between the pixels on the distorted two-dimensional (2D) PSP images and 3D points on the vanes can be reliably acquired. Reprojection errors are used to evaluate the performance of the proposed technique. The maximum and average errors decrease from 30 to 4 pixels and from 4.8 pixels to 0.8 pixels, respectively. Subsequently, the DDCE PSP technique is applied for the pressure measurement on turbine guide vanes with outlet Mach number ranging from 0.65 to 0.95. Endoscopic PSP images of a structural vane and two aero-vanes are recorded, and the 2D pressure fields of the three vanes are defined through in situ calibration of the PSP. Finally, the 3D pressure fields are reconstructed by mapping the 2D pressure field to the 3D point cloud using the DDCE PSP technique. [ABSTRACT FROM AUTHOR]

A pressure distribution inside a two-dimensional rectangular cavity with a ratio L / D = 5.0 of the cavity length L to the depth D over a supersonic flow was obtained using an improved fast anodized-aluminum pressure-sensitive paint (AA-PSP). The freestream Mach number was M ∞ = 1.9 and the frequencies of the dominant cavity modal phenomena, called "Rossiter" modes, were on the order of 1–10 kHz. The fast AA-PSP using a free-based porphyrin luminophore and a high-frequency-repetition double-pulsed laser were applied, and instantaneous pressure fields were captured. This measurement system has a 60 kHz sampling rate and is suitable for the purpose of a direct measurement of the Rossiter mode phenomena. The result of the power spectral density (PSD) of the PSP measurement showed that this measurement system is capable of observing phenomena of approximately 18 kHz. Time-resolved pressure transducer measurement was also employed, and PSD obtained by the PSP measurement was validated. The frequency spectra and the amplitudes of PSD obtained by the PSP measurement were in good agreement with those obtained by the pressure transducer data. A spectral proper orthogonal decomposition (SPOD) analysis was also conducted, and the symmetric and asymmetric spatial modes were extracted at each peak frequency. In this analysis, the seventh Rossiter mode phenomena of approximately 21 kHz were visualized. The peak frequencies of symmetric modes were in good agreement with those of the Rossiter mode, and lower than that of asymmetric modes. The energy of the symmetric modes at each peak frequency was several times higher than that of the asymmetric mode. The phase of the SPOD mode revealed the propagation direction of the pressure waves. It showed the existence of the upstream propagation waves and standing waves inside the cavity. [ABSTRACT FROM AUTHOR]