Pressure Sensitive Paint Research Articles

Research on global calibration technology of pressure sensitive paint based on airtight chamber

Pressure sensitive paint (PSP) technology has been widely applied in wind-tunnel test. Generally, PSP calibration data are obtained using a calibration sample in laboratory priori calibration device, which the sample is sprayed at the same time with the test model.In this study, taking the real test model as the calibration object, a global calibration technology of PSP coating on the surface of the test model is proposed, which is verified in the airtight chamber, and the effective PSP calibration data are obtained. A two-component fast response PSP coating was used in the study. In the validation test, a flying wing model is used, the flying wing model sprayed with PSP coating was placed in the airtight chamber. 11 groups of calibration tests were carried out in the environment of 0.06 MPa ~ 0.14 MPa and 30°C ~50°C, and the calibration curves obtained showed good consistency.

Time-series image denoising of pressure-sensitive paint data by projected multivariate singular spectrum analysis

Time-series data, such as unsteady pressure-sensitive paint (PSP) measurement data, may contain a significant amount of random noise. Thus, in this study, we investigated a noise-reduction method that combines multivariate singular spectrum analysis (MSSA) with low-dimensional data representation. MSSA is a state-space reconstruction technique that utilizes time-delay embedding, and the low-dimensional representation is achieved by projecting data onto the singular value decomposition (SVD) basis. The noise-reduction performance of the proposed method for unsteady PSP data, i.e., the projected MSSA, is compared with that of the truncated SVD method, one of the most employed noise-reduction methods. The result shows that the projected MSSA exhibits better performance in reducing random noise than the truncated SVD method. Additionally, in contrast to that of the truncated SVD method, the performance of the projected MSSA is less sensitive to the truncation rank. The projected MSSA achieves denoising effectively by extracting smooth trajectories in a state space from noisy input data. Expectedly, the projected MSSA will be effective for reducing random noise in not only PSP measurement data, but also various high-dimensional time-series data.Graphic abstract

Random-dot pressure-sensitive paint for time-resolved measurement of deformation and surface pressure of transonic wing flutter

Random-dot pressure-sensitive paint for time-resolved measurement of deformation and surface pressure of transonic wing flutter

Film cooling performance on rotating-blade pressure side with three-row film holes at different incidence angles

Different incidence angles mean the different flow fields in the blade channel, resulting in the different film cooling performance on the blade surface. This study experimentally measures the cooling effectiveness on the rotating-blade pressure side at positive, zero, and negative incidence angles (corresponding to 421 rpm, 600 rpm, and 691 rpm). The film cooling distributions obtained by the pressure-sensitive paint technique for three blades with different compound angles (0°, 45°, and −45°) under different blowing ratios (0.3–2.0) are presented. The results show that the stagnation line shifts to the pressure side and the deflection angle of the film trajectory is larger at the positive incidence angle. The stagnation line shifts to the suction side and the cooling jet near the leading edge flows vertically upward at the negative incidence angle. The cooling effectiveness for the negative compound angle (−45°) is reduced at the positive incidence angle. For blades with compound angles (−45° and 45°), the cooling effectiveness downstream of the pressure side varies little at the negative incidence angle.

Study on the film cooling effectiveness of shaped holes in the suction surface gill region of the turbine blade

In the suction surface gill region of the turbine blade, three representative regions with a favorable pressure gradient (FPG), adverse pressure gradient (APG), and pressure gradient transition (from FPG to APG) were chosen to explore the film cooling characteristics. A row of 11-11-11 holes (a modified hole of 7-7-7 holes with a spanwise expansion angle and a streamwise expansion angle of 11°) was set up in these three regions. The distribution of film cooling effectiveness (η) in three different regions was explored using the pressure sensitive paint (PSP) technique. On this basis, a row of cylindrical holes was set in both regions with pressure gradient transition and APG on the suction surface of the turbine blade. The difference in film cooling characteristics between the 11-11-11 hole and the cylindrical hole was analyzed. Meanwhile, numerical calculations of the experimental model were carried out to analyze the flow and mixing characteristics of the cooling jet in the three regions. The laterally averaged η of the 11-11-11 hole in the region with FPG is higher than that in the region with pressure gradient transition and APG under each blowing ratio. It was found that the film coverage was promoted along the flow direction in the region with FPG on the turbine blade. In the region with APG, film coverage was suppressed along the flow direction. However, APG slightly enhances film coverage in the spanwise direction and significantly enhances film coverage in the wall-normal direction. In the region with APG, 11-11-11 holes have an advantage over cylindrical holes only in the near-hole limiting area.

Swirling main flow effects on film cooling: Time resolved adiabatic effectiveness measurements in a gas turbine combustor model

Lean burn swirl stabilized combustors represent the key technology to reduce NOx emissions in modern aircraft engines. The high amount of air admitted directly trough the injection system and the higher levels of pressure and temperature requested by the engine cycle make the design of even more efficient cooling systems and the correct estimation of combustor liners heat load a crucial task for the combustor durability. One of the technologies used for the cooling of these components is the effusion cooling, which promotes the formation of a cold layer to protect the liner walls, whose cooling capabilities are described with the adiabatic effectiveness parameter. The effectiveness of these systems is severely influenced by the swirling flows generated by the swirler injectors which promote the mixing between cold and the hot gases of the combustion process. The development of the swirling flow structures inside the combustor chamber and the grade of interaction between swirling flow and the liner walls can be described by the swirl number (SN). In order to investigate the impact of the effects of the SN parameter on the adiabatic film effectiveness, a dedicated non-reactive single-sector linear combustor test rig was designed and equipped with three different axial injectors (SN=0.6−0.8−1.0) and a cylindrical holes effusion plate to simulate the liner cooling system. Film effectiveness was acquired using Fast response Pressure Sensitive Paint (FPSP) technique; the scale of the model and the acquisition frequency of 1 kHz allowed to track the effusion jets and main flow interactions. The collected results show the importance of using an unsteady analysis to perform an in-depth characterization of the mixing phenomena between the main flow and the coolant which are significantly affected by the swilring characteristics.

Upstream and Passage Endwall Film Cooling of a Transonic Turbine Vane

Adiabatic film cooling effectiveness was measured on the endwall of a turbine vane under transonic flow conditions using binary pressure-sensitive paint. The combined effect of upstream and passage film cooling holes was evaluated. The experiments used a five-vane annular cascade in a blowdown wind tunnel. The mainstream velocity was set to exit isentropic Mach numbers of 0.7 and 0.9. The total coolant-to-mainstream mass flow ratio (MFR) was varied from 0.75 to 2.50%. Coolant-to-mainstream density ratios (DRs) of 1.0 and 2.0 were investigated. The first row was located upstream of the vanes, and the second and third rows were located in the passage between the vanes. Coolant was supplied by a divided plenum, allowing independent control of the MFR to the upstream and the passage holes. The coolant MFR was evenly split between the upstream and passage holes. Generally, increasing the MFR, the DR, and the Mach number increased the film cooling effectiveness. However, increasing the DR at MFRs of 0.625% and below decreased the laterally averaged film cooling effectiveness by as much as 60%, largely because mainstream flow was ingested through the second row. Upstream coolant provided some protection through the passage, with effectiveness as high as 0.2 at the second row.

Film Cooling and Cold Streaks Tracking on a Fully Cooled Nozzle Guide Vane Under Representative Combustor Outflow Conditions

Abstract The pronounced nonuniform temperature distribution in the core engine flow path is a recurring problem of gas turbine engine design process. Specifically, turbine entry conditions are usually characterized by severe temperature distortions, often referred to as hot and cold streaks, ascribed to combustor burners and combustor liners cooling systems. Temperature distortions remain an issue even at the exit section of the nozzle guide vane (NGV), where additional cold streaks coming from the vane film-cooling system are injected into the flow. A precise knowledge of thermal field and its evolution is thus essential to mitigate their impact on turbine performance and lifetime. Various studies focus on the description of streaks migration through a direct investigation of the thermal field, providing an effective evaluation of the global phenomenon. As a deeper understanding is often required, experimental techniques based on the detection of tracer gases can be successfully adopted. In this study, a realistic combustor outlet swirl profile was imposed on a fully cooled NGV cascade to analyze both film-cooling behavior and cold streaks migration and redirection. A concentration probe based on the fluorescence behavior of an oxygen sensor, fully characterized in a previous work, was here employed to track the position of the film cooling flows at the NGV cascade exit plane, while the adiabatic film-cooling effectiveness was evaluated on the NGV surfaces employing the pressure sensitive paint (PSP) technique. Overall, the swirling structure strongly affects both the film-cooling behavior and cold streaks migration through and downstream the vane. The importance of examining the unsteady aspect is also highlighted to better estimate actual components operating temperatures. A global understanding of the occurring phenomena is therefore provided, as well as significant pieces of information that can be extremely useful for the design phases of both the NGV and the following rotor cascade.

Interference of Graphene Presence in Formation Mechanism of Metalloporphyrin (PtTFPP) Complex with Oxygen

Introduction Pressure sensitive Paints (PSP) are widely applied in aerodynamic surface tests, as they allow fast data acquisition and pressure mapping across the entire surface during flight simulation [1]. The PSP used in this work is mainly composed of Fluoro-Isopropyl-Butyl (FIB) (Figure 1.A), a polymer that allows oxygen permeability in the paint and platinum tetra(pentafluorophenyl)porphyrin (PtTFPP), responsible for pressure sensitivity (Figure 1.B) [2]. Considering the PSP unique properties, it is possible to obtain an electrical response that enables the use of this paint in airplanes pressure sensors, during flight. For this, an electrical charge of graphene derivative is added to the PSP.Graphene has properties that make it interesting for several applications. Its final application is related to its production method. Electrochemical exfoliation of graphite was used to produce the carbonaceous electrical charge, which has advantages such as ecofriendly reagents, simple product purification and ease of subsequent steps [3, 4]. Seeking to reach the PSP application potential as an oxygen sensitive material that generates an electrical response on pressure, it is necessary that the added electrical charge is compatible with the paint, producing a homogeneous material, high electrical conductivity and mechanical properties suitable for aerospace applications. Thus, the interaction of graphene derivatives with paint and how this influence on its sensitivity to oxygen was studied. This sensitive material can be used in an aeronautical sensor redundant to the Pitot Tube. Therefore, the main objective of the proposed research is to increase the safety of air navigation using a graphene-derived composite with a pressure-sensitive metalloporphyrin paint (PSP).Materials and methods Initially, the production of graphene derivatives was carried out by electrochemical exfoliation of graphite, in which plates of thin graphite sheets pressed were used as working electrode and counter electrode. As an electrolyte solution, a mixture of salts (NH4)2SO4 and (NH4)2HPO4 was used at a concentration of 0.1 mol.L-1 and a proportion of 70/30 v/v%. Exfoliation took place at a fixed potential of 10 V, applied by an electrical power supply. At the end of this process, two drying methodologies were tested: kiln at 70°C (Graphene A) and lyophilization (Graphene B). The composite production consists of mixing the graphene derivative and PSP, at a concentration of 1 mg.mL-1, with the aid of an ultrasound tip for 30 minutes. In addition to the carbonaceous material, a commercial graphene (Graphene C) was also used. After mixing, the material is dripped onto an aluminum surface. The characterizations performed were Raman Spectroscopy and X-Ray Diffraction Spectroscopy to analyze the morphology of the graphene used and Stereo Microscopy, XRD and electrical impedance for the composites.Results and discussion Analyzing the Raman spectra, Graphene A has a more disorder in the carbon chain, higher degree of stacking between planes and a greater association of defects (D4, 2D1 bands, respectively). The lyophilized material showed less interactions between the edges (D1+D4 band) configuring smaller and less agglomerated particles. Graphene C also showed a certain degree of defects and functionalization by oxygenated groups. The diffractogram of Graphene B and C indicates greater disorder in the bonds of the carbon rings with sp2 hybridization than that presented in Graphene A, with A being the material with the highest number of layers and the smallest lamellar distance. Stereo microscopy (Figure 2) images of the composites showed that the mixture is not homogeneous, especially after drying and presents roughness, being these characteristics that can be a problem for the final application. The composite diffractograms show the same peaks only for the paint, with a difference in intensity. The amorphous peak at 16.4°, referring to the polymer, becomes more intense and crystalline with Graphene A and C indicating possible interaction and intercalation of graphene layers with the polymer. The Electrical Impedance of the composites was performed in variable vacuum without flow. Composites with Graphene A and B are resistive, without variation in the presence of different amounts of oxygen. With Graphene C, the response was capacitive-resistive, and was sensitive to pressure changes, but still needs calibration (Figure 3).[1] PUKLIN, E. et al. Ideality of pressure-sensitive paint. I. Platinum tetra(pentafluorophenyl)porphine in fluoroacrylic polymer. Journal of Applied Polymer Science, v. 77, n. 13, p.2795-2804, 2000.[2] GAMAL, E.; et. al. Oxygen pressure measurement using singlet oxygen emission. Review of Scientific Instruments 76, 054101, 2005.[3] KARIMOV, K. S.; et. al. Development of pressure-sensitive thermo-electric cell using graphene and n-Bi2Te3. Emergent Materials 2, pages 387–390, 2019.[4] ANJU, M.; et. al. Graphene-dye hybrid optical sensors. Vol 17, 194 – 217, 2019. Figure 1

Study on Effects of Spanwise-Expansion Parameters on Film Cooling Effectiveness of Diffusion Shaped Hole Configurations

Abstract Diffusion shaped holes are widely used on aero-engine turbine blades for film cooling. The effect of the spanwise-expansion angle and spanwise width of the hole exit on the film cooling effectiveness of diffusion shaped holes was investigated in this study. The film cooling effectiveness was obtained through the pressure-sensitive paint (PSP) technique on a plate model at five momentum ratios (0.11, 0.43, 0.97, 1.73, and 2.71). A numerical simulation was performed to analyze the flow mechanism. The laid-back fan-shaped (LBFS) holes and the fan-shaped holes with three spanwise-expansion angles (FS-A: 7 deg, 11 deg, and 15 deg) and with three spanwise widths of the hole exits (FS-B: 1.7d, 2.3d, and 3.4d) were used for the study. The results revealed that the film cooling effectiveness of fan-shaped holes (FS-A) increases monotonically as the spanwise-expansion angle increases, while the film cooling effectiveness of the LBFS holes increases first and then decreases as the spanwise-expansion angle increases. However, the film cooling effectiveness of the two kinds of holes (LBFS and FS-B) both increase first and then decrease with the increase of the spanwise width of hole exit. The mainstream intrusion occurred at the same spanwise width of the hole exit of 3.4d for both kinds of holes. The laid-back fan-shaped hole possessed high resistance to cooling performance decline. The importance of the spanwise width of the hole exit as a key parameter was emphasized in this study.

Film Effectiveness Downstream the Trenches with Tilted Target Wall

Film cooling is a commonly-accepted effective way to protect the gas turbine hot sections from the high temperature products of the combustion chamber. Numerous film hole geometries have been the subject of investigation by many researchers over the past three decades with the aim of keeping the target wall under the maximum allowable temperature with the least amount of precious cooling air and minimum aerodynamic losses. In this study, we are proposing a new trench geometry that is fed by 30°-inclined embedded circular film holes entering from the trench sidewall. The cooling jets impinge on the opposite wall of the trench which is tilted towards the jets and then is pushed over the coverage wall by the main flow. Three trench geometries with the same exit area and tilt angles (the angle between the trench side- and top-wall) of 75°, 90°, and 105° degrees are tested for three blowing ratios of 0.5, 0.75, and 1.0, and the film effectiveness results are compared using the adiabatic pressure sensitive paint technique. CFD analyses are also performed using the realizable <math xmlns="http://www.w3.org/1998/Math/MathML" id="M1"> <mi>k</mi> <mo>−</mo> <mi>ε</mi> </math> turbulence model with the enhanced wall function option. Major conclusions of this study were that the trench geometry with the trench tilt angle of 75°, corresponding to the smallest trench volume, had the best performance at the lowest blowing ratio, and good agreement was observed between the CFD and test results.

Enhancement of blade tip cooling with different position on tip cooling slot

One of the leading causes of thermally induced failure in gas turbine blade tip is a tip leakage flow. To protect blade tip efficiently from strong tip leakage flow, slot cooling is adopted in blade tip considering the application of additive manufacturing. For slot cooling scheme in blade tip, slot location ranging from PS slot to SS slot is a crucial role in film cooling effectiveness of blade tip. Therefore, we investigated the effect of the cooling-slot location on film cooling effectiveness and flow characteristics of blade tip with slot cooling considering the application of additive manufacturing. The local film cooling effectiveness on the blade tip floor and upper surface of the rim are obtained using pressure sensitive paint method. The case of coolant discharge from the PS slot was both stable and evenly spread, resulting in an outstanding coolant coverage of the entire tip regions. However, under severe effect of hot main gas flow behavior, the case of the SS slot resulted in an uneven FCE distributions over the entire tip region from the LE to the TE region. Under the studied tip gaps and coolant mass flow rates, the PS slot configuration provided a superior blade tip cooling performance under most operating conditions, but the SS slot configuration provided an outstanding cooling performance on blade tip only at a large amount of coolant mass flow rate compared to PS slot. Thus, the blade tip with a PS slot is recommended as a robust cooling design. However, the blade tip with a SS slot may have a limited application for design and off-design conditions.

Temperature sensitivity elimination in sprayable fast-responding pressure-sensitive paint

Temperature-induced error is a major issue in pressure-sensitive paint (PSP) measurement, which usually comes from the inherent thermal quenching effect of luminophores. Herein, we successfully eliminate the temperature sensitivity in a sprayable fast-responding PSP. This PSP contains two luminophores (coumarin 6 and PtTFPP) with opposite temperature sensitivities, which cancel the temperature effect in the 515–800 nm spectral range, making it a temperature-canceled PSP (TC-PSP). The sensing properties of the TC-PSP (pressure sensitivity, temperature sensitivity, signal level, and response time) are characterized and compared with those of a single-luminophore PSP with the same mesoporous particle binder (MP-PSP). The TC-PSP exhibits an extremely low temperature sensitivity of 0.015 %/℃ in the 20–60 ℃ range, a value approximately 1 % that of the MP-PSP (1.35 %/℃). Its temperature sensitivity and corresponding temperature-induced error are significantly lower than the previously reported temperature-insensitive fast PSPs. In a jet impingement experiment conducted for validation, the TC-PSP showed excellent performance in eliminating the temperature-induced error. Overall, the developed TC-PSP holds great potential for high-speed aerodynamic testing applications. • We developed a sprayable fast PSP with extremely low temperature sensitivity. • The PSP contains two luminophores with opposite temperature sensitivities. • Temperature-induced error is completely removed in a jet impingement experiment.

Review of Film Cooling in Gas Turbines with an Emphasis on Additive Manufacturing-Based Design Evolutions

Film-cooling technology is used in high-temperature components of gas turbines to extend their service lives. Hot-gas path components are susceptible to damage or failure in the absence of film cooling. Much of the optimization research efforts have been focused on film hole shapes, heat/mass transfer measurement techniques, and film cooling performance under various mainstream and coolant side operating conditions. Due to recent rapid advancements in the areas of measurement techniques (e.g., pressure-sensitive paints and fast high-resolution imaging) and metal additive manufacturing (AM), film cooling technology has undergone significant changes and shows potential new development. In this review, a historical perspective is discussed covering over five decades of innovation: the geometrical effects from injection angle and hole shapes; flow effects from density ratio, momentum-flux ratio, blowing ratio, advective capacity ratio, and freestream conditions; and more items related to AM. The impact of AM on film hole design strategies, the challenges posed by state-of-the-art AM technology, and pathways for future research are discussed. A comparative analysis of AM assisted film hole fabrication and conventionally manufactured film holes is elaborated.

Practical Fast-Response Anodized-Aluminum Pressure-Sensitive Paint Using Chemical Adsorption Luminophore as Optical Unsteady Pressure Sensor.

We developed and evaluated an anodized-aluminum pressure-sensitive paint (AA-PSP) with new formulations of free-base porphyrin, , as an optical unsteady pressure sensor. The luminophore has quite a short fluorescent lifetime (2.4 ns on the condition of the AA-PSP). The fluorescence spectroscopy result shows that the excitation wavelength of corresponds to violet-colored (425 nm) and green-colored (longer than 520 nm) lights. The pressure sensitivity is sufficiently high for the pressure sensor (0.33–0.51%/kPa) and the temperature sensitivity is very low (0.07–1.46%/K). The photodegradation of the AA-PSPs is not severe in both excitation light sources of the green LED and the Nd:YAG laser. The resonance tube experiment result shows the cut-off frequency of the AA-PSPs is over 9.0 kHz, and the results of the shock tube experiment show the 10 µs order time constant of the normal shock wave.

Effects of a Gaseous Atmosphere on the Pressure Sensitivity and Constancy of Pressure-Sensitive Paints

Pressure-sensitive paint (PSP) technology is an innovative optical measurement method that has been applied towards studying the aerodynamic characteristics of Martian spacecraft under low-pressure conditions. In this study, the static characteristics and constancy of the oxygen pressure sensitivity of PSPs fabricated using either poly[1-(trimethylsilyl)-1-propyne], particle-ceramic, or mesoporous silica particles as binders were studied under low oxygen pressure conditions using various gas mixtures with oxygen pressure ratios ranging from 1% to 20.9%. The results showed that the oxygen pressure ratio did not affect the oxygen sensing property and temperature dependency. PTMSP-PSP exhibited the highest oxygen pressure sensitivity of 26.78%/hPa and the lowest temperature dependency of -0.22%/K among the three PSPs under low oxygen pressure conditions. By comparing the oxygen pressure sensitivities before and after stored in different gaseous atmospheres, the degradation of PTMSP-PSP was verified to be related to the total pressure and unrelated to oxidation, and the degradation declined as the total pressure was increased. The static calibrations conducted in gaseous atmospheres with high total pressure and low oxygen pressure ratio not only improve the constancy of PTMSP-PSP and avoid the calibration error under low pressure conditions, but also alleviate the stringent sealing requirements of the test system.

Response of a plate with piezoelectric elements to turbulent pressure fluctuation in supersonic flow

The aeroelastic response of a plate with supersonic freestream flow on one side and a shallow cavity on the other to turbulent pressure fluctuations is investigated computationally and experimentally. An empirical model is developed for the pressure fluctuations in a turbulent boundary layer that accounts for spatial and spectral variations in the pressure field. Supersonic wind tunnel tests were conducted in a Mach 2.5 flow with and without an impinging shock at the plate surface. In both cases the boundary layer was turbulent. The impinging shock creates shock-wave boundary-layer interaction, which alters the characteristics of the pressure fluctuations. Pressure-sensitive paint was used to measure the unsteady pressure on the surface of a rigid plate and characterize the pressure field (local mean, rms, and the spatial coherence length) and piezoelectric patches were used as sensors to measure the response of an elastic plate. The extracted pressure parameters were used to simulate the fluid–structure response and correlate with experiments. The computed pressure perturbation due to plate motion is found to be small relative to the natural pressure fluctuation for the fluid/structural configuration studied. Computed and measured power spectra of the piezoelectric element voltage show good agreement over a wide range of structural natural frequencies. Aeroelastic response sensitivity to pressure fluctuation coherence length was also investigated computationally. It is found that with small fluid elements, which represent small-scale uncorrelated noise, the structural response is relatively small because the excitation is filtered by the plate dynamics. Experimental results suggest that the effective excitation spatial scale is on the order of the boundary layer thickness.

Development of a Miniature Embedded Imaging System For Internal Flow Measurements

Through this work, the foundation has been laid for the development of a system for small-scale, integrated, image- based flow diagnostics for ground and flight tests. This system addresses many of the challenges associated with alternative methods of performing these measurements. For this work a 120 fps imager was embedded in the ceiling of a Mach 2.0 wind tunnel to perform oblique shock impingement measurements. Illumination was provided via a ring-light system of micro-LEDs embedded around the camera lens aperture. The entire system was controlled using a Raspberry Pi 4 Model B to capture and process image data. The integrated system possesses a total aperture diameter of 20 mm. Pressure sensitive paint and UV oil flow visualization experiments capturing an oblique shock/boundary layer interaction were performed using this system.

A dual-camera single-shot lifetime method with fully controllable exposure gates for pressure-sensitive paint measurements on fast-rotating surfaces

This paper proposes a dual-camera single-shot lifetime method for pressure-sensitive paint (PSP) measurements on fast-rotating surfaces. Two cameras with fully controllable exposure gates are used for image acquisition to reduce the motion blur due to the open-ended exposure of the interline transfer charge-coupled device camera which was typically used for the single-shot lifetime method. The images can thus be processed without deblurring for a wider rotating speed range than is possible with existing techniques. More importantly, both frames have equal exposure times and therefore equal blur lengths. This enables precise pixel-to-pixel image matching and minimizes image registration errors. In addition, the signal strengths of the frames can be balanced, enabling shot-noise-induced errors to be reduced by independent adjustment of the aperture ratio. A pressure uncertainty estimation model is established to evaluate the measurement errors, which helps determine the system parameters. The dual-camera PSP system is calibrated and then validated through the surface pressure measurement of a fast-rotating disk. It is found that the exposure time t e has little effect on the PSP sensitivity, whereas the delay time t d affects both the pressure sensitivity and the measurement error. Both t e and t d are set to 5 μs in the rotating disk experiment. Images with a blur length of 1.4 pixels are captured and processed without deblurring to yield reasonable surface pressure results. The pressure error is decreased from 1.05 to 0.65 kPa by increasing the aperture ratio F from 2 to 4.

Photopolymerisable liquid crystals for additive manufacturing

Liquid crystals are often regard as a fourth state phase of matter alongside solids, liquids and gases. It has been estimated that one out of every ten new synthetic compounds is a liquid crystal, mainly due to the fact that liquid crystals have been used in Liquid Crystalline Displays (LCDs) for over 50 years. Liquid crystals, often referred to as mesogens, exhibit an unique range of ordered mesophases with anisotropic physical properties, such as optical, magnetic and dielectric anisotropy, for example. These highly anisotropic properties and the ability of liquid crystals to self-organize on surfaces, has led to them being, are used in a wide range of non-LCD applications. These applications include photochromics, pressure sensitive paints, optical retarders and optical compensation films, etc. Highly crosslinked, anisotropic polymer networks, derived from photopolymerisable liquid crystals, so-called reactive mesogens (RMs), have enabled solution-fabricated organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs) for plastic electronics. This review will be focus on the relatively recent application of liquid crystals, i.e., the 3D/4D printing of reactive mesogens and subsequent polymerization to form anisotropic polymer networks in advanced additive manufacturing applications. It will highlight the challenges of the synthesis and use of new liquid crystalline materials in 3D/4D printing for additive manufacturing applications. It will show how the study of the successful development of design strategies for the synthesis of novel liquid crystals for flat panel displays is inspiring the development of novel photopolymerisable liquid crystals for additive manufacturing. It is intended that this review will serve to inspire chemists, with little or no knowledge of liquid crystals, or liquid crystal chemists, to design and synthesize new liquid crystals for 3D/4D printing. Photopolymerisable liquid crystals (reactive mesogens) with advanced functional aromatic cores and two photoreactive endgroups are used to fabricate stimulus-responsive liquid crystalline elastomers (LCEs) using 3D/4D printing techniques, such as fused-deposition modeling (FDM), direct ink writing (DIW), digital light-processing (DLP) and two-photon polymerization (2PP). Reactive mesogens represent a highly promising class of advanced functional for new types of actuators, sensors, soft robotics, drug delivery systems, energy-absorbing and reinforced devices, etc., primarily due to their liquid crystalline properties, such as anisotropic swelling, high elastic modulus and sensitive actuation. • Stimulus-responsive photopolymerisable liquid crystals (PLCs) for additive manufacturing. • Structure-property discussion for PLCs with advanced aromatic cores and photoreactive endgroups. • 3D/4D printing PLCs for application in smart devices (actuators, sensors, soft robotics, etc). • Highly promising PLCs due to anisotropic swelling, high elastic modulus and sensitive actuation.