Particle Image Velocimetry Results Research Articles

Aerodynamic Analysis of Variable Camber-Morphing Airfoils with Substantial Camber Deflections

In recent years, morphing wings have become not only a concept, but an aerodynamic solution for the aviation industry to take a step forward toward future technologies. However, continuously morphing airfoils became an interesting answer to provide green energy solutions. In this paper, the authors conducted experimental research on a continuously camber-morphing airfoil using the Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD) methods. The main objective of this work was to research a variety of morphing airfoils with different camber deflections. An average velocity distribution and turbulence distribution were compared and are discussed. The two-dimensional PIV results were compared to the CFD simulations to validate the numerical method’s accuracy and obtain the aerodynamic coefficient’s trends. A further comparison revealed that morphing airfoils have better aerodynamic performance than conventional airfoils for very low camber deflections and create substantial amounts of drag for significant camber deflections.

A Computational Investigation of the Effects of Temporal Synchronization of Left Ventricular Assist Device Speed Modulation with the Cardiac Cycle on Intraventricular Hemodynamics.

Patients with advanced heart failure are implanted with a left ventricular assist device (LVAD) as a bridge-to-transplantation or destination therapy. Despite advances in pump design, the risk of stroke remains high. LVAD implantation significantly alters intraventricular hemodynamics, where regions of stagnation or elevated shear stresses promote thrombus formation. Third generation pumps incorporate a pulsatility mode that modulates rotational speed of the pump to enhance in-pump washout. We investigated how the timing of the pulsatility mode with the cardiac cycle affects intraventricular hemodynamic factors linked to thrombus formation. Computational fluid dynamics simulations with Lagrangian particle tracking to model platelet behavior in a patient-specific left ventricle captured altered intraventricular hemodynamics due to LVAD implantation. HeartMate 3 incorporates a pulsatility mode that modulates the speed of the pump every two seconds. Four different timings of this pulsatility mode with respect to the cardiac cycle were investigated. A strong jet formed between the mitral valve and inflow cannula. Blood stagnated in the left ventricular outflow tract beneath a closed aortic valve, in the near-wall regions off-axis of the jet, and in a large counterrotating vortex near the anterior wall. Computational results showed good agreement with particle image velocimetry results. Synchronization of the pulsatility mode with peak systole decreased stasis, reflected in the intraventricular washout of virtual contrast and Lagrangian particles over time. Temporal synchronization of HeartMate 3 pulsatility with the cardiac cycle reduces intraventricular stasis and could be beneficial for decreasing thrombogenicity.

Liquid Flow Patterns and Particle Settling Velocity in a Taylor-Couette Cell Using Particle Image Velocimetry and Particle Tracking Velocimetry

Summary Controlling the downhole pressure is an important parameter for successful and safe drilling operations. Several types of weighting agents (i.e., high-density particles), traditionally barite particles, are added to maintain the desired density of the drilling fluid (DF). The DF density is an important design parameter for preventing multiple drilling complications. These issues are caused by the settling of the dense particles, an undesired phenomenon also referred to as sagging. Therefore, there is a need to understand the settling characteristics of heavy particles in such scenarios. To this end, simultaneous measurements of liquid phase flow patterns and particle settling velocities have been conducted in a Taylor-Couette (TC) cell with a rotating inner cylinder and stationary outer cylinder separated by an annular gap of 9.0 mm. Liquid flow patterns and particle settling velocities have been measured using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques, respectively. Experiments have been performed by varying the rotational speed of the inner cylinder up to 200 rev/min, which is used in normal drilling operations. Spherical particles with diameters of 3.0 mm or 4.0 mm and densities between 1.2 g/cm3 and 3.95 g/cm3 were used. The liquid phases studied included deionized (DI) water and mineral oil, which are the basic components of a non-Newtonian DF with a shear-thinning viscosity. The DF is a mud-like emulsion of opaque appearance, which impedes the ability to observe the liquid flow field and particle settling in the TC cell. To address this issue, a solution of carboxymethyl cellulose (CMC) with a 6% weight concentration in DI water was used. This non-Newtonian solution displays shear-thinning rheological behavior and was used as a transparent alternative to the opaque DF. For water, PIV results have shown wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTVF), which agrees with the flow patterns reported in the literature. For mineral oil, circular Couette flow (CCF) was observed at up to 100 rev/min and vortex formation at 200 rev/min. For CMC, no vortex formation was observed up to 200 rev/min, only CCF. The settling velocities for all particles in water matched with the particle settling velocities predicted using the Basset-Boussinesq-Oseen (BBO) equation of motion. For mineral oil and CMC, the results did not match well with the predicted settling velocities, especially for heavy particles due possibly to the radial particle migration and interactions with the outer cylinder wall.

POD Analysis of Flow around Torpedo-Like Geometry with a Hemispherical Nose

There has been an increased interest in underwater vehicles for a wide range of applications over the past decade. In the current study, flow characteristics around a common, torpedo-like geometry with a Myring profile were investigated at a length-based Reynolds number of Re=20000 using the Particle Image Velocimetry (PIV). As a result of PIV and Proper Orthogonal Decomposition (POD) analyzes in this study; instantaneous streamline topology Ψ, instantaneous vorticity ωL⁄U_∞ contours, instantaneous streamwise velocity component u⁄U_∞ graphs, cross-streamwise velocity component v⁄U_∞ graphs, instantaneous vorticity ωL⁄U_∞ graphs, perpendicular to the flow direction, instantaneous vortex graphs and time-averaged TKE graphs were evaluated and compared. At the same time, as a result of PIV analysis, time-average streamline topology <Ψ> and Time-averaged vorticity <ωL⁄U_∞ > contours values are given. When the flow characteristics were compared by using the obtained POD method of the PIV results, it was determined that although the POD data were generally quite similar to the PIV results, the POD analysis results had a more uniform flow structure and vortex turbulence was lessened.

Investigation of the influence of the bluff-body temperature on a lean premixed DME/air flame approaching blowoff

In flames stabilized by a two-dimensional (2D) bluff body, the lean blowoff (LBO) limit can be extended by increasing the bluff-body temperature, which is verified experimentally in premixed dimethyl ether (DME)/air flames in this work. Two bluff-body temperatures of 573 K and 773 K are tested, respectively. High-speed OH* chemiluminescence (CL) imaging is applied to record the spatial distribution of the heat release. Particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) are performed simultaneously to explore the flow field and the combustion characteristics. Based on the results of OH*-CL, the heat release of the area near the bluff body is strengthened in the case of higher bluff-body temperature, and the enhanced chemical reactivity will further influence the downstream area. The turbulent flame speed obtained by OH-PLIF is increased in the entire area of interest. Due to the higher velocity gradient adjacent to the bluff body in the upstream region (y < 35 mm), the flame surface density (FSD), brush thickness, and flame wrinkling ratio are not sensitive to the bluff-body temperature. However, in the downstream region (y > 35 mm), a noticeable change can be found in these three parameters due to a higher turbulent flame speed and a much lower velocity gradient. Based on the PIV results, a limited effect on the velocity field by increasing the bluff-body temperature by 200 K. Furthermore, the probability density functions (PDF) of the vorticity and strain rate on the flame front are computed. The results indicate that the enhanced flame stability leads to a more pronounced overlapping between the flame front and the high-vorticity region, further increasing the values of these two parameters.

Experimental study on frost heave characteristics and micro-mechanism of fine-grained soil under dynamic load for heavy-haul railway subgrades in seasonally frozen regions

In seasonally frozen regions, there is frequent uneven frost heave of heavy haul railway subgrades, which reduces the smoothness of the track and affects the operational safety of trains. To clarify the frost heave characteristics and micro-mechanism of subgrade filling under the action of unidirectional freezing and dynamic loading, unidirectional freezing tests were performed on a fine-grained subgrade filling under open conditions, and the frost heave characteristics under different initial water contents and dynamic loads were analyzed. The particle image velocimetry (PIV) technique was applied to analyze the development of local deformation at different locations in the samples. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were performed on the samples before and after freezing to reveal the development mechanism of the microstructure. The test results showed that with the increase in the initial water content and load amplitude, the frost heave increased, while the water replenishment and frost depth decreased. Combined with the PIV results, it was found that the soil in the frozen and unfrozen areas exhibited frost heave and compressive deformation, respectively, during the freezing process, further revealing the local deformation law of the soil. The samples mainly contained small pores and micropores before freezing and small pores and medium pores after freezing, indicating that the effect of freezing and swelling had the greatest influence on the small and medium pores inside the soil. The higher the initial water content, the higher the porosity of the sample after freezing; with the increase in the load amplitude, the porosity of the frozen samples decreased. The negative temperature effect of the change in phase from water to ice drove the particle movement, thereby increasing the inter-particle pore space, leading to a macroscopic frost heave deformation of the soil samples. Our results can serve as a basis in the maintenance and safety of railway subgrades in cold regions.

Experimental and numerical comparisons of geometric scaling criteria for lean premixed swirl combustor

This study experimentally and numerically investigates the applicability of the DaI and Re criteria for scaling the geometry of a lean premixed swirl combustor during a reaction and in the absence of it. We first set up an experimental system to test the loss of pressure, the flow field, and NOx emissions in a prototype combustor and two models of it scaled to 3/5 of its size. The results showed that the friction in the flow in the prototype decreased with an increase in its intensity, and the corresponding constant DaI model (M-D) exhibited a similar trend, while the constant Re model (M-R) exhibited an adverse trend to that of the prototype. The results of particle image velocimetry (PIV) of the flow field in the non-reactive state showed that regardless of the criterion used and the state of the reaction, the flow fields of the prototype and the models were similar under flows of different strengths. However, a quantitative comparison of their distributions of velocity showed that the peak velocity of the rotating jet of M-R was significantly lower than that of the prototype. PIV results of the flow field in the reactive state exhibited similar phenomena. Moreover, the NOx emissions of M-D were consistent with those of the prototype, while emissions from M-R were significantly higher. The numerical results also showed that the shape of the flame and the pattern of flow of M-R were significantly different from those of the prototype.

Coupling effect of multiple factors on the diffusion behavior of leaking natural gas in utility tunnels: A numerical study and PIV experimental validation

The ignitable and explosive nature of natural gas poses a significant threat to its safe operation when incorporated into utility tunnels. Currently, the safety technology for gas pipelines in utility tunnels is not yet perfect, and understanding the diffusion law of leaked gas is fundamental to gas accident prevention and control technology. To accurately predict the gas diffusion pattern under the coupling effect of multiple factors, this study investigated the adaptability of Realizable k-ε model for simulating impinging jets through particle image velocimetry (PIV) experiments and computational fluid dynamics (CFD) simulations, simulated the gas diffusion behavior under various working conditions, and revealed the influence of different factors on the warning response time and the combustible gas cloud volume. The results demonstrated that the Realizable k-ε model accurately represented the flow field structure of the impinging jet, and the main characteristic parameters of each flow field zone closely aligned with the PIV results. Furthermore, the overall difference between the simulation results of this study and experimental results was within 4.8% in the validation of CH4 concentration, these findings indicated that the Realizable k-ε model was suitable for simulating gas diffusion processes in utility tunnels. The leakage direction significantly influenced the diffusion behavior within the first 10 s but had less impact later on. The leakage location, pipeline operating pressures, leakage size, leakage shape, and air change rate considerably impacted the warning response time, and the longitudinal plane over the center of the natural gas pipeline was the preferred plane for the installation of gas detectors. The coupling effects of air change rates and leakage size significantly affected the combustible gas cloud volume. Moreover, the coupling effect of multiple factors contributed to the most dangerous working condition in the range of this study, with the combustible gas cloud volume reaching a maximum of 8.25 m3. In conclusion, the numerical simulation model based on Realizable k-ε model could accurately predicted the diffusion behavior of leaked natural gas in utility tunnels under the coupling effect of multiple factors and built up the most dangerous gas leaking accident scenario. The findings of this study will contribute to the development of an accident warning and control plan for utility tunnels.

An experimental study of off-centred rotating thermal convection: a laboratory model for the tidal effects

A novel experiment was performed in rotating Rayleigh–Bénard convection (RRBC), wherein the convection cell with radius $R$ was shifted away from the rotation axis by a distance $d$ . In this case, the centrifugal force felt by a fluid parcel (characterized by the Froude number $Fr$ ) can be decomposed into an axisymmetrical part $Fr_R$ and a directed one $Fr_d$ . It has been reported that the global heat transport enhances at $Fr_{d,c}$ and then reaches an optimal state at $Fr_{d,max}$ (Hu et al., Phys. Rev. Lett., vol. 127, 2021, 244501). In this paper, the local properties after the offset effects set in are investigated further, which show different features before and after $Fr_{d,max}$ . The local temperature measurements at the cell centre reveal that the bulk flow turns from a turbulent state into a laminar state at $Fr_{d,max}$ , which is consistent with the particle image velocimetry results. This transition can be qualitatively understood by an equivalent tilted RRBC system. As for the hot and cold coherent structures near the sidewall, their vertical temperature variations reach a minimum at $Fr_{d,max}$ , implying that these structures are mostly uniform in the vertical direction at $Fr_{d,max}$ . Their temperature contrasts show a linear dependence on $Fr_d$ and start to deviate from this linear behaviour when $Fr_d&gt;Fr_{d,max}$ . Besides the dominant effects of $Fr_d$ , the secondary effects of $Fr_R$ are also investigated. Due to the positive effect of $+Fr_R$ on the cold structure and the negative effect of $-Fr_R$ on the hot one, the cold structure is more coherent than the hot one, but its size is smaller. The shift of the cold cluster centre from the farthest point is also larger than the shift of the hot one from the nearest point.

Impact of buoyant jet entrainment on the thermocline behavior in a single-medium thermal energy storage tank

This paper presents the characterization and management of dynamic thermocline behaviors in a single-medium thermocline (SMT) thermal energy storage tank with the aim of its performance improvement. In particular, the flow mixing induced by the entering thermal jet, its impact on the temperature stratification and its mitigation measure are systematically explored by both numerical and experimental methods. Results of CFD simulation and Particle Image Velocimetry (PIV) visualization clearly demonstrate the jet entrainment phenomenon and the typical flow patterns featured by the rising buoyant plumes. For the storage tank with simple inlet port, this thermal jet would cause the thermal overturning, the strong fluid mixing and convection heat transfer, resulting in the degradation of temperature stratification and the thermocline decay (Rigradient<0.25 at certain positions of the tank). It has also been shown by PIV measurement that the impact of thermal jet, characterized by the jet penetration length, becomes stronger with the increasing injecting flow rate and with the decreasing temperature difference between the injecting and existing fluids.Orifice baffle-type distributor has then been proposed and optimized, showing clearly its effectiveness for mitigating the impact of thermal jet on the temperature stratification. Both the initial uniform orifice baffle and the optimized orifice baffle distributors are then fabricated and installed into a lab-scale cuboid SMT storage tank. Charging operations are performed under different inlet flow rates (Qin: 0.3 to 1.5 L·min−1) and temperature differences between hot and cold fluids (∆T: 30 to 50 K). Experimental results obtained show that the optimized distributor could always lead to the better thermal performance (capacity ratio up to 0.94 and charging efficiency up to 0.8) than the initial uniform baffle distributor, providing more flexible operating conditions of the SMT storage systems in different industrial sectors.

Evaluation of spacer-induced hydrodynamic mixing using particle image velocimetry: Impact on membrane distillation performance

Net-type spacers are used to promote hydrodynamic mixing in the feed channel of crossflow membrane filtration. The induced fluid flow mitigates concentration and temperature polarization effects on the membrane surface, leading to the enhancement of heat/mass transfer across the membrane. The objective of this research is to study the effect of spacer geometry on fluid flow and heat/mass transfer in the feed channel. The particle image velocimetry (PIV) technique was used to measure flow velocity in the feed channel with net-type spacers. Flow characteristics at a wide range of Reynolds numbers were described in terms of time-averaged mean velocity and turbulence kinetic energy (TKE). The PIV result revealed distinct profiles of mean velocity and TKE at different channel heights with bi-planar spacers. The spacer with the largest hydrodynamic angle of 120° (Net120) was found to be the most efficient in promoting flow unsteadiness because it led to the largest channel-averaged TKE among the selected spacers. The unsteady flow regime on Net120 was accompanied by the greatest pressure drop over the feed channel. Moreover, the effect of spacer-induced mixing on heat/mass transfer across the membrane was further evaluated via the flux measurement with vacuum membrane distillation experiments. In comparison with other spacers, Net120 resulted in a relatively higher flux because of the improved hydrodynamic mixing. These findings reveal the validity of the experimental approach in identifying the impact of key spacer design parameters on hydrodynamic mixing. Nusselt number was calculated to relate the hydrodynamic flow and thermal flow in the feed channel of membrane distillation, and a modified Nusselt number correlation was proposed to better predict convective heat transfer in the spacer-filled channel in VMD.

Investigation of flame and flow response in the swirler with different divergence cups and central body under external excitation

Effects of swirl divergence cup and the central bluff body on premixed flame response with external excitation are experimentally investigated. Flame transfer functions (FTFs) associated with different swirlers are measured in 50–450 Hz. The corresponding flame and flow responses are examined with the help of chemiluminescence images and Particle Image Velocimetry (PIV) method. Results show that FTF gain curves of swirlers with different divergence cups are characterized by alternating regions with first a minimum and then a maximum value as the excitation frequency increases. Increasing the divergence cup may greatly reduce the corresponding FTF minimum gain. Dynamic mode decomposition and proper orthogonal decomposition analysis indicate that flames with large divergence cup angles are dominated by the flame angle oscillations at the minimum gain point, while the flame with zero cup presents both the flame angle oscillations and vortex shedding. PIV results indicate that vortical structures located at the outer shear layer (OSL) could induce high-flame response, while the impacts of vortical structures located at inner shear layer are much weaker. Increasing the divergence cup could largely weaken the strength of vortical structures at OSL. In addition, effects of the central bluff body on flame response are significant. The flame in the swirler without the central bluff body is mainly governed by flame angle oscillations, and the elongated flame induced by the swirler with a large body is almost not sensitive to acoustic excitations. These results are useful for the understanding of flame response mechanisms in premixed swirling combustion.

Investigation of rocking mechanism of shallow foundations on sand via PIV technique

AbstractAdoption of the rocking isolation concept in foundation design is considered as an effective method in reducing seismic loads of structures. Despite much research conducted on the rocking behavior of foundations, concerns regarding the practical application of the rocking foundation design concept still prevail. The concerns primary stem from the lack of accurate understanding and knowledge associated with the soil‐foundation deformation mechanisms during rocking motions. Determination of deformation mechanisms and soil mass failure modes during foundation rocking helps to gain insight into the rocking behavior, recognize influential factors on foundation settlement or uplift, and propose appropriate improvement strategies to control foundation deformations. The primary objective of this study is to investigate the deformation behavior and failure modes of the soil mass beneath a rocking foundation with various initial static vertical factors of safety (F.S.v) and embedment depths. To this end, a series of reduced‐scale slow‐cyclic tests under 1g condition have been conducted using a single degree of freedom (SDOF) model. To determine soil deformation mechanisms, soil displacement fields have been measured using Particle Image Velocimetry (PIV) technique. Soil deformation mechanisms during loading and unloading paths, as well as causes leading to the foundation settlement or uplift have been evaluated and discussed. Additionally, changes in the effective soil‐foundation contact area in different loading cycles have been examined based on the PIV results. Based on the results, soil deformation mechanisms in the loading portions include soil densification, wedge deformation and scoop deformation. As the footing embedment depth increases, wedge deformation mechanism becomes limited, while scoop deformation mechanism becomes stronger. Additionally, as the foundation F.S.v increases, the depth of influenced zone of the rocking foundation decreases and the soil displacement occurs to a more limited depth.

The frost heave characteristics of a coarse-grained volcanic soil quantified by particle image velocimetry

The increasing use of the seasonally frozen and permafrost regions for civil engineering constructions and the effects of global warming on these regions have stimulated research on the behaviors of frozen soils. In the present study, the frost heave characteristics of a coarse-grained soil with volcanic nature was experimentally investigated. A large soil tank model was established in laboratory for this purpose. The effects of temperature boundary, external water supply, and water transfer type on the frost heave characteristics of the volcanic soil were studied, through a series of frost heave tests. The particle image velocimetry (PIV) technique was used to quantify the full field deformation of the soil specimen. The results suggest that temperature gradient inside the soil specimen is the driving force for the migration of pore water and vapor. The largest increment in water content generally agrees well with the frost penetration depth. The contribution of vapor to the frost heave of the soil specimen is typically small. The applied seeding method, selected subset size, image-object space calibration, and calculation processes ensured accurate PIV results. Discussions regarding the presented experimental investigation and the employment of PIV technique for quantifying frozen soil deformation are summarized. These findings and discussions can provide valuable insights into the frost heave behavior of the studied soil in particular, as well as promote the application of PIV for frozen soil engineering.

A 3-D Printed Optically Clear Rigid Diseased Carotid Bifurcation Arterial Mock Vessel Model for Particle Image Velocimetry Analysis in Pulsatile Flow

Abstract In recent years, blood flow analyses of diseased arterial mock vessels using particle image velocimetry (PIV) have been hampered by the inability to fabricate optically clear anatomical vessel models that realistically replicate the complex morphology of arterial vessels and provide highly resolved flow images of flow tracer particles. The aim of this paper is to introduce a novel approach for producing optically clear 3-D printed rigid anatomical arterial vessel models that are suitable for PIV analysis using a common 3-D inkjet printing process (using a Formlabs Form 2 3-D printer) and stock clear resin (RS-F2-GPCL-04). By matching the index of refraction (IOR) of the working fluid to the stock clear resin material, and by printing the part in a 45-deg print orientation, a clear anatomical model that allows clear visualization of flow tracer particles can be produced which yields highly resolved flow images for PIV analyses. However, a 45-deg print orientation increases the need for post-processing due to an increased amount of printed support material. During post-processing, the part must be wet sanded in several steps and surface finished with Novus Plastic Polish 3 Step System to achieve the final surface finish needed to yield high-resolution flow images. The mock arterial vessel model produced in this work is a 3-D printed diseased carotid bifurcation artery developed from CTA scan data. A PIV analysis was conducted on the developed mock arterial vessel model installed in a complex transient flow loop to assess the flow profiles within the model and the clarity of the model. A computational fluid dynamics (CFD) simulation was conducted on the same carotid bifurcation arterial geometry, and the results were used as a benchmark comparison for PIV results. The results obtained in this work show excellent promise for using the developed approach for developing 3-D printed anatomical vessel models for experimental PIV analyses. The fabrication methodology of the clear anatomical models, PIV results, and CFD results is described in detail.

Comparison of the Measurement Results of PIV with Different Tracer

Particle Image Velocimetry (PIV) was used to measure the solenoidal vector field of the Taylor-Couette flow with different tracers. It can be seen that both of them, the polyamide and flocs can be a suitable performance tracer particles for PIV in flow field measurement. The results indicated that the instantaneous velocity vector maps obtained with different tracer particles which could denote the characteristics of the flow structure, the size and the vortex centers of the vortex. At the meantime, the experimental results demonstrated that the velocity vector obtained by the flocs generated in real-time as tracer particles was similar with suitable performance to those obtained by polyamide.

Computational Design Analysis of a Hydrokinetic Horizontal Parallel Stream Direct Drive Counter-Rotating Darrieus Turbine System: A Phase One Design Analysis Study

This paper introduces a phase one computational design analysis study of a hydrokinetic horizontal parallel stream direct-drive (no gear box) counter-rotating Darrieus turbine system. This system consists of two Darrieus rotors that are arranged in parallel and horizontal to the water stream and operate in counter-rotation due to the incoming flow. One of the rotors directly drives an armature coil rotor and the other one a permanent magnet generator. A two-dimensional (2-D) and three-dimensional (3-D) computational fluid dynamic (CFD) simulation study was conducted to assess the hydrokinetic performance of the design. From a high computational cost and time perspective, the simulation setup was reduced from a 3-D to a 2-D analysis. Although useful information was obtained from the 3-D simulations, the output performance could be assessed with the 2-D simulations without compromising the integrity of the turbine output results. A scaled experimental design prototype was developed for static (non-movement of the rotors with dynamic fluid flow) particle image velocimetry (PIV) studies. The PIV studies were used as a benchmark for validating and verifying the CFD simulations. This paper outlines the prototype development, PIV experimental setup and results, computational simulation setup and results, as well as recommendations for future work that could potentially improve overall performance of the proposed design.

Numerical modeling of sneeze airflow and its validation with an experimental dataset.

In this study, we aimed at providing datasets using experimental results to validate the sneeze airflow. In addition, the boundary conditions for the sneeze simulation that could reproduce the sneeze airflow in the experimental results are presented and reviewed. The validation datasets were created by performing ensemble-average analysis with the experimental results of particle image velocimetry, and these were used to explore the boundary conditions to reproduce the sneeze airflow. As a result of the sneeze airflow reproduced by computational fluid dynamics simulation, the magnitude ranges of maximum velocity at the interface were observed to be 21.1-23.9m/s for males and 17.9-20.3m/s for females, which were higher than those of coughing. Compared with the experimental results, the root-mean-square error range for the overall airflow distribution was 0.19-0.23 m/s, whereas the error range for the magnitude of the maximum velocity at a criterion point was 0.03-0.08 m/s. The total sneezing airflow volume was in the range of 0.36-0.48 L, which was relatively low compared with that of coughing. Thus, this study provides important fundamental boundary conditions for computational fluid dynamics analysis, validated by experimental results, to interpret the spread of infectious particles by sneezing.

Examination of Cinnamomum camphora interlocked grain adopting X-ray computed tomography combined with particle image velocimetry

Trees develop wood grain more or less parallel to the tree axis as they grow laterally. However, many tree species also develop interlocked grain that is expressed as a change in the wood grain orientation, periodically switching between left- and right-handed spirals over the years. Wood grain information is critical to determining the wood quality and is an important record of cellular events in a cambium. This study examined the wood grain of axial xylem cells in the semi-ring porous hardwood Cinnamomum camphora by first visualizing the three-dimensional structure using a conventional X-ray computed tomography instrument producing tomography images. We propose the use of particle image velocimetry (PIV) and the two-dimensional fast Fourier transform (2D-FFT) to analyze computed tomography images in obtaining grain angle (δ) information from the vessel deviation. We found undulation on the radial variation of the grain angle (δ) that indicates periodical changes in the wood grain orientation as left- and right-handed spirals ranging from − 25° to 16° and − 22° to 18° using the 2D-FFT and PIV, respectively. Furthermore, despite the major orientation of vessels inclining in the tangential direction, the PIV result revealed a minor deviation with vessels inclining in various orientations along the tree radius.

PIV and IRT measurements of hydrothermal performance in a U-shaped heat exchanger with 3D printed detached curved ribs

Novel detached curved ribs are proposed in this study and their influence on turbulent thermofluidic features in a two-pass U-shaped square channel is experimentally investigated using particle image velocimetry (PIV) and infrared thermography (IRT). Due to their geometric complexity, the ribs are fabricated with the 3D printing technology-fused deposition modeling and mounted in line inside the channel with a hydraulic diameter (DH) of 45.5 mm. Examined parameters include the rib convergence angle (α), divergence angle (β), clearance ratio (C/H), and Reynolds number, which are respectively in the range of (25°, 35°, 45°), (30°, 40°, 50°), (0.25, 0.38, 0.56, 0.75, and 1), and (5,000–20,000). The PIV and IRT results show that that the detached curved ribs accelerate the core flow and significantly strengthen the Dean vortices in the turn region, leading up to 70% enhancement in Nusselt number ratio (Nu¯/Nu∞) in that region compared with previous best results. Further parametric studies reveal that at α=25˚and β = 40°, Nu¯/Nu∞ and Fanning friction factor ratio (f¯/f∞) first increase and then decrease with increasing C/H, with the maximum thermal performance factor (TPF) of 1.4 occurring at C/H = 0.38, slightly higher than the previous highest data for f¯/f∞= 10-50. Finally, empirical formulations of Nu¯/Nu∞ and f¯/f∞ with α, β, C/H, and Re for the present design are proposed with an average difference of 2.24% and 4.95%, respectively.