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This study introduces an innovative Grade 1 paper-based microfluidic device designed for the rapid, sensitive, and cost-effective detection of methanol in alcoholic beverages. The device integrates chemical reagents and sample fluid on a single paper strip, facilitating a straightforward and portable testing mechanism. The detection of methanol is achieved through a colorimetric reaction involving potassium permanganate, sulfuric acid, sodium bisulfite, and chromotropic acid. Upon interaction with methanol, the reagent mixture produces a distinct color change to purple, which can be visually assessed or quantified. The device works well with small sample volumes (usually less than 50 μl), making it ideal for field applications with minimal resources. The experimental validation confirmed that the device can detect methanol concentrations ranging from 5% (v/v) to 30% (v/v). This range of detection encompasses the critical concentrations found in contaminated alcoholic beverages responsible for methanol poisoning. In addition, numerical simulations were conducted at various time intervals for methanol concentrations, leading to the development of a colorimetric index specifically for measuring alcohol concentration ranging from 5% to 30% (v/v). Furthermore, experiments on both branded and locally made alcoholic beverages validated the accuracy of our developed colorimetric index. This paper-based technology provides various benefits compared to conventional methods, such as lower expenses, simplicity of operation, and the possibility of large-scale manufacturing and distribution in areas with limited resources. [ABSTRACT FROM AUTHOR]

Hematocrit and hemoglobin levels are common blood tests used to assess the overall health status of patients as well as the oxygen-carrying capacity of the blood. The gold-standard technologies to determine the hematocrit and hemoglobin levels are precise and fast, but they are not pragmatic in extreme point-of-care settings due to the prohibitive cost, process complexity, and sophisticated facilities. Therefore, here, we report the development of a microfluidic paper-based analytical device to determine hematocrit and hemoglobin levels simultaneously. This device exploits the area of the stain formed by a spreading drop of 20 μl of whole blood on Whatman filter paper immobilized with sodium chloride and ethylenediaminetetraacetic acid for hematocrit level, whereas for hemoglobin concentration, it utilizes the gray color intensity of a 20 μl droplet of a mixture of blood and de-ionized water. The performance of the device is verified by comparing with gold-standard results of the automated hematology analyzer, showing a high degree of correlation (R2) of 0.9651 and 0.9701 for hematocrit and hemoglobin levels, respectively. The bias and standard deviation of the differences between the two measurements for hematocrit determination are 0.002 and 1.005, respectively, while the bias and standard deviation of differences between the two methods for hemoglobin determination are 0.065 and 0.398, respectively. This device is likely to provide a simple, fast, disposable, and inexpensive tool to determine the hematocrit and hemoglobin levels in resource-constraint settings. [ABSTRACT FROM AUTHOR]

Capillary wicking in a thicker gel blot microfluidics paper has been investigated through a combination of an analytical framework, experiments, and numerical simulations. The primary objectives of this work are to investigate the concentration-dependent wicking process inside thicker microfluidic paper and to estimate the concentration-dependent permeability using both theoretical models and experimental data. An additional goal is to estimate the parameters for saturation-dependent flow modeling in thicker microfluidic paper. To comprehend the wicking phenomenon on thicker gel blot paper, a series of experiments employing aqueous food dye solutions at varying concentrations has been conducted. In order to calculate the temporal wicking length analytically, the Brinkman-extended Darcy equation is implemented. By modifying the permeability expression for a simple rectangular unidirectional fiber cell and pure liquid, the expression of effective permeability for the analytical framework has also been introduced. The concentrations of the food dye solutions appear to have a substantial influence on the wicking phenomenon. Effective permeability and wicking length have been found to follow a decreasing pattern at lower concentrations while both increase at higher values. Intriguingly, employing a microfluidics paper with a relatively greater thickness facilitates the visualization of the fluid front. This phenomenon is identified by the formation of an acute angle at intermediate time instants, while the fluid front angle assumes an angle nearly ∼90° during smaller and higher time instants. In order to evaluate the saturation-dependent capillary pressure and permeability, the empirical correlation of concentration-dependent Brooks and Corey parameters is additionally determined experimentally. These parameters are subsequently employed in numerical simulations to illustrate the saturation-dependent flow field using Richards' equation. Furthermore, numerical simulations based on these estimated model parameters have been conducted, and it turns out that the saturation field has an excellent agreement with the experimental results. The results of the current study can be used to design low-cost paper-based diagnostic devices for usage in healthcare and environmental applications. [ABSTRACT FROM AUTHOR]

The search for efficient capillary pumping has led to two main directions for investigation: first, assembly of capillary channels to provide high capillary pressures, and second, imbibition in absorbing fibers or paper pads. In the case of open microfluidics (i.e., channels where the top boundary of the fluid is in contact with air instead of a solid wall), the coupling between capillary channels and paper pads unites the two approaches and provides enhanced capillary pumping. In this work, we investigate the coupling of capillary trees—networks of channels mimicking the branches of a tree—with paper pads placed at the extremities of the channels, mimicking the small capillary networks of leaves. It is shown that high velocities and flow rates (7 mm/s or 13.1 μl/s) for more than 30 s using 50% (v/v) isopropyl alcohol, which has a 3-fold increase in viscosity in comparison to water; 6.5 mm/s or 12.1 μl/s for more than 55 s with pentanol, which has a 3.75-fold increase in viscosity in comparison to water; and >3.5 mm/s or 6.5 μl/s for more than 150 s with nonanol, which has a 11-fold increase in viscosity in comparison to water, can be reached in the root channel, enabling higher sustained flow rates than that of capillary trees alone. [ABSTRACT FROM AUTHOR]

Transparent and nontransparent exoskeleton wearable heaters are used in automobile and aircraft deicing, oil-pipeline defrosting, smart windows, underwater protection clothing, winter sportswear, bioelectronics, personal healthcare, athletic rehabilitation, and thermotherapy applications. In this study, we introduce Korean traditional Han paper (or Hanji), which comprises eco-friendly cellulose fibers from the mulberry bark, as a substrate for nontransparent wearable heaters. Hanji consists of cellulose fibers and is highly flexible, making it suitable for low-cost roll-to-roll scalable production. Graphene flakes are readily and firmly embedded inside the fibrous structure of Hanji by the catastrophic impact inflicted by supersonic spraying. Additionally, Hanji can withstand temperatures of up to 100 °C before suffering thermal damage. The heater with the thicker graphene layer had the lowest electrical resistance and exhibited the highest heating temperature at a constant voltage level. Graphene flakes are firmly held inside the fibrous structure of Hanji, securing the material's mechanical durability. Additionally, tests at various bending radii were conducted to demonstrate the mechanical strength of the Hanji graphene heater. Graphene flakes deposited on an unyielding alumina substrate withstood temperatures of up to 280 °C, thereby facilitating the use of the substrate in high-temperature applications. Graphene-coated textiles were heated and stretched up to 50%, thus demonstrating the application of such materials in human-body thermotherapy. [ABSTRACT FROM AUTHOR]

In the present work, spontaneous imbibition of shear-dependent fluids is numerically investigated in a two-layered, rectangular/fan-shaped, paper-based diagnostic kit using the modified Richards equation. It is shown that the average velocity at the test line of the kit is strongly influenced by the absorbent pad's microstructure with its contact angle playing a predominant role. Assuming that the test fluid is shear-thinning, a generalized version of the Richards equation, valid for power-law fluids, was used to investigate the effect of shear-thinning on the quasi-steady regime. The shear-thinning behavior of the test fluid is predicted to shorten the duration of the constant-velocity regime on the nitrocellulose membrane used as the test cell. By manipulating the contact angle and/or choosing appropriate microstructure for the absorbent pad, it is still possible to establish a constant velocity regime at the test line for nearly five minutes even for such fluids. A comparison between our numerical results and published numerical results obtained using simplistic theories has revealed the key role played by the transition, partially saturated zone near the advancing front during the liquid imbibition. The general conclusion is that use should preferably be made of robust models such as Richards equation for the design of lateral-flow, paper-based assays. [ABSTRACT FROM AUTHOR]

The clogging or jamming of particle suspensions is a ubiquitous problem, hindering the efficiency of particle–liquid and particle–particle separations. Motivated by pressure screening in the pulp and paper industry, we characterize jamming of dilute and semi-dilute mono-disperse rigid-rod suspensions passing through channels mimicking dead-end and cross-flow filtration membranes, experimentally, using particle-tracking velocimetry. We observe that jams nucleate by either bridging of isolated particles across the constriction, or by localized mechanical entanglement of the particles, i.e., flocculation. Uniquely, we observe floc-formation during acceleration into the aperture and report this as primary mechanism for jamming events. We characterized the accumulation-release cycles of the jamming event using an exponential probability distribution; this distribution is indicative of a Poisson process. For jams nucleated by single-particle bridging, the distribution is (primarily) related to the number of fibers passing through the aperture; this is similar to dry, granular materials. For floc-based nucleation events, the distribution is (primarily) related to the suspension concentration with the average time between jams decreasing inversely with the square-root of the initial suspension concentration. For the conditions tested, the distribution was insensitive to changes in constriction geometry. [ABSTRACT FROM AUTHOR]

This study provides a complete rheological characterization of bidimensional (2D) nanomaterial dispersions, employed as 2D-inks precursors in printed electronics. Three different 2D nanomaterials [molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride (hBN)] were dispersed in a Newtonian fluid (toluene) and a viscoelastic fluid (toluene + ethyl cellulose) with different polymer concentrations. The presence of nanosheets does not change the shear rheology of the carrier fluid. Regarding the extensional rheology, the results showed that the pinch-off phenomenon is present in all toluene suspensions; however, the presence of the ethyl cellulose introduces elasticity in the system, even leading to the formation of beads-on-a-string, and the relaxation times of the suspensions depend on the kind of nanosheets present in the fluid. As controlling the droplet size when dispensing 2D-inks is of paramount importance for printed electronics as well as for many other applications, here it is presented a correlation between the rheological properties of these 2D-inks precursors and their droplet size when generated from a capillary nozzle in the dripping regime. [ABSTRACT FROM AUTHOR]

The drainage properties of a gas diffusion layer (GDL) are essential factors in the performance of proton exchange membrane fuel cells. The GDL consisting of a three-dimensional (3D) carbon paper microstructure was developed and meshed with pore-scale reconstruction models in this paper. Localized binder and polytetrafluoroethylene (PTFE) structures were added to the carbon paper microstructure through 3D morphological imaging processing. The monitoring data of 1000 planes were multi-peaky fitted as a function of gas permeability and height to amend the macroscopic porous medium model. We analyzed drainage properties under different contact angles (θ) for the carbon paper with binder and PTFE. We described the mutual intrusion of moisture and air in GDL under different pressure differences. The results show that the pore-scale reconstruction model has the advantages of describing the flow in GDL accurately and with details, detecting low-flow resistance channels that spontaneously formed in GDL, and describing the variation of permeability as a function of location. In a hydrophobic environment, the liquid film connected to a GDL is challenging to split spontaneously. At the same time, the splitting motion of discrete droplets is more prominent than that of the liquid film. The pressure that enables complete water intrusion into the GDL is between 1 and 10 MPa. [ABSTRACT FROM AUTHOR]

Flat paper stained with water buckles and wrinkles as it swells and deforms out of the original plane. Here we quantify the geometry and mechanics of a strip of paper that swells when it imbibes water from a narrow capillary. Characterizing the hygroexpansive nature of paper shows that thickness-wise swelling is much faster than in-plane water imbibition, leading to a simple picture for the process by which the strip of paper bends out of the plane. We model the out-of-plane deformation using a quasi-static theory and show that our results are consistent with quantitative experiments. [ABSTRACT FROM AUTHOR]

A flow passing through a bluff body can produce Karman shedding vortex streets in its wake flow, resulting in strong unsteady loading and vibration. Existing passive control methods can disturb the wake flow, but are usually effective only under certain conditions and cannot adapt to changing environments due to their fixed topographies. Kirigami structures (the art of paper cutting) demonstrate programable out-of-plane buckling deformation under simple force actuations. By stretching and relaxing these kirigami sheets, an array of tilted surface elements can be easily activated and deactivated on the surface of a bluff body. For the first time, kirigami structures are used to achieve dynamic passive flow control. The control performance on the wake flow of a cylinder is validated in a wind tunnel using particle image velocimetry. Activated kirigami structures can push the shedding vortices further downstream from the cylinder by about four times of the uncontrolled one and reduce peak values of the turbulent intensity and Reynolds shear stress by 70% and 50%, respectively. The control performance is largely dependent on the height and shape of the kirigami structures. [ABSTRACT FROM AUTHOR]

In Phys. Fluids 19, 118105 (2007), I. Lunati disputes my earlier paper [Phys. Fluids 18, 047102 (2006)], in which I pointed out an anomaly arising from Thomas Young’s concept of solid/fluid surface tension. The present article examines Lunati’s reasoning and concludes that my earlier paper is correct. [ABSTRACT FROM AUTHOR]

A flexible sheet clamped at both ends and submitted to a permanent wind is unstable and propagates waves. Here, we experimentally study the selection of frequency and wavenumber as a function of the wind velocity. These quantities obey simple scaling laws, which are analytically derived from a linear stability analysis of the problem and which also involve a gravity-induced velocity scale. This approach allows us to collapse data obtained with sheets whose flexible rigidity is varied by two orders of magnitude. This principle may be applied in the future for energy harvesting. [ABSTRACT FROM AUTHOR]

Yu I et al. i [1] presented an interesting investigation on the flow and aerodynamic heating characteristics of air and hydrogen-oxygen combustion gas under the same total temperature and pressure. The authors concentrated on the variations of temperature and velocity of the combustion gas flow in a nozzle and the shock standoff distance and stagnation pressure for the combustion gas flows around a sphere. Fluid mechanics covers a vast scope of flow phenomena that occur in nature, biology, and numerous engineering fields. [Extracted from the article]

Over the past few decades, there has been a significant increase in the use of paper-based microfluidic devices in various fields, including environmental monitoring, food safety analysis, and medical diagnostics. As a result, flow through paper-based substrates has gained much attention in the research community. Liquid flows through a paper substrate due to the inherent capillary suction pressure. In order to predict the flow through a paper substrate, we used macro- and microscopic methodologies to construct an analytical and numerical model. We have considered the effect of different factors, e.g., roughness, swelling, dynamic contact angle, and evaporation simultaneously to predict liquid wicking. A modified capillary radius technique is used to incorporate the effects of roughness and swelling into the numerical model, while a sink factor in Darcy's equation is used to model the evaporation. Experiments are performed to validate the developed models, and it is found that both models are in good agreement with the experiments, with a maximum error of 5%. The proposed analytical and numerical models can be used to forecast the capillary rise in a paper-based substrate, which has implications for paper-based microfluidic devices. [ABSTRACT FROM AUTHOR]

In this Brief Communication, we examine in detail the motion of light particles—or dense gas bubbles—rising under gravity in a cellular flow. We follow the methodology of Maxey [Phys. Fluids 30, 1915 (1987)], and we examine a range of parameters not fully discussed in the past, corresponding to particles lighter and yet more inertial than the surrounding fluid if the added mass effect is considered. We observe a nonmonotonic behavior of the particle rise velocity, which exhibits a maximum for density of the particles only slightly smaller than the density of the fluid. The maximum value of the average rise velocity corresponding to the “optimum” density is several times (more than 40) higher than those obtained for small density changes around the optimum. The occurrence of this maximum is due to the combined effects of particle inertia and fluid added mass, which segregate the rising particles into specific, fast pathlines where the local fluid velocity adds to the particle gravitational velocity. A plot covering particle rise velocity for this range—not covered by the analysis of Maxey—is provided. [ABSTRACT FROM AUTHOR]

A previously developed lattice-Boltzmann lattice-spring method is applied to simulate a wet press process. In simulations, multi-individual flexible fibers are settled on a wire screen by the force of gravity, and a fiber network is formed on the top surface of the wire screen. Next, the coordinates and velocities of fluid and fiber solid particles are copied to a computer press simulator composed of two perforated plates. A pressure pulse is imposed at the fluid contact line of the two press plates. Water is squeezed out of the fiber network by the pressure. During simulations, fiber rigidity, fiber concentrations, and pressure pulses are varied and their effects on water removal and re-wet phenomena are systematically studied. [ABSTRACT FROM AUTHOR]

The unsteady behaviors of adiabatic effectiveness under oscillating flow conditions were studied extensively using the fast-response pressure-sensitive paint technique. Nitrogen was used as the coolant and was discharged from a 35°-inclined round hole. The oscillation frequencies of the mainstream were set to 0, 5, 10, and 20 Hz. The unsteady features of the measured effectiveness were quantified in terms of standard deviations, cross correlations, proper orthogonal decomposition (POD), and dynamic mode decomposition (DMD). Compared to the steady state, the measured effectiveness for the f = 10 and 20 Hz cases varied greatly during each cycle and led to significant enhancement in fluctuations. Cross correlations were used to determine the spatial signatures of large-scale structures (i.e., counterrotating vortex pairs, the horseshoe vortex, and structures near the hole) at various oscillation frequencies. Further POD and DMD analyses successfully decomposed the instantaneous fluctuations into a series of energetic modes, which vividly illustrated the strong modulations in adiabatic effectiveness imposed by flow oscillations and unsteady events. [ABSTRACT FROM AUTHOR]

Liquids spreading over a solid substrate under the action of various forces are known to exhibit a long wavelength contact line instability. We use an example of thermally driven spreading on a horizontal surface to study how the stability of the flow can be altered, or patterns selected, using feedback control. We show that thermal perturbations of certain spatial structure imposed behind the contact line and proportional to the deviation of the contact line from its mean position can completely suppress the instability. Due to the presence of mean flow and a spatially nonuniform nature of spreading liquid films the dynamics of disturbances is governed by a non-normal evolution operator, opening up a possibility of transient amplification and nonlinear instabilities. We show that in the case of thermal driving the non-normality can be significant, especially for small wave number disturbances, and trace the origin of transient amplification to a close alignment of a large group of eigenfunctions of the evolution operator. However, for values of noise likely to occur in experiments we find that the transient amplification is not sufficiently strong to either change the predictions of the linear stability analysis or invalidate the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for aiding the convergence of complex flows simulations on large grids. In this work, large grids are considered those that are of the order of 100 × 106 cells or more. These large grids, which, for example, model the flow around a powered airplane, are typically difficult to generate and modify. If a high-fidelity solution is needed, as in the case of predicting sonic boom, the amount of numerical dissipation must be minimized. This reduced dissipation, however, may result in solution divergence, triggered by improperly resolved large gradients due to grid deficiency. Using a highly dissipative limiter for the entire grid could avoid solution divergence, but the resulting solution may be less accurate. To avoid the loss of solution accuracy due to too much numerical dissipation, we present an approach in which the flow solver uses two limiters: a low-dissipation limiter for the vast majority of the computational domain, and a high-dissipation limiter for the regions where the grid is not adequate for capturing the flow variation and would otherwise lead to the divergence of the solution. The paper demonstrates that (1) the overall solution is not modified by the local use of the high-dissipation limiter, and (2) for a case in which the use of low-dissipation limiter (Venkatakrishnan) resulted in solution divergence, a converged solution is obtained by using the low-dissipation limiter on the vast majority of the grid and a high-dissipation limiter (van Albada) on the region where the mesh was problematic. The effect of a local high-dissipation limiter on the overall solution is explored on a double-wedge canonical airfoil. The multi-limiter approach is then used to predict the near field pressure of the X-59 airplane. [ABSTRACT FROM AUTHOR]

Unsteady separated flow is a common flow condition causing many detrimental effects in aerospace and other fields. Open-loop control is a potential means to eliminate these drawbacks. At present, the unsatisfactory performance of open-loop control mainly attributes to the high-dimensional parameter optimization procedure and the lack of efficient knowledge-guided control law design methods. This paper proposes a method managing to directly obtain the anti-resonant frequency from the input and output amplitude-frequency characteristic curves of the reduced-order model of the flow-control coupled system. Simultaneously, a negative gain criterion is proposed to judge whether the target control effect can be achieved under the current parameter combination. For the control of low Reynolds number flow around a cylinder, the simulation results show that the optimal open-loop control frequency is 1.268 times the natural frequency of the flow, which is consistent with the anti-resonant frequency, and 26.8% of the lift fluctuation is suppressed. This paper also studies the influence of parameters such as flow frequency change, control start time, jet mass flow rate, and so on. Furthermore, control position is the key parameter affecting the amplitude-frequency characteristics. The anti-resonance points on the curves corresponding to different control positions can also guide the design of the optimal control frequency, and the negative gain criterion is still applicable. This method greatly reduces the time consumption in parameter optimization and improves the engineering application prospect of the open-loop control in unsteady separated flow control. [ABSTRACT FROM AUTHOR]

In this paper, exploding foil overpressure actuator was used to experimentally study the law of detonation wave collision in small-size charge conditions. In order to quantitatively study the growth, propagation, and duration of the ultrahigh-pressure phenomenon created by the detonation wave collision, photon doppler velocimetry was used to measure the pressure value of the detonation waves. And, further tests were conducted to isolate and measure the duration and pressure trend of this phenomenon by height gradient experiments. Meanwhile, the influence of two-point initiation and four-point initiation on the ultra-pressure value were compared. The results indicated that with the increase of explosive height, the colliding wave would undergo a regular oblique reflection to Mach reflection and finally to attenuation. This paper lays a foundation for the multipoint initiation of insensitive explosive and shaped charge. [ABSTRACT FROM AUTHOR]

Large-scale dynamic distortion vortexes are generated in advanced complex inlet systems, which can cause serious dynamic distortion flows and influence the performance of engines. Thus, this paper proposes a novel dynamic distortion simulator design method, which uses a column to produce a large-scale streamwise vortex and a rotating valve to enhance the dynamic characteristics, to simulate the complex distortion flow field. Experimental studies were conducted in this paper. The results show that circumferential total pressure and swirl distortion were generated regardless of the valve position. The range of the distortion region decreased significantly when the valve changed from fully closed to fully opened. When the valve rotated continuously, the dynamic total pressure and swirl distortion were generated behind the simulator. At the section, three diameters away from the simulator, the comprehensive distortion index was 7.69%, and the turbulence intensity was 46.4%. The main frequency of the distortion flow field was the same as the switching frequency of the inner channel in the column. [ABSTRACT FROM AUTHOR]

This paper reports the results of a comprehensive investigation to identify turbulent multiphase fluid dynamics through the NexGen burner used for fireworthiness certifications by the Federal Aviation Administration. The burner geometry consists of a draft tube, a stator to swirl the incoming air, a turbulator that is placed immediately downstream of the stator to increase the turbulence intensity of the swirling flow, and a burner cone that exhausts into the atmosphere. A Delavan type-W fuel nozzle, attached downstream of the turbulator injects Jet A into the burner cone, where it mixes with the turbulent swirling air, vaporizes and subsequently burns. The operating conditions consist of air and fuel mass flow rates of 0.0384 kg/s and 2.5 Gph at room temperature and pressure conditions. In this paper, we report on non-reacting fluid dynamics; the reacting flow analysis will be presented in a subsequent manuscript. To systematically analyze the flow configuration, three calculations are conducted. First, to validate our large eddy simulation-based framework, a case without the burner cone is conducted—our results are in reasonable agreement with experimental measurements. In the second configuration, to isolate the effect of liquid injection on turbulent flow physics, simulations are conducted with the burner cone but without fuel spray. Detailed analyses are conducted, including identification of flow structures, swirl generation, and the turbulent kinetic energy budget. Finally, Jet A is injected into the burner, and the spray and gaseous flow fields are quantified and compared with the flow structures developed without spray injection. [ABSTRACT FROM AUTHOR]

When one brings a wet paintbrush into contact with a vertical watercolor paper, the paint may wick into the porous sheet completely or run down to ruin the art. We study a simple model of this spreading dynamics of liquids on hydrophilic porous sheets under the effects of gravity, using a capillary as a liquid source and thin fabrics of non-woven polyethylene terephthalate. Upon finding the maximum flow rate, Qw, that can be absorbed into the fabric, we show that the model can be used to obtain an estimate of the in-plane permeability of fabrics in a simpler manner than the conventional schemes. The shape of a wetting area that grows when the flow rate exceeds Qw to lead to rivulet formation is also theoretically given. The nose shape of the wetting front is shown to be time-invariant, while its profile depends on the properties of the liquid and the fabric. This study can be applied to understand and improve the liquid absorption behavior of hygiene items, heating, ventilation, and air-conditioning equipments, and fuel cell membranes in addition to elucidating the mundane painting activity. [ABSTRACT FROM AUTHOR]

In order to accurately predict the motion trajectory of ice shedding and ensure the safe flight of aircraft, the motion characteristics of ice shedding under two-dimensional (2D) and three-dimensional (3D) conditions are simulated and analyzed. Considering the influence of any possible shape of shedding ice and its rotation and the magnitude and direction of acceleration with time under aerodynamic force, a six degree-of-freedom analysis method is introduced in this paper. This paper proposes a theoretical model, which can be used to calculate the 3D trajectory of ice shedding with arbitrary shape. The dynamic analysis of real 3D shedding ice is carried out, and the motion behavior of shedding ice with different positions and shapes is calculated. The results show that the movement mode of the shedding ice after leaving the aircraft is translation and rotation. The shape of the low-speed region on the leeward side of the shedding ice will first increase, then decrease, and then increase with the rotation of the ice body. The influence of ice shape on ice shedding trajectory is mainly that the shedding ice continues to flip during the downstream movement of the flow field, and the projected area of the effective windward area in the lift and the drag direction changes with time. The average deviation of the shedding ice at position 5 along the spanwise is only 22.9% of that at position 1. Finally, the closer the initial position of ice shedding is to the airfoil root, the greater the probability of ice shedding hitting the aircraft fuselage. In this paper, the probability of ice shedding hitting the aircraft fuselage is 8%, which all occurred in the case with position 1 as the initial position of ice shedding. [ABSTRACT FROM AUTHOR]

This paper studies the shock oscillation and the fluctuating behavior of wall pressure on a V-shaped blunt leading edge. Utilizing numerical simulation and the proper orthogonal decomposition technique, this study analyses the primary modes of shock oscillation and their effect on wall pressure for both a V-shaped blunt leading edge and an improved heat flux reduction configuration. The findings reveal that the shock interaction structures on these models are responsive to the downstream subsonic flow, thereby triggering two distinct oscillation modes: "swinging" and "breathing." These modes drive the main shock interaction structure and the near-wall shock interaction structure in a quasi-periodic motion. Concurrently, the complex shock oscillation phenomenon exerts three distinct influences on wall pressure: the positional oscillation of the shock wave/boundary layer interaction structures, the instability of the shear layer bounding the supersonic jet, and the positional oscillation of the jet collision structure near the stagnation point. Furthermore, the study demonstrates that the improved heat flux reduction configuration is more effective at suppressing wall pressure fluctuations, indicating its potential value in designing hypersonic vehicles. This paper offers valuable insights into understanding shock oscillations and their effect mechanisms on wall pressure within hypersonic flows. [ABSTRACT FROM AUTHOR]

The design and control of turbomachinery require a wealth of spatiotemporal data. Thus, the low-cost and robust estimation of global aerodynamics from extremely limited data and noisy measurements is an important problem. This paper describes a data-driven approach to estimate the full-field pressure distribution of a turbine cascade flow in combination with sparse-distributed sensor measurements. For the offline library building and online reconstructing, the reduced-order model based on standard proper orthogonal decomposition (POD) and least squares approximation, and sparse representation based on overcomplete dictionary and L1 norm minimization are leveraged. To enhance the reconstruction accuracy and robustness with noisy measurements and varied sensor selections, a novel blocked K-means clustering strategy is developed to reconstruct the global flow field through the superposition of multiple local clusters. The statistical results indicate that sparse representation outperforms gappy POD in high-noise measurement environments due to its superior noise robustness and effective feature selection. By applying the proposed blocked clustering strategy, the accuracy and robustness of sparse estimation are significantly improved. The mean square error of gappy POD can be reduced by 9.86% for pressure reconstruction at 90% span of the turbine blade. Sparse representation produces excellent robustness enhancement when the noise intensity exceeds 0.3. Overall, the local reconstruction framework developed in this paper exhibits outstanding advantages in reconstruction accuracy and robustness. [ABSTRACT FROM AUTHOR]

The research objective of this paper is to obtain an efficient space engine chamber wall adherent kerosene blow-off solution, the research methodology uses computational fluid dynamics method and experiments are conducted to verify the numerical calculation accuracy. The effect of gas pressure, gas temperature, ambient temperature, and gas type on the blow-off efficiency was obtained, in which increasing the pressure and temperature of the blow-off gas increased the treatment efficiency by 14.16% and 9.85%, respectively, and the blow-off efficiency was significantly improved. Increasing the operating ambient temperature and changing the type of purge gas increased the treatment efficiency by 4.76% and 5.88%, respectively. Finally, the removal scheme was optimized by increasing the blow-off gas pressure and temperature, and the treatment efficiency of the optimized scheme was improved by 37.5% compared to the original scheme. The findings of this paper provide important guidance for the efficient blow-off off of kerosene adhering to the inner wall of complex structural cavities. [ABSTRACT FROM AUTHOR]

High maneuverability is required for high-speed aircraft. However, the traditional control method with mechanical rudder surface deflection has some defects such as weak control ability and long response time. In this paper, numerical simulations analyze the ability of high-energy jet to improve the control efficiency of X-51A aircraft. The deflection angle of the rudder is 0°–18°, and the high-energy jet is applied to the head of the aircraft and the windward side of the rudder surface. The control effects of the two control methods are compared and analyzed. The results show that within the range of the rudder deflection angle mentioned in this paper, applying high-energy jet control on the head of the aircraft will weaken the rudder surface control efficiency of the X-51A-like aircraft, while applying high-energy jet control on the wind-side of the rudder surface can enhance the rudder surface control efficiency of the aircraft by 13.78%. In this study, numerical simulations were used to analyze the effect of applying high-energy jets at different positions to enhance the efficiency of the rudder surface of a high-speed aircraft. This paper offers a novel concept for employing active flow control methods to enhance the efficiency of high-speed aircraft's rudder surfaces, thereby improving the application potential of such aircraft. These findings can serve as a reference for future research on the efficiency of rudder surfaces in high-speed aircraft. [ABSTRACT FROM AUTHOR]

This paper explores the use of Deep Reinforcement Learning (DRL) to improve the aerodynamic stability of compressible flow around a vibrating cylinder. In uncontrolled conditions, the cylinder experiences a drag coefficient of 1.35 and an oscillatory lift coefficient with an amplitude of 0.35. By applying a classic Deep Q-Network (DQN), the lift oscillation amplitude is significantly reduced to ±0.025, marking an improvement of over 100%. The study further investigates the effects of episode count, neural network architecture, and DQN variants on performance, demonstrating the robustness of the approach. While changes to the neural network structure within the classic DQN yield limited improvements in reducing lift oscillations, both the classic and dueling DQN variants effectively control lift oscillations. Notably, the dueling DQN provides greater stability, reducing lift oscillation amplitude to as low as ±0.001. The paper also examines the effect of varying jet positions, offering valuable insights into the adaptability and generalization of the proposed DRL-based control strategy. [ABSTRACT FROM AUTHOR]

The side channel pump generates several disadvantage vortices due to abrupt structural changes at the junction of the impeller and side channel, leading to unstable flow, which may induce severe vortex cavitation at the inlet section of the side channel, its impact on the pump's unstable flow mechanism and on the energy conversion characteristics has yet to be thoroughly investigated. This paper explores the effect of backflow vortex on pump performance through optimizing side channel inlet angles by combining the Ω criterion, helicity, and entropy production methods. The computational fluid dynamics numerical simulation's accuracy has been experimentally verified. It was found that increasing the side channel inlet angle could improve internal flow, thereby suppressing backflow vortices and promoting dynamic vortices formation in the inlet section. The backflow vortex is the primary source of high localized energy loss in the inlet section, significantly influencing the reduction of flow loss. It also reduces low pressure areas caused by backflow vortices, thus, restricting cavitation origin. In addition, within a certain range, the flat side channel pump enhances its hydraulic performance, exhibiting the best performance at a 60° inlet angle with an efficiency improvement of 4.6% at the Best Efficiency Flow Point (BEP), which has the most effective backflow vortex suppression, and therefore, lowest flow losses. However, the head improvement was negligible. The performance improvement is due to complete energy conversion within the inlet section. This paper offers new insights into the mechanisms underlying internal energy loss and cavitation characteristics in refining side channel pumps. [ABSTRACT FROM AUTHOR]

Currently, the hydrodynamic simulation strategies for high-speed vessels exhibit a wide diversity. Direct three-dimensional (3D) Computational Fluid Dynamics simulation would be the most suitable choice if not for its time-consuming nature. To save computational resources and accelerate calculation speed, research works that utilize two-dimensional (2D) approaches to address three-dimensional problems have emerged over the past few decades, which represented by strip theory and two-dimensional plus time (2D+t) theory. Among them, Cartesian grid-based 2D+t method could be the most accurate one. However, this method, though often used to simulate ship-generated waves, is rarely applied to unsteady motion. A Cartesian grid-based unsteady 2D+t method is developed in this paper, which enables the simulation of the unsteady motions of high-speed vessels at semi-planning or near-planning states. A method for incorporating unsteady motion within the framework of 2D+t theory is proposed in the paper, along with the introduction of a novel central processing unit based multi-threaded task parallel method for multi-section parallel computation. With this method, a 3D unsteady motion problem of high-speed vessels is transformed into several 2D unsteady motion problems of deformable bodies. The proposed model is validated with selected cases, showing that the model is capable of simulating unsteady motion problems of high-speed vessels. [ABSTRACT FROM AUTHOR]

This paper introduces Interface Equilibrator (IE), a new graphical-user-interface software for simulating the equilibrium shape of fluid–fluid interfaces in a wide range of wetting and capillarity problems. IE provides an easy-to-use three-dimensional computer-aided-design environment to define the problem's geometry (i.e., the solid surfaces and the fluids' volumes), by simply loading opportune triangular meshes, and chemistry, by selecting the value of the relevant experimental parameters (e.g., Young's contact angle). No other input is required. Then, IE calculates the fluid–fluid interface's equilibrium shape using a novel numerical methodology, presented in this paper, that consists in an energy-minimization Monte Carlo simulation alongside other built-in automated methods to, e.g., refine the fluid–fluid interface mesh according to its local curvature and polish it. The energy-minimization algorithm is based on a numerical approach introduced a few years ago [Soligno et al., "The equilibrium shape of fluid-fluid interfaces: Derivation and a new numerical method for Young's and Young–Laplace equations," J. Chem. Phys. 141, 244702 (2014)] that is generalized here to handle unconstructed meshes with any topology and to include also new types of forces (e.g., due to a rotating system or to a line tension). In addition, several illustrative and scientifically interesting novel results are presented in this paper to demonstrate IE's versatility and capability of addressing a broad spectrum of research problems, relevant for many technological applications, such as microfluidics, fluid management at various length scales, printing, colloids, soldering for chip manufacture, etc. Finally, the paper reports numerous validation tests, where known analytic or numerical solutions are compared with IE's results to verify the correctness and accuracy of IE's calculations. [ABSTRACT FROM AUTHOR]

The rotating detonation engine (RDE) has attracted considerable interest as a potential new propulsion system, owing to its ability to self-pressurize, its high thrust-to-weight ratio, and its simple structure. This paper provides a comprehensive review of the latest research advancements and challenges associated with the application of liquid fuels in RDEs. The study begins by focusing on the applicability of various liquid fuels in RDEs, examining the effects of fuel parameters—such as the equivalence ratio, the total temperature, the degree of pre-evaporation, and the droplet diameter—on detonation wave propagation and engine performance. Subsequently, the impact of inlet parameters and the optimization of combustor performance on detonation waves, along with control methods for mode-switching mechanisms, are investigated. Finally, the paper summarizes the common issues and challenges encountered in the application of liquid fuels in RDEs. These include droplet atomization, mixing and evaporation, detonation wave control, and combustor cooling. To address these challenges, future developments in RDEs may focus on four key areas: the use of complex fuels (such as blending fuels, sustainable aviation fuel, and other biofuels), detonation wave mode control, combustor cooling technologies, and the integration of RDEs with turbomachinery. These advancements will further propel the development of liquid-fueled rotating detonation technology. [ABSTRACT FROM AUTHOR]

The dynamic behavior of hydro-turbine rotor system is a complex multi-field and nonlinear problem, which has been studied by many researchers. The analysis of the rotor system dynamic characteristics is usually carried out based on the behavior analysis of bearings, hydraulics, electromagnetics, etc., while the thermo-elasto-hydrodynamic characteristics of bearings are extremely important to numerical accuracy. Therefore, this paper first summarizes the research progress in bearing lubrication performance, and further summarizes the research on hydro-turbine rotor system dynamic characteristics, including the modal characteristics and dynamic response characteristics. Finally, this paper summarizes the main research progress of the hydro-turbine rotor system and proposes possible directions in future research. Literature review shows that the hydro-turbine runners and bearings have achieved multi-field coupling analysis of three-dimensional (3D) models, and some work on multi-field coupling of rotor systems has been carried out. The transition of 3D multi-field coupling from single component to rotor system is significant to accurately predict the rotor system dynamic characteristics and the solution of engineering problems, which requires further in-depth research on the multi-field coupling theory, numerical methods, 3D model integrity, simulation software, etc., and the spatiotemporal synergy between multi-fields should be fully considered. [ABSTRACT FROM AUTHOR]

This paper develops a wave radiation analysis model in horizontal oscillation mode for concentric cylindrical arrays with arbitrary numbers and arrangements within the framework of linear potential flow theory. The concentric cylinders have solid inner cylinders and porous outer cylinders, and they are both bottom-mounted and surface-piercing. The porous boundary conditions of the outer cylinders are treated using Darcy's law, and the flow field is divided into one outer region and N (number of cylinders) inner regions with the outer cylinders as the boundary. Employing eigenfunction expansion and region-matching methods, expressions for the radiation velocity potential of each region are obtained, and then expressions of the added mass and damping coefficient of each cylinder are obtained. Following a rigorous verification of the results against published literature, this paper proceeds to analyze the impact of various parameters, including oscillation modes, outer cylinder permeability, radius ratio, spacing, and the number of cylinders, on the wave radiation characteristics of tandem-arranged cylindrical arrays. The research reveals that when the oscillation direction of the structure is parallel with its arrangement direction, the hydrodynamic coefficient curves exhibit significant spikes, attributed to the influence of the Dirichlet trapped mode. Outside the peak regions, the hydrodynamic coefficient curves display regular fluctuations, which are attributed to the alternating occurrence of constructive and destructive interference effects within the wave field. [ABSTRACT FROM AUTHOR]

In this paper, results of preparatory tests for a space experiment "Marangoni in Films" on board International Space Station are reported. The setup is thermalized at a setpoint temperature so that (thermal) Marangoni convection is exclusively a result of evaporative cooling of the film, here composed of a Hydrofluoroether (HFE)-7100, evaporating into nitrogen at a given setpoint pressure. The present paper is entirely devoted to the evaporation rates, whereas the Marangoni convection itself will be analyzed in future studies. Apart from the temperature and nitrogen pressure, various setpoints for the initial relative saturation in HFE-7100 vapor are explored. A special design of the test cell with a square chimney surrounding a square opening of the liquid layer permits to largely stabilize the evaporation rates during a longest-lasting middle stage (beyond the initial transients and the final film dry-out). In addition, it facilitates the use of vapor (digital-holographic) interferometry for measuring the evaporation rates, the results of which are compared with independent measurements by means of the pressure evolution within our sealed cell of a fixed volume. An excellent agreement is found before the final dry-out stage for all setpoint parameter combinations tested. The study is accompanied by numerical finite-element simulations in an axisymmetrized geometry, neglecting a possible influence of the Marangoni convection and verifying certain premises used in interferometric post-processing. Even if the simulation results might somewhat over-/underpredict in each particular case, the overall dependence of the evaporation rate on the setpoint parameters is well reproduced and the role of the buoyancy convection is thereby explored. [ABSTRACT FROM AUTHOR]

The concept of the integration of offshore wind power and ocean ranch represents a development trend of intensive use of the sea. With the rise of this concept, this paper proposes a new type of porous marine structure. Based on the assumptions of the linearized theory of water waves, the wave diffraction and radiation problems of the bottom-standing surface-piercing porous compound coaxial cylinder are studied in this paper. Two seabed conditions are considered: (a) the ideal state, where the seabed is impermeable, and (b) the actual state, where the seabed is porous. The analytical models for the hydrodynamic problems of the porous cylinder placed on the impermeable and porous seabed are established. The wave diffraction and radiation problems are solved by using the eigenfunction expansion method and the velocity potentials of the fluid motion are derived. To verify the correctness of the program, the present model is reduced and compared with existing models. After completing the verification, the effects of the porous seabed and structural parameters on the hydrodynamic characteristics of the porous cylinder are studied. The results indicate that the porous seabed has effects on the wave run-up on the porous cylinder, and the higher the seabed porous effect parameter, the smaller the wave run-up on the porous cylindrical surface of the outer cylinder and the impermeable cylindrical surface of the inner cylinder. Enlarging the porous effect parameter and the radius ratio of the compound cylinder leads to decreases in the wave force, moment, added mass, and radiation damping. By changing the parameters of the porous cylinder, the hydrodynamic characteristics of the porous cylinder can be greatly reduced. This study is expected to provide support for engineering design of relevant marine structures. [ABSTRACT FROM AUTHOR]

Flow reconstruction based on limited measurement data, which can be considered as a state estimation problem, constitutes a fundamental task within the realm of fluid mechanics. In recent years, the physics-informed neural networks (PINNs) have been proposed to achieve flow field reconstruction by integrating the measurements with governing equations during network training. However, the performance is compromised by the presence of high-level data noise, and the uncertainty of the reconstructed flow fields remains unattainable. In this paper, we first perform a systematic study to investigate the impact of data noise on the reconstruction result of PINNs. Subsequently, we present strategies of early stopping and loss regularization, which can suppress the overfitting issue to some extent. Ensemble learning is also employed to quantify the uncertainty of the results from vanilla PINNs. In addition, we propose to use a Bayesian framework of PINNs (BPINNs) for flow field reconstruction, which incorporates the Bayesian neural network with PINNs. It is demonstrated that BPINNs are capable of reconstructing the velocity and pressure fields from sparse and noisy velocity measurements, while providing comprehensive uncertainty quantification of the flow fields simultaneously. Compared to the vanilla PINNs, BPINNs are more accurate and robust when there is a high level of data noise. We conduct experiments on two-dimensional cavity flow and the flow past a cylinder to validate the effectiveness of the proposed methods throughout the paper. [ABSTRACT FROM AUTHOR]

Adaptive mesh refinement (AMR) technology and high-order methods are important means to improve the quality of simulation results and have been hotspots in the computational fluid dynamics community. In this paper, high-order discontinuous Galerkin (DG) and direct DG (DDG) finite element methods are developed based on a parallel adaptive Cartesian grid to simulate compressible flow. On the one hand, a high-order multi-resolution weighted essentially nonoscillatory limiter is proposed for DG and DDG methods. This limiter can enhance the stability of DG/DDG methods for compressible flows dominated by shock waves. It is also compact, making it suitable for the implementation of AMR with frequent refinement/coarsening. On the other hand, a coupling method of DG and immersed boundary method is proposed to simulate flow around objects. Due to the compactness of DG, the physical quantities of image points can be directly obtained through the DG/DDG polynomial of the corresponding cells. It avoids the wide interpolation stencil of traditional IBM and makes it more suitable for the parallel adaptive Cartesian grid framework in this paper. Finally, the performance of the proposed method is verified through typical two- and three-dimensional cases. The results indicate that the method proposed in this paper has low numerical dissipation in smooth areas and can effectively handle compressible flow dominated by discontinuities. Moreover, for transonic flow over a sphere, the error of results between the proposed method and direct numerical simulation is within 1%, fully validating the accuracy of the method presented in this paper. [ABSTRACT FROM AUTHOR]

Hyperloop systems, where a pod travels at high speed within a tube under rarefied conditions, have a maximum speed limit due to the Kantrowitz effect. One solution to overcome this limit is to include a circuit with a fan that can also assist the pod's propulsion through a nozzle at the vehicle's rear. This paper focuses on analyzing the propulsive efficiency of these coaxial jets within a tube at low-pressure conditions. The paper's objective is to use a computational fluid dynamics tool to design an experiment in a wind tunnel with a steady tube and vehicle that could reproduce the actual operation of a stationary tube and a moving vehicle. Several issues are dealt with. First, the effect of the vehicle's front design on the coaxial jets, which resulted be negligible. Additionally, the increase in temperature in the compressor circuit can be neglected, simplifying the experimental arrangement. Third, scaling the wind tunnel prototype shows that the difference in size can be compensated by setting the test pressure at ambient conditions. Finally, considering steadiness in the vehicle in the test leads to a different velocity pattern in the coaxial jets. Several changes in the tube's geometry are proposed and analyzed to address this problem. The results demonstrate that it is possible to replicate the actual coaxial jets in steady conditions with a small tapered section in the tube. Furthermore, this modification can be used over a relatively large range of operating conditions and for different rear pod designs. [ABSTRACT FROM AUTHOR]

Super-resolution reconstruction of turbulent flows using deep learning has gained significant attention, yet challenges remain in accurately capturing physical small-scale structures. This study introduces the Conditional Enhanced Super-Resolution Generative Adversarial Network (CESRGAN) for reconstructing high-resolution turbulent velocity fields from low-resolution inputs. CESRGAN consists of a conditional discriminator and a conditional generator, the latter being called CoGEN. CoGEN incorporates subgrid-scale (SGS) turbulence kinetic energy as conditional information, improving the recovery of small-scale turbulent structures with the desired level of energy. By being aware of SGS turbulence kinetic energy, CoGEN is relatively insensitive to the degree of detail in the input. As shown in the paper, its advantages become more pronounced when the model is applied to heavily filtered input. We evaluate the model using direct numerical simulation (DNS) data of forced homogeneous isotropic turbulence. The analysis of Q-criterion isosurfaces, energy spectra, and probability density functions shows that the proposed CoGEN reconstructs fine-scale vortical structures more precisely and captures turbulent intermittency better compared to the traditional generator. Particle-pair dispersion simulations validate the physical fidelity of CoGEN-reconstructed fields, closely matching DNS results across various Stokes numbers and filtering levels. This paper demonstrates how incorporating available physical information enhances super-resolution models for turbulent flows. [ABSTRACT FROM AUTHOR]

The insight to the hydrodynamics of the flapping hydrofoils can be utilized to comprehend the fluid-mechanical mechanisms for the variation of the hydrofoil's propulsion performance, and optimize the design of the bio-inspired underwater robots. This paper numerically investigates the hydrodynamic performance of a two-dimensional NACA 0012 (defined by National Advisory Committee for Aeronautics) hydrofoil undergoing combined pitching and heaving motions, based on the discrete vortex method. A novel boundary method which couples the Joukowsky transformation and the circle theorem is used to deal with the vortex elements inside the hydrofoil surface. The numerical method is validated by the experiments from the available relative cases by comparing the hydrodynamic forces and the wake patterns with the pure pitching and pure heaving hydrofoil. Via the vortex dynamics, the discussion is carried out to explain the thrust deterioration within the large Strouhal number and large pitching amplitude in the combined motion. Further, a parameter optimization study is conducted under different heaving amplitudes and pivot locations. When the heaving amplitude is 1.25c and the pivot location is at 0.45c, the propulsion efficiency of the flapping hydrofoil is found maximized. Finally, by combining the time history of hydrodynamic forces and the formation and release of the leading-edge vortex and trailing-edge vortex in the vorticity field, this paper explains the reason why the optimal efficiency is obtained. [ABSTRACT FROM AUTHOR]