Tangential Airflow Research Articles

Numerical simulation of metal sheet damage under high-speed tangential airflow and laser irradiation

Numerical simulation of metal sheet damage under high-speed tangential airflow and laser irradiation

Peeling off behavior of centimeter-level molten pool subjected to subsonic tangential airflow during laser ablation process

In this paper, a computational fluid dynamics model considering the interaction between subsonic tangential airflow and centimeter-level molten pool was established to investigate the melt peeling off behavior during laser ablation process. The results showed that the airflow resulted in violent fluctuations on the surface of molten pool and then flowed upward at a velocity of 2–10.5 m/s, accelerating the surface melt to move upward. A liquid column was formed and elongated slender along the metal surface pushed by the subsonic tangential airflow. An upward-bending tail appeared at the end of the liquid column, which was accelerated up to 6 m/s and then cut off by the airflow, making the melt peel away from the molten pool. Compared with the partial melt peeling off at 0.3 Ma, almost all of the melt was pushed out of the molten pool to peel off when the airflow velocity was increased to 0.5 Ma. When the airflow velocity was further increased to 0.8 Ma, the metal on the surface was accelerated in short time, leading to the peel-off occurring in advance. In addition, the melt temperature decreased due to the forced convection cooling effect of airflow. When the melt solidified, the solid-liquid interfacial tension generated in the liquid column provided tangential force conducive to cutting off the liquid column and peeling off. The decrease rate of the melt temperature with time accelerated significantly and then expedited the melt solidifying and peeling off when the airflow velocity was increased to 0.5 Ma. The decrease rate further accelerated and the temperature decrease occurred earlier at 0.8 Ma, reaching a stable state in a shorter time.

The Effect of a Three-Blade Tube on the Pneumatic Transport of Pebble Particles

In this paper, the Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) coupling method was used to simulate the pneumatic transport of pebble particles in a three-blade spiral tube. The results showed that the flow field distribution rotated along the circumference after loading. The maximum velocity of the flow field after loading was manifested as rotation along the circumference. In addition, the swirl intensity decreased exponentially with the increase in conveying distance, and the maximum swirl intensity had a saturation value. After reaching the saturation value, it is not evident that increasing the initial air velocity significantly affected swirl variation. The smaller the pitch, the greater the initial swirl intensity. The swirling flow was conducive to the fluidization of particles, but it would bring a significant energy loss. Increasing the swirl can increase the degree of particle dispersion. There is an optimal tangential airflow velocity, which allows the particles to fully spin and stay in the suspension zone without being thrown onto the pipe wall by excessive centrifugal force. At this time, the energy efficiency reaches the highest level. A 5.87 m/s velocity was deemed the optimal tangential airflow velocity for conveying 3 mm particles.

Fiber movement during twisting in air vortex spinning

In order to clarify the twisting mechanism of the air vortex spinning machine, this paper investigates the motion law of air vortex spinning fiber from the guided access into the twisting chamber during the whole process. While considering the bi-directional coupling effects of the airflow and fiber, the airflow–fiber fluid–solid coupling solution model of the guiding parts is established, and the fluid–solid bi-directional coupling solution platform is built based on ANSYS Workbench software. The movement trajectories of fibers in the process of single and double fibers entering the twisting zone from the guiding channel to the hollow spindle guiding channel were obtained, respectively. Through the fluid–solid coupling analysis, (1) under the action of airflow, the fiber movement is complex and variable, while the movement of the fiber affects the distribution of the surrounding airflow velocity and pressure. (2) Due to the asymmetric structure of the guiding channel, the airflow distribution on both sides of the fiber in motion is uneven, so that the fiber as a whole is wavy forward, and from time to time collisions occur with the tube wall. (3) The fibers are sucked into the twisting chamber under the effect of pressure difference, and the fibers are twisted under the combined effect of axial airflow and tangential airflow. The head end of the fiber enters the guided access in the middle of the hollow spindle under the guidance of the guiding pins. (4) In double fiber movement, there will be mutual adsorption, fibers becoming closer together, contact, stagger, separation and other phenomena that also affect the fiber in the airflow under the action of the twisting winding movement process.

Perforation Effect of Continuous Laser on Glass Fiber Reinforced Polymer Matrix Composites Under Subsonic Tangential Airflow

Perforation Effect of Continuous Laser on Glass Fiber Reinforced Polymer Matrix Composites Under Subsonic Tangential Airflow

Experimental and Computational Investigation upon Combustion Characteristics of Liquid Fuel in a Novel Combustor with Hybrid Swirl and Recirculation Bowl.

In the present study, a novel hybrid swirl combustor is designed to reduce the size and complexity of a conventional gas turbine combustor. In this combustor, a dual-swirl pattern is adopted by providing the central vane swirler (45° vane angle) and circumferential tangential injection scheme to achieve higher recirculation of heat and combustion products inside the combustor. Numerical and experimental studies are carried out to understand the flow patterns and combustion characteristics in this high mass-heat interacting environment. Initially, computational studies were carried out to find the optimum geometry for greater recirculation and interaction among the reacting species inside the combustor. Liquid fuel (kerosene) is sprayed into the combustor for two thermal inputs of 25 and 50 kW. Three cases were studied to analyze the effect of bowl recirculation and tangential air inputs in addition to the swirlers. The hybrid swirl, formed by the counter-flow pattern, helps in achieving low and uniform temperature throughout and assists in flame anchoring. The tangential air flow provides a push to the combustion products from the downstream to the central recirculation zone of the combustor. The combined effect of central and tangential swirlers helps in attaining a more distributed combustion. The CO and NO emissions reduced with the use of hybrid swirl.

Particle Emission Fluctuation in Turbulent Diffusion Flames

ABSTRACT Particle emission fluctuation was studied experimentally with a free convection diffusion flame, which used primary reference fuels consisting of n-heptane and iso-octane. The smokeless weak turbulent flame was turned into a smoky strong turbulent flame by disturbing it with a tangential airflow. A diffusion charger (DC) particle sensor was used to measure the transient particle mass (PM) emissions. The turbulence increased the PM significantly, particularly for a higher fraction of iso-octane fuel. Statistical results showed that the PM fluctuation follows the chi-square distribution. Furthermore, the theoretical analysis proved that the PM is related with the square of the fluctuation velocity.

Modeling the microwave transmittance of glass fiber-reinforced plastics subjected to laser ablation

The microwave transmittance of glass fiber-reinforced plastic (GFRP) slabs subjected to continuous-wave laser ablation was studied in the framework of continuum mechanics. First, a one-dimensional physical model involving laser absorption, heat conduction, resin pyrolysis, thermal radiation, and convection heat transfer was established to obtain the temperature field. An experiment-based absorption coefficient was proposed to capture the bulk-to-surface absorption transition during laser ablation. Second, the complex dielectric constant was modeled using a solid-state kinetic model describing the graphitization of pyrolysis products. The microwave reflectivity and transmittance were calculated based on the dielectric constant distribution. The agreement of the temperature and microwave transmittance with the experimental results suggests the feasibility of the model. The influence of laser power density, material thickness, and tangential airflow velocity on microwave transmittance was studied based on the model. The microwave transmittance changed nonmonotonically with increasing slab thickness owing to the competition between different physical mechanisms. The existence of tangential airflow reduced the decrease in microwave transmittance, particularly for weaker lasers. This study provides a useful physical model for predicting the microwave transmittance performance of GFRP in extreme heat environments.

Capsule-Based dry powder inhaler evaluation using CFD-DEM simulations and next generation impactor data

Capsule-based, single-dose dry powder inhalers (DPIs) are commonly-used devices to deliver medications to the lungs. This work evaluates the effect of the drug/excipient adhesive bonding and the DPI resistances on the aerosol performance using a combination of empirical multi-stage impactor data and a fully-coupled computational fluid dynamics (CFD) and discrete element method (DEM) model. Model-predicted quantities show that the primary modes of powder dispersion are a function of the device resistance. Lowering the device resistance increases its capacity to transport a wider range of particle size classes toward the outlet and generate more intense turbulence upstream therein. On the other hand, a higher device resistance increases the velocity of the tangential airflow along the device walls, which in turn increases the intensity of particle/device impaction. Correlating model data and experimental results shows that these differing powder dispersion mechanisms affect different formulations differently, with finer aerosols tending to result when pairing a lower resistance device with formulations that exhibit low API/excipient adhesion, or when pairing a high resistance device with more cohesive formulations.

Consideraciones físicas y geométricas acerca del crecimiento de Pichia pastoris en tiras de espuma de poliuretano

This work introduces the use of polyurethane foam (PUF) slabs for solid-substrate fermentation. Attention is paid to the distribution and properties of the liquid broth within the slabs in relation to the growth parameters of Pichia pastoris. The experimental setup was made of thin slabs supported horizontally by screens within cylindrical chambers. This way, water loss due to compression or gravity drain was minimal and exposure to tangential air flow was maximal. The highest biomass was Xmax = 39.5±3.3 gL-1 with (So) of 150 gL-1 of glucose. Biomass yield, Yx/s followed the correlation, Yx/s = 0.525-0.0018S0 (R2 = 0.996), and the growth rate m = 0.24 h-1/(S0/34.6). The respiratory quotient, RQ, followed a biphasic pattern with a maximal RQ » 1 when S0 = 50 gL-1. PUF micrographs showed that liquid was not retained when the integrity of the polyurethane network was disrupted at cutting edges of the slabs with an approximate depth of 0.025 cm, but the fraction of disrupted PUF would be small for wide slabs and h = 0.7 cm. The use of horizontal PUF slabs with thickness of 0.7 cm seems to be a practical way to upscale solid state fermentation (SSF) since a squared meter of this material could produce 83 g of yeast.

Effects of tangential supersonic airflow on the laser ablation of laminated CFRP

Ablation behaviors of laminated carbon fiber reinforced plastics (CFRP) subjected to intense continuous wave laser in the supersonic wind tunnel are investigated experimentally. Comparable laser ablation tests in other environments, i.e., static air, static nitrogen and open airflow, are also carried out. Laser ablation rate in the supersonic wind tunnel is significantly larger than those of the other environments, in particular, at least twice of that in an open tangential airflow condition. The ablation morphology can be classified into two regions, coupled ablation zone (CAZ) and downstream affected zone (DAZ). Coupled thermal-fluid-solid analysis including thermochemical ablation and thermomechanical erosion models reveals that the contribution of each laser mechanisms is distinctive at the different positions of the laser ablation pit.

Characteristics and influences of plume during CW laser-CFRP interaction under tangential gas flow

The characteristics of plumes during continuous wave laser irradiation of laminated carbon fiber reinforced plastics (CFRP) under tangential air flow or nitrogen gas flow are investigated. The temperature of the plume is measured by the infrared thermal imager. The change in relative mass concentration of the plume is studied by the laser extinction method. The front surface emissivity-corrected temperature maps of CFRP are measured by the infrared thermal imager to estimate the influences of plumes. The highest temperature in the plume is closely related to the absorption of the laser by the plume rather than the combustion effects of the plume. The differences of the plumes, temperature, the material surface temperature and the heat affect zone, under the two different kinds of gas flows, are all due to the effect of the burning of the plume under air flow. As the mass concentration of plumes decreases, these differences gradually disappear or no longer increase. The results of this work can be referenced for the application of the laser processing and the laser damage.

Evaporation-induced soil water flux to design suction drain for low-carbon ground stabilisation: Experimental investigation and modelling

The suction drain is a novel concept for low-carbon temporary ground stabilisation in clayey soils alternative to jet grouting and ground freezing. Boreholes are drilled into the ground and air is injected to the borehole end through a delivery pipe. The air flowing through the gap between the pipe and the borehole surface backward towards the borehole entry removes water by evaporation and, hence, increases the undrained shear strength of the soil surrounding the drain. There are no studies that allow quantifying soil water evaporation generated by tangential airflow for the case of ‘wind tunnel’ only a few centimetres high over an evaporating surface a few meters long. This paper first presents an experimental investigation on water evaporation induced by air flow. A 3 m long wet surface was subjected to tangential air flow into a 40 mm gap. Tests were carried out by considering different air velocities and inlet air relative humidities. A model was then formulated to quantify the water evaporation rate for any length of the wet surface. The model parameters were calibrated against one experimental dataset and the model was then validated against an independent dataset. Finally, an empirical equation is proposed to estimate model parameters without the need of carrying out experimental tests. This is based on the vapour transfer coefficient established empirically for evaporation from open water (external air flow), which was found to remain valid for confined evaporation (internal air flow). The paper therefore provides a tool to estimate airflow-induced evaporation to successfully design the suction drains.

Shift of the laser ablation center on CFRP induced by the vortex in the boundary layer of tangential airflow

The oxidation ablation of carbon fiber-reinforced polymer (CFRP) induced by a continuous wave (CW) laser under tangential airflow was modeled in this study. The fluid of the airflow and the diffusion of the oxygen in the boundary layer were simulated. The numerical predictions indicated that the center of the ablation pit deviated from the center of laser spot, which moved to the downstream area from the upstream area as the ablation time increased. These results were proven by the laser ablation experiments. The vortex appeared in the airflow when the ablation pit was deep enough. It significantly modified the mass transport of oxygen due to the recirculation in the ablation pit. Based on this model, the impacts of the airflow velocity, the laser power density, and the laser spot radius on the shift were investigated. The results of this work can be referenced for the applications of laser processing and laser damage.

Study on Ignition Delay Time of Al/Mg Fuel-rich Propellant under Tangential Air Flow

Solid propellant, as the power source of propulsion system, has obvious influence on the internal ballistic characteristics of ramjet. The ignition and combustion charac-teristics of solid propellant help to reveal the combustion mechanism and have im-portant guiding significance for estimating the performance of propulsion system. In this paper, the ignition and combustion characteristics of Al/Mg fuel-rich propellant under tangential air flow were studied. Laser ignition experiment was carried out on the Al/Mg fuel-rich propellant at different tangential air flow rates and tangential air flow components. The results show that the air flow rate and air flow composition can affect the flame shape and the brightness of the propellant. At the same time, with the increase of air flow rate, the more obvious the erosion combustion effect on the pro-pellant burning surface. The air flow rate also affects the ignition delay time. When the air flow rate is low, the ignition delay time decreases with the increase of air flow rate. When air flow rate is 0.8L/min, the ignition delay time is reduced to the mini-mum of 350ms, but with the air flow rate continues to increase, the ignition delay time is increasing. As the oxygen content in the air flow increases, the ignition delay time increases. However, when the oxygen content is less than 14% or higher than 21%, the effect of oxygen content on the ignition delay time is weakened.

Influence of the Physical Properties of Mixed Biofuels on the Spray Characteristics

An analysis has been made of the influence of the physical properties of mixed biofuels on the characteristics of spraying by centrifugal atomizers. It has been shown that the characteristics of the jet downstream of devices effectively atomizing oil fuels can significantly degrade in using biofuels. To avoid collapse of the fuel bubble, it is necessary to calculate the form of the fuel sheet. We have constructed the boundary curves in coordinates fuel Reynolds number–Laplace number characterizing the transition from the ″tulip″ form of disintegration of the sheet to its atomization and enabling one to determine the boundaries of the spraying region for any atomizer. The swirl of the air surrounding the atomizer in the same direction as the twist of the fuel sheet markedly upgrades the spraying characteristics of strongly bound fuels. The determining influence on the form of the sheet is exerted thereby by the value of the tangential air flow velocity, and the value of the axial velocity is immaterial.

Empirical Parameter Identification for a Hybrid Thermal Model of a High-Speed Permanent Magnet Synchronous Machine

An accurate thermal model will commonly require empirical parameter identification, specifically for the convection coefficients and interface resistances. A high-speed permanent magnet synchronous machine test platform, equipped with various temperature and power measuring equipment, is used to determine these parameters. Specifically, two tests, a dc injection test and rotational test with no load connected, were performed. The results were compared with a lumped thermal model and the parameters updated until an acceptable match was achieved. There were significant differences in the temperature rise when activating forced air cooling, thus significantly influencing the convection coefficients. Also, a significant difference in the interface resistances showed that in these high-speed machines, doing only the dc injection test will not give accurate interface resistance values. The work is novel through combining systematic empirical parameter identification to determine the convection coefficients and interface resistances for a machine where the end windings are cooled by forced tangential air flow.

Motion of water drops on hydrophobic expanded polymer mat surfaces due to tangential air flow

Abstract Hydrophobic expanded polymer mats are used in a wide range of industries for many purposes. Their relatively low cost, availability in a wide range of polymer materials, and consistency of pore size distribution are advantageous for some applications such as the separation of liquid drops from gas streams. When fabricated of a non-wetting material, liquid drops tend to stay on one side of the mat and can move across the mat surface due to drag of the gas flow. The rate of movement of drops on the surface can affect the rate of coalescence, the drop size, the loading of drops on the surface of the mat, and ultimately the effectiveness of the mat to separate the drops from a gas stream. In this work the movements of water drops on the surfaces of expanded polymer mats due to tangential air flow are observed to determine the effects of mat material properties and geometrical characteristics, drop dimensions and air flow conditions. A correlation for a drag coefficient of drop movement on the mat surface is developed. A second correlation for the minimum Reynolds number of the gas to initiate the movement of drop on the surface of the mat is also developed.

切向气流作用下激光辐照对尼龙材料的热烧蚀规律

切向气流作用下激光辐照对尼龙材料的热烧蚀规律

切向气流对激光辐照效应影响的研究进展

切向气流对激光辐照效应影响的研究进展