Air Jet Flow Research Articles

MODEL OF THE PROCESS OF PROCESSING THE EDGES OF AEROSPACE PARTS WITH FREE ABRASIVE USING AIR JETS

In this work, models of the process of machining the surfaces of parts edges with free abrasive in a fluidized state using air jets were developed to determine the process parameters that ensure a high level of quality. Theoretical studies were carried out on the proposed model of the process of machining the surfaces of parts edges with free abrasive grain in a fluidized state using air jets. In the research, the initial equations were based on the known dependencies for the dynamic pressure of air jets hitting an obstacle and the change in the parameters of plane jets along the path of their expansion from the nozzle cut to the treated surface. At the same time, the scheme of expansion of the plane jet flowing from the nozzle and the dependencies for determining its main parameters were considered. A model of the process of machining the surfaces of the edges of parts with a free abrasive in a fluidized state using air jets was developed. According to the proposed model, the surface of the edge of the part is treated by exposure to the abrasive medium, which is in a fluidized state, with an air jet. In this case, the symmetry axis of the air jet is directed along the bisector of the angle of the workpiece edge. When the air jet flows out of the nozzle, it expands symmetrically about its axis. Analytical studies of the proposed model of the process of machining the surfaces of parts’ edges made it possible to establish the main regularities and determine the main parameters of the machining process. Based on the developed model and the obtained regularities of the process of machining the edges of parts with a free abrasive in a fluidized state using air jets, the technological features of machining the surfaces of the edges of parts that provide a high level of quality parameters have been established.

Laboratory Experimental Investigation on the Structural Optimization of a Novel Coupled Energy Tunnel

Freezing damage to tunnels in cold regions has long posed a threat to the safe operation of high-speed trains and other means of transportation. Finding a reasonable and effective solution to this problem, while also considering green, low-carbon, energy-saving, and environmental protection measures, has garnered widespread attention. Herein, the concept of a novel coupled energy tunnel is proposed, which combines the technologies of an air curtain and ground source heat pump (GSHP). The aim is to effectively address the issue of freezing damage in tunnels located in cold regions, while ensuring traffic safety. First, the multifunctional experimental apparatus for testing the anti-freezing and insulation performance of a coupled energy tunnel was independently designed and developed for laboratory experiments. Second, single-factor experiments and orthogonal experiments are conducted, and the influences of five key factors (i.e., the air outlet hole diameter, air outlet hole spacing, circulating water temperature of the GSHP, wind speed at the tunnel model entrance, and airflow jet angle) on the internal temperature field of the tunnel model are discussed. Third, combined with range analysis and variance analysis, the ranking of importance for each key factor and the optimal scheme of the coupled energy tunnel are obtained as follows: wind speed at the tunnel model entrance D > circulating water temperature of GSHP C > airflow jet angle E > air outlet hole spacing B > air outlet hole diameter A, and the optimal scheme is A2B1C4D1E2, i.e., the air outlet hole diameter is 3 mm, the air outlet hole spacing is 10 mm, the circulating water temperature of GSHP is 50 °C, the wind speed at the tunnel model entrance is 1.5 m/s and the airflow jet angle is 45°. In conclusion, the research achievements presented in this paper can offer a new perspective for the structural design of tunnels in cold regions. Additionally, they contribute to the early achievement of a carbon dioxide emissions peak and carbon neutrality, and provide some valuable and scientific references for both innovators and practitioners.

Exploring the use of atmospheric freeze drying for dehydrating pharmaceutics in vials: Baseline water sublimation investigation

Atmospheric freeze-drying (AFD) is a relatively new freeze-drying technology without the need for a vacuum, making it easy to operate and cost-effective. Although there have been studies using AFD to dehydrate solid foods, there is currently no research on using AFD to dehydrate frozen liquids in pharmaceutical vials. In this study, several approaches were evaluated to enhance the atmospheric sublimation of water in pharmaceutical vials. Using −4 °C impinging jet airflow to dry frozen water samples in the vial, it was found that convective action significantly affected the sublimation rate. On this basis, a 3D-printed air-guide model was designed to improve airflow circulation in the vial, and it was found that the drying rate was highest when airflow energy loss was minimized, and airflow velocity at the sample surface was maximized. Additionally, the geometric characteristics of the vial also influenced the sublimation rate; vials with a larger bottom area and shorter height showed the highest sublimation rate. Increasing the vial’s bottom radius from 11 mm to 13 mm, under atmospheric pressure and using cold air at approximately −5 °C, reduced the drying time of 1 g of frozen water from 8.5 h to 6 h; each 5 mm height increase added 0.5 h to the drying time. Using cold air at −10 °C to dry 1 g of frozen water in a 5 mL vial, the combination of ultrasonic-induced energy (at a frequency of 39.46 kHz) and the air-guide model effectively reduced the sublimation time from 7 h to 5 h, compared to using only the air-guide model. However, this technique may be vulnerable to melting at the vial-transducer contact point, should the transducer be directly attached to the vials.

Investigation of unswept ramp system with lobe shape nozzle for fuel mixing of hydrogen jet at a scramjet engine

The role of efficient fuel mixing and a stable flame holder is crucial in enhancing the performance and capabilities of scramjet engines for high-speed flight. The present research paper has tried to disclose the fuel mixing efficiency of 3-lobe annular nozzle on the mixing mechanism of the fuel jet behind the strut. In addition, using internal air jet flow for increasing the circulation strength and fuel mixing behind the strut is also examined in this study. Numerical simulation of the flow and fuel jet behind the strut is done to reveal the main physics related to the mechanism of fuel mixing inside the combustor with the proposed injection system. The results of our simulation show that using annular 3-lobe fuel jet improve the fuel mixing via production of the multiple vortex pairs within the combustor behind the strut. The use of internal air jet also enhances the fuel mixing efficiency up to 90% in combustor of scramjet engine.

Study on the Influence of High-Altitude Helical Tunnel Curvature on Jet Fan Spatial Layout

During the operational ventilation process of high-altitude helical tunnels, the installation method of jet fans is a key factor in determining the ventilation efficiency of the tunnel. In this study, the CFD numerical simulation method is adopted to establish three-dimensional ventilation models of helical tunnels with different curvature radii. Through orthogonal experiments, the effects of tunnel curvature radius on the characteristics of the air jet flow field, under the coupled influences of factors such as lateral spacing of jet fans, vertical height of fans, longitudinal spacing, and lateral offset, are investigated. The results show that when R = 500 m, 600 m, 700 m, and 800 m, the longitudinal spacing has the most significant impact on ventilation efficiency, followed by vertical height, with lateral offset and fan spacing having the least impact. The optimal spacing and vertical height of the fan groups remain consistent under different curvature radii, at 1.25D (fan diameter) and 15 cm, respectively. The optimal longitudinal spacing of the fan groups is 90 m, 90 m, 135 m, and 90 m, respectively. Shifting the fan groups 0.25 to 0.75 m towards the inner side of the tunnel helix (for R < 700 m) can optimize the flow field distribution within the tunnel. Finally, expressions for the relationship between the helical radius and the lateral offset and longitudinal spacing of the fan groups are established for the optimal installation parameters of fan spatial positions under different helical tunnel radii.

Экспериментальное исследование влияния температуры распылителя на характеристики сжигания дизельного топлива в атмосферном горелочном устройстве

In this work, using diesel fuel as an example, we studied the combustion characteristics of liquid hydrocarbons when atomized by a high-speed air jet. This approach to spraying liquid fuel in combustion processes has a number of advantages over traditional spraying: the ability to supply fuel with a low degree of purification and to reduce the likelihood of fuel equipment coking. Using an atmospheric burner device with natural air supply into the mixing chamber, the depen¬dences of the composition of intermediate and final combustion products were studied, and the flame temperature was measured at various fuel flow rates and parameters of the atomizing air jet (flow rate, temperature). A comparison was made of the obtained characteristics for equivalent modes at different temperatures of the supplied atomizer. It was found that when heated air is used as a sprayer, higher flame temperatures are ensured, which ensures a more complete fuel burnout and a decrease in CO concentration in the flue gases, but at the same time, a slight increase in NOx is observed.

Direct numerical simulations of a novel device to fight airborne virus transmission

The SARS-CoV-2 (COVID-19) pandemic has highlighted the crucial role of preventive measures in avoiding the spread of disease and understanding the transmission of airborne viruses in indoor spaces. This study focuses on a novel personal protective equipment consisting of a fan-peaked cap that creates a jet flow of air in front of the individual's face to reduce the concentration of airborne viruses and decrease the risk of infection transmission. Direct numerical simulation is used to analyze the effectiveness of the device under certain conditions, such as the velocity of the airflow, flow orientation, ambient conditions, and geometrical factors.

Combustion of diesel fuel sprayed with cold or heated air in an atmospheric burner

In this work the combustion characteristics of liquid hydrocarbons when atomized by a high speed air jet were studied, using diesel fuel as an example. This approach to spraying liquid fuel in combustion processes has a number of advantages over traditional spraying: the ability to supply fuel with a low degree of purification, reducing the chance of coking of fuel equipment. Using an atmospheric burner device with natural air supply into the mixing chamber, the dependences of the composition of intermediate and final combustion products were studied, and the flame temperature was measured at various fuel flow rates and parameters of the atomizing air jet (flow rate, temperature). A comparison of the obtained characteristics was made for equivalent modes at different temperatures of the supplied atomizer. It was found that when heated air is used as a sprayer, higher flame temperatures are ensured, which ensures more complete fuel burnout and a decrease in CO concentration in the flue gases, but at the same time, a slight increase in NOx was observed.

Study on Three-dimensional Impinging Jet Flow and Heat Transfer of Dryer for Gravure Printing and Coating Machine

Drying system is the largest energy consumption of equipment parts of solvent-based printing and coating equipment. How to optimize to design the equipment is of the highlights of this research field. According to this demand, a mathematical model of fluid flow of the drying oven is developed. By building a testing platform and using RNG k-epsilon two-equation turbulence model in Fluent Software to analyze three-dimensional impinging jet flow and heat transfer process of hot air drying in conventional drying oven. The results show that the separation of some boundary layers and undesirable swirls, which result in the non-uniform velocity field and temperature field of hot air from nozzles and no promotion to the drying effect, because of unreasonable design of the drying oven.

Experimental study of perturbation growth in a round laminar jet

AbstractJet flows have many applications in various technical processes such as temperature control, mixing, spraying and so forth. Along with wide usage in technology and manufacturing, jet flows are the object of fundamental scientific interest. In particular, a proper understanding of laminar‐turbulent transition in jets is highly important. In this experimental work, we study round laminar submerged jet flow of air and the evolution of controlled perturbations. First, the modal perturbation growth mechanism was under consideration. Thin metal rings were put into the jet at a small distance from the orifice to amplify unstable eigen modes of the jet by oscillating at different frequencies. Experimental and theoretically predicted wavelengths, radial distributions of velocity fluctuations and amplification curves of modal perturbations were compared and a good correspondence was found. Second, the non‐modal perturbation growth mechanism was under consideration. To excite algebraic perturbation growth, we put special wavy structures (deflectors) into the jet, which provide a roller‐like transverse motion in the perturbed jet. The features of the transition to turbulence caused by this non‐modal growth were considered. Based on obtained experimental results, we definitely identify the non‐modal ‘lift‐up’ growth mechanism of introduced disturbances. The development of perturbations qualitatively corresponds to the theoretically calculated optimal perturbations.

Copper oxide particle emission and the spread in a public washroom from a high-speed jet air dryer

The high-speed jet discharged by hand dryers with brushed motors may release hazardous particles. In this study, the particles released from the hand dryer were trapped using high-efficiency particulate air filters for chemical composition analysis in a small test room. A manikin was placed to mimic a user standing in front of the dryer. Number and mass concentrations of the released particles were measured to estimate the particle emission rates and inhalation exposure. The particle emission rate reached 2.64 × 106 particles/s when starting the dryer. The released particles were found to contain a copper element, subsequently extrapolated to copper oxide. Secondly, in the large test room, jet airflows were measured using a three-dimensional ultrasonic anemometer. The results revealed that the horizontally placed palms caused the discharged jets to bend toward the human body, resulting in an upward motion of the air into the breathing zone. After running the dryer for 30 s, the peak mass concentration in the breathing zone for particles with a less than 2.5-μm diameter was 13.1 µg/m3. Installing high-efficiency particulate air filters to the air outlets of hand dryers was found to be effective in minimizing the exposure to CuO.

Examination of Gas Active Arc Extinguishing and Lightning Protection for Transmission Lines

The study investigated the gas active arc extinguishing and lightning protection for transmission lines. Lightning is one of the most significant sources of over voltages in overhead transmission lines. The lightning over voltages could lead to failure of the devices connected to the transmission line. Fundamental constraint on the reliability of an electrical power transmission system is the effectiveness of its protective system. The role of the protective system is to safeguard transmission system components from the effects of electrical overstress. Shield wire and surge arresters are an important means of lightning protection in transmission and distribution systems. Therefore, it is necessary to analyze the influence of over voltages caused due to lighting. The requirements of system security for lightning protection technology reach the high standard that lightning strike tripping and wire breakage are not allowed. Both the power supply side and the demand side have very high requirements for lightning protection of transmission lines, but the lightning accident rate remains high. This situation poses a great threat to the reliability and safety of power network, it is urgent to solve this problem. The gas active interrupter principle is put forward. From two latitudes of lightning overvoltage and power frequency over current, the effective control of lightning accident rate caused by large probability and multiple lightning strike is realized. This paper is aimed at evaluation of protection level of transmission line by using gas active arc extinguishing, shield wire and line surge arresters against lightning overvoltage. When lightning strikes, the internal short gap of the main body and the air gap break down, and the lightning arc enters the arc-extinguishing body through the breakdown channel. Arc is compressed by force to form internal and external gradients temperature in order to produce jet airflow. Jet airflow acts on the subsequent power frequency follow current arc, a model coupling an arc and a compressed jet airflow in a multi-fracture compression airflow arc-extinguishing structure is established and simulated. The increase in voltage due to lightning are investigated by using the MATLAB software. Direct and induced, types of lightning strokes are considered. The model of a 33kV three-phase overhead power transmission line is developed considering the RL circuit. The simulations are performed based on time domain analysis. Also, numerical analysis is made for 133kV tower structure transmitting power over 220km from 132 KV Sub-transmission Lines in port Harcourt region. Based on the simulation study this research study gas active arc extinguishing and lightning protection for transmission lines, are very important in computer application like Electromagnetic Transient Propagation (EMTP) and Power System Computer Aided Design (PSCAD) which are used in future study. These soft wares provide an alternative way to bring the precise result in study of lightning protection level of high voltage transmission line.

A method combining half width of point spread function with maximum gradient of image gray for single-camera three-dimensional spray velocity detection

When a defocus image is obtained by direct imaging, it is hard to determine whether the detected object is in the front or rear of the focal plane. This is called the ambiguity problem and it causes great trouble in the 3D-particle tracking velocimetry (PTV) defocus method, which obtains the defocus location by directly obtaining depth information from the intensity along the radial direction of particles. This study proposes a method to obtain the true position of a particle based on the asymmetry feature of the defocus image with respect to the focal plane. The method distinguishes two ambiguous positions with equal width of point spread function (PSF) width by introducing a parameter derived from the maximum gradient of image gray. The method also derives a mathematical expression for the half width of PSF(χ) considering aberration. The method is validated by a calibration technique, which shows that in 19 out of 20 experimental conditions correct results are obtained. We apply the method to measure the 3D velocity of an airflow jet with 3D-PTV and compare it with computational fluid dynamics results, which show a maximum error of 8.8 %. Furthermore, the method is used to measure a real spray as an example, and obtains a 3D vector map and velocity cumulative distribution of the measured area.

Optimizing structure of photovoltaic thermal solar air heaters with baffles and hole plates

Based on previous research, a mathematical model of photovoltaic thermal solar air heaters with baffles and hole plates (PVTSAH-B) was proposed to analyze the influence of the opening ratio on the flow and heat transfer characteristics of PVTSAH-B and to further improve its performance. The results showed that the air velocity and temperature distributions were affected by the opening ratio of hole plates. The vortex zones in PVTSAH-B could be broken by air jet flow when the opening ratio of hole plates was less than 0.4. The PV modular surface temperature and the area of the high-temperature zones decreased with the decreasing of the opening ratio of hole plates. Lowering the opening ratio of hole plates could increase the thermal and power efficiency. However, the fan energy consumption increased due to the decrease in the opening ratio of hole plates increasing the pressure loss. Therefore, the effective power efficiency decreased. 0.4 opening ratio of hole plates recorded the highest performance of PVTSAH-B. Meanwhile, the maximum values of the effective power efficiency, thermal efficiency and the total efficiency were 0.129, 0.567 and 0.696 respectively, which were 5.97%, 12.30% and 11.07%, higher than the opening ratio 1.0, respectively.

Experimental characterization on slamming loads of a truncated ship bow under asymmetrical impact

Due to the complex three-dimensional flows such as fluid separation, fluid breaking and bubble flows, accurate prediction of slamming loads on 3D ship bow is still limited. In this paper, the asymmetrical slamming load characteristics of a truncated ship bow under the combination of heel and pitch postures are clarified through drop experiment. An angle device designed in the experiment has effectively adjusted the heel and pitch posture of the test model independently. The study provides a complete dataset (water entry velocity and pressure), which provides reference for future numerical verifications. Load characteristics of bow impact under asymmetrical water entry attitudes are analysed. The results show that some air cavity and jet flows are easy to cause the multiple pressure peaks, and affect the pressure oscillation. The influence of heel and pitch angles on impact pressure is further discussed. Finally, load characteristics with different water entry velocities are discussed to further improve its application. Results find that some abnormal pressure characteristics appear in some locations, that is, the pressure decreases with the increment of water entry velocity. The research results are expected to lay a foundation for further improving the predicting accuracy of hull slamming loads.

Comparative Study on the Wedge-Shape Gap Column Cooling Characteristics and the Usual

As the key heat transfer element of natural draft dry cooling towers, the columnar cooling tube bundle radiator is composed of four rows pipe or six rows pipe, and usually arranged as per delta, which would induce a large vortex around the delta under crosswind conditions, and then impact the cooling performance of cooling deltas and that of the total Tower. To overcome this shortage, this study proposed a cooling column with a gap between the upstream pipes and downstream pipes in one cooling column, which can introduce a stream of air jet flow into the columnar cooling tube bundle and then impact the aerodynamic field of the tube bundle and the corresponding cooling delta. A three-dimensional numerical model has been established to compare and study the cooling characteristics of the cooling columns with wedge-shape gap and the usual. The results show that the wedge gap can increase the heat transfer coefficient of the radiator and decrease its flow resistance coefficient. At 7 m/s crosswind, the outlet water temperature of dry tower by using the usual radiator is 36.46 °C, while that is 34.23 °C for dry cooling tower with wedge radiator.

Influence of two-dimensional expiratory airflow variations on respiratory particle propagation during pronunciation of the fricative [f

Propagation of respiratory particles, potentially containing viable viruses, plays a significant role in the transmission of respiratory diseases (e.g., COVID-19) from infected people. Particles are produced in the upper respiratory system and exit the mouth during expiratory events such as sneezing, coughing, talking, and singing. The importance of considering speaking and singing as vectors of particle transmission has been recognized by researchers. Recently, in a companion paper, dynamics of expiratory flow during fricative utterances were explored, and significant variations of airflow jet trajectories were reported. This study focuses on respiratory particle propagation during fricative productions and the effect of airflow variations on particle transport and dispersion as a function of particle size. The commercial ANSYS-Fluent computational fluid dynamics (CFD) software was employed to quantify the fluid flow and particle dispersion from a two-dimensional mouth model of sustained fricative [f] utterance as well as a horizontal jet flow model. The fluid velocity field and particle distributions estimated from the mouth model were compared with those of the horizontal jet flow model. The significant effects of the airflow jet trajectory variations on the pattern of particle transport and dispersion during fricative utterances were studied. Distinct differences between the estimations of the horizontal jet model for particle propagation with those of the mouth model were observed. The importance of considering the vocal tract geometry and the failure of a horizontal jet model to properly estimate the expiratory airflow and respiratory particle propagation during the production of fricative utterances were emphasized.

Analysis of fluid dynamic behavior and impact load on oblique water entry of a two-dimensional seaplane based on VOF method

Seaplane landing is a typical water entry impact phenomenon. However, our understanding on the development of jet flow and air cavity, and corresponding load characteristic is still limited. In this paper, the impact problem of oblique water entry of a two-dimensional seaplane is studied to clarify the relationship between theses complex flows and loads. A gas-liquid two-phase model is established to model these complex fluid flows, where the air-water interface is captured based on a VOF algorithm. The accuracy is validated by the published experimental data. Some hydrodynamic impact characteristics related to seaplane model under different oblique water entry postures, including air-water free surface and local impact pressure are discussed. Complicated flows (air cavity and jet flow impact) are the internal cause to some unusual load characteristics such as multiple pressure peaks, negative pressure, simultaneity of impact load on the airfoil, and great difference of load at different positions on the cabin. The evolution of jet flow and air cavity is further discussed through combing free surface and pressure distribution. Results clarified the mechanism of complex flows under the influence of bottom cabin and inclined postures, which will be helpful to further understand the impact phenomenon of seaplane landing.

Influence of nozzle geometry on torch parameters during gas combustion

In this paper, when performing and analyzing the series of calculated results of the analysis of the sides of a rectangular nozzle for the parameters of a turbulent free air jet and a flame of a propane-butane mixture based on three-dimensional parabolic Navier-Stokes bonds for multicomponent reacting jets. To estimate the turbulent viscosity, differential equations of the kinetic and dissipation of the kinetic energy of turbulence are observed with refined empirical constants that are acceptable in turbulent combustion, as in the calculations, the initial values of the kinetic energy of turbulence did not exceed 5% of the dimensionless velocity of the main jet. It was found that when an air jet flows out of a nozzle with an aspect ratio of (1:2) and (1:4) in the initial sections of the jet, its shape behaves like an ellipse and, with the distance, it turns into a round one, with dimensionless, x greater or equal to 20 for the nozzle (1:2) and x greater or equal to 30 for (1:4), and for this variant there is again a transition to an elliptical shape. Studies of the diffusion combustion of a propane-butane mixture flowing out of a rectangular nozzle with an aspect ratio of (1:2) and (1:4) showed that with the ratio of the speed of the oxidizer to fuel mu, the flame length increases when mu between 0 and 0.164, and then, with an increase of mu more than 0.41, the torch length is shortened. The axial distributions of the momentum flux density with the aspect ratio (1:4), the jet core is shortened by 2÷2.5 times, compared with the aspect ratio (1:2) with the other parameters unchanged. Setting the tangential velocity at the mouth of the nozzle (ω=6.1 m/s) leads to a decrease in the torch length by 11% compared to its value equal to zero.

Effectiveness of plexiglass barriers in mitigating spread of aerosolized droplets in a cough

Plexiglass barriers have been prevalently used in the workplace during the Covid-19 pandemic as protective measures against the airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through interactions between potentially infected and uninfected individuals. Doubts have been raised about their effectiveness and concerns have even been expressed about the implications for room ventilation on their overuse. To aid public awareness of the role of such plexiglass barriers, we use flow visualization, aided by particle count measurements, to examine in a laboratory setting the effectiveness of typical workplace barriers in impeding the spread of aerosol-size airborne droplets. Such droplets are emitted in coughs and other respiratory exhalations and serve as modes of transmission for viruses. The visualizations and the supporting particle count measurements indicate that barriers do impede the forward momentum of the droplet-laden airflow jet that result from a cough, but portions of the expelled aerosols can spread around the barriers. Our study suggests that in comparison with the case in the absence of a barrier, a 2.5 ft or higher barrier can reduce the concentration levels of aerosols of size <10 μm on the side of the barrier away from the source by over 90% and those of size <3 μm by over 82%. However, an opening at the bottom of a barrier, for example, representing access for transactions between a worker and customers, can significantly reduce the effectiveness of the barrier. Finally, we illustrate how the aerosol dispersion in this case can be dramatically altered by ambient background airflows.