Fluid Dynamics Simulation Method Research Articles

The influence of time steps and turbulence model in numerical predicting total resistance on Japan Bulk Carrier with and without pre-duct

Abstract As a numerical fluid dynamic simulation method, Computational Fluid Dynamic (CFD) must guarantee the accuracy of the simulation results carried out, where the accuracy of the simulation results depends on: numerical method, grid generation, mesh independence, grid type, turbulence model, etc. This paper explains the influence of turbulence model and time step on the resistance prediction results of the Japan Bulk Carrier (JBC) ships, with CFD simulations using the ANSYS CFX software package. The model is simulated with several turbulence models including: k-Epsilon (k-ε), k-Omega (k-ω) and Shear Stress Transport k-ω (SST k-ω), apart from that the turbulence model is simulated in several time steps. From the results of the CFD modelling carried out, the influence of the turbulence model and time step on the accuracy of predicting ship resistance from the JBC ship was analysed, by comparing the CFD modelling results with experimental results from National Maritime Research Institute (NMRI). In general, the turbulence model and time step influence modelling and mesh selection, the correct time step provides accurate and convergent modelling results.

A Study on the Influence of Mobile Fans on the Smoke Spreading Characteristics of Tunnel Fires

Mobile fans, as flexible and convenient new longitudinal ventilation and smoke extraction equipment for tunnels, demonstrate more significant effectiveness in an emergency response to tunnel fires compared to traditional smoke extraction methods. This study employs computational fluid dynamics simulation methods, selecting two fire scenarios to investigate the effects of fan inclined angles and fan airflow volumes on the longitudinal temperature distribution and smoke back-layering length in tunnels. The results indicate that when using mobile fans for longitudinal ventilation in tunnels, at a lower fan airflow volume, the temperature distribution along the longitudinal axis is nearly symmetrical. The fire source and the fan installed in the upstream are within a certain range, and it is more effective to use the horizontal angle for longitudinal ventilation. As the fan airflow volume increases, the back-layering length significantly decreases (210,000 m3/h < V < 270,000 m3/h). However, as the fan flow volume continues to increase (270,000 m3/h < V < 300,000 m3/h), the reduction in the back-layering length becomes less pronounced, the smoke spread distance of the latter is only 11% of that of the former. Therefore, selecting appropriate fan airflow volumes and fan inclined angles them can effectively enhance the performance of tunnel smoke extraction systems. Moreover, by comparing with traditional fans, we find that mobile fans provide an alternative effective strategy during firefighting by allowing adjustments in distance from the fire source and fan inclination angles, enhancing fire suppression effectiveness while reducing energy losses. The research findings can serve as a reference for tunnel fire prevention design.

Numerical Study on the Operational Ventilation Patterns of Alternative Jet Fans in Curved Tunnels

In tunnel operation ventilation systems, the arrangement of jet fans plays a decisive role in ensuring ventilation efficiency. Curved tunnels, due to their unique radius of curvature, exhibit significant differences in fan installation parameters and jet flow field distribution compared to traditional straight-line tunnels. In order to investigate the distinct characteristics, this research utilized computational fluid dynamics (CFD) simulation methods to analyze the ventilation performance of both an innovative, adjustable jet fan system and conventional jet fans within the context of curved tunnel configurations. The findings reveal that by adjusting the horizontal deflection angle of the novel jet fan, the flow field distribution can be effectively optimized, and the jet effect can be enhanced, thereby improving ventilation efficiency. Compared to traditional jet fans, the novel fan demonstrates a significantly greater capability in flow field optimization, especially when its horizontal deflection angle is adjusted, showing a trend where the jet effect initially increases and then decreases, with the longitudinal impact range being adjustable within a range of 5 m to 25 m.

Using three turbulence simulation methods for modeling the flying of high-speed railway tunnel lining blocks under piston airflow

The detached tunnel lining concrete blocks poses a serious threat to the safety of moving high-speed train. Understanding the flight characteristics of detached blocks from the tunnel soffit under train piston airflow is essential for devising appropriate measures to mitigate such risks during train operation. Computational Fluid Dynamics (CFD) simulation methods, known for their high efficiency and good repeatability, are effective approaches to study this subject. Large Eddy Simulation (LES), Improved Delayed Detached Eddy Simulation (IDDES), and Unsteady Reynolds-Averaged Navier-Stokes (URANS) are three commonly used turbulence simulation methods in the CFD simulation of train/tunnel aerodynamics. In this study, a three-dimensional CFD simulation model based on the three turbulence simulation methods is established for the airflow-tunnel-train-detached block system, and an experiment is conducted for validating the CFD model. Using the established models, the influence of different turbulence simulation methods on the flight trajectory and aerodynamic coefficients of detached lining blocks under train-induced airflows is compared. By visualizing the macroscopic flow field inside the tunnel and the local flow field near the detached block, the flow mechanisms of detached blocks under different turbulence simulation method conditions are revealed. The results showed that in the 1st stage (BTT stage), the flight of the detached block is influenced by the airflow near the train body, while in the 2nd stage (ATT stage), it is mainly affected by the train wake vortex. Compared with experimental results, the errors of LES and IDDES in simulating the longitudinal direction displacement of the block are only 2.3 % and 5.5 %, respectively, while the error of URANS is 10.6 %. The simulation error of URANS for the longitudinal direction flight speed reached 8.8 % in the ATT stage. In the BTT stage, LES and IDDES predicates more and larger leeward side vortex structures of the detached block, while URANS predicates fewer and smaller vortex structures. Compared with URANS method, the dissipation rate of the vortex structures simulated by LES and IDDES in the ATT stage is slower. These are the main reasons explaining why the flight characteristics of detached lining blocks obtained by URANS method are different from the LES and IDDES methods.

Energy performance and pressure fluctuation in multi-stage centrifugal pump with floating impellers under various axial oscillation frequencies

A novel multi-stage centrifugal pump with floating impellers is gaining traction in energy systems because it easily links stages in series for varying high head requirements. However, the axial oscillation frequency of the floating impeller introduces uncertainties in the pump's energy performance and pressure fluctuation. To address these issues, a comprehensive analysis of multi-stage centrifugal pumps was conducted, utilizing a computational fluid dynamics simulation method that incorporats dynamic mesh and multiple reference frame techniques, validated through three experimental trials. The findings show that average head coefficient and average efficiency are not significantly affected by the axial oscillation of impeller, but that pressure fluctuations, efficiency, and head coefficient all show periodic variations that are connected to the frequency of impeller oscillation. The amplitude of variations in the head coefficient and efficiency could increase by as much as 112.3 % and 172.4 %, respectively, under the influence of impeller oscillations, thereby heightening the instability of pump operation. Trigonometric functions for the energy performance during impeller oscillations are proposed to facilitate rapid assessment of pump stability. This study offers valuable insights into the unsteady characteristics of novel multi-stage centrifugal pumps and serves as a reference for further understanding their dynamic behavior.

Aerodynamic effects of an offshore floating photovoltaic platform undergoing pitch and heave motions

The offshore floating photovoltaic (OFPV) platform is a renewable energy generation system that has gained attention in recent years due to several advantages. OFPV exhibits higher sensitivity to wind loads than other offshore platforms, owing to its lightweight design and large aerial coverage. In contrast to the fixed photovoltaic systems, the OFPV platforms experience continuous oscillations induced by waves, which significantly influence the aerodynamic characteristics. In this study, the aerodynamic effects of an oscillating OFPV are investigated using the computational fluid dynamics (CFD) simulation method, including the three-dimensional effects, the Reynolds number effects, and the aerodynamic loads with various kinematic parameters. Some major findings are as follows. Firstly, a large-scale tip vortex exists when OFPV oscillates in pitch and heavy directions, which cannot be detected in two-dimensional simulations. Consequently, the lift coefficient, CL, and the drag coefficient, CD, are highly overestimated in 2-D simulation. Secondly, CL and CD decrease significantly as the Reynolds number increases for cases where Re < 106 while there is only a slight decrease for Re > 106. Thirdly, the aerodynamic forces are highly related to the amplitude of the pitch motion and the phase lag between the pitch and the heave motions. A fitting formula is proposed to calculate CL and CD based on the maximum angle of attack. Lastly, the evolution of the flow fields around the oscillating OFPV is analyzed. The separation of the leading edge mainly causes the aerodynamic force.

Enhancing optical and thermohydraulic performance of linear Fresnel collectors with receiver tube enhancers: A numerical study

Linear Fresnel collector system is a type of solar thermal utilization installation. It is mainly used to focus solar radiation on the receiver tube to generate high temperature thermal energy which can be applied in many aspects. This study investigates five different types of receiver tube models using water as the flowing medium, which leads to improving heat transfer performance by means of being equipped with enhancers. The optical results and thermohydraulic performance of the Linear Fresnel collector system are evaluated through Monte Carlo Ray Tracing and Computational Fluid Dynamics (CFD) simulation methods. The obtained optical results reveal that the distribution of energy flux density concentrating on the receiver tube surpasses that of the parabolic trough collector system. In order to maintain an energy reception rate of 90.0% or higher, the installation height range of the receiver tube should be between 1468–1532 mm. When the sun-tracking error increases from 0.0° to 1.0°, the overall optical efficiency of the Linear Fresnel collector system decreases from 98.9% to 79.7%. The thermohydraulic performance shows that the enhancers can generate a swirling flow as its main feature, which effectively promotes the homogenization of the temperature field and destroys the boundary layer near the receiver tube wall, thus greatly improving the convective heat transfer in the receiver tube. However, the introduction of the enhancers also means that the pressure drop loss of the receiver tube increases. Furthermore, the impact of the Kenics mixer's enhancer on heat transfer and flow characteristics is further amplified as the rotation rate decreases, owing to its alternating and complex structure. Through a comparative analysis of the influence of different receiver tube models on Nusselt number (Nu), Frictional resistance coefficient (f) and comprehensive evaluation criterion (PEC) under four rotation rate conditions (y = 6.3, 8.1, 11.34, 18.9), the conclusions present that the receiver tube with an enhancer at a low rotation rate has a larger Nu than that at a high rotation rate, while the Frictional resistance coefficient changes little at different rotation rates. Therefore, the PEC is higher when the receiver tube is equipped with a low-rotation-rate enhancer. Moreover, the receiver tube equipped with a Kenics mixer at a rotation rate of 6.3 was found to be the overall optimum case, with the PEC value varying from 1.47 to 1.73.

Study on the Influence of Protuberance Amplitude on the Performance of Vertical Axis Wind Turbines

Abstract The performance of vertical axis wind turbine (VAWT) is mainly affected by the dynamic stall process of the blade. Inspired by the anti-stall performance of the humpback whale flipper, leading edge protuberances (LEPs) are applied to 2-blade VAWT. Based on computational fluid dynamics simulation method, the effects of LEPs amplitude on VAWT performance are investigated when blade tip speed ratio is 2.19. The results show that the larger the amplitude of the LEP, the lower the average power coefficient. When the number of protuberances is 3, the average power coefficient of the VAWT with a protuberance amplitude of 6.625mm is 1.8% higher than prototype blade. Considering the impact of increasing the chord length of biomimetic blades, the average tangential force coefficient of all biomimetic VAWTs decreases. The peak section performance of the bionic blade decreases significantly while the trough section performance increases significantly. The difference between the peak section and trough section of the LEPS plays an important role in improving the performance. This study provides a reference for the application of bionic protuberances in VAWTs.

Heat transfer coefficient simulation and temperature distribution prediction of wire loops in the Stelmor air‐cooling system

AbstractDuring the Stelmor air‐cooling process, the temperature distribution has a significant impact on the wire loops' final mechanical properties. The temperature distribution during the air‐cooling process is accurately solved by establishing three‐dimensional model and numerical simulations. The heat transfer coefficient at the highly dense region is much smaller than that of wire loops at the low dense region, and changes periodically over time, according to a computational fluid dynamics simulation method. It is also found that the heat transfer coefficient on the cross‐section of the wire loop is very different, with a difference of 70–100 W/m2 K. Finally, the finite difference method is used to calculate the mathematical model of the temperature distribution during the Stelmor air‐cooling process. Comparing the results with the measurement data, the simulation results and measurement data match up well.

Continuous ultrasonic ozone coupling technology-assisted control of ceramic membrane fouling coupled enhanced multiphase mixing to treat dye wastewater and CFD flow field simulation

In this study, ozone catalysts (hydrogenation-modified red mud, HM-RM) successfully prepared by hydrogenation-modification of industrial hazardous solid waste red mud (RM) as a raw material in accordance with the viewpoint of treating waste with waste and using waste. Meanwhile, as for the common phenomenon of membrane fouling, uneven distribution of multiphase solid catalysts and ozone in liquids, the addition of ultrasound can not only disperse materials, but also play a role in online cleaning of ceramic membranes and catalysts. The optimum treatment conditions for Rhodamine B (RhB) solution with volume of 2 L and concentration of 40 mg/L were catalyst concentration of 0.4 mg/L, reaction temperature of 45 °C, ultrasonic time of 1 h, ultrasonic intensity of 600 W, removal rate of RhB was up to 90 %. In addition, the computational fluid dynamics (CFD) simulation method was used to investigate the fluid flow between the two gas-liquid phases and the effect of the negative pressure of the membrane pump on the fluid by the analysis of flow, pressure and ozone flux of the ceramic membrane(CM) reaction apparatus. The CFD simulation results showed that at the inlet gas-liquid flow rate of 3 m/s and the negative pressure of 20,000 Pa, the maximum flow rates of CM-1 were 3 m/s, 0.752 m/s for CM-2, and 0.228 m/s for CM-3, respectively. Vortices, which are beneficial to solid-liquid mixing and gas-liquid mass transfer, formed between the suction port CM-1 of CM-1 and the inlets of CM-2 and CM-3. This discovery is consistent with relevant experimental research results. Significantly higher concentrations of both •OH and dissolved ozone were observed in the US/HM-RM/O3 system compared to other systems, indicating the significant improvement in ozone utilization rate through the application of ultrasound. The superiority of the US/HM-RM/O3 device was demonstrated. The real dye effluent was tested under optimum operating conditions and the results showed that COD and TOC were reduced by 81.34 % and 60.23 % respectively after 180 min of treatment. The above research can provide technical support for the treatment of dye wastewater using Ultrasound-enhanced ozone oxidation ceramic membranes.

Analysis of the dynamic characteristics of an eccentric cylinder in axial flow

The simple pendulum model is a fundamental and widely studied concept in physics, its movement follows a tendency to stabilize towards the side with lower gravitational potential energy. Consequently, the simple pendulum structures have been extensive applications in petroleum, aerospace machinery, and others, particularly in gravity induction and actuator systems. The utilization of this model offers versatile solutions for complex engineering challenges. The research object of this study is an eccentric cylindrical stabilized platform. A nonlinear dynamic model of the eccentric cylindrical stable platform in axial flow with variable damping is established. Due to the complexity of the analytical solution of the simple pendulum motion, we adopt the method of numerical analysis to building the simulation and analysis model. Combined with the fluid calculation and dynamics simulation methods, the motion characteristics of the eccentric cylindrical model under steady and unsteady flow fields are analyzed by adjusting the rotational speed, inclination angle, and initial pendulum angle. The experimental platform is built to analyze the motion law of the eccentric cylinder under the action of axial flow, and the experimental results of the motion law of the eccentric cylindrical platform are consistent with the numerical calculation results.

The Analysis of the Impact of Building Openings Design Variations on Thermal Comfort and Airflow Velocity by using CFD Simulation

Thermal comfort is very important to support a building’s user productivity. This study was conducted to investigate thermal comfort and airflow velocity in the engineering laboratory building at the State University of Malang.Preliminary observations have shown that the average room air temperature was around 27 - 31°C, which caused the uncomfortable condition. Thermal comfort enhancement in this study is investigated by applying several variations and treatments to existing openings. By using descriptive quantitative and experimental methods, the analysis uses the Computational Fluid Dynamics (CFD) simulation method with the ANSYS Workbench 19.0 Program. The simulation was applied to seven rooms with various types of openings. Parameters used in the simulation process are: 1) room geometry data consisting of images, room area, and location of ventilation openings, and 2) measurement reference points such as airflow velocity and room temperature. The dimensions of the openings will be observed by varying the treatment in each room, namely by opening all the inlets in the room (S), opening the inlets on the air vents only (J), and opening the inlets on the windows only (V). Primary data in the form of room temperature, airflow velocity, relative humidity, and physical dimensions of buildings are obtained through direct observation. The simulation results show that the maximum airflow velocity of the rooms (0.34 m/s) is found in the largest dimension variation of the inlet area of the opening (13.15 m2). The lowest temperature is found in the rooms with the smallest dimension of inlet (28oC) with the value of room temperature in the range of 27.5oC – 30.2°C. The statistical analysis of one-way ANOVA shows that by using a significance level of 0.05, there is an effect of variations in the design of openings on the level of thermal comfort in each room.

Fluid dynamics simulation on water lubricating performance of micro-/nano-textured surfaces considering roughness structures

With the development of surface precision machining technology and extensive studies on lubrication and friction reduction, the use of surface texture to reduce friction has attracted widespread attention, but few studies have considered the influence of surface roughness on lubrication characteristics. By employing the computational fluid dynamics (CFD) simulation method, the lubrication models with rectangular textures and the introduction of rough asperity structures at the same time are established. The effects of the corresponding structure parameters on the lubrication performance of textured and roughed surfaces are studied under water lubrication conditions. Our results suggest that the adjustment of geometric parameters on the micro-/nano-structured surfaces can influence the load-bearing capacity of the water lubrication film, thus affecting the hydrodynamic lubrication performance on the surface. In addition, the generation of vortex in the micro-textures can bring changes in vorticity, which causes energy dissipation and affects frictional forces. In the lubrication model with rectangular textures, optimal hydrodynamic lubrication performance is obtained under the appropriate depth ratio &lt;i&gt;H&lt;/i&gt; = 0.6. Meanwhile, the corresponding lubrication performance can be enhanced by increasing the width ratio (&lt;i&gt;W&lt;/i&gt;) of surface texture. After introducing random asperity structures on the micro-textured surface with a standard deviation &lt;i&gt;δ&lt;/i&gt; = 0.5, the bearing capacity is increased by 44%, and the friction coefficient is reduced by 30.9%. Moreover, the introduction of half-sine rough asperity structures can only result in relatively minor differences in the lubrication performance, i.e. the changes of bearing capacity and friction coefficient are less than 10%. However, the introduction of compound hierarchical structure consisting of random asperity structures and half-sine rough asperity structures can result in an increase in the corresponding bearing capacity by 42% and a reduction in the friction coefficient by 31.1%, which implies a significant enhancement in the hydrodynamic lubrication performance.

Development of a forward design method for train airtightness: A case study of a metro express line

Focusing on metro express lines, this study develops a train airtightness forward design method by deconstructing whole-vehicle pressure change and dynamic sealing index requirements into key airtight component static sealing indices. This is achieved through the utilization of theoretical calculations, simulation calculations, laboratory tests, and field tests. Firstly, a research framework for the train airtightness forward design method is established. Subsequently, a sealed train is manufactured based on existing capabilities, and the following research is conducted: 1) Establishment of a conversion formula between key airtight component static sealing indices and the theoretical whole-vehicle static sealing index. 2) Examination of the theoretical weight relationship between key airtight components and the whole-vehicle theoretical static sealing performance, revealing that the doors and the carriage body each contribute to almost 50 % of the entire train's static sealing performance. 3) Investigation into the relationship between whole-vehicle theoretical and actual static sealing indices, revealing that test values for head/tail car pressure retention duration and static sealing index are 16 % below theoretical values, while those for the middle car are 13 % lower than the theoretical values. 4) Assessment of the validity of current standards. 5) Establishment of a calculation method for the relationship between whole-vehicle dynamic and static sealing indices, discovering that the whole-vehicle dynamic sealing index is 0.034–0.081 times the whole-vehicle static sealing index. 6) Development of a Computational Fluid Dynamics (CFD) simulation method to calculate metro trains' external wall pressure, which is validated through real-vehicle test data. Finally, within this framework, the train airtightness forward design method is formulated by determining the unknown relationships among airtightness parameters, standard indices, and simulation methods. Importantly, the forward airtightness design process and method established in this study are not limited to metro trains alone. They also serve as valuable references for airtightness research and development in various other products with similar requirements, including locomotives, electric multiple units, high-speed trains, and maglev trains.

Effectiveness of SplashGuard Caregiver prototype in reducing the risk of aerosol transmission in intensive care unit rooms of SARS-CoV-2 patients: a prospective and simulation study

The contagiousness of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is known to be linked to the emission of bioaerosols. Thus, aerosol-generating procedures (AGPs) could increase the risk of infection among healthcare workers (HCWs). To investigate the impact of an aerosol protection box, the SplashGuard Caregiver (SGGC) with suction system, by direct analysis of the presence of viral particles after an AGP, and by using the computational fluid dynamics (CFD) simulation method. This prospective observational study investigated HCWs caring for patients with SARS-CoV-2 admitted to an intensive care unit (ICU). Rooms were categorized as: SGCG present and SGCG absent. Virus detection was performed through direct analysis, and using a CFD model to simulate the movement dynamics of airborne particles produced by a patient's respiratory activities. Of the 67 analyses performed, three samples tested positive on quantitative polymerase chain reaction: one of 33 analyses in the SCCG group (3%) and two of 34 analyses in the non-SGCG group (5.9%). CFD simulations showed that: (1) reduction of the gaps of an SGCG could decrease the number of emitted particles remaining airborne within the room by up to 70%; and (2) positioning HCWs facing the opposite direction to the main air flow would reduce their exposure. This study documented the presence of SARS-CoV-2 among HCWs in a negative pressure ICU room of an infected patient with or without the use of an SGCG. The simulation will help to improve the design of the SGCG and the positioning of HCWs in the room.

Investigating the impact of gaspers on airborne disease transmission in an economy-class aircraft cabin with personalized displacement ventilation

Overhead gaspers provide directional fresh airflow, and thus affect the local airflow pattern and contaminant distribution. To investigate the impact of gaspers on airborne disease transmission in an aircraft cabin with a personalized displacement ventilation system, numerical calculations were conducted in a seven-row, single-aisle, fully occupied, economy-class aircraft cabin with the computational fluid dynamics (CFD) simulation method. We first investigated the impact of source gasper direction and flow rate on the airborne transmission near the contaminant source. We then investigated the protective effect of the receptor's gasper. For a source passenger's gasper, the direction and flow rate of the gasper flow either increased or decreased the air contaminant transmission to other passengers. Directing the source gasper to the abdomen with a medium flow rate performed best by reducing the receptors' mean exposure index by at least 45%, as this approach minimized the contaminant circulation in the cabin. Turning on a receptor passenger's gasper could be an effective strategy to protect the receptor, and the working mechanism was revealed. The gasper-induced jet flow entrained the surrounding air into the jet region, and the protective effect was related to the contaminant concentration at ceiling level. With a suitable gasper direction and flow rate, the gasper jet formed a virtual barrier between the source passenger and the receptor. When the contaminants were transported upwards to a receptor's breathing zone, turning on the receptor's gasper reduced the contaminant concentration, since the downward gasper jet altered the airflow pattern in front of the receptor.

Eco-friendly strategy for CO2 enrichment performance in commercial greenhouses based on the CO2 spatial distribution and photosynthesis

CO2 enrichment is an essential environmental control technology due to its significantly enhancing effect on crop production capacity. Despite being a key energy consumer in protected agriculture (i.e. greenhouse systems), CO2 enrichment remains at a low energy use efficiency level, highlighting the need for developing more energy-efficiency strategies for CO2 enrichment. Therefore, this study employed the computational fluid dynamics (CFD) simulation method to replicate the CO2 diffusion process resulting from CO2 enrichment in three commercial strawberry greenhouses with varying geometric characteristics. Based on the CFD-simulated CO2 concentration distributions, the leaf photosynthetic rate was calculated using a mathematical model group. The CO2 enrichment efficiency was then analysed by calculating the ratio of increased photosynthesis across the cultivation area to the amount of energy (in CO2 equivalent) used. The efficiency peaked when the average CO2 concentration was approximately 500 μmol mol−1, thereby providing guidance for determining the target concentration of CO2 enrichment in production. Although this study is limited as the CFD simulation only considered a typical short-period CO2 enrichment event, future research will provide a broader analysis by considering changes throughout the day.

Ammonia blend ratio impact on combustion characteristics and NOx emissions during co-firing with sludge and coal in a utility boiler

This study investigates the effects of the ammonia blend ratio and the number of nozzle layers on boiler combustion characteristics and NOx emissions by the computational fluid dynamics simulation method. The conclusions indicate that, as ammonia is injected from a single-layer of secondary air nozzles, with the ammonia blend ratio increases, the combustion temperature decreases, when the blend ratio is 60%, the combustion temperature decreases by about 300 K. When ammonia is injected into the furnace from multiple-layers of nozzles, and under the premise of the same ammonia blend ratio, the overall impact on the furnace temperature is smaller than that of ammonia entering from a single-layer of nozzles. When the blend ratio of the ammonia is 40%, the NOx emission of ammonia entering the furnace from two layers of secondary air nozzles is about 22.47% higher than when it is injected into the furnace from a single-layer of nozzles. After raising the ammonia mixing ratio, the NOx at the furnace outlet shows an inverted-parabola change, which first decreasing and then increasing.

Novel Calculation Method for Windage Power Loss of Double-Helical Gear Transmission

Abstract This paper presents a novel fast calculation method for windage power loss (WPL) of the meshing double-helical gear pair. Firstly, based on the basic equations of fluid mechanics and computational fluid dynamics simulation method, the calculation method for single-tooth windage torque at the zone of meshing/nonmeshing is established; Secondly, the WPL of meshing gear pair with different gear parameters and operating conditions are obtained according to the single-tooth windage torque during a rotation period and the windage torque at the end faces, and the accuracy of the proposed WPL method is verified through the WPL test measurement and simulation; Finally, the effect of gear parameters and operating conditions on the WPL is studied.

Research on Multiphase Flow and Nozzle Wear in a High-Pressure Abrasive Water Jet Cutting Head

Research on the mixing process of gas–liquid–solid multiphase flow in a high-pressure abrasive water jet (HP-AWJ) is of great significance in improving the performance of water jet cutting. In this paper, the Euler method-VOF model, a computational fluid dynamics (CFD) simulation method, is used to solve the multiphase flow of air–water in an abrasive water jet (AWJ). The Euler–Lagrange method is further used to study the multiphase flow of abrasive particles. The method considers the shape factor of the particle, uses the Rosin–Rammler function, and defines an effective model for the particle-to-wall wear model. By solving the velocity of the continuous phase and particulate phase in the AWJ cutting head, the problem of nozzle wear caused by particles is studied. Finally, the exit velocity of the AWJ and particle wear are investigated by varying the model’s parameters. The results show that the double abrasive tube model effectively improved the problem of one-sided wear inside the nozzle, and the tangential velocity of the air affected the acceleration process of the abrasive inside the nozzle, with smaller abrasive velocity resulting in less wear on the model. Simultaneously, the effects of the abrasive inlet tube and mixing chamber size on abrasive exit velocity and nozzle wear are analyzed. The results obtained provide valuable guidance for addressing the multiphase flow mixing issues in the AWJ, improving the abrasive acceleration process and extending the nozzle’s lifetime.