Flow Field Distribution Research Articles

CFD simulation and optimization study on the shell side performances of a plate and shell heat exchanger with double herringbone plates

The purpose of this study is to investigate the flow and heat transfer performance of the plate and shell heat exchanger (PSHE) with double herringbone plates under low temperature difference conditions, while introducing the CFD-ANN-NSGA II method to optimize the corrugated parameters. A PIV experimental bench is built to validate the flow field distribution in the shell side, and the average velocity error between simulation results and experiment results is 2.93%, with a maximum relative error of 13.24%, confirming the accuracy of the turbulence model and numerical method. The flow characteristics analysis and parameter study are conducted within the research scope. For the considered parameters, i.e., the corrugation angle β, corrugation depth b, and corrugation pitch λ, the maximum heat transfer efficiency is achieved when β is 60°. Moreover, the corrugation angle has the greatest impact on both pressure drop and heat transfer performance. β = 30°, λ = 7.4 mm, and b = 7.5 mm are the best performance indicators for the respective operating conditions. Using CFD results as samples, the R2 of ANN training is greater than 0.99, and the multi-objective optimization yields the best configuration of β, λ, and b, which are 33.1°, 11.8 mm, and 7.5 mm, respectively, with the optimal thermal-hydraulic performance.

Flow Field Simulation Tool of Solid Propulsion Control Systems for Missile Applications

In order to achieve hit-to-kill miss distances against manoeuvrable ballistic missile targets, future generation missiles calls for fast response non-conventional propulsion control systems during terminal homing period in high-endo to exo-atmosphere regions augmenting aero control. Based on advances in thrust modulation controlling throat area in solid propulsion pintle motor, control systems are developed for missile Divert and Attitude Control Systems (DACS) applications using multiple nozzles in pitch/yaw directions connected to common gas generator. Control thrust vector for lateral and attitude corrections is generated with proportional distribution of total thrust in pitch/yaw directions through real time thrust modulation of pintle nozzles
 Towards development of propulsion control systems based on solid propulsion, prototype systems: Thrust Controlled Motor (TCM) and Divert Thruster Flight Propulsion Control System (DTFPCS) are developed to demonstrate thrust modulation/ control thrust vector generation in solid propulsion and finalize unified controller for various missile control applications. Design & development process of prototype systems calls for flow field simulation tool for parametric design analysis/optimization and generate performance maps/control parameters based on detailed flow distributions. Present paper presents flow field simulation tools with Steady Flow Field (SFF) model and Dynamic Flow Field (DFF) model integrating dynamics of pintle movement with steady flow solver. Parametric analysis of geometrical profiles of pintle/throat regions and effect of pintle speed on system response are presented for system design optimization. Performance maps and controller maps of prototype systems are generated based on flow field distributions for nozzle thrust modulation. Simulated results are compared with open loop hot tests and unified controller parameters are updated for control thrust vector generation. Finally flow field distributions of DTFPCS operating modes: neutral-thrust and lateral-thrust are presented demonstrating the utility of simulation tool in design analysis and system development. Present simulation tool is critical in system design optimization and unified controller development for various flight control applications with minimum number of developmental tests. Further work of integrating propellant grain geometry variation during motor hot tests, with flow field model is in progress to predict control system performance for various missile control applications.

Analysis of the Energy Loss Mechanism of Pump-Turbines with Splitter Blades under Different Characteristic Heads

The operating efficiency of high-head pump turbines is closely related to the internal hydraulic losses within the system. Conventional methods for calculating hydraulic losses based on pressure differences often lack detailed information on their distribution and specific sources. Additionally, the presence of splitter blades further complicates the hydraulic loss characteristics, necessitating further study. In this study, Reynolds-averaged Navier–Stokes (RANS) simulations were employed to analyze the performance of a pump turbine with splitter blades at three different head conditions and a guide vane opening (GVO) of 10°. The numerical simulations were validated by experimental tests using laser doppler velocimetry (LDV). Quantitative analysis of flow components and hydraulic losses was conducted using entropy production theory in combination with an examination of flow field distributions to identify the origins and features of hydraulic losses. The results indicate that higher heads are associated with lower growth rates of total hydraulic losses. In particular, the significant velocity gradients at the trailing edge of the splitter blades contribute to higher hydraulic losses. Furthermore, the hydraulic losses in the runner (RN) region are predominantly influenced by velocity gradients and not by vortices, with the flow conditions in the RN region impacting the hydraulic losses in the draft tube (DT).

In Vitro Experimental Study on Hemodynamics of Transcatheter Aortic Valve Replacement

The patient-specific aortic silicone model was established based on CTA data. The digital particle image velocimetry (DPIV) test method in the modified ViVitro pulsatile flow system was used to investigate the aortic hemodynamic performance and flow field characteristics before and after transcatheter aortic valve replacement (TAVR). The results showed that the hemodynamic parameters were consistent with the clinical data, which verified the accuracy of the model. From the comparative study of preoperative and postoperative effective orifice area (0.33 cm2 and 1.78 cm2), mean pressure difference (58 mmHg and 9 mmHg), percentage of regurgitation (52% and 8%), peak flow velocity (4.60 m/s and 1.81 m/s) and flow field distribution (eccentric jet and uniform jet), the immediate efficacy after TAVR is good. From the perspective of viscous shear stress and Reynolds shear stress, the risk of hemolysis and thrombotic problems was low in preoperative and postoperative patient-specific models. This study provides a set of reliable DPIV testing methods for aortic flow field, and provides biomechanical basis for the immediate and long-term effectiveness of TAVR from the perspective of hemodynamics and flow field characteristics. It has important application value in clinical diagnosis, surgical treatment and long-term evaluation.

Analysis of effects of moving wall direction in a one sided semi-circular porous cavity on mixed magneto-bioconvection in the presence of hybrid nanofluid with oxytactic bacteria

A computational analysis on the effects of direction of wall movement in a one sided semi-circular porous cavity on mixed magneto-bioconvection of hybrid nanofluid in the presence of oxytactic bacteria has been performed. The working fluid is the hybrid nanofluid. The enclosure is cooled from semi-circle side and heated from moving lid under the effect of uniform magnetic field in the horizontal direction. The numerical solution of governing equations is obtained by using the higher order finite element method (FEM). The reliability of designed solver is tested through the experimental and numerical data available in the literature. Two cases of the boundary conditions are considered related to the tendency of right vertical lid of the cavity. Other parameters are Richardson number, Darcy number, Hartmann number, Peclet number and porosity. It is found that moving lid direction is the most effective parameter for the flow field, isotherms, oxygen and microorganism distributions. Moreover, higher heat transfer rate is obtained in Case-I for different values of Darcy number. Around 10% increment is occurred on mass transfer with different Pe number in case of downward moving lid due to increment of convection mode of heat transfer inside the cavity.

Numerical and Experimental Investigation on Flow Field of the Turbine Stage under Different Axial Gaps

In order to reduce efficiency losses and improve the aerodynamic efficiency of axial turbines used in industry, the flow fields of the turbine stage were investigated numerically and experimentally under different axial gaps in this work. The influence of the axial gaps on the flow unsteadiness and the flow field distribution is discussed. The results show that the aerodynamic efficiency of the turbine stage increases when the axial distance is reduced. The difference in entropy increases under different axial distances are mainly found in the section from the stator inlet to the rotor inlet: the turbine not only has a better time-average aerodynamic performance, but also has a better transient aerodynamic performance under working conditions with a small axial distance. Additionally, the maximum disturbance amplitudes of the stator and rotor are located near the trailing edge of the stator and the leading edge of the rotor, respectively. Compared with the wake disturbance of the upstream stator to the downstream adjacent rotor, the reverse disturbance of the downstream stator to the adjacent upstream rotor is more sensitive to the change in the blade spacing.

Heat Transfer and Entropy Generation in a Lithium-Ion Battery Pack Against Battery Spacing and Discharge Rate

Abstract Three-dimensional continuity, momentum, and energy equations have been solved in a battery pack of a unit module with 3 × 3 × 3 and 4 × 4 × 4 Li-ion cells to obtain the flow field and temperature distribution around the batteries. The battery spacing to hydraulic diameter ratio in x, y, and z directions have been varied in a wide range from 0.04458 to 0.08172, 0.00833 to 0.07133, and 0.007496 to 0.08052 for 4 × 4 × 4 cells, and 0.06 to 0.11, 0.0111 to 0.09649, 0.01 to 0.11 for 3 × 3 × 3 to obtain the optimum configuration for maximum heat transfer and minimum entropy generation. Air is pumped through the battery pack as a transport medium for heat transfer with Reynolds number (Re) varying in the laminar range from 400 to 2000. The results are plotted in terms of the average surface Nu over the battery surface and average volumetric temperature of the battery and air. It is found that the temperature of the battery pack remains almost constant against Sx. However, a significant rise in battery temperature is observed when we increase Sy. The scenario becomes different when spacing is varied in the z-direction. An optimum spacing for the minimum temperature of the battery pack is obtained at Sz/Dh = 0.03. The temperature variation trend is almost identical in 3 × 3 × 3 and 4 × 4 × 4 cells; however, the absolute temperature inside the pack is lower in 3 × 3 × 3 cells. In each case, the maximum temperature is seen on the batteries located at the top and bottom corners of the outlet. Among all the cases, the maximum temperature of 355 K has been found in 4 × 4 × 4 cells with a 3.6C discharge rate at Sy/Dh of 0.07133. Different discharging rates (1C, 2C, 3.6C, and 4C) have been considered to generate different amounts of heat inside the battery. However, it is numerically and theoretically proved that Nu and the nondimensional volumetric average temperature inside the pack are independent of the heat generation rate inside the battery pack.

A solid-liquid mixing reactor based on swirling flow technology

Solid-liquid mixing is often applied in the chemical industry to keep solids in suspension for, amongst others, crystallization, adsorption, heterogeneous catalysis, etc. The most widely used technology to obtain a good degree of mixing is the mechanically stirred tank reactor. However, this technology is limited to small reactor volumes in case of high pressure/temperature processes due to sealing issues. An alternative for solid-liquid mixing is the application of swirling flow. This work studies the mixing capacities of a specially designed reactor geometry, the Swirling Flow Reactor (SFR). Computational Fluid Dynamics (CFD) is used to simulate the flow field and particle distribution in the SFR, where the RNG k−ϵ model and the Eulerian-Eulerian (E-E) multi-phase approach with a Kinetic Theory of Granular Flow (KTGF) model are applied for their proven effectiveness in the study of dense solid-liquid mixing problems. The effectiveness of mixing in the SFR is assessed by the axial particle distribution and homogeneity H. The mechanism of particle recirculation in the SFR is also identified, in which a Coanda jet flow (CoJF) formed by a specially designed inlet nozzle plays an important role in washing the reactor bottom surface. Additionally, Spectral Proper Orthogonal Decomposition (SPOD) is used to identify and reconstruct the coherent structures in the swirling flow. The results indicate that precessing coherent flow structures are present, which include the dominant double layer double helical vortex core and its second order harmonic, the double layer quadruple helical vortex core.

A Study of the Gelatin Low-Temperature Deposition Manufacturing Forming Process Based on Fluid Numerical Simulation.

Low-temperature deposition manufacturing has attracted much attention as a novel printing method, bringing new opportunities and directions for the development of biological 3D printing and complex-shaped food printing. In this article, we investigated the rheological and printing properties of gelatin solution and conducted numerical simulation and experimental research on the low-temperature extrusion process of gelatin solution. The velocity, local shear rate, viscosity, and pressure distribution of the material in the extrusion process were calculated using Comsol software. The effects of the initial temperature, inlet velocity, and print head diameter of the material on the flow field distribution and printing quality were explored. The results show that: (1) the fluidity and mechanical properties of gelatin solution vary with its concentration; (2) the initial temperature of material, inlet velocity, and print head diameter all have varying degrees of influence on the distribution of the flow field; (3) the concentration change of the material mainly affects the pressure distribution in the flow channel; (4) the greater the inlet velocity, the greater the velocity and shear rate in the flow field and the higher the temperature of the material in the outlet section; and (5) the higher the initial temperature of the gel, the lower the viscosity in the flow field. This article is of great reference value for the low-temperature 3D printing of colloidal materials that are difficult to form at room temperature.

Assessment of groundwater salinization impact in coastal aquifers based on the shared socioeconomic pathways: An integrated modeling approach

Seawater intrusion (SWI) has become a significant threat to human health and sustainable economic development in coastal areas with the rapid pace of climate change. Therefore, it is crucial to determine the response of SWI to climate change. However, most studies cannot reflect the direct impact of future climate change on groundwater salinity. This study first established the SWAT-MODFLOW coupled model after unifying both spatiotemporal computational units. Streamflow, groundwater level observation data, etc., were used to calibrate and validate the coupled model. And then SEAWAT model was loaded into the coupled model to form a new integrated model. Finally, precipitation of six Global Climate Models (GCMs) under two shared socioeconomic pathways (1–2.6 and 5–8.5 scenarios) was imported into the above calibrated integrated model separately to make SWI prediction from December 30, 2020, to December 30, 2030. The results show that this integrated model accurately reflected the study area's current flow and concentration field distribution. Precipitation under different ssps had little effect on future SWI, while the uncertainty of SWI prediction was mainly derived from different GCMs. This study provides important implications for exploring the occurrence and the prediction of SWI in the coastal aquifer. It has specific reference significance for the optimal management of water resources in coastal areas and the effective mitigation of SWI.

Simulation Investigation on the Structure and Its Influence on the Impinging Pressure of the Carbon Dioxide Jet.

An improved understanding of the mechanisms of SC-CO2 jet drilling technology is important for the application of this new technology. The flow field structure and dynamic fluctuation of SC-CO2 jets are the key factors affecting the jet erosion performance. To improve the erosion performance of the SC-CO2 jet, it is necessary to study the relationship between the different flow fields of the jet. In this study, a numerical simulation model for SC-CO2 jet drilling technology is established. Based on the modified real-gas model, the pressure distribution and flow field characteristics of the SC-CO2 jet were obtained by the simulation investigation, and the reliability of the model was verified. The results show that the flow field structure of a supercritical CO2 jet has typical compressible flow field characteristics. As the jet is fully expanded, its pressure fluctuation is slight and less affected by the distance between the nozzle and the wall. When the jet is in the state of under-expansion, the flow field structure characteristics have a significant impact on the pressure distribution and peak pressure. At the same time, when the distance is large, when nozzle pressure ratio = 5, the pressure ratio has a more significant impact on the flow field and the pressure peak and distribution. The pressure distribution of different flow fields should be fully considered in the application.

Study on acoustic characteristics of air pipeline with guide vane and bionic guide vane

In this paper, experiments and numerical simulations have been performed to demonstrate that both the guide vane and bionic guide vane can effectively reduce the aerodynamic noise. Both the hybrid calculation method and the acoustic-structure coupling method are employed to calculate the aerodynamic noise of the air pipeline. The impact of the guide vane positioning on the pipeline velocity field and fluctuating pressure is scrutinized and deliberated. Utilizing principles from bionics technology, the bionic groove structure is applied to the bend guide vane, forming a new bionic guide vane. The results show that the bionic guide vane can improve the flow field distribution and substantially mitigates the aerodynamic noise of the elbow effectively.

Enhancement of the classification and recovery process of fine mineral particles via a newly developed volute feed hydrocyclone.

Ore resources in the mining process form a large number of unmanageable tailings, mostly inhalable fine mineral particles, into the environment will cause serious pollution, and recycling is a precious resource. The cyclone classification provides the possibility for the recovery and exploitation of fine particles, but the recovery and utilization rate of conventional cyclone separation is seriously low, and the performance urgently should be optimized. In the present study, a new type of volute feed was proposed to strengthen the classification and recovery process of fine mineral particles. Combined with numerical simulation and experimental research, the effects of various structural parameters and operating parameters on the flow field distribution, particle motion, and classification performance were systematically examined. The obtained results reveal that the new volute feed structure can effectively reduce the internal turbulence and improve the flow field stability and particle classification efficiency. Compared with the traditional hydrocyclone, the classification efficiency of fine particles with new feed structure increases by 10-18%. Increasing underflow diameter and feed pressure and reducing overflow diameter and feed concentration are also beneficial to lessening classification particle size and enhancing classification performance. The currently achieved outcomes can provide valuable guidelines for further development of novel hydrocyclones.

Aerodynamic Noise Reduction Based on Bionic Blades with Non-Smooth Leading Edges and Curved Serrated Trailing Edges

The flight of the owl is silent owing to non-smooth leading edges of the owl’s wings and the curved serration of the feathers. This study applied this concept of bionics to blade design for horizontal axis wind turbines to reduce aerodynamic noise. The flow and sound field distribution around a rotating wind turbine with three blades were investigated. A numerical simulation method that combines large eddy simulation (LES) and FW-H acoustic equation was adopted to compare aerodynamic noise between the blade prototype and the bionic blade. The comparison revealed that the sound pressure level of the bionic blade was reduced over middle and high frequencies, thereby achieving a noise reduction of 6.9 dB. The intensity of the wake vortex shedding of the bionic blade was lower, and the interaction between the shedding vortices in the bionic blade was smaller compared with that in the prototype blade, indicating that the aerodynamic noise induced by the shedding vortex was effectively reduced.

Optimization of electrolyte flow field for electrochemical boring of inner cavity in 07Cr16Ni6 high-strength steel

Inner cavity structures are a type of functional feature that can reduce the weight and increase the operating speed of spindles. They have been widely used in the aviation, aerospace, and automobile fields. Since these cavities are located deep inside spindles, boring tool bars need to be designed to be sufficiently long, which results in tool chatter. Moreover, this makes the machining accuracy and surface quality difficult to control. Herein, a new method of electrochemical boring is proposed. In this method, the workpiece rotates around its axis, a long-nozzle tool is linearly fed along the diameter direction, and the entire inner cavity is processed in a single tool-feed operation. In this work, a flow-field model for electrochemical boring was established, and the axial flow-field distribution of the nozzle was simulated. To improve the uniformity of the electrolyte flow field, a nozzle structure with a variable cross section is proposed. An optimized nozzle structure was obtained via the golden-section method. Finally, comparative electrochemical boring experiments with constant and variable cross-section tools were conducted for an inner cavity length of 420 mm in 07Cr16Ni6 high-strength steel with 20 wt% NaNO3 solution. The results indicate that the specimen processed by the optimized variable cross-section tool had higher inner-diameter accuracy. The diameter deviation of the final inner cavity was found to be within ± 0.04 mm, the wall-thickness deviation of the specimen was within ± 0.02 mm, and the inner surface roughness was less than Ra = 0.5 µm. These experimental results verify the effectiveness of the flow-field simulations and the optimization of the cathode structure.

Characterization of seawater intrusion based on machine learning and implications for offshore management under shared socioeconomic paths

With the increase of climate change and the risk of human activities, seawater intrusion has become an essential threat to human health and sustainable economic development in coastal areas. Therefore, identifying the critical features of seawater intrusion is significantly important, but the existing research on it is insufficient. Moreover, most of the work cannot reflect the direct impact of different shared socioeconomic paths on groundwater salinity in the future. To solve this problem, this study first established a numerical model of variable density flow for the Dagu River Basin based on SEAWAT to analyze the main aquifers' current flow field and concentration field distribution. Then two machine learning methods, random forest and mutual information methods, are introduced to identify critical features of seawater intrusion for the first time. Finally, taking the characteristics affected by climate are used as variables for selecting GCMs, the seawater intrusion in the study area is predicted by six GCMs under shared socioeconomic paths (ssp1-2.6 and ssp5-8.5) from 2020.12.30 to 2030.12.30. The findings indicate that regional precipitation and groundwater extraction exert significant influence on seawater intrusion, with the hydraulic conductivity of the primary aquifer also demonstrating crucial importance. Moreover, it is observed that the potential impact of different shared socioeconomic paths on future variations of seawater intrusion is negligible. This study verifies the effectiveness of machine learning in seawater intrusion analysis to a certain extent and has specific reference significance for the optimal management of water resources in coastal areas and the effective mitigation of seawater intrusion.

Numerical analysis and control technology of gas accumulation in a large-scale specially-shaped tunnel passing through coal bearing strata

To solve the construction ventilation problem of super long (length greater than 10000 m) tunnel passing through discrete lenticular gas bag tunnel under complex working conditions in carbonaceous shale stratum, relying on the construction of Banzhulin tunnel of the new Xuyong-Bijie Railway (Sichuan-Yunnan). Using the finite element analysis software, the flow field distribution of the tunnel return air flow in the case of simultaneous excavation of multiple working faces is simulated, and the formation position and influence range of the vortex area which is easy to form gas accumulation are analyzed. On this basis, the technical team developed the PLC uninterruptible self starting ventilation power supply control program. By comparing the changes in the time required for ventilation power supply failure before and after the adoption of this technology, and the comparison of the gas concentration in the return air flow within a relatively short time of the failure, it is proved that this technology reduces the fault response time to 15.74% of the original time, and can well avoid gas accumulation within the failure time, It provides some reference for similar engineering construction.

Influence of resistance due to locomotion mechanism configurations of a new high-speed amphibious vehicle (HSAV-Ⅱ)

Amphibious vehicles are capable of moving on both water and land, which makes their design more complex than that of ships. The locomotion mechanism of an amphibious vehicle is the main distinguishing feature from ships and is also the primary source of water resistance. The resistance characteristics of amphibious vehicles with different locomotion mechanisms are mainly studied in this paper. Firstly, a numerical calculation method based on the RANS method is established and verified by experiments. Secondly, the resistance characteristics of the amphibious vehicle under a series of speeds are analyzed, and the importance of reducing pressure resistance is demonstrated. Then, the resistance characteristics of different amphibious vehicle configurations are compared. Hull 1 has the smallest resistance at low speed, with a maximum resistance reduction rate of 9.3%; Hull 3 has the best performance at high speed, with a maximum resistance reduction rate of 12.5%. The influence of different configurations is analyzed from the perspectives of the flow field, vehicle attitude, and pressure distribution. Finally, the resistance values and their proportion of total resistance acting on different locomotion mechanisms are analyzed. The results show that the resistance at low speed is related to the complexity of the surface, and the resistance at high speed is more dependent on the attitude. The conclusions of this study have guiding significance for the design of high-speed amphibious vehicles.

Flow Field Characteristics and Structure Improvement of Double-stage Safety Valve

The paper proposes a new double-stage large flow protection relief valve based on the double-stage linkage structure, to solve the problem that when it is impacted by the top plate, the traditional hydraulic support protective relief valve has smaller overflow and lower sensitivity, which causes the column circuit to be damaged. The flow field characteristics of double-stage protective relief valve are numerically simulated by the computational fluid dynamics method and semi-implicit connection pressure equation calculation model. Then the dynamic characteristics of the flow field distribution of the double-stage protective relief valve are obtained. According to the law of fluid flow, the structure of main valve core is optimized for the negative pressure, cavitation and vortex area. The flow field characteristics of the optimized double-stage protection valve are simulated and analyzed. In the end, the flow field characteristics of optimized double-stage protective relief valve are compared with the original. The results show that the negative pressure value of double-stage protective relief valve is reduced by 15%, and the outlet velocity of double-stage protective relief valve is reduced by 21% compared to the unoptimized when the main core is fully opened. The research results provide reference for the evolution design of high-flow, impact-resistant hydraulic support safety valve structure.

The effect of intake port shape on in-cylinder flow field and turbulence distribution in a high-tumble production engine with endoscope accesses

Three cylinder heads with varied intake port shapes are experimentally investigated to evaluate intake flow structures and their influence on near top dead centre (TDC) flow fields and turbulence distributions in a motored high-tumble engine. The endoscopic high-speed particle image velocimetry (eHS-PIV) is implemented in multi-cylinder engines with two laser endoscopes and a camera endoscope installed in the cylinder head. For a range of engine load and speed conditions, particle seeded and laser illuminated high-speed movies are recorded for 100 cycles with which ensemble-averaged flow fields and spatial-filtered high-frequency flow magnitude distributions are analysed. The results show that a straighter intake port producing a more lateral flow direction results in a larger swinging arc, which is related to enhanced flow later in the compression stroke. The tumble vortex shows an asymmetric structure; the flow field during the compression stroke exhibits higher magnitude vectors at the leading head. This surging flow head becomes stronger with a straighter intake port, which leads to enhanced tumble vortex formation near TDC. As it becomes very strong, the flow vectors originally directed towards the exhaust valves bounce back towards the intake valves, causing a very complex flow structure involving multiple flow components. The result is enhanced turbulence throughout the late compression stroke including the spark timing. However, the impact of the straighter intake port shape on TDC turbulence becomes less significant at lower engine load and speed conditions as the lower intake air momentum limits the enhancement.