Changes In Flow Field Research Articles

Hazardous chemical accident prediction for drinking water sources in Three Gorges Reservoir

Water pollution accidents occur in drinking water sources may pollute water environment, destroy water ecological balance, and threaten the drinking water safety for residents. Based on water quality hydrodynamic mathematical equations and Digital Elevation Model, a new water pollution accident prediction program for drinking water sources in Three Gorges Reservoir under different hydrological conditions was developed. Moreover, this new program was firstly used to forecast and analyze flow field changes and concentration reduction of a hazardous chemical pollution accident in Huangjuedu drinking water source. By comparing the calculated values and the measured ones of February 10 to February 19, 2016, the maximum relative error was less than 10%, which indicated that the new program was feasible and reasonable. For pollution accident prediction in the drinking water source, the results showed that the maximum transverse velocity had stabilized as 2.070 m/s, 2.411 m/s and 2.717 m/s since 20 min after the accident responding to discharge flow of Xiangjiaba with 1800 m3/s, 2700 m3/s,and 3600 m3/s, respectively. The maximum vertical one was 1.372 m/s, 1.598 m/s and 1.872 m/s respectively since 20 min after accident under the corresponding conditions. Furthermore, the water quality of the drinking water source met the standard 23 min after the accident under the condition that the discharge flow of Xiangjiaba was 1800 m3/s. For conditions that discharge flows were 2700 m3/s and 3600 m3/s, the corresponding times to meet the standard were 21 min and 20 min after the accident, respectively. Thence, relatively large dispatch flows would help reduce the impacts of pollution accidents and accelerate water quality improvement of drinking water sources. This study provides a new and useful tool for predicting the diffusion and migration of pollutants in drinking water sources of Three Gorges Reservoir. And it also gives a practical reference for decision makers to forcast hazardous chemical pollution accidents in drinking water sources.

From dome dune to barchan dune: Airflow structure changes measured with particle image velocimetry in a wind tunnel

The evolution from the initial sand accumulation to a mature barchan dune can be divided into five general stages. The first two stages are transient sand patches that disperse easily during downwind movement of the dune. In this study, we focused on the flow field changes around the dunes during the last three stages of dune evolution, namely the dome, protobarchan, and mature barchan stages. By means of particle image velocimetry, we measured the mean and turbulent flow fields around 3D-printed scale models of real dunes in a wind tunnel and discuss the significance of the airflow variation for dune evolution. We found that topographic forcing plays an important role in the changes of the mean and turbulent airflow structures. The airflow patterns on the windward slope were similar at all three stages, with deceleration at the windward toe and horizontal acceleration combined with vertical upward movement of the airflow along the windward slope. On the leeward sides of the dune during the three stages, the airflow structure evolved from airflow diffusion to airflow diffusion accompanied by transient flow separation, and then to complete airflow separation and reattachment. The turbulence intensity near the dune surface increased significantly as the dune matured and two zones with a high Reynolds shear stress appeared: in the middle of the windward slope and in the lee of the dune. Based on our results, we discuss the impact of changes in the airflow structure at different evolutionary stages on the evolution of dune morphology.

Prediction Model for Morphological Distribution and Evolution of Submarine Cuttings Piles in Offshore Drilling

Summary Offshore oil and gas has effectively alleviated the global shortage of oil and gas resources, and drilling operations are becoming increasingly frequent. However, the cuttings discharged during surface drilling are transported and deposited to form cuttings piles, which pose a serious threat to the marine ecological environment. In this study, we consider the randomness and uncertainty of cuttings movement to divide the transport process into parabola and collision motion between the moving particles and slope particles after falling on the slope surface of cuttings piles. Through specific analysis of the stress state of a single particle in the transport process and changes in momentum distribution of the particle swarm, the evolution model of the morphological distribution of cuttings piles and the nearby flow field is established. This model can quantitatively analyze the evolution law of the morphological distribution of cuttings piles under the action of ocean current and the disturbance law of the flow field near the cuttings piles caused by the invasion of cuttings particles. Comparing the measured data at an offshore drilling field and prediction results of the model of Sun et al. (2020), the relative error of the model amounts to less than 15%, which demonstrates its rationality. The simulation results show that the morphological distribution of cuttings piles and the nearby flow field change significantly under the action of ocean current, and the intensity of evolution is related to the current velocity and cuttings size, which is of great significance for the quantitative analysis of the evolution of cuttings piles under the action of ocean currents and accurate prediction of their morphological distribution.

Simulation and experimental verification study on the process parameters of ZnO-MOCVD

Metal-organic chemical vapor deposition (MOCVD) is a key technique for developing and manufacturing zinc oxide (ZnO) devices. The film quality and performance of these devices are influenced by the process parameters. In this study, the film deposition rate and film uniformity obtained from the simulations and experiments under different process parameters, such as the substrate temperature, operating pressure, mass fraction of the source gas, and inlet flow rate, are compared and verified. In addition, the corresponding temperature field, flow field, distribution of source mass fraction, and velocity field are analyzed using the computational fluid dynamics (CFD) method to explain the influence of the flow field change on deposition rate and film uniformity. This study also presents the correlation test for the film uniformity between the simulation and experimental results; it was found that all the 16 sets of results are significantly correlated and that more than half of them are highly correlated. To ensure the consistency of the experimental results and to prove their reliability, the repeatability test and stability test are conducted.

Effects of using a porous disk on the dynamic features of phase change process with PCM integrated circular pipe during nano-liquid forced convection in discharging operation mode

Impacts of using a porous disk on the performance of a phase change material filled cylindrical container during forced convection of nanoliquid in discharging mode are investigated with finite element method. Simulations are performed for various values of porous disk permeability (10−5≤Da≤5×10−2), radius (0≤pr≤hr) and height (0.2hz≤pz≤0.8hz) of the porous disk while time is considered between 0 and 40 min. As the heat transfer fluid, nanoliquid of water containing cylindrical shaped alumina nanoparticle is considered with solid volume fraction of 2%. It was observed that the flow field, temperature and phase change process dynamic features are influenced by varying the porous disk permeability and its geometrical parameters. An optimum permeability value of the disk is observed at Darcy number of 5 × 10−3 for which the discharging time is minimum and its reduction is 40.7% as compared to case with the lowest permeability of the disk. The phase change process becomes fast with higher radius of the porous disk while the effect is reverse for higher height of the disk. The reduction is discharging time is 22% with highest radius while is it increased by about 61% at the highest height. A predictive model based on feed-forward artificial neural networks is considered with 25 neurons in the hidden layer which delivers accurate results for the effects of porous disk on the dynamic features of phase change process.

Study on flow dynamic characteristic of bladder pressure pulsation attenuator based on dynamic mesh technology

To solve the problem that the flow dynamic characteristic of the bladder pressure pulsation attenuator cannot be quantitatively analyzed, a bladder pressure pulsation attenuator was taken as the research object, and the dynamic mesh technology was combined with the User-Defined-Function (UDF) to numerically simulate the working process of the attenuator. Overcoming the divergence problem in finite-element fluid calculation and the negative volume problem in mesh updating process, the bladder pressure pulsation attenuator was dynamically simulated under different fluctuating frequencies and different inflatable pressure, the change of internal flow field was monitored in time. The results show that the resistance loss through the attenuator increases with the increase of the frequency and the increase of the charging pressure. The local resistance loss is much higher than the frictional resistance loss. The simulation results match the experimental results, that verifies the model's validity and correctness, and also provides a new method and idea to improve bladder attenuator's resistance loss and analyze the variable boundary problem.

Coupling analysis of contra-rotating fan interstage pressure pulsation and blade vibration based on wavelet reconstruction.

In recent years, the flow characteristics research of the interstage region in counter-rotating axial fans in terms of fluid dynamics has attracted much attention. Especially, the dynamic relationship between interstage pressure pulsation and blade vibration in counter-rotating axial fans has not yet been clarified. This paper performs the signal processing method of wavelet decomposition and reconstruction in time-frequency analysis process. Under different flow conditions, weak-coupling numerical simulation program is employed to analyze the fluid-structure coupling interaction between interstage pressure pulsations and blade vibrations in counter-rotating axial fans. The results indicate that the fluid-structure coupling interaction field in the interstage of counter-rotating axial fans mainly excites the first-order vibration of the second-stage blade. At the same time, the consistency between the pulsation frequency and the vibration frequency of the airflow reflects the good coupling property. Two stage blades cut the airflow to cause field changes and airflow pulsation, and then, airflow pulsation causes blades deformation and produces vibrations of the same frequency at the blade. The deformation of the blades, in turn, causes the flow field changes. Rotating stall, vortex movement and breakdown produced low-frequency airflow pulsation and vortex vibration of the blade.

Simulating the flow around a train passing through a tornado

A flow simulation was developed to understand the flow surrounding a train that was passing through a tornado and the resulting aerodynamic forces acting on the vehicle. Unsteady Reynolds averaged Navier-Stokes equations were solved to reproduce a previously-conducted laboratory experiment, in which a model train runs through a stationary tornado-like swirling flow. The simulation reproduced the unsteady aerodynamic forces acting on the train reported in the experiment. Furthermore, the computation successfully revealed how the flow field changes as a train passes through a tornado-like swirling flow.

Changes of groundwater flow field of Luanhe River Delta under the human activities and its impact on the ecological environment in the past 30 years

The Luanhe River Delta is located in the center of the Circum-Bohai Sea Economic Zone. It enjoys rapid economic and social development while suffering relatively water scarcity. The overexploitation of groundwater in the Luanhe River Delta in recent years has caused the continuous drop of groundwater level and serious environmental and geological problems. This study systematically analyzes the evolution characteristics of the population, economy, and groundwater exploitation in the Luanhe River Delta and summarizes the change patterns of the groundwater flow regime in different aquifers in the Luanhe River Delta according to previous water resource assessment data as well as the latest groundwater survey results. Through comparison of major source/sink terms and groundwater resources, the study reveals the impacts of human activities on the groundwater resources and ecological environment in the study area over the past 30 years from 1990 to 2020. The results are as follows. The average annual drop rate of shallow groundwater and the deep groundwater in the centers of depression cones is 0.4 m and 1.64 m, respectively in the Luanhe River Delta in the past 30 years. The depression cones of shallow and deep groundwater in the study area cover an area of 545.32 km2 and 548.79 km2, respectively, accounting for more than 10% of the total area of the Luanhe River Delta. Overexploitation of groundwater has further aggravated land subsidence. As a result, two large-scale subsidence centers have formed, with a maximum subsidence rate of up to 120 mm/a. The drop of groundwater level has induced some ecological problems in the Luanhe River Delta area, such as the zero flow and water quality deterioration of rivers and continuous shrinkage of natural wetlands and water. Meanwhile, the proportion of natural wetland area to the total wetland area has been decreased from 99% to 8% and the water area from 1776 km2 to 263 km2. These results will provide data for groundwater overexploitation control, land subsidence prevention, and ecological restoration in plains and provide services for water resources management and national land space planning.© 2021 China Geology Editorial Office.

Experimental Study of Twin Connected Pipe Jets

Two parallel pipe jets of 20 mm diameter were placed 1.2 mm diameter apart and were connected by a 4 mm wide channel all along the central plane of the jets. The mean velocity flow field of the jets was investigated for three Reynolds number 16300, 34400 and 49200. The Reynolds number was based on the exit velocity of the jets and jet diameter. The experiment was performed in an air jet facility and yaw meter was used for measurement of mean velocity and its direction. Their variations along the longitudinal, transverse, and lateral directions have been analyzed. A significant change of the jet flow field is observed near the exit of the jet. The combined effect of the jets diminishes the presence of recirculation region at the immediate exit rather enhances the energy and momentum transfer between their individual flow fields. Static pressure and kinetic energy distribution are also studied and a momentous variations have been noticed with varying Reynolds number.

Experimental Study of Twin Connected Pipe Jets

Two parallel pipe jets of 20 mm diameter were placed 1.2 mm diameter apart and were connected by a 4 mm wide channel all along the central plane of the jets. The mean velocity flow field of the jets was investigated for three Reynolds number 16300, 34400 and 49200. The Reynolds number was based on the exit velocity of the jets and jet diameter. The experiment was performed in an air jet facility and yaw meter was used for measurement of mean velocity and its direction. Their variations along the longitudinal, transverse, and lateral directions have been analyzed. A significant change of the jet flow field is observed near the exit of the jet. The combined effect of the jets diminishes the presence of recirculation region at the immediate exit rather enhances the energy and momentum transfer between their individual flow fields. Static pressure and kinetic energy distribution are also studied and a momentous variations have been noticed with varying Reynolds number.

NUMERICAL SIMULATION OF WAVE-DRIVEN FLOWS ON A MORPHOLOGICALLY EVOLVING BEACH

Wave-driven flows in the nearshore zone are responsible for the erosion and transport of beach sediments, causing a continuous cycle of bathymetric change that is linked with changes to wave transformation and nearshore hydrodynamics. Numerical models have been used to investigate the evolving nearshore wave field corresponding to beach morphology change in field studies (e.g., Ruiz de Alegria-Arzaburu et al., 2013). In the present study, the non-hydrostatic wave-flow SWASH model (Zijlema et al., 2011) is applied to five laboratory cases to investigate the change in wave and flow fields corresponding to evolving beach morphology during a simulated storm event.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LZQQuuiqsPY

Research on multi-physical field coupling of solid electrothermal storage unit

In recent years, the solid-state electro-thermal storage device has been connected to the power supply side of the power system for peak regulation by virtue of its high voltage and large capacity characteristics, which plays a positive role in the consumption of wind power, photovoltaic and other new energy. Based on the coupling effects of heat, current, electricity, magnetism, force and other physical fields in the equipment, this paper studies the optimal design of thermal storage structure. A multi-physical field and multi-criteria collaborative optimization design method was proposed to design the surface load of heating power, heat transfer channel of heat storage body, and porosity of body. Through the multi-field coupling numerical simulation and experiment verification, the thermal field, flow field, stress field, electric field and other changes are analyzed, and it is verified that the design method can effectively overcome the malpractice of low heat transfer rate temperature imbalance of thermal storage materials. The experimental results provide theoretical guidance for device design and engineering application.

Numerical and experimental research on flow and aerodynamic noise characteristics of coach

The researches on flow and aerodynamic noise characteristics of coaches are urgently needed to improve with the rapid development of new energy coaches. In this paper, tests in model wind tunnel and numerical calculations were carried out to study the phenomenon of flow and aero-noise on 1:25 scale model coach. Based on large eddy simulation (LES) and detached eddy simulation (DES), reliable numerical calculation method of flow and aero-noise on coach was established and verified. It is found that the maximum difference on turbulent pressure between test and LES is less than 10 dB(A) while that of DES is about 20 dB(A). Due to the results got from 1:25 scale model, the W_LES_HOA model is used to obtain the flow field and sound field information outside the coach. To find out the different propagation characteristics of turbulent pressure pulsation and acoustic pressure, proper orthogonal decomposition (POD) and band-pass filter analysis are used for further analysis. For rearview mirror, the energy of first mode is 6.1%, and only the first nine modes have an energy for more than 3.0%. By the reconstruction of first four modes, it can be seen that the complicated transverse vortex shedding couples with A pillar vortex and reaches the body surface. However, the coupling of turbulent pressure can only be seen clearly under low frequency around 250 Hz while the coupling of acoustic pressure can be seen under 750 Hz. Meanwhile, with the analysis of low frequency round 250 Hz and 500 Hz, the change of flow field generated by airflow impingement on the windward surface and A pillar makes the front of the coach becomes the main sources of aerodynamic sound sources.

Generalizability of Convolutional Encoder–Decoder Networks for Aerodynamic Flow-Field Prediction Across Geometric and Physical-Fluidic Variations

Abstract The generalizability of a convolutional encoder–decoder based model in predicting aerodynamic flow field across various flow regimes and geometric variation is assessed. A rich master dataset consisting of 11,000+ simulations including cambered, uncambered, thin, and thick airfoils simulated at varying angles of attack is generated. The various Mach and Reynolds number (Re) chosen allows analysis across compressible, incompressible, low, and high Re flow regimes. Multiple studies are carried out with the model trained on datasets that are categorized based on the aforementioned parameters. In each study, the loss of prediction accuracy by training the model on a larger dataset (generalizability), versus a smaller categorically sorted dataset, is evaluated. Largely disparate flow features across the Re range lead to a 25.56% loss, while the generalization across Mach range led to an average of 23.95% loss. However, flow-field changes induced due to geometric variation exhibited a better generalization potential, through an increased accuracy of 12.4%. The encoder–decoder architecture allows extraction of relevant geometric features from largely different geometries (geometric generalization) providing a better out-of-sample prediction accuracy in comparison to physics-based generalization. It is shown that, through user-informed choice of training data (removal of geometrically similar samples), computational costs incurred in generating training data can be reduced. This is important for the application of such methods in the design optimization of platforms and components that require the analysis of the fluid flows.

Effects of Secondary Elements on Vortex-Induced Vibration of a Streamlined Box Girder

Box girders are aerodynamically favorable, and the paper presents a study on the vortex-induced vibration (VIV) of this girder type at large angles of attack. Taking a box girder as an example, the form of the guardrails and the position of the maintenance tracks were improved to increase the VIV performance. The aerodynamic mechanism was further investigated according to the change in flow field around the girder. Results showed that the VIV performance of the box girder at positive angles of attack is worse. Improving secondary elements is an effective way to increase the VIV performance. Adding four rectangle bars above the original guardrails could achieve the target by preventing the generation of the vortex and blocking its movement. Moving the maintenance tracks inwards with a reasonable distance could also achieve the target as the flow passes through the girder more smoothly. With the combination of the optimal form of the guardrails and the optimal position of the maintenance tracks, the VIV performance of the bridge is higher. The countermeasures provide reference for the inhibition of the VIV of box girders.

The Influence of the Blade Outlet Angle on the Flow Field and Pressure Pulsation in a Centrifugal Fan

This paper takes centrifugal fan as the research object and establishes five impeller models with different blade outlet angles. By means of computational fluid dynamics (CFD), the external characteristics of the centrifugal fan and the internal characteristics, including the velocity, pressure, and turbulent energy distribution, at the middle span plane of the impeller or fan were obtained and compared. In addition, the pressure fluctuations surrounding the impeller outlet were also analyzed. The results showed that the change of the blade outlet angle of the centrifugal fan had a great influence on the performance; the total pressure and efficiency of the fan were the highest when the outlet angle of the blade was increased to 29.5° under the design flow rate; and the influence of the outlet angle on the fan performance was different in off-design conditions. On the other hand, at different flow rates, the change of the internal flow field with the increase of the outlet angle was different. For the pressure fluctuation of the fan, by increasing the blade outlet angle properly under high flow conditions, the fluctuation amplitude of the fan at the blade frequency and its frequency multiplication could be reduced, which is conducive to decreasing the impeller noise. The research results have good guiding significance regarding the design of the pneumatic performance and noise reduction performance of centrifugal fans.

Sediment-Containing Sewage Separation Using Intermittent-Discharge Columnar Hydrocyclones

Traditional hydrocyclones can be used for the concentration of sewage-containing sediments, but the low underflow concentration and the high content of fine particles result in a large subsequent dehydration workload. This study aimed to investigate the effect of columnar hydrocyclone column height on separation performance and the change in the internal flow field after the underflow orifice of the hydrocyclone was closed, so as to provide a theoretical basis for improving the ability to treat the sewage of the hydrocyclone. Numerical simulation was used to examine the change in the separation performance of the hydrocyclone and the effect of column height on the separation performance of the hydrocyclone in the case of the closed underflow orifice during intermittent discharging. The results indicate that a proper increase in column height was beneficial to improve the separation performance of the hydrocyclone. With the increase in the closing time of the underflow orifice, the particle content at the bottom of the hydrocyclone increased significantly. The experiment proves the feasibility of the intermittent discharge method in practice, and this working method can effectively increase the underflow concentration.

Analysis of Operating Principles and Flow Field Characteristics for a Diving Ballast Tank

Operating principle and flow field characteristics of a diving ballast tank for application in submerged vehicles were investigated in the present study. As understanding the complex changes in the interior air-water two-phase flow field of the ballast tank during the diving process is difficult, this study specifically performed a ballast tank diving experiment. Experimental and numerical simulations to analyse the diving motions of the ballast tank were conducted. Authors comprehensively evaluated the flow field changes in the ballast tank and its surroundings. The experimental and numerical results were compared in terms of the observed displacements and velocities during diving. Both the results indicated similar motion trajectories and velocities. Authors effectively observed the air-water two-phase flow field change inside the ballast tank using this numerical method. Therefore, the numerical model constructed in this study can be useful for analysing the diving motions of ballast tanks and can effectively predict the interior flow field characteristics of a ballast tank.

Simulation and analysis of wind turbine ice accretion under yaw condition via an Improved Multi-Shot Icing Computational Model

Abstract Wind turbine icing under yaw condition is a special phenomenon affecting the operation of wind turbine in cold climate. Under yaw condition, the periodical change of flow field significantly enhances the blade unsteady icing characteristics, which poses a great challenge for icing research. In order to simulate the yaw icing process, an Improved Multi-Shot Icing Computational Model (IMSICM) is proposed, in which an efficient computational strategy is designed according to different time scales. An icing experiment of NACA0012 airfoil is carried out in the Icing Wind Tunnel of CARDC to validate IMSICM. Then, the yaw icing process of NREL Phase VI wind turbine is simulated. The results show that, influenced by yaw condition, the ice horns rotate to the upper side of airfoil due to the reduction of AoA. At the same time, the height of the lower ice horn is enhanced while the angle between the upper and lower ice horns is decreased. The yaw icing features result in different aerodynamic performance of ice accreted airfoils along the blade, which has a close relationship with the flow separation. The IMSICM can be used as an efficient tool to shed light on the complex icing problems of wind turbine.