Velocity Distribution Law Research Articles

Study on the inlet backflow characteristics and particle deposition of screw mixed-flow deep-sea mining pump under small flow conditions

Abstract When a screw mixed-flow deep-sea mining pump operates under small flow conditions, significant backflow occurs at the impeller inlet and in the inlet pipe, which seriously affects the pump performance. To investigate this backflow characteristic, this paper presents a numerical study of the internal flow field of the mining pump based on the CFD-DEM coupling method. The flow state at the impeller inlet, the velocity distribution law in the inlet pipe, and the particle motion state under the flow rate condition of 0.52Qd are obtained. The results show that, when the pump operates under small flow conditions, the leakage from the tip gap of the impeller head causes a screw high-speed backflow with the same rotation direction as the impeller on the wall of the inlet pipe. The backflow intensity attenuates as it propagates towards the pump inlet. The backflow mixes with the main flow in the middle of the pipe and reaches a balanced state, which causes the particles to deposit here. The deposition process can be divided into a formation stage and a stable stage. When the particles in the middle of the pipe reach the stable stage, their shape and position become stable. The velocity pulsation of the monitoring points near the wall is periodic, and its pulsation frequency is the same as the impeller rotation frequency.

Theoretical and experimental analysis of the critical velocity of interface instability in gas jet forming

Gas jet forming can be used for creating optical reflectors, but under certain conditions, the surface shape fluctuation of the gas-liquid interface, that is, interface instability, may occur during the forming process. This study investigated the mechanism of interface instability in gas jet forming by combining the Kelvin-Helmholtz instability and the gas jet flow velocity distribution law. Theoretical analysis revealed that when the nozzle height is fixed, interface instability occurs when the gas flow rate reaches a certain value, which increases with the distance between the nozzle and the liquid surface. In order to verify the results of the theoretical analysis, experiments were carried out within the range of nozzle height from 0 to 42 mm, based on the formulas of the transition section between the potential core region and the self-similarity region in the gas jet. Within this range, the critical velocity of interface instability was found to be the minimum, 9.946 m/s, when the nozzle height was 0 mm, and the maximum, 15.562 m/s, when the nozzle height was 42 mm. The results of the theoretical analysis and experiments were used to establish a predictive model for the critical condition of interface instability, with a mean prediction deviation of 0.119 m/s. This model can provide a basis for selecting parameters for gas jet forming.

A Multiscale Euler–Lagrange Model for High-Frequency Cavitation Noise Prediction

Abstract To simulate the microscale bubble distribution and its effect on high-frequency cavitation noise, we present a two-way transition and coupling Euler–Lagrange model. The model accounts for both cavity fission and environmental nucleation as sources of microscale bubbles, which are limited in the traditional mesh-based Euler models. We evaluate the model with the experimental data of truncated NACA0009 hydrofoil as well as the measured bubble size distributions, showing satisfactory results for velocity distribution, cavity patterns, and power law scalings of bubble size. Based on an acoustic analogy, we find that the model produces sound waves with smaller wavelengths and higher frequencies than the Euler model, which are mainly attributed to two factors: (1) microscale bubbles with high natural frequency and (2) intense multiple cavity collapse/rebound behavior. This model is promising for predicting the full-spectrum of cavitation noise.

A new numerical model of gas leakage noise from elliptical sealing defects in pipelines

During the assembly of aviation conduits, various quasi-elliptical sealing anomalies often arise due to diverse factors. This paper presents a new numerical model for analyzing the noise distribution pattern of quasi-elliptical holes. Analogous to the velocity distribution law of an elliptical jet, the velocity distribution function of an elliptical defect boundary is constructed, and then the gas leakage flow field is solved by using the large eddy simulation method, and then the near-field noise distribution is calculated by using CFD. The model discerns that the rate of sound pressure level reduction along the minor axis surpasses the major axis as the aspect ratio increases. Within the azimuth angles plane, sound pressure levels gradually decrease from the minor to the major axis direction, and the discrepancy between sound pressure levels along these two axes diminishes with an increase in aspect ratio. Experimental validation underscores the model's precision, with accuracy exceeding 90% in approximating noise pressure levels near leakage sites.

On the impact of runaway stars on dwarf galaxies with resolved interstellar medium

ABSTRACT ‘Runaway stars’ might play a role in driving galactic outflows and enriching the circumgalactic medium with metals. To study this effect, we carry out high-resolution dwarf galaxy simulations that include velocity ‘kicks’ to massive stars above eigth solar masses. We consider two scenarios, one that adopts a power law velocity distribution for kick velocities, resulting in more stars with high-velocity kicks, and a more moderate scenario with a Maxwellian velocity distribution. We explicitly resolve the multiphase interstellar medium (ISM) and include non-equilibrium cooling and chemistry. We sample individual massive stars from an IMF and follow their radiation input and SN feedback (core-collapse) channel at the end of their lifetime. In the simulations with runaway stars, we add additional (natal) velocity kicks that mimic two- and three-body interactions that cannot be fully resolved in our simulations. We find that including runaway or ‘walkaway’ star scenarios impacts mass, metal, momentum, and energy outflows as well as the corresponding loading factors. The effect on the mass loading factor is small, but we find an increase in the metal loading by a factor of 1.5 to 2. The momentum loading increases by a factor of 1.5–2. The energy loading increases by roughly a factor of 5 when runaway stars are included. Additionally, we find that the overall level of star formation is increased in the models that include runaway stars. We conclude that the inclusion of runaway stars could have an impact on the global star formation and subsequent outflow properties of dwarf galaxies.

Experimental Study of the Hydrodynamics of an Open Channel with Algae Attached to the Side Wall

The construction of large-scale water diversion projects has effectively alleviated the current situation of the uneven distribution of water resources in China. However, due to the siltation of very fine sediment and organic matter on the side wall of an open channel, and the slow velocity of the side wall flow field, it is easy for epipelic algae to be produced, which affects water quality. Because prototype observation cannot be used to predict the series of flow in real time, and the calculation of the mathematical model is affected by parameter limitations, these two methods often cannot truly reflect the hydrodynamic characteristics of an open channel with epipelic algae. Therefore, by referring to the design parameters of the water diversion project channel, this study took the epipelic algae growing on the side wall of an open channel as the research object and used the scale of 1:30 to carry out a generalized flume experiment. Through the analysis of the physical characteristics of the prototype sample, and the simulation of the cohesive force between the oblique side wall and the epipelic algae, multi-group and multi-series hydrodynamic tests were carried out. The velocity distribution law and flow field distribution law were analyzed. The research results show that the presence of epipelic algae has a certain hindering effect on the flow velocity and significantly reduces the range of the peak velocity of the channel along the water depth. The position of the maximum velocity on the vertical line of the channel flow appears at the relative water depth of 0.6. In the case of small flow, the epipelic algae group only reduces the average flow rate of the channel by 5~6%; in the case of large flow, the effect of epipelic algae on the channel flow rate is minimal. This paper includes important scientific guiding significance and practical value for the regulation of water quantity and water quality safety, as well as the protection of long-distance projects.

Analytical solutions of flow velocity profile based on the morphological response of flexible vegetation

Hydrodynamics affected by vegetation in channel is one of the hot topics in ecological hydraulics. Flexible vegetation plays an important role in natural flow region, which changes flow structure and affects the transport of pollutants. Therefore, it is important to illustrate the physical process of the interaction between water flow and morphological response of flexible vegetation. Due to the complex resistance characteristics of flexible vegetation, the simulation of velocity distribution is more complicated. In this paper, velocity distribution in the form of Bessel function is derived by solving the governing equation based on linear resistance-velocity expression of flexible vegetation. Meanwhile, a new power law of velocity distribution is established by adopting the concept of vegetated riverbed. Moreover, a new expression of Darcy–Weisbach friction is derived for flow with flexible vegetation, and the relationship between vegetation bending angle and hydraulic parameters is given. Quantitative relationship between the power law index and the Darcy–Weisbach friction coefficient in the free surface layer is derived for flexible vegetated flow. This research reveals the velocity distribution characteristics under the influence of flexible vegetation and the resistance features on vegetated riverbed.

Effect of vegetation on flow hydraulics in compound open channels with non-prismatic floodplains

Abstract The present paper aims to evaluate the effect of emergent rigid vegetation density on the flow's turbulence structure and hydraulic parameters at the non-prismatic floodplains. The experiments were performed using the physical model of the asymmetric non-prismatic compound channel. The results show that the velocity distribution in the vegetation flow is more influenced by the drag force caused by the vegetation than by the bed shear stress and does not follow the law of logarithmic velocity distribution throughout the non-prismatic section. The intense velocity gradient at the interface of the main channel and the floodplain leads to the development of strong secondary currents, increased Reynolds shear stresses, apparent shear stresses and momentum exchange in this region. Vegetation also decreases mean kinetic energy in the floodplain and increases it in the main channel. The mean turbulence exchange coefficient for the non-prismatic compound channels without vegetation was 0.23 and for the divergent and convergent compound channels was 0.035 and 0.020, respectively. The comparison of the local drag coefficient results shows that the fluctuations of this parameter are greater in the divergent section than in the convergent section due to the strong secondary currents in the interface.

Study on the ground impact vibration intensity model of high energy warhead explosion

Introduction: In the warhead explosion process, the ground impact vibration intensity will directly affect the target buildings and instruments safety, and it is also of great significance to accurately evaluate the ammunition explosion damage power.Methods: In this study, the finite element numerical simulation method was used to analyze the explosion shock wave pressure and ground shock vibration velocity of TNT explosive with a mass of 100 kg∼1000 kg, and the ground transmission medium of sandy soil, C35 and C140 concrete, and the shock wave pressure and ground shock vibration velocity propagation and distribution law was clarified. Based on the explosion similarity law and dimensional analysis method, a ground impact vibration velocity theoretical calculation model with clear physical significance is established by introducing the property ground propagation medium parameters, taking into account the factors affecting the ground impact vibration velocity.Results: The model calculation accuracy is verified by the measured data. The verification results show that the model calculation accuracy is higher than 91.8%, which improves the calculation accuracy of the explosion site ground impact vibration velocity.Discussion: This research provides more accurate and scientific theory and data support for the ammunition explosion damage power evaluation, and provides a reference for the shock and vibration resistance performance design of instruments, equipment and buildings. It has strong engineering application value.

Velocity distribution of liquid phase at gas-liquid two-phase stratified flow based on particle image velocimetry

Horizontal gas-liquid flows are commonly encountered in the production section of the oil and gas industry. To further understand all parameters of the pipe cross-section, this paper use particle image velocimetry to study the circular pipe cross-section liquid velocity distribution rule. Firstly the focus is on the software and hardware combination of image correction system, to solve the influence of different refractive indexes of medium and pipeline curvature caused by image distortion. Secondly, the velocity distribution law of the corrected stratified flow (the range of liquid flow of 0.09-0.18 m3/h, and gas flow range of 0.3-0.7 m3/h) cross-section at different flow points of the pipeline cross-section at x=0 and in the Y direction at the maximum liquid velocity is studied. It is found that these distribution laws are caused by the influence of the interphase force of the gas-liquid interface and the resistance of the pipe wall. The current measurements also produce a valuable data set that can be used to further improve the stratified flow model for gas-liquid flow.

Experimental Analysis of the Annular Velocity of a Capsule When Starting at Different Positions of a Horizontal Bend Pipe

The study of the annular slit flow field is important for energy consumption, transport efficiency, and the force on the capsule for hydraulic capsule transportation. A combination of physical experiments and theoretical analysis was used to study the annular flow field around a capsule that was set in motion at different positions of a horizontal bend pipe. We study the flow velocity distribution of the gap flow field at different bend positions of the capsule by changing the position of the capsule at the bend. We found that the distribution of the flow field remained similar for different starting positions of the capsule, but the flow velocity increased suddenly and dramatically at the inflow section of the ring gap. We recorded different velocity distributions of the annular gap on the concave and convex sides of the pipe; on the convex side, the streamline of the gap was smooth, and the change in velocity was relatively small. The flow velocity of the slit flow varied more notably on the concave side of the pipe, and there was a greater fluctuation in the flow velocity distribution. Because the effects of the capsule and the pipe on water flow were not the same, we found large fluctuations in gap flow velocity at different measuring points on the concave side. Gap flow velocity was most influenced by axial flow velocity. We found that the axial flow velocity was about one order of magnitude greater than the radial flow velocity or circumferential flow velocity. In this paper, we analyze the changes in the ring gap flow field of the capsule at different bending positions and analyze the reasons for the flow field changes and the flow velocity distribution law. This is of great significance to the study of the transport efficiency and energy consumption of the capsule. The results of this paper complement the study of capsule initiation at different positions in the bend and provide a reference point in terms of transport efficiency, energy consumption, and capsule stress. The results of this study promote the development of hydraulic capsule transportation.

Field Study of Three–Parameter Flow Resistance Model in Rivers with Vegetation Patch

Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameters in hydraulic engineering, mechanical engineering, fluvial morphology, and environmental studies. Based on this necessity, in this study, the values of bed shear stress in four reaches of rivers in Iran were estimated and compared using the methods of boundary layer characteristics, logarithmic law, and Darcy–Weisbach. Data collection in this study started in February 2021 and ended in April 2021. Estimation of flow resistance is a key factor in many numerical and physical models. In order to obtain a reasonable evaluation of this factor, it is necessary to measure and calculate the key variables of resistance to flow. Accordingly, the experimental design in this study includes surveying operations, velocity measurement, and sampling of bed sediments. The results show that due to bed forms, vegetation patches, and variations of flow depth and grain size in the river, the universal velocity distribution law (the log law) may not be suitable to estimate the shear velocity, which is a key parameter of flow resistance. This calls for more justifiable methods which are not affected by near–the–bed conditions. Accordingly, a three–parameter flow resistance model is presented, which shows an average error of 17%, indicating the accuracy of the model. The investigation of 71 measured velocity profiles shows the occurrence of the Dip phenomenon in the velocity profiles near the vegetation patches. However, by moving away from the vegetation patches, the effect of this phenomenon is decreased, and the profiles illustrate an S–shaped distribution. The results show that the relative differences between the logarithmic law and Darcy–Weisbach methods compared to the boundary layer characteristics method (BLCM) are equal to 87% and 39%, respectively, indicating a more reasonable agreement between the Darcy–Weisbach method and the boundary layer characteristics method. This is due to the application of key parameters of the boundary layer theory to calculate shear velocity by BLCM. However, to simplify data collection in the field, the application of the Darcy–Weisbach method is suggested.

Study on the distribution law of airflow velocity in rectangular and semicircular roadway sections

AbstractReliable ventilation is the cornerstone of safe production in coal mines, and accurate monitoring of ventilation parameters is the fundamental guarantee of ventilation technology decision‐making. To improve the accuracy of airflow velocity monitoring in coal mine roadways, theoretical analysis, numerical simulation, and field tests were utilized to study the distribution law of airflow velocity in typical roadway sections. First, the calculation model of position of mean airflow velocity line in rectangular and semicircular arch roadway is established based on Boussinesq theory and Pelant turbulence theory. Then, to verify the correctness of the theoretical model, 25 groups of numerical simulation tests were conducted by using COMSOL‐Multiphysics 3.5a software. The errors between theoretical analysis and numerical simulation are all less than 4%. In addition, the numerical results also show that the contour line of airflow velocity in roadway section is consistent with the shape of roadway section, and the isoline of airflow velocity is basically parallel to the roadway wall. In addition, the closer to the roadway wall, the denser the airflow velocity isoline, indicating that the airflow velocity gradient near the wall is larger. And the thickness of the boundary layer decreases with the increase of airflow inlet velocity. Finally, field tests have been conducted in Chongqing Research Institute and Sima Coal Mine to further verify the correctness of the calculation model and numerical simulation results. The measured distribution law of airflow velocity is consistent with the numerical simulation. And the errors between theoretical analysis and field tests are all less than 4%.

Research on the velocity distribution law of the coke in the chute of blast furnace based on discrete element method

Research on the velocity distribution law of the coke in the chute of blast furnace based on discrete element method

Flow field investigation of a straight–swirling integrated jet for radial jet drilling

Radial jet drilling (RJD) technology is applied to low permeability oil-gas reservoirs, coalbed methane, and shale gas. A self-propelled bit is an integral component. The external flow fields of a new-type of straight–swirling integrated jet (SSIJ) were tested under non-submerged conditions and the key parameters of the jet were studied in this paper. A rock-breaking experiment at a specific target distance was conducted to verify the PIV test results. It is indicated that, from the introduction of a central straight jet, the central low-axial-velocity zone can be eliminated, and the maximum radial and tangential velocities are not at the jet axis. Second, the hydraulic parameters do not affect the velocity distribution law, but significantly affected by nozzle structures. The straight-to-swirl ratio and the dip-angle of an impeller slot should be 0.8 and 45°, respectively, to obtain a flow field with both a higher central velocity and larger coverage area. Through the rock-breaking experiment, it was found that when the dip-angle is 45° (swirl number of 0.45), both the borehole depth and diameter are larger, and the bottom is the flattest, simultaneously, the correctness of the PIV test is verified. Finally, since the two jets (straight & swirling) have interacted and mixed after ejected from the nozzle, there is no constant velocity core, the SSIJ has no initial and basic sections compared with the conventional combined jet, and could be divided into a transition section and uniform-mixing section along the axial. By analyzing the swirl numbers at different positions, it was found that the SSIJ has a straight, weak-swirl, strong-swirl, and periphery jet zones along the radial. The results can guide rock-breaking mechanism revelation and the optimal design of an SSIJ bit for the RJD technology.

Hierarchical Statistics-Based Nonlinear Vertical Velocity Distribution of Debris Flow and Its Application in Entrainment Estimation

The vertical distribution of debris flow profile velocity is the key to studying debris flow, impulse and the sediment carrying process. At present, the linear distribution model based on flume test results cannot describe the vertical distribution of debris flow velocity effectively due to the limitation of measurement methods. In this paper, the smooth particle hydrodynamics (SPH) numerical model based on the Herschel–Bulkley–Papanastasiou (HBP) constitutive model is utilized to invert the three-dimensional dynamic process of debris flow based on a large-scale debris flow flume experiment. With a hierarchical statistical approach, a huge number of particle velocity data were analyzed and processed to obtain the vertical distribution law of velocity. We proposed a nonlinear vertical distribution model of debris flow velocity based on logarithm function accordingly. We also applied the proposed model to the existing debris flow entrainment estimation framework. A flume dam break test case was inverted to verify the performance of erosion calculations. The results show that the numerical simulation results of erosion depth are close to the experimental values. The error percentage of maximum erosion depth is 4.1%. The average error percentage of erosion depth simulation results is 15.5%.

Study on flow distribution of irrigation canal system based on image velocimetry

• The YOLOV5 algorithm combined with the monocular ranging principle is used for fast flow measurement of UAV images for UAV hovering type measurement of local river surface flow fields. • Based on the smooth circular arc channel distribution model, the velocity distribution law of Yongji section, Yonggang section and Yonglan section is studied and summarized. • Based on The Rule of Tyson polygon, combined with the representative point of average velocity, the measurement of flow through water section is calculated, and the contactless measurement is realized. With the development of computer technology, it has become possible to measure surface flow velocity using video technology. Ripples are produced when flowing, and flow velocity can be determined based on the ripples and floating objects in water. A UAV velocity measurement system based on optical flow method and YOLOV5 algorithm in deep learning has been established, to realize the monitoring of surface flow field of large rivers. The optical flow method and the deep learning algorithm are used to track the target, convert the pixel distance to actual distance by monocular ranging, and calculate the actual flow velocity. The method was successfully applied to the surface flow field measurement of the Yongji canal in the river-loop irrigation area of Inner Mongolia, and the results showed that the orthophoto graphic images obtained by the method were of high quality, the flow field calculation results were reasonable, and the calculation results agreed well with the measurements.

Temperature distribution and pressure oscillation characteristics of di-tert-butyl peroxide overpressure relief in a confined space

Pressure relief can effectively reduce the damage caused by the thermal runaway reaction of organic peroxides in the chemical process. To further understand the overpressure relief mechanism of di- tert -butyl peroxide (DTBP), pressure vessel test system and numerical simulation method were combined to systematically analyze the dynamic relief characteristics of DTBP in a confined space. The three-dimensional spatial distribution and variation law of temperature, pressure, and airflow velocity during the relief process were also revealed. The results show that a high-speed under-expanded jet is generated when DTBP overpressure relief occurs, and low temperature and negative pressure are produced inside the vessel and near the vent. The airflow velocity first increases and then decreases during the relief process, with a maximum value of 487 m/s. Both the internal temperature and pressure show prominent damping oscillation characteristics, and the oscillation period is between 2.1 ms and 2.3 ms. The pressure oscillation curves at different positions present different peak shapes, and the closer to the vent, the smaller the pressure amplitude. The consistency between the experimental results and simulation data also verifies the reliability of the numerical model.

Study on the Effect of Blasting Vibration on Rock Bolt and Shotcrete

The blasting tunneling construction method is often used in the underground engineering projects such as tunnels, coal mines roadway, chambers and so on, rock bolt and shotcrete support is used. Although the blasting construction method has many advantages, but also will be accompanied by adverse effects. Blasting vibration of blasting construction not only to the surrounding environment, building (structure) and other adverse effects, but also on the support of the underground project itself has a negative impact. In order to discuss the impact of blasting vibration on shotcrete and rock bolt support in the process of blasting tunneling of roadway, a certain amount of explosives is detonated in the hole of the working face, the finite element software ANSYS/LS-DYNA was used to establish the numerical calculation model, through time history analysis calculation, the distribution law of the vibration velocity on the shotcrete surface along the section and the variation law of the longitudinal tension and compression stress of the rock bolt are obtained. The results show that the blasting vibration produced by blasting tunneling has a great influence on the shotcrete at the shoulder, but little influence on the axial force of the rock bolt.

Experimental investigation of flow characteristics in a vertical vibration two-phase loop thermosyphon

In this paper, flow characteristics of a two-phase loop thermosyphon under vertical reciprocating vibration are visually investigated with N-pentane as the working fluid. The tests are performed for a heating power range of 20 W to 40 W, the filling ratio of 30 % to 70%, and a 30 m?s-2, 35 Hz vertical reciprocating vibration. The effect of vertical vibration on flow characteristics of the two-phase loop thermosyphon is investigated by comparing the obtained results with those acquired in static, thereby providing a basis for explaining the heat transfer process of two-phase loop thermosyphon under vibration. The results indicate that vertical vibration promotes the rupture of a liquid plug and the transformation of the plug flow to annular flow or wavy flow. Furthermore, the vertical vibration does not change the distribution law of liquid flow velocity in the two-phase loop thermosyphon. However, it will reduce the overheating and flow velocity in the two-phase loop thermosyphon at the start-up. With an increase in the heating power, the influence of vertical vibration on liquid flow velocity is reduced due to continuous disturbance of the working medium in the two-phase loop thermosyphon.