Shape Effect of Polymetallic Nodules on Suction Forces and Flow Field During Seabed Hydraulic Collection

2021 ◽  
pp. 1-21
Author(s):  
Guocheng Zhao ◽  
Haining Lu ◽  
Longfei Xiao ◽  
Jingchao Hu
Keyword(s):  
Flow Field ◽  
Time History ◽  
Basic Research ◽  
Shape Effect ◽  
Detached Eddy Simulation ◽  
Field Methods ◽  
Dye Tracing ◽  
Suction Force ◽  
Polymetallic Nodule ◽  
Suction Flow

Abstract Turbulent suction pipe flow around a near-wall ellipsoid nodule, as basic research of polymetallic nodule hydraulic collection, is investigated numerically and experimentally in this paper. Seven ellipsoids with axe ratios (a/b) ranging from 1 to 2 are considered as nodule models to reveal the shape effect on the characteristics of suction forces and suction flow field. Methods of particle image velocimetry (PIV) and dye tracing were used to visualize the suction flow field. The results indicate that: (1) suction force coefficients increase with a/b; (2) the shape effect is more significant in the cases with smaller ratios of bottom clearance to semi-thickness of the ellipsoid (h/c); (3) the weak vortex shedding in suction flow results in small-amplitude fluctuations of time-history suction forces; (4) the detached-eddy simulation (DES) method based on shear stress transport (SST) model is validated to be accurate and feasible for predicting the suction forces and suction flow field. It is expected to provide references for the design of nodule pick-up devices and to help us further understand the mechanism of hydraulic collection.

scholarly journals Experimental Research on Hydraulic Collecting Spherical Particles in Deep Sea Mining

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1938 ◽  
Author(s):  
Guocheng Zhao ◽  
Longfei Xiao ◽  
Tao Peng ◽  
Mingyuan Zhang
Keyword(s):  
Flow Field ◽  
Deep Sea ◽  
Economic Benefits ◽  
Spherical Particles ◽  
Vertical Force ◽  
Incipient Motion ◽  
Force Coefficient ◽  
Suction Force ◽  
Suction Flow ◽  
Force Characteristics

Hydraulic collecting is the key technology in deep sea mining and dredging engineering. It determines economic benefits of the project and environmental issues. However, mechanistic studies of hydraulic collecting are rarely described. In this study, the mechanism of collecting spherical particles is researched by dimensional analysis and experimental study. The experimental system is established to carry out three kinds of tests including 253 different test cases. The empirical model of collecting performance prediction is established by the tests of vertical force characteristics and vertical incipient motion characteristics of particles in suction flow field. The results show that the vertical suction force coefficient (Cvs) decreases exponentially with the ratio of bottom clearance to diameter of the particle (h/d), increases linearly with the ratio of diameter of the suction pipe to diameter of the particle (D/d), and is nearly independent of Reynolds number (Re). The empirical formula of vertical force and criterion-formula of vertical incipient motion of particles are obtained with the maximum tolerance less than 15%. The phenomenon that the vortex could help strengthen the suction force was observed in the tests. In addition, the characteristics of suction flow field were obtained by flow visualization tests, and applied to explain the force characteristics of particles in the suction flow field.

scholarly journals Experimental and numerical investigation on total pressure distortion generated by a rectangular movable flat baffle

2021 ◽  
Vol 13 (2) ◽  
pp. 168781402199439
Author(s):  
Baofeng Tu ◽  
Bin Xuan ◽  
Chuanpeng Li ◽  
Xinyu Zhang ◽  
Jun Hu
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Total Pressure ◽  
Quantitative Relationship ◽  
Interface Plane ◽  
Detached Eddy Simulation ◽  
Insertion Depth ◽  
Distortion Coefficient ◽  
Pressure Region ◽  
Blocking Coefficient

A distortion generator equipped with a motor-activated movable flat baffle was installed just upstream of a rectangular plenum entrance to investigate the effects of inlet total pressure distortion on the stability and performance of an auxiliary power unit (APU). Experiments and numerical simulations on a direct connect scale inlet model of the APU were carried out to obtain a quantitative relationship between the insertion depth of the flat baffle in the flow stream and the total pressure distortion intensity and region. In the experiments, the blocking coefficient and total pressure distortion coefficient were controlled by adjusting the insertion depth of the flat baffle and the mass flow. In the simulations, detailed flow field was analyzed based on the detached-eddy simulation (DES) method. The results show that the pressure distribution of the distorted flow on the aerodynamic interface plane (AIP) can be divided into a high-pressure region, a transition region, and a low-pressure region. The area affected by the distorted flow was larger than the inserting area of the flat baffle. That area was more related to the relative blocking coefficient, and less affected by the mass flow. The total pressure distortion coefficient had a linear relationship with the mass flow rate and is positively correlated with the relative blocking coefficient. As the relative blocking coefficient increased to a certain value, an exponential growth in the total pressure distortion coefficient occurred, and consequently, the flow field distortion was intensified. In the flow field, a pair of corner vortices were formed at the corner between the flat baffle and the bottom wall of the inlet pipe, and a large separation zone was formed behind the flat baffle and exhibits certain unsteady characteristics.

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Wei Ma ◽  
Feng Gao ◽  
Xavier Ottavy ◽  
Lipeng Lu ◽  
A. J. Wang
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Leading Edge ◽  
Suction Side ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Linear Compressor Cascade

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

scholarly journals Dynamic Analysis of Cavitation Tip Vortex of Pump-Jet Propeller Based on DES

2020 ◽  
Vol 10 (17) ◽  
pp. 5998 ◽  
Author(s):  
Jianping Yuan ◽  
Yang Chen ◽  
Longyan Wang ◽  
Yanxia Fu ◽  
Yunkai Zhou ◽  
...  
Keyword(s):  
Flow Field ◽  
Energy Loss ◽  
Dynamic Characteristics ◽  
Vortex Core ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Detached Eddy Simulation ◽  
High Rotational Speed ◽  
Propulsion Efficiency ◽  
Cavitation Bubbles

When a pump-jet propeller rotates at high speeds, a tip vortex is usually generated in the tip clearance region. This vortex interacts with the main channel fluid flow leading to the main energy loss of the rotor system. Moreover, operating at a high rotational speed can cause cavitation near the blades which may jeopardize the propulsion efficiency and induce noise. In order to effectively improve the propulsion efficiency of the pump-jet propeller, it is mandatory to research more about the energy loss mechanism in the tip clearance area. Due to the complex turbulence characteristics of the blade tip vortex, the widely used Reynolds averaged Navier–Stokes (RANS) method may not be able to accurately predict the multi-scale turbulent flow in the tip clearance. In this paper, an unsteady numerical simulation was conducted on the three-dimensional full flow field of a pump-jet propeller based on the DES (detached-eddy-simulation) turbulence model and the Z-G-B (Zwart–Gerber–Belamri) cavitation model. The simulation yielded the vortex shape and dynamic characteristics of the vortex core and the surrounding flow field in the tip clearance area. After cavitation occurred, the influence of cavitation bubbles on tip vortices was also studied. The results revealed two kinds of vortices in the tip clearance area, namely tip leakage vortex (TLV) and tip separation vortex (TSV). Slight cavitation at J = 1.02 led to low-frequency and high-frequency pulsation in the TLV vortex core. This occurrence of cavitation promotes the expansion and contraction of the tip vortex. Further, when the advance ratio changes into J = 0.73, a third type of vortex located between TLV and TSV appeared at the trailing edge which runs through the entire rotational cycle. This study has presented the dynamic characteristics of tip vortex including the relationship between cavitation bubbles and TLV inside the pump-jet propeller, which may provide a reference for the optimal design of future pump-jet propellers.

Two-dimensional pressure field and backflow in the annular skirt of vortex gripper

2020 ◽  
pp. 095440622097404
Author(s):  
Jianghong Zhao ◽  
Xin Li
Keyword(s):  
Flow Field ◽  
Pressure Distribution ◽  
Local Stress ◽  
Vortex Chamber ◽  
Physical Contact ◽  
Two Dimensional ◽  
Stress Concentrations ◽  
Suction Force ◽  
Maximum Value ◽  
Gap Height

The vortex gripper is a kind of pneumatic noncontact gripper that does not produce a magnetic field and heat. It can grip a workpiece without physical contact, which avoids any unintentional damage such as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study focused on the two-dimensional pressure distribution field on a workpiece surface under the vortex gripper. Theoretical, experimental, and computational fluid dynamics results were combined to study the backflow phenomenon in the annular skirt, which can decrease the gripper’s suction force after the maximum value is reached. First, the pressure distribution in the annular skirt was theoretically modeled. A comparison with the experimental results showed that increasing the gap height between the gripper and workpiece generates a circumferentially asymmetrical flow field in the skirt. Based on this, it was hypothesized that an airflow in the circumferential direction may exist. The experimental data and simulation results were analyzed under large gap height conditions to observe the backflow in detail and it was found that an uneven pressure distribution with positive and negative pressure regions generated by the uneven flow is the root cause of the backflow. Finally, the effect of the backflow on the flow field in two different flow regions (in the annular skirt and inside the vortex chamber) was analyzed and the reason why the suction force of the vortex gripper has a maximum value was determined.

Assessment of LNG Pump Tower Loads

2019 ◽  
Author(s):  
Michael Thome ◽  
Jens Neugebauer ◽  
Ould el Moctar
Keyword(s):  
Structural Design ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Impact Loads ◽  
Detached Eddy Simulation ◽  
Morison Equation ◽  
Field Methods ◽  
Delayed Detached Eddy Simulation ◽  
Tower Structure

Abstract The assessment of design loads acting on Liquefied Natural Gas (LNG) pump tower are widely based on Morison equation. However, the Morison equation lacks consideration of transverse flow, impact loads and the interaction between fluid and structure. Studies dealing with a direct simulation of LNG pump tower loads by means of Computational Fluid Dynamics (CFD), which can cover the aforementioned effects, are currently not available. A comparative numerical study on LNG pump tower loads is presented in this paper focusing on the following two questions: Are impact loads relevant for the structural design of LNG pump towers? In which way does the fluid-structure interaction influence the loads? Numerical simulations of the multiphase problem were conducted using field methods. Firstly, Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, extended by the Volume of Fluid (VoF) approach were used to simulate the flow inside a three-dimensional LNG tank in model scale without tower structure. The results were used to validate the numerical model against model tests. Motion periods and amplitudes were systematically varied. Velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations with the Morison equation. Morison equation, URANS and Delayed Detached Eddy Simulation (DDES) computed tower loads were compared. Time histories as well as statistically processed data were used. Global loads acting on the full (with tower structure) and simplified structure (no tower structure, but using Morison equation) are in the same order of magnitude. However, their time evolution is different, especially at peaks, which is considered significant for the structural design.

scholarly journals Comparative Study on CFD Turbulence Models for the Flow Field in Air Cooled Radiator

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1687
Author(s):  
Chao Yu ◽  
Xiangyao Xue ◽  
Kui Shi ◽  
Mingzhen Shao ◽  
Yang Liu
Keyword(s):  
Flow Field ◽  
Transient Flow ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Compartment Model ◽  
Navier Stokes ◽  
Engine Compartment ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Relevant Calculation

This paper compares the performances of three Computational Fluid Dynamics (CFD) turbulence models, Reynolds Average Navier-Stokes (RANS), Detached Eddy Simulation (DES), and Large Eddy Simulation (LES), for simulating the flow field of a wheel loader engine compartment. The distributions of pressure fields, velocity fields, and vortex structures in a hybrid-grided engine compartment model are analyzed. The result reveals that the LES and DES can capture the detachment and breakage of the trailing edge more abundantly and meticulously than RANS. Additionally, by comparing the relevant calculation time, the feasibility of the DES model is proved to simulate the three-dimensional unsteady flow of engine compartment efficiently and accurately. This paper aims to provide a guiding idea for simulating the transient flow field in the engine compartment, which could serve as a theoretical basis for optimizing and improving the layout of the components of the engine compartment.

Detached Eddy Simulation: Recent Development and Application to Compressor Tip Leakage Flow

2021 ◽  
pp. 1-400
Author(s):  
Xiao He ◽  
Fanzhou Zhao ◽  
Mehdi Vahdati
Keyword(s):  
Flow Field ◽  
Model Development ◽  
Main Flow ◽  
Transition To Turbulence ◽  
Leakage Flow ◽  
Detached Eddy Simulation ◽  
Grid Spacing ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Eddy Simulation

Abstract Detached Eddy Simulation (DES) and its variants are emerging tools for turbomachinery simulations. In this paper, the state-of-the-art upgrades of DES are reviewed, and their capabilities in predicting compressor tip leakage flow are discussed. The upgrade with the best potential is identified as the Delayed DES (DDES) method with the grid spacing FKHΔhyb, which unlocks the physics of the Kelvin-Helmholtz instability in compressor tip leakage flow. The upgraded grid spacing FKHΔhyb is compared against the widely used default one Δmax in a backward-facing step and a low-speed axial compressor rotor. Results show that the DDES method with FKHΔhyb predicts both the main flow field and the turbulence field with reasonably good accuracy. However, the original DDES method with Δmax predicts a delayed transition to turbulence, which leads to an inaccurate prediction of the main flow field when using a coarse mesh. The findings in this paper highlight the future opportunities for using the DDES-FKHΔhyb method to predict tip-driven compressor stall and generate a turbulence database for turbulence model development.

Evolution of Vortices Behind Single Diamond-Shaped Cylinders in Free Stream

2000 ◽  
Author(s):  
Shuichi Torii ◽  
Wen-Jei Yang ◽  
Shinzaburo Umeda
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Free Stream ◽  
Finite Difference Methods ◽  
Time History ◽  
Experimental Program ◽  
Flow Phenomena ◽  
Vector Distribution ◽  
Two Dimensional Flow ◽  
Karman Vortex

Abstract Two-dimensional flow over a single diamond-shaped cylinder in the free stream are experimentally and theoretically investigated. The experimental program includes visualization of the flow field using the tracer method. In the theoretical program, the Navier-Stoeks equations are discretized using finite difference methods to determine the time history of velocity vector distribution in the flow field. Efforts directed to examine the effects of the Reynolds number, Re, and the upstream angle of the diamond shape, θ, on flow phenomena. The study discloses that (i) the generation of von Karman vortex streets behind the diamond-shaped cylinder are intensified with an increase in the Reynolds number, (ii) the flow pattern in the wake region of the diamond-shaped island is affected by θ, and (iii) the relationship among the Strouhal number, St, Re and θ is determined and compared with the existing St-Re relationship for flow over a circular cylinder.

Experimental and numerical analyses of gas–solid-multiphase jet in cross-flow

2012 ◽  
Vol 227 (1) ◽  
pp. 61-79 ◽  
Author(s):  
Yao Fu ◽  
Tong Wang ◽  
Chuangang Gu
Keyword(s):  
Flow Field ◽  
Transient Flow ◽  
Cross Flow ◽  
Jet Flow ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Calculation Methods ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Reynolds Averaged Navier Stokes

In this article, jet influence on a gas–solid-multiphase channel flow was experimentally and numerically studied. The jet flow was found to have a diameter-selective controlling effect on the particles’ distribution. Jet flow formed a gas barrier in the channel for particles. While tiny particles could travel around and large particles could travel through, only particles on the 10 -µm scale were obviously affected. Three different calculation methods, Reynolds averaged Navier–Stokes, unsteady Reynolds averaged Navier–Stokes, and detached eddy simulation, were used to simulate this multiphase flow. By comparing the calculation results to the experimental results, it is found that all the three calculation methods could capture the basic phenomenon in the mean flow field. Nevertheless, there exist great differences in the transient flow field and particle distribution.

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