Dynamic Mesh Technique Research Articles

Numerical Simulation of Hydrodynamics Characteristics in a Tank with an Up-down Reciprocating Agitator

The hydrodynamics characteristics in a tank with an up-down reciprocating disc agitator were numerically investigated using computational fluid dynamics (CFD) simulations. A dynamic mesh technique along with a user-defined function (UDF) was used to solve the reciprocating movement of the disc agitator in the tank. The dynamic flow field and averaged values of some important parameters were obtained. The verification of the simulation was completed by comparing its results with experimental data in the literature. It is found that the flow pattern in the tank with a reciprocating agitator is characterized by two dynamic vortices, which are above and below the disc, respectively. Flow field, force acting on the disc and power requirement change periodically in the tank. The increase of frequency, amplitude and disc diameter leads to the increase of the averaged velocity in the tank as a whole. Nevertheless, the uniformity of velocity distribution is slightly improved, worsened and greatly improved respectively under the above operating conditions. The averaged values of the force acting on the disc and power consumption are in the second and the third power relations with the reciprocating frequency and amplitude, respectively. The ratio of fluid averaged velocity in one cycle to averaged disc speed, and Newton number are hardly affected by reciprocating frequency and amplitude, while they increase with the enlarged size of the disc agitator.

Numerical simulation of fuel supply of multi-tandem fuel tanks in flight vehicle

Multi-tandem fuel tanks have a complex structure, low flow rate between tanks, and, unlike single-fuel tanks, uneven pressure distribution, which makes their fuel supply and pressurization difficult to control. This paper uses a volume-of-fluid model based on the finite-volume method to track the fuel motion in different states of a flight vehicle and obtains the liquid-surface sloshing and the liquid flow in the connecting pipe. The model uses the dynamic meshing technique combined with the pressure at the solid wall to track the motion of the one-way stop valve diaphragm in the connecting pipe, thereby better predicting the fuel transfer in the connecting pipe. The calculation covers the whole process of flight vehicle erection, standby, flight, pumping, and pressurization and provides the distribution of pressure in different fuel tanks and the fuel flow characteristics in the connecting pipe. The calculation results are consistent with the experimental results, which verifies the accuracy of the model. By calculating different working cases, the results show that the different states of the flight vehicle strongly affect the sloshing of the liquid in the fuel tank, the pressure distribution, and the opening and closing of the valves. The maximum mass flow rate through the three valves, pressure at the bottom of the tank, and pressure at the pumping port all increase after the pressurization in the fuel tank. The flow of fuel between different tanks can be increased by changing the structure of the connecting pipe, which affects the pressure at different locations in the tank and at the pumping port.

Numerical study of transient flow characteristics of gas-liquid two-phase flow in inclined upward tube under periodic vibration

The transient flow characteristics of gas-liquid two-phase flow in inclined upward tubes exhibit a high degree of complexity. The tube vibration caused by multiple uncertain factors, such as seawater impacts or subsea earthquakes, poses more significant challenges for flow safety assurance. Thus, it becomes increasingly crucial to explore the transient flow characteristics of gas-liquid two-phase flow in inclined upward tubes under various vibration conditions. In this paper, the transient flow characteristics of gas-liquid two-phase flow in an inclined upward tube under different vibration conditions are numerically studied based on CFD dynamic mesh technique. In the current study, the studied parameters include vibration direction (heaving, transverse and coupling), vibration amplitudes (0.5D, 1.0D and 1.5D), and inlet velocity (jsg=0.5∼1.0m/s; jsl=0.1∼1.0m/s). The transient flow structure, cross-sectional void fraction and pressure drop are analyzed. The findings indicate that the transient flow structure of the slug flow demonstrates periodic variation characteristics under transverse and coupling vibrations, and the cross-sectional void fraction increase. For transition flow, the cross-sectional void fraction increases under transverse and coupling vibrations, while displays an increase initially and subsequently a decrease significant with an increase in the heaving vibration amplitude. Additionally, all considered vibration conditions intensify the pressure drop of the transition flow and decrease the cross-sectional void fraction of the turbulent flow.

A Thermal Fluid–Solid Coupling Simulation of Gas Fuel Control Valves for High-Precision Gas Turbines

Gas fuel control valves play important roles in the control of gas flow in high-precision gas turbines. To clarify the influence of coupling between the structure and the fluid system, a thermal fluid–solid coupling mechanism is presented based on numerical investigations carried out using a dynamic mesh technique. Valve core deformation can affect the outlet gas flow accuracy. At 2% valve opening, the gas temperature contributes 93% to the deformation. The effect of deformation on the flow accuracy at 6% valve opening and 4% valve opening is increased by 4.8% and 7.3%, respectively. The fluctuation range of the gas temperature and pressure in front of the valve should be strictly controlled to ensure the high precision and high stability of the outlet flow. These results help to clarify the processes that occur in the valve flow path, leading to the flow control instability observed in the control valve.

A numerical study of passing ship effects on a moored ship in confined waterways with new benchmark cases

This study aims at a comprehensive investigation of passing ship effects on a moored ship in confined waterways with high blockage, referring to the new benchmark cases from the latest MASHCON conference. The whole process of a KCS container ship passing a moored Neo-Panamax container ship is simulated by combining the URANS method with the dynamic overset mesh technique. The hydrodynamic forces and moments, attitudes of the moored ship, and ship-generated waves are predicted. Firstly, the case with 10% UKC is simulated for validation. The results indicate that the numerical layout with a larger initial longitudinal distance between the two ships presents more accurate results agreeing well with the test data. Then, based on the validated method, the effects of tank width, water depth, lateral passing distance and passing ship speed are analyzed and are quantified by curve fittings in terms of the amplitudes of hydrodynamic quantities. It is found that these parameters have remarkable impacts on the moored ship, among which the passing speed is the most significant factor. In addition, the ship-generated drawdown dominates in the whole passing process, which causes prominent variations of the hydrodynamic quantities and induces pronounced pressure reductions on the moored ship.

The study on the impact of AAA wall motion on the hemodynamics based on 4D CT image data.

Purpose: To analyze the effect of the physiological deformation of the vessel wall on the hemodynamics in the abdominal aortic aneurysm (AAA), this paper compared the hemodynamics in AAA based on the moving boundary (MB) simulation and the rigid wall (RW) simulation. Method: Patient-specific models were reconstructed to generate mesh based on four-dimensional computed tomography angiography (4D CT) data. The dynamic mesh technique was used to achieve deformation of the vessel wall, surface mesh and volume mesh of the fluid domain were successively remeshed at each time step. Besides, another rigid wall simulation was performed. Hemodynamics obtained from these two simulations were compared. Results: Flow field and wall shear stress (WSS) distribution are similar. When using the moving boundary method (MBM), mean time-averaged wall shear stress (TAWSS) is lower, mean oscillatory shear index (OSI) and mean relative residence time (RRT) are higher. When using the 10th and 20th percentile values for TAWSS and 80th and 90th percentile values for RRT, the ratios of areas with low TAWSS, high OSI and high RRT to the entire vessel wall are higher than those assuming the vessel as rigid. In addition, one overlapping region of low TAWSS, high OSI and high RRT by using the MBM is consistent with the location of thrombus obtained from the follow-up imaging data. Conclusion: The hemodynamics results by using the MBM reflect a higher blood retention effect. This paper presents a potential tool to assess the risk of intraluminal thrombus (ILT) formation based on the MBM.

Numerical simulation and mathematical models of ash deposition behavior considering particle properties and operating conditions

A unified model is proposed considering thermophoresis, erosion, dynamic mesh techniques and mixed particle adhesion model based OpenFOAM open-source software. The effects of particle concentration, particle size distribution, flow velocity, probe and air temperature were discussed. Results show that the unified model predicts the deposition thickness at the probe with an average error of 7.66%. Deposition and impact efficiency always show opposite trends to factor changes, which are dominated by particle temperature and size distribution, respectively. Impact efficiency is distributed in 50–65% and the deposition efficiency is 5–25%, which get the efficiency of forming deposition of any ash particles in the boiler may be 2.5–16.25%. Different factors affect the deposition efficiency by influencing the particle temperature, the average particle temperature rises by 30 K with a double increase in flow rate. Also, a change of 10 to 30 K in particle temperature corresponds to a change of 100 K in air temperature. Mathematical models of PCA and BP neural networks based on broad data were proposed, which predict the maximum deposition thickness and probe deposition morphology with an error of 15% and 8.9%. The results of this study can provide a monitoring method and reference for boiler operators and researchers.

Numerical investigation of pyrolysis coking characteristics of supercritical hydrocarbon fuels in sinusoidal cooling channels

Carbon deposits in the high-temperature cooling channels of aero engines can lead to severe heat transfer deterioration. So it is significant to reduce the amount of carbon deposit and thus improve the safety of aero-engine operation. In this paper, a two-dimensional axisymmetric CFD model with coupled pyrolysis and coking reactions is developed, and the unsteady formation of carbon is directly simulated by the dynamic mesh technique. The pyrolysis, coking, flow and heat transfer characteristics of supercritical n-decane in smooth and sinusoidal channels during heated for 20 min were studied comparatively. The results show that the coking mass in the sinusoidal channel is basically maintained at 66% of the smooth channel, and the coking layer thickness was relatively declined by 20 μm, which is attributed to the lower precursor concentration and wall temperature in the sinusoidal channel. Specifically, due to a thinner boundary layer and a larger heat transfer area, the maximum difference in fuel conversion rate is 24.4%, with a maximum increase in Nu of 70 and a relative decrease in wall temperature of 85 K. Besides, the flow characteristics are mainly reflected in a significant increase in turbulence at the expense a pressure drop of 15.74 kPa.

Underwater ejection multifield coupling model and response characteristics

This article presents a numerical simulation analysis of the ejection process of a rigid projectile under the coupling effect of a support structure, ejection gas and transverse flow in a launch tube. Based on the computational fluid dynamics method and nested dynamic mesh technique, the dynamic response model of the support structure is used to simulate the deformation loads of the support structure inside the tube and construct a multifield coupled model for underwater ejection. Through computational analysis, we focus on the evolution characteristics of the multiphase flow field during the ejection process, the development mechanism of the bubble at the tube outlet, and the trajectory and load response characteristics of the projectile. In addition, the effects of different launch conditions, such as transverse flow velocity and interphase heat and mass transfer effects, on the projectile ejection process are also analyzed. The results show that the established model can effectively characterise the ejection motion process of the projectile. The impact of the lateral flow causes drastic changes in the motion displacement and velocity of the projectile as well as the rotation angle and rotation angular velocity. Furthermore, the interphase heat and mass transfer effects have less influence on the ejection process of the projectile due to the temperature change of the high-temperature ejected gas caused by the intermittent interface between the bubble and the aqueous medium.

A Numerical Study on the Effects of Ship-Generated Waves on a Moored Ship in Restricted Waterways Considering Initial Acceleration Process

In order to develop a reliable numerical method to investigate the effects of ship-generated waves on a moored ship in restricted waterways, this paper takes the MASHCON2022 benchmark model test case as the study object and simulates the whole process of a ship passing a moored ship by using the unsteady Reynolds-Averaged Navier-Stokes (URANS) method coupled with the dynamic overset mesh technique. The initial acceleration process of the passing ship before approaching the moored ship is considered in the numerical simulations to reproduce the benchmark model tests more realistically. The numerical simulations with four acceleration modes are conducted. The comparisons among the numerical results and the test data verify that the prediction accuracy considering the acceleration process is obviously higher than that without the acceleration process, especially for the solitary wave system, and the results based on the linear acceleration agree with the test data best. The flow field results indicate that the impacts of the solitary wave system and the primary wave system on the moored ship are different: the solitary wave system induces significant positive pressures on the hull, while the primary wave system leads to remarkable negative pressures; both result in pronounced attitude variations of the moored ship, but the hydrodynamic forces and moments affected by the primary wave system are more pronounced.

Ash deposition characteristics of flue gas across a tube using the Eulerian multiphase model with dynamic mesh technique

The ash deposition problem majorly affects the stability, safety, and economy of industrial production processes. To investigate the transient ash deposition characteristics of the flue gas flowing across a tube, the Eulerian multiphase model combined with a dynamic mesh technique is first used in this work. The deposition and the removal processes are both taken into account. Four deposition mechanisms are considered in the deposition process, including Brownian and eddy diffusion, gravity, thermophoretic, and turbophoretic forces. Based on the experimental verification results, it is found that the Eulerian multiphase model combined with a dynamic mesh technique can more accurately predict the ash deposition behavior. The overall fouling characteristics are analyzed by the changes in net deposition mass and deposition morphology under seven different working conditions. The results showed that the ash deposits are mainly formed in two regions: β = 165° ∼ 195° and β = 305° ∼ 55°. In addition, one peak is observed in the deposition region on the windward side, and three peaks exist in the deposition region on the leeward side. The periodic shedding regularity of vortices, the separation process of the boundary layer, and the flow patterns of each feature point on the tube surface are studied to investigate the influence of the flow field characteristics on the deposition characteristics. In addition, the causes of the ash deposition in various locations are discussed in detail from the perspective of the deposition mechanism. The findings of this study are beneficial for understanding the ash deposition process and provide an improved approach for ash deposition simulation.

Dynamic Evolution Characteristics of the Gear Meshing Lubrication for Vehicle Transmission System

The transmission in automobiles is the core component to ensure operational stability. Heat accumulation in the meshing process will reduce the transmission efficiency and affect the service life. Here, the essential physical process to improve transmission heat dissipation is the dynamic evolution process and the thermal transfer characteristics of lubricating oil fields during gear meshing. This paper presents a modeling and solving method for gear meshing lubrication and thermal transfer features based on the volume of the fluid model and piecewise linear interface construction (VOF-PLIC). The dynamic mesh technique combines spring smoothing and reconstruction to optimize the numerical solution process. The dynamic evolution law of gear meshing lubrication and thermal transfer is obtained by analyzing the lubrication evolution process under different speed/steering conditions. The results show that the proposed modeling and solving method could well reveal the lubrication and thermal transfer laws of the gear meshing. The temperature of the gear meshing regions was higher than that in the other regions, and the lubrication temperature showed an increasing linear trend with the stirring process. As the gear speed increased, the meshing resistance moment increased, the transmission power loss increased, and the lubrication oil temperature was larger than that of the gearbox. The power loss under the clockwise rotation of the driving gear G4 was higher than that under the counterclockwise rotation of the driving gear. The relevant results can provide theoretical references for the dynamic analysis of automotive transmission lubrication and technical support for gear profile design and lubrication optimization.

Drag Reduction Design of Transonic Airfoil Based on Particle Swarm Optimization Algorithm

The particle swarm optimization algorithm was introduced and the six-hump camelback function problem was verified and tested. The flow field of the RAE2822 airfoil was simulated by the Navier-Stokes equation and compared with the experiment very well. Based on the aerodynamic optimization case of an airfoil, an optimization design and drag reduction design with a lift coefficient fixed were developed. In this problem, geometric constraints and aerodynamic constraints are both involved. A population of 30 individuals was generated. The CST airfoil parameterized method was used to generate the new airfoil, and the dynamic mesh technique was used to update the new mesh. The aerodynamic characteristics of each airfoil was simulated by Navier-Stokes equation and obtain the individual fitness value. A total of 20 iterations of the design were carried out. There was a strong shock wave and a large shock drag in the baseline airfoil transonic flow. The shock strength is obviously weakened after optimization. The pressure drag is obviously reduced, and the lift-drag ratio is increased by 75%.

Numerical investigations of the flow control effect on a thick wind turbine airfoil using deformable trailing edge flaps

Numerical investigations have been carried out regarding the aerodynamic performance of deformable trailing edge flaps (DTEFs) to reduce the unsteady loads on the FFA-W3-241 airfoil under dynamic stall conditions. Simulations were conducted within the framework of OpenFOAM using Reynolds-averaged Navier-Stokes (RANS) approach with the SST k-ω turbulence model and dynamic mesh technique. The control effects of the DTEF size and deflection angle on the stationary airfoil were evaluated through comparative calculations. Then, comprehensive simulations were conducted to gain a deeper insight into the aerodynamic characteristics of a combined simultaneous airfoil-DTEF oscillating motion. Effects of the flap size, oscillation amplitude, frequency, and phase shifts on the airfoil lift and drag hysteresis loops have been analyzed. When the DTEFs oscillate in the same frequency as the airfoil pitch motion and with the phase shift angle of π, the dynamic load can be effectively alleviated. Under this condition, with the appropriate arrangement of flap size and oscillation amplitude, reduction of the lift fluctuations during dynamic motion can be achieved by a maximum of 42.78%, and the corresponding lift-to-drag ratio can also be regulated within a small variation range at a relatively high level.

Method to simulate transient pressure behaviors in subsea natural gas pipelines with a moving smart isolation device

The pipeline maintenance technology using smart isolation devices is an effective mean to prevent potential accidents occurred in subsea natural gas pipelines. The devices need to move with the flowing fluid and finally stop at a desired location inside the pipe, to achieve successful communication with the external link. The sudden change of the moving velocity of the device may cause severe transient pressures, which is one of the determining factors of the moving process of the device and its final stopping location inside pipe. This paper proposes a method using a coupled dynamic mesh technique to simulate the transient pressure behaviors in natural gas pipelines with a moving device. The implicit and explicit coupled method has been developed to achieve the simulation of the moving interfaces and improve the ability of incorporating complex influence factors. Verifications have been conducted using the results from the experimental method, and the reasonable agreement between the results from these two methods validates that the proposed method can be used to simulate the transient pressure behaviors in gas pipelines with a moving device. The proposed simulation method coupling with the moving state of the device has been developed and applied to a practical case to predict the moving process and thus the final stopping location of the device.

Mechanism and reduction of windage power losses for high speed herringbone gear

With the objective of reducing windage power losses (WPL) in herringbone gears, WPL experiments involving the use of a shroud are conducted. Based on computational fluid dynamics (CFD), a herringbone gear numerical model is established. Based on the renormalization group (RNG) k–ε two-equation turbulence model and dynamic mesh technique, the features of flow field distribution around the gear; mechanism of reduction of WPL; shroud installation distance, coverage, and installation position; and influence law of WPL are analyzed. The CFD and experimental results, which exhibit good consistency, are used to infer the WPL behavior with respect to the input parameters.

Numerical Modeling of Interactions between Solitary Waves and Floating Breakwaters

In the current numerical work, a 2D wave tank has been planned to explain the shared impacts among three different solitary waves and three different floating breakwaters by applying Reynolds-Averaged Navier-Stokes models and the volume of fluid method. Three dissimilar floating breakwaters (i.e., square breakwater, circular breakwater, and modified breakwater) were chosen. A total of eighteen cases were investigated, including three different floating breakwaters, a solitary wave (SW) with three different wave heights, and two different densities of floating breakwaters. We achieved the production of a solitary wave by moving a wave paddle (WP) and the motion of floating breakwater in two various directions by applying two different codes as user-defined functions. The dynamic mesh technique has been employed for re-forming mesh during the motion of the wave paddle and the floating breakwater. The numerical calculations have been confirmed by some numerical, analytical, and experimental case studies. First, the generation of a SW using the WP movement and the free motion of a heaving round cylinder on the free surface of motionless water were modeled and validated. Additionally, the effects of various parameters, including floating breakwater shape, floating breakwater density, and solitary wave height, on the hydrodynamic performances of the floating breakwater, the floating breakwater’s motions, and the free-surface elevation were considered under various conditions.

Research on a water-treading bionic propeller with variable pitch

Lizards living in the rainforests of the Americas can run and tread on the water surface. It was found that a lizard's feet are constantly reorienting in the water to adapt to the flow field during treading and running, thus providing greater driving forces and faster speeds than other animals with the same mass. Inspired by this, we utilized planetary gears and a crank rocker mechanism to design a water-treading paddle propeller in order to imitate the behavior of a lizard, and we also derived a mathematical model of the propeller during motion. Using FLUENT's sliding dynamic mesh technique, the water-treading and variable-pitching propeller and a conventional fixed-pitch propeller were simulated under different operating conditions. The results showed that the performance of the newly designed propeller was better than that of the conventional propeller, mainly due to the change in the blade angle of the new propeller. The front edge of the pitching propeller touched the water surface first at the moment of water entry and generated a positive thrust, while the blade's vertical exit reduced the drag. The maximum efficiency of the pitching propeller was obtained at an advance coefficient of J=1.25. Compared with the case of J=1.85, it was found that at the moment of water entry for the case of J=1.25, the large leading-edge vortex around the blade's lower surface made the thrust coefficient higher. At the moment of water exiting, a large vortex at the front of the propeller created a low-pressure area, which caused the propeller to be subject to less drag. By considering the effect of the rotation speed on the performance of the variable-pitch propeller, it was found that the efficiency at a rotational speed ω2=4πrad/s was always higher than those at ω1=0.5ω2 and ω3=2ω2, and the thrust and lift coefficients decreased with the increase in the rotation speed.

Simulation Study of the Transport Characteristics of the Ice Core in Ice Drilling with Air Reverse Circulation

Ice core drilling with air reverse circulation is a promising technology that uses high-speed airflow to transport the ice core from the bottom of the hole along the central passage of the drill pipe to the surface. Understanding how the ice core moves through the pipe is crucial for this technology in order to calculate the pneumatic parameters. In this paper, experimental study and the CFD dynamic mesh technique are used to analyze the ice core transport process and flow field characteristics. In order to prove the correctness of the dynamic mesh technique, the simulation results were verified with the experimental results, and it was found that all the simulation data were in agreement with the experimental data trend, and the maximum error was less than 10%. According to the study, once the ice core’s velocity reaches its maximum throughout the transport process, it does not change. The ice core’s maximum velocity increases with the diameter ratio and decreases with the length-to-diameter ratio, while eccentricity has no impact on the maximum velocity. When the air velocity reaches 21 m/s, the diameter ratio for the ice core with a length-to-diameter ratio of 2 increases from 0.80 to 0.92, and the maximum velocity increases from 8.92 m/s to 17.45 m/s. Data fitting demonstrates that the equation Vmax=−1.04V0 + 1.04Va describes the relationship between the ice core’s maximum velocity, Vmax, and air velocity, Va. Finally, we obtain the ice core’s suspension velocity model using CFD simulation to calculate the suspension velocity, V0.

Hydrodynamic pressure on lateral side of dam excited by harmonic seismic vibration: A novel formulation

Dam vibration caused by earthquakes will lead to the hydrodynamic pressure (HP thereafter) on the lateral sides of dams, which has a significant effect on the dynamic response of dams in earthquake events. In this study, the dynamic mesh technique in CFD is adopted to perform the numerical computation of the HP on dams excited by harmonic vibration. Based on the computational results, the influences on the HP on dams caused by the amplitude, period of dam vibration, and depth of reservoir water are studied systematically. Meanwhile, a novel formulation named Ye's formulation is proposed to quickly determine the HP on dams excited by harmonic vibration. Compared with the traditional Westergaard simplified formulation, Ye's formulation not only has greatly improved the accuracy but also is applicable to both vertical and arbitrarily inclined dam surfaces, as well as is applicable for nonbreaking and breaking waves, indicating that Ye's formulation has better applicability in engineering practice.