Simulation Study Of Flow Research Articles

Numerical simulation of thermal enhancement in pulsating inflow grooved channel based on hydrodynamic instability

In this paper, a numerical simulation study of flow and heat transfer in a grooved channel consisting of ten rectangular grooves with steady and pulsating flow is carried out. Numerical simulations of the steady flow with small perturbations applied at Re = 800, 1200, 1600, and 2000 show that the same intrinsic frequency fN exists at different positions, amplitudes, and durations, and it disappears gradually with the development of the flow. A sinusoidal pulsating flow with different frequencies is applied to the grooved channel with the dimensionless amplitude A fixed at 0.2. The flow and heat transfer properties of the grooved channel are investigated in the case of pulsating inflow, and it is found that there exists a vortex periodic formation–development–convergence–dissipation process inside each groove. The results show that the increase in the time-averaged Nusselt number is 44.12%, 57.75%, 53.21%, 52.93%, the time-averaged friction factor is increased by 58.23%, 133.04%, 140.80%, 151.26%, and the PECs is decreased with the increase in Reynolds number to be 1.24, 1.19, 1.14, and 1.12, respectively, when compared with the constant flow. When the forcing frequency is equal to the hydrodynamic instability frequency, the time-averaged Nusselt number of the grooved channel will reach its maximum value. Also, the dynamic mode decomposition analysis shows that the pulsation mode energy is maximum when the forcing frequency is equal to the hydrodynamic instability frequency. It shows that the applied pulsating flow has a positive effect of enhanced heat transfer, and the positive effect decreases with the increase in Reynolds number.

Micro-scale flow simulation study of low-yield wells in tight gas reservoirs

Abstract The mechanism of gas-water flow in reservoirs has traditionally been characterized macroscopically based on flow experiments, but the microscopic mechanisms of gas-water flow in porous media cannot be precisely described experimentally. This paper categorizes low-yield gas wells into Types I, II, and III. With microscopic visualization principles, three different types of core thin-section photos were selected to construct a pore structure model, allowing for micro-scale flow simulation to examine micro-scale percolation patterns in various types of low-yield gas well reservoirs. The results show that there is a shorter displacement time in Type I reservoirs compared to Type II and III reservoirs which exhibit more pronounced fingering phenomena.

Simulation study of flow and heat transfer in wavy microchannel heat sink with manifolds and secondary channels composite

With the continuous increase in power density of electronic devices, traditional cooling methods have gradually shown their limitations. Microchannel heat sinks (MCHSs) have enormous potential in thermal management for electronic devices due to their excellent heat dissipation performance. To improve the flow and heat transfer performance of MCHSs, a numerical study was conducted on 56 types of wavy microchannel heat sinks with manifolds and secondary channels composite (WMCHS-MSCs). The results indicate that compared to the original manifold wavy microchannel heat sink (MWMCHS), the optimal WMCHS-MSC increases the thermal enhancement factor by 45.1 % when the inlet volume flow rate Q = 1.0 × 10−6 m³/s. At the same time, the overall thermal resistance, the maximum temperature difference on the bottom wall, and the pressure drop of the optimal WMCHS-MSC are reduced by 7.6 %, 21.9 %, and 10.6 %, respectively. Compared to the original MWMCHS, the increase in Q for WMCHS-MSCs results in an overall trend of increased thermal performance, decreased temperature non-uniformity and hydraulic performance, and initially increased and then decreased overall performance. The flow field distribution of the secondary channels of WMCHS-MSCs intuitively demonstrates the improved hydraulic and thermal performance brought about by disrupting the thermal boundary layer and mixing the flow. The study presents a novel approach for the design of wavy MCHSs, potentially paving the way for enhanced thermal management solutions in electronic devices.

3-D Geological Modeling for Numerical Flow Simulation Studies of Gas Hydrate Reservoirs at the Kuparuk State 7-11-12 Pad in the Prudhoe Bay Unit on the Alaska North Slope

3-D Geological Modeling for Numerical Flow Simulation Studies of Gas Hydrate Reservoirs at the Kuparuk State 7-11-12 Pad in the Prudhoe Bay Unit on the Alaska North Slope

Fast flow simulation study of pulsating ventilation performance on air contaminant removal

Fast flow simulation study of pulsating ventilation performance on air contaminant removal

Particle Flow Simulation Study of Damage Evolution in Expansive Slurry–Fractured Rock Mass Composites under Direct Shear Conditions

Particle Flow Simulation Study of Damage Evolution in Expansive Slurry–Fractured Rock Mass Composites under Direct Shear Conditions

A fluid–structure interaction study to analyze the severity of carotid artery stenosis at different locations and its effect on various hemodynamic biomarkers

The study on arterial stenosis has gained rapid interest among researchers in the last decade because of its chronic consequences. Several researchers have tried to investigate stenosis and plaque progression in the carotid artery with different simulation models. In this study, a realistic 3-D geometry of the carotid artery has been used to analyze the effect of varying degrees of stenosis present at different locations of the carotid artery on various hemodynamic parameters. An extensive range of stenosis degrees, starting from a healthy artery(0 %stenosis) to 10%, 30%, 50%, 75%, and 90% stenosis, have been studied. These degrees of stenosis were planted at different locations of the artery grown simultaneously. The whole study was done under the realm of Fluid–Structure Interaction multiphysics. The change in velocity profiles at the areas of stenosis has been found along with the wall shear stress and arterial displacement. The magnitude of velocity and wall shear stress in the case of multiple stenosis locations has been found to be dependent on each other. The presence or absence of one stenosis affects the other, and given the regular and irregular patterns of the velocity profile, wall shear stress, and displacement, their inclusion in blood flow simulation studies having multiple stenoses should be considered.

EROSION OF TUBULAR HEAT EXCHANGERS

This paper presents the results of an erosion study of a tubular heat exchanger operating on a railroad sleepersaturation processing line. The object of the study is a DN 800 oil condenser cooling the creosote oil vaporsflowing through the condenser tubes, fixed in the sieve plate of the upper and lower condenser bottom.Subject to the erosion are the upper part of the tubes and the weld connecting the tubes to the upper sieveplate. This resulted in unsealing of the connection, which led to the contamination of the cooling medium.The key problem, therefore, is to protect the entire condenser bottom from erosion. Since only the centralpart of the surface of the top sieve plate was eroded, the conclusion is that the velocity of the vapor streamover the inlet to the condenser tubes in the central part and beyond is varied. This thesis was confirmed bythe correspondence of the actual eroded area with the cavitation area resulting from a simulated flow inAutodesk CFD 2019 Ultimate software after increasing the height of the upper condenser bottom, placinga stream dispersing element between the liquid vapor inlet to the condenser and the upper sieve plate, andafter applying a protective sieve plate. Flow simulation studies for each of these variants, or a combinationof them, made it possible to evaluate the tested solutions in terms of protection against erosion, includingcavitation erosion, of the upper sieve plate of the condenser.

Numerical Simulation Study of Gas-Liquid Two-Phase Flow in a Pressurized Leaching Stirred Tank

The gas-liquid flow and oxygen content in a pressurized leaching stirred tank significantly influence the chemical reaction rates, while the specific dynamics of gas-liquid flow in the sulfuric acid system remain largely unexplored. In this study, a mathematical model of gas-liquid flow within a stirred tank is developed using the Euler-Euler approach, with the turbulence and drag force models being validated against experimental data. Utilizing this validated and reliable model, this study investigates the impacts of the sulfuric acid concentration, baffles, air inlet velocity, and bubble diameter on the flow field and gas holdup in a two-phase system consisting of a sulfuric acid solution and oxygen. The findings indicate that introducing a specific concentration of sulfuric acid decreases the solution velocity and increases the gas holdup within the tank. However, once the sulfuric acid concentration reaches a certain threshold, further increases have a diminished effect on the gas-liquid phases. The installation of baffles enhances the turbulent kinetic energy and increases the gas holdup while only resulting in a minimal 1.2% increase in power consumption. Additionally, the inlet velocity and bubble diameter have a relatively minor impact on the tank’s flow field. However, increasing the inlet velocity significantly boosts the gas holdup, whereas an increase in the bubble diameter marginally reduces it. Furthermore, introducing a sulfuric acid solution into the tank can enhance the gas holdup when the gas inlet velocity is low. Conversely, when the gas inlet velocity is high, the addition of sulfuric acid results in a decrease in the gas holdup. The conclusions from this study contribute to enhancing the mixing effectiveness and oxygen content within the tank, providing a substantial theoretical basis for optimizing the design and operating conditions of pressurized leaching stirred tanks.

CFD simulation study of internal mixing and flow of a modified airlift bioreactor

Abstract When the airlift bioreactor is applied to the field of industrial fermentation, there is a common problem of low mixing and flow efficiency due to its simple structure. In order to expand the application of airlift bioreactor in the field of industrial fermentation, a new type of airlift bioreactor with three-dimensional bumps in the draft tube has been designed to enhance the mixing and flow of gas-liquid two-phase in the reactor. In order to determine the specific influence of the three-dimensional bumps on the internal flow field of the reactor, and to provide technical reference for the improvement of the structure of the airlift bioreactor, in this paper, the CFD simulation of this type of bioreactor is carried out. Based on the Euler multiphase flow, the Realizable k-ε model was used to analyze the flow field of the reactor with average gas-liquid flow linear velocity and temperature as parameters. The results show that under certain conditions, the three-dimensional bumps inside the draft tube can effectively accelerate the gas-liquid two-phase flow and better promotes the mixing of pig manure fermentation broth and air.

Lesion Eccentricity Plays a Key Role in Determining the Pressure Gradient of Serial Stenotic Lesions: Results from a Computational Hemodynamics Study

PurposeIn arterial disease, the presence of two or more serial stenotic lesions is common. For mild lesions, it is difficult to predict whether their combined effect is hemodynamically significant. This study assessed the hemodynamic significance of idealized serial stenotic lesions by simulating their hemodynamic interaction in a computational flow model.Materials and MethodsFlow was simulated with SimVascular software in 34 serial lesions, using moderate (15 mL/s) and high (30 mL/s) flow rates. Combinations of one concentric and two eccentric lesions, all 50% area reduction, were designed with variations in interstenotic distance and in relative direction of eccentricity. Fluid and fluid–structure simulations were performed to quantify the combined pressure gradient.ResultsAt a moderate flow rate, the combined pressure gradient of two lesions ranged from 3.8 to 7.7 mmHg, which increased to a range of 12.5–24.3 mmHg for a high flow rate. Eccentricity caused an up to two-fold increase in pressure gradient relative to concentric lesions. At a high flow rate, the combined pressure gradient for serial eccentric lesions often exceeded the sum of the individual lesions. The relative direction of eccentricity altered the pressure gradient by 15–25%. The impact of flow pulsatility and wall deformability was minor.ConclusionThis flow simulation study revealed that lesion eccentricity is an adverse factor in the hemodynamic significance of isolated stenotic lesions and in serial stenotic lesions. Two 50% lesions that are individually non-significant can combine more often than thought to hemodynamic significance in hyperemic conditions.Graphical

Experimental study and numerical simulation of water-sand two-phase flow in fracture network

ABSTRACT The flow characteristics of water-sand two-phase in fractured rock mass has an important influence on underground engineering. A series of laboratory experiments are carried out by using a self-made fracture network test system. Based on the Euler-Lagrange method, a numerical simulation study of water-sand two-phase flow is conducted. The effects of sand mass fraction w, sand particle size Φ and combination of inlet and outlet on the flow characteristics of water-sand are systematically analyzed. The results show that the water-sand outflow is directly proportional to the fracture openings, and the growth rate of water-sand outflow is significantly different under multiple inlet-outlets configurations. The final volume proportions of water-sand are 14.1%, 35.9% and 50% respectively. Fluidity I exhibits an inverse correlation with fracture opening, w and Φ. Under the condition of the single inlet and outlet, the minimum fluidity I for 0.6 mm opening is 3.28E–7 m2+ns2- n/kg, the maximum fluidity I for 2.0 mm opening, reaching 3.88E–6 m2+ns2- n/kg. Based on the response surface regression method, a multivariate regression model for three fracture openings was established, boasting exceptional predictive accuracy and reliability. Particle residence time correlates positively with w and Φ. The turbulent kinetic energy k is significantly affected by the fracture opening and decreases with the increase of w and Φ. The variation range of k is 0.38 m2/s2 ~0.63 m2/s2. The results deepen our understanding of the migration behavior of water-sand in the fracture network, and provide a theoretical guidance for groundwater resource protection and other underground engineering.

Traffic flow simulation study under large gathering activities based on VISSIM

Based on the above background, this paper starts from the theory of traffic flow and the macro-basic diagram, and simulates and researches the traffic congestion problems generated in the period of large-scale gathering activities during festivals. First of all, this paper summarizes the time correlation and spatial correlation of traffic flow, analyses the judgement method and rating index of traffic congestion, and completes the macroscopic basic map; after defining the simulation parameters of each road segment and signal intersection in the road network, it is implemented by using the VISSIM simulation software; finally, it carries out the simulation analysis with the example of the New Year's Eve firework display at the Chaotianmen Gate in Chongqing, and calculates and analyses the traffic flow state of the road network with output data, and then compares the output data with that of the road network. Finally, we use the output data to calculate and analyses the traffic flow status of the road network, compare it with the traffic flow data under the smooth period, judge the congestion characteristics, draw the macroscopic basic map of the road network under each period, simulate the changes of the macroscopic basic map, analyses the impact of traffic congestion on the traffic flow of the road network, calculate the degree of improvement of the traffic status of the network, and put forward the reasonable optimization scheme to provide a decision-making basis for the evacuation of the traffic under the festival and large-scale gathering activities.

Natural Ventilation and Indoor Air Quality in Domestic School Building: CFD Simulation and Improvement Strategies

Natural ventilation is a process of replenishing used air from the interior environment with fresh outer air without the use of mechanical equipment. This project aims to investigate the feasibility and performance of implementing natural ventilation in dilapidated classroom designs of actual geometry. Computer models of an existing classroom were created using SOLIDWORKS based on real-scale building floor plans, while the same software was applied to compute flow simulation studies to visualise the airflow pattern, temperature distribution, relative humidity, and the thermal comfort level of occupants in the classrooms. Estimated climate parameters were input in the simulation process to illustrate better the effect of hot and humid climate conditions in Malaysia towards the thermal comfort level of occupants. In this project, a visualised wind tunnel was created to simulate the prevailing wind source that supplies wind to the designed classroom, and the airflow pattern across the designed building was analysed. From the initial simulation results, it was discovered that the airflow into the classroom is uneven, whereby some locations in the building are experiencing extremely low wind breeze, which eventually affects the comfort level of occupants in the room. On the other hand, an internal analysis focusing on the interior comfortability of the classrooms was applied to examine the thermal comfort condition while using the naturally ventilated classrooms. Recommendation optimisation approaches such as the louvre angle and introduction of a windcatcher was presented in this project to improve the natural ventilation performance of the designed classroom.

Simulation and Experimental Study of Fluid Flow and Solidification Behavior in Thin Slabs Continuous Casting Process under Secondary Electromagnetic Stirring

During the thin slab continuous casting process of silicon steel, electromagnetic stirring (EMS) can control the flow, heat transfer, and solidification of molten steel through electromagnetic force. Herein, a 3D mathematical model coupling the fluid flow, heat transfer, solidification, and the electromagnetic field is built. The effects of varied current intensities on the flow, heat transfer, and solidification of molten steel in the thin slab under secondary EMS are explored based on applying the electromagnetic brake in the mold region. In the findings, it is demonstrated that increasing the current intensity increases the flow rate and vorticity of the molten steel in the second cooling zone, eliminating the superheating phenomenon and improving the uniformity of the molten steel's temperature distribution. Meanwhile, based on the nucleation and growth parameters determined from thermal simulation experiments, the cellular automation finite‐element model is used to simulate the microstructure evolution during the solidification of thin slab. In the results, it is shown that the stirring energy increases when the current intensity increases, potentially promoting equiaxed crystal growth and grain refinement. Compared to the production sample, a reasonable qualitative agreement is achieved for the grain morphology, equiaxed crystal ratio, and columnar to equiaxed transition.

Numerical simulation study of flow and heat transfer characteristics of the spiral ribbed tube with elliptical dimples

In this study, a new type of spiral rib-reinforced heat transfer tube with elliptical dimples (referred to as SRTED) is proposed. Numerical simulations were performed to investigate the effect of different geometric parameters on the flow and heat transfer characteristics. The field synergy theory was adopted to reveal the enhanced heat transfer mechanism. The results demonstrated that the flow velocity reaches the maximum at the smallest cross-sectional area in the tube; besides, it tends to decrease with the increase of the cross-sectional area in the tube. The distribution trend of the local heat transfer coefficient (h) of SRTED has a periodic pattern; the average value is 1.41 times that of the plain tube and 1.13 times that of the dimpled tube. In the calculated Re range, the Nu/Nu0 of SRTED varies from 2.84 to 4.46, and f/f 0 varies from 8.98 to 23.51. The overall thermal performance evaluation criterion (PEC) value varies from 1.18 to 1.78, with higher PEC at low flow rates.

Experimental and fluid flow simulation studies of laser-electrochemical hybrid manufacturing of micro-nano symbiotic superamphiphobic surfaces.

Micro-nano symbiotic superamphiphobic surfaces can prevent liquids from adhering to metal surfaces and, as a result, improve their corrosion resistance, self-cleaning performance, pollution resistance, and ice resistance. However, the fabrication of stable and controllable micro-nano symbiotic superamphiphobic structures on metal surfaces commonly used in industry remains a significant challenge. In this study, a laser-electrochemical hybrid subtractive-additive manufacturing method was proposed and developed for preparing copper superamphiphobic surfaces. Both experimental and fluid simulation studies were carried out. Utilizing this novel hybrid method, the controllable preparation of superamphiphobic micro-nano symbiotic structures was realized. The experimental results showed that the prepared surfaces had excellent superamphiphobic properties following subsequent modification with low surface energy substances. The contact angles of water droplets and oil droplets on the surface following electrodeposition treatment reached values of 161 ± 4° and 151 ± 4°, respectively, which showed that the prepared surface possessed perfect superamphiphobicity. Both the fabrication method and the test results provided useful insights for the preparation of stable and controllable superamphiphobic structures on metal surfaces in the future.

Homogeneous Field Measurement and Simulation Study of Injector Nozzle Internal Flow and Near-Field Spray

The homogeneous field measurement of internal flow and spray of internal combustion engine injector nozzles under high pressure has always been one of the difficulties in experimental research. In this paper, an actual-size aluminum alloy nozzle is designed, and the simultaneous measurement of internal flow and near-field spray is successfully realized with the help of synchrotron radiation X-ray phase contrast imaging technology under an injection pressure of 30~90 MPa. For a 0.25 mm aperture nozzle, different radii of the inlet corner can induce different cavitation layer thicknesses, and the measured flow section shrinkage ratio is 0.70. The flow characteristics in the nozzle are entirely connected to the jet characteristics, indicating a tight correlation between internal flow and jet morphology. Finally, the internal cavitation of the nozzle was studied by the CFD simulation, and the simulation results are in good agreement with the experiment.

Numerical Analysis of the Differential Flowmeter: Standard Orifice and Slotted Orifices

The paper presents the results of simulation studies of fluid flow through a standard orifice and two slotted orifices. The research that has been carried out concerns the analysis of the effect of the orifice geometry on the velocity profiles, turbulence kinetic energy and turbulence energy dispersion. The profile studies were conducted at different distances behind the orifice so that the results could be compared with each other. The studied flow included an airflow whose inlet velocity was 15 m/s. The turbulence model k-ε was used for numerical calculations. The tested orifices were characterized by an orifice constriction equal to β = 0.5. The calculations involved flow through a pipeline with a diameter of 160 mm. The results show that for a standard orifice, the maximum velocity of the flow is about 95 m/s and this is recorded at a distance of about 10–20 cm behind the orifice, and then it decreases, and at a distance of about 60 cm, the flow velocity is about 27 m/s. In the case of slotted holes, the maximum velocity is about 30% lower compared to the flow rate through a standard orifice design. The maximum velocity behind slotted orifices occurs directly behind the orifice, and in the cases of slotted orifice 1 and slotted orifice 2, was about 70 m/s and 67 m/s, respectively. For slotted orifice 1, at a distance of 20 cm behind the orifice, the flow assumed a velocity of about 19 m/s, whereas for slotted orifice 2, the flow reached a speed of about 18 m/s, at a distance of about 30 cm behind the orifice. The values of the maximum kinetic energy of turbulence for the tested orifices are about 420 m2/s2 for the standard orifice, and about 250 m2/s2 and 220 m2/s2 for slotted orifices 1 and 2, respectively. The obtained simulation results demonstrated that slotted orifices lead to faster stream homogenization and do not disturb the flow as much as a standard orifice. Slotted orifices exhibit a higher flow coefficient.

Numerical simulation and experimental study of two-phase flow in downhole spiral gas-liquid separator

Gas-liquid separator is an important surface equipment in oilfield development. Improving the separation efficiency of separator is of great significance to the overall economic benefit of oilfield. Spiral separator is a high efficiency separation device that has been widely used, but at present, there are not enough studies on separation efficiency in number of spiral turns and pitches. In view of this problem, this paper analyzed the gas–liquid separation efficiency of spiral separators with different number of spiral turns and pitches via the fluent numerical simulation software and laboratory experiments. The results showed that a greater number of spiral turns and a larger particle diameter could lead to higher separation efficiency. The separation efficiency has an optimum value for the pitch. The performance of the downhole spiral separator was verified by laboratory experiments, and the separation efficiency was above 90% under the conditions where the treatment amount was either unchanged or changed. These results can provide a reference for the application of spiral separators in oil fields.