Simulated Flow Patterns Research Articles

OVERLAND FLOW ANALYSIS USING TIME SERIES OF SUAS-DERIVED ELEVATION MODELS

Abstract. With the advent of the innovative techniques for generating high temporal and spatial resolution terrain models from Unmanned Aerial Systems (UAS) imagery, it has become possible to precisely map overland flow patterns. Furthermore, the process has become more affordable and efficient through the coupling of small UAS (sUAS) that are easily deployed with Structure from Motion (SfM) algorithms that can efficiently derive 3D data from RGB imagery captured with consumer grade cameras. We propose applying the robust overland flow algorithm based on the path sampling technique for mapping flow paths in the arable land on a small test site in Raleigh, North Carolina. By comparing a time series of five flights in 2015 with the results of a simulation based on the most recent lidar derived DEM (2013), we show that the sUAS based data is suitable for overland flow predictions and has several advantages over the lidar data. The sUAS based data captures preferential flow along tillage and more accurately represents gullies. Furthermore the simulated water flow patterns over the sUAS based terrain models are consistent throughout the year. When terrain models are reconstructed only from sUAS captured RGB imagery, however, water flow modeling is only appropriate in areas with sparse or no vegetation cover.

Modeling by computational fluid dynamics simulation of pipeline corrosion in CO2-containing oil-water two phase flow

In this work, computational fluid dynamics (CFD) simulations were performed to determine the oil/water volume fraction distribution and wall shear stress in oil-water two phase fluid flow in pipelines. A CFD based empirical model was developed to predict the corrosion rate of pipelines in CO2-containing oil-water two phase flow. The flow pattern simulation is able to locate potential corrosion occurrence in pipelines by identifying the sites for water accumulation. For horizontal pipes, at low flow velocities, i.e., 0.2, 0.3 and 0.5m/s, the water phase accumulates at the bottom of the pipe. For upward inclined pipelines, at low flow velocities, the water phase accumulates at the bottom of the pipe, especially the upward part of the inclined pipe, even in fluids containing a very small amount of water, such as 5% water. For downward inclined pipelines, at low flow velocities, both the straight and the downward parts of the pipe around the elbow are the locations to accumulate water, presenting the likely area for corrosion to occur. The water-wetting of the pipe wall can be improved by increasing the flow velocity. The maximum wall shear stress is observed at the top of the elbow and the bottom of the upper part of the upward inclined pipe, where an accelerated corrosion would be experienced. For the downward inclined pipe, the bottom of the elbow and the top of the downward part of the pipe experience the highest wall shear stress. The bottom of the elbow may suffer from enhanced corrosion. The CFD based empirical model is able to predict corrosion rate of pipelines, with the modeling results validated by actual measurements.

Large eddy simulation of flow and mass exchange in an embayment with or without vegetation

This paper presents a 3D large eddy simulation model to investigate the flow phenomena in an embayment with or without vegetation in a straight channel. This model takes into account the existence of vegetation by adding the vegetation drag force to the momentum equations. The equations of mass, momentum were implemented in σ-coordinate, and the operator splitting method is used based on finite difference schemes. A fluctuating velocity generated by synthetic eddy method is imposed at the inlet boundary. The model is first validated by two cases: flow in an embayment without vegetation in a straight channel, and flow in an open channel with submerged vegetation. The comparisons show a good agreement with the measurements. The model is then applied to simulate flow patterns and mass exchange in the embayment with vegetation and/or varying the embayment aspect ratios. Lastly, the model is applied to the field.

Flow pattern and normal pressure distribution in flat bottom silo discharged using wall outlet

Flow patterns and normal wall pressures in a flat bottom silo discharged from a wall outlet were investigated through experiment and discrete element method. The fine sand was used to study the flow pattern while glass beads to study both the flow pattern and the distribution of normal wall pressure. Effects of wall outlet dimensions and shapes on the flow pattern and normal wall pressure were also presented. During the discharge, the bulk material in the silo was divided into three zones, which were the static zone, the pressure ear zone and the flow funnel. Normal wall pressures in the static zone and the pressure ear zone during discharge were much greater than that in the static state. The discharge overpressure factor was about 1.64 in the static zone, and had value of over than 2.0 in the zone of pressure ear. And the normal pressure in the flow funnel zone during discharge could be lower than that in the static state. Discrete element simulations on a silo storing glass beads were carried out to study the flow pattern and the distribution of normal wall pressure. The flow patterns in discrete element simulation agreed well with the test results while the normal wall pressures were about 5% higher than the test results. At the same time, the flow pattern inside the bulk material and the formation of flow channel in the discrete element model was presented by slicing the model apart, which could not be observed in the model test.

Numerical Simulations of Flow Patterns and Possible Implications for Deposition around Circular Patches of Vegetation

ABSTRACT Kim, H. S.; Choi, J., and Park, M., 2016. Numerical simulations of flow patterns and possible implications for deposition around circular patches of vegetation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1367 - 1371. Coconut Creek (Florida), ISSN 0749-0208. This study presents flow patterns and possible deposition around circular patches of vegetation using a two-dimensional numerical model. Because flow can pass through the patch, the formation of the von-Karman vortex street is delayed and its position moves further downstream as solid volume fraction (SVF) increases. The vortex downstream of the patch is formed as SVF≥0.08. When the two patches are very close to each other, a single vortex street is formed. As the distance between two patches is large, the effect of the interaction is weak and the vortex is developed behind indivi...

Numerical modeling of flow pattern in dam spillway’s guide wall. Case study: Balaroud dam, Iran

Flow pattern recognition using the physical modeling and numerical simulation helps designers to propose optimal shape for hydraulics structures. Optimal shape of hydraulic structure causes increasing their performance. In this study, the effect of geometries of guide walls on the flow pattern and rating curve of Balaroud dam spillway’s (Iran) was simulated using numerical and physical simulation. Numerical simulation of flow pattern through the guide walls was carried out using Flow 3D software as computational fluid dynamic (CFD) tool. To this task, three plans for the guide walls were evaluated. The results showed that the plan (3) has best performance for removing cross waves and smoothly passing the flow through the approach channel and over the spillway. Evaluating the turbulence models showed that the RNG-K-epsilon becomes the best performance to show the cross waves.

On the influence of helix angle and face width on gear windage losses

This paper investigates the windage power losses generated by helical gears rotating in pure air based on experimental results and a computational fluid dynamic code. It is found that the simulated flow patterns are totally different from those calculated for spur gears and that both tooth face width and helix angle are influential. The windage losses derived from Dawson’s and Townsend’s formulae are critically assessed using computational fluid dynamic results thus highlighting the limits of a unique formulation for accurate windage loss prediction. Finally, an analytical approach is suggested which gives good results providing that the flow rates at the boundaries of the inter-tooth domains can be estimated.

Impact of drilling fluid rheology and wellbore pressure on rock cuttings removal performance: numerical investigation

AbstractDrilling fluids exhibits non‐Newtonian behavior that is generally described in the literature by two rheological models: Power Law and Herschel–Bulkley models. We have used Eulerian–Eulerian multiphase flow model to evaluate the drilling fluid flow patterns and filter cake formation patterns for both models for ultra‐deep drilling conditions. Simulated drilling fluid flow patterns clearly show that the Herschel–Bulkley model exhibits fewer vortices around the drilling pipe, indicating better rock cuttings removal performance. In addition to mud rheology, we have analyzed the pressure drop variation with the filter cake formation on the wellbore during ultra‐deep drilling process. We have shown that filter cake thickness at the wall linearly increases with differential pressure between the well and formation. This implies that the differential pressure needs to be optimized. Very thin filter cake may lead to excessive fluid seepage into the permeable subterranean vertical zone resulting in a loss of fluid circulation and hence in a loss of rock cuttings removal. Yet, very thick filter cake reduces the effective diameter of the hole, which may lead to a poor rock cuttings removal performance and stuck pipe. The mathematical model presented here needs to be experimentally validated when filter cake thickness data in deep drilling conditions become available. The model could be useful to provide drilling engineers insight on the filter cake formation and drilling fluid flow pattern and give guidelines to optimize the filter cake as field experimental data are scarce. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Regional Hazard Analysis For Use In Vulnerability And Risk Assessment

Abstract A method for supporting an operational regional risk and vulnerability analysis for hydrological hazards is suggested and applied in the Island of Cyprus. The method aggregates the output of a hydrological flow model forced by observed temperatures and precipitations, with observed discharge data. A scheme supported by observed discharge is applied for model calibration. A comparison of different calibration schemes indicated that the same model parameters can be used for the entire country. In addition, it was demonstrated that, for operational purposes, it is sufficient to rely on a few stations. Model parameters were adjusted to account for land use and thus for vulnerability of elements at risk by comparing observed and simulated flow patterns, using all components of the hydrological model. The results can be used for regional risk and vulnerability analysis in order to increase the resilience of the affected population.

Dynamic Modelling of Rip Currents for Swimmer Safety on a Wind-Sea–Dominated Mesotidal Beach

ABSTRACT Sembiring, L.; van Dongeren, A.; Winter, G., and Roelvink, D., 2016. Dynamic modelling of rip currents for swimmer safety on a wind-sea–dominated mesotidal beach. This study applied the process-based model XBeach to predict bathymetrically controlled rip current flow occurrence, velocities and duration in the wind-sea–dominated environment of Egmond aan Zee, The Netherlands. The model is validated against data obtained during a 5-day field experiment with GPS-equipped floating drifters. Numerical model results show good agreement with data and simulate flow patterns that resemble the offshore flow through the rip channel and subsequent alongshore drift of the drifters. The average relative error of the drifter position is 0.15 and 0.19 for the cross-shore and the alongshore position, respectively. Results from the numerical experiments suggest that the rip current intensity is tidally modulated. For the period of analysis, the rips are initiated approximately 5 hours before low tide, reaching a m...

Granular Flow and Heat-Transfer Study in a Near-Blackbody Enclosed Particle Receiver

Concentrating solar power (CSP) is an effective means of converting solar energy into electricity with an energy storage capability for continuous, dispatchable, renewable power generation. However, challenges with current CSP systems include high initial capital cost and electricity price, and advances are needed to increase outlet temperature to drive high-efficiency power cycles while simultaneously maintaining stability of the heat-transfer medium and thermal performance of the receiver. Solid-particle-based CSP systems are one alternative projected to have significant cost and performance advantages over current nitrate-based molten salt systems. NREL is developing a design that uses gas/solid, two-phase flow as the heat-transfer fluid (HTF) and separated solid particles as the storage medium. A critical component in the system is a novel near-blackbody (NBB) enclosed particle receiver that uses an array of absorber tubes with a granular medium flowing downward through channels between tubes. Development of the NBB enclosed particle receiver necessitates detailed investigation of the dimensions of the receiver, particle-flow conditions, and heat-transfer coefficients. This study focuses on simulation and analysis of granular flow patterns and the resulting convective and conductive heat transfer to the particulate phase using Eulerian–Eulerian two-fluid modeling techniques. Heat-transfer coefficients in regions with good particle/wall contact are predicted to exceed 1000 W/m2 K. However, simulations predict particle/wall separation in vertical flow channels and a resultant reduction in heat transfer. Particle-flow visualization experiments confirm particle/wall separation, but also exhibit complex periodic behavior and flow instability that create intermittent side-wall contact and enhance heat transfer above that predicted by the theoretical simulations.

Large Eddy Simulation of Air Escape through a Hospital Isolation Room Single Hinged Doorway--Validation by Using Tracer Gases and Simulated Smoke Videos.

The use of hospital isolation rooms has increased considerably in recent years due to the worldwide outbreaks of various emerging infectious diseases. However, the passage of staff through isolation room doors is suspected to be a cause of containment failure, especially in case of hinged doors. It is therefore important to minimize inadvertent contaminant airflow leakage across the doorway during such movements. To this end, it is essential to investigate the behavior of such airflows, especially the overall volume of air that can potentially leak across the doorway during door-opening and human passage. Experimental measurements using full-scale mock-ups are expensive and labour intensive. A useful alternative approach is the application of Computational Fluid Dynamics (CFD) modelling using a time-resolved Large Eddy Simulation (LES) method. In this study simulated air flow patterns are qualitatively compared with experimental ones, and the simulated total volume of air that escapes is compared with the experimentally measured volume. It is shown that the LES method is able to reproduce, at room scale, the complex transient airflows generated during door-opening/closing motions and the passage of a human figure through the doorway between two rooms. This was a basic test case that was performed in an isothermal environment without ventilation. However, the advantage of the CFD approach is that the addition of ventilation airflows and a temperature difference between the rooms is, in principle, a relatively simple task. A standard method to observe flow structures is dosing smoke into the flow. In this paper we introduce graphical methods to simulate smoke experiments by LES, making it very easy to compare the CFD simulation to the experiments. The results demonstrate that the transient CFD simulation is a promising tool to compare different isolation room scenarios without the need to construct full-scale experimental models. The CFD model is able to reproduce the complex airflows and estimate the volume of air escaping as a function of time. In this test, the calculated migrated air volume in the CFD model differed by 20% from the experimental tracer gas measurements. In the case containing only a hinged door operation, without passage, the difference was only 10%.

Numerical Simulation of Electromagnetic Field and Flow Pattern in a Continuous Slab Caster with In-roll Type Strand Electromagnetic Stirring

The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer (SEMS) pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shifting along the slab wide face with time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction. Different stirring parameters (i. e. current and frequency) and stirrer configurations affect the stirring strength and the flow recirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model provides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.

Simulation of subcritical flow pattern in 180° uniform and convergent open-channel bends using SSIIM 3-D model

In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since river bends are not uniform-some are divergent and others convergent-in this study, after the SSIIM 3-D model was calibrated using the result of measurements along a uniform 180° bend with a width of 0.6 m, a similar but convergent 180° bend, 0.6 m to 0.45 m wide was simulated using the SSIIIVt 3-D numercal model. Flow characteristics of the convergent 180° bend, including lengthwise and vertical velocity profiles, primary and secondary flows, including lengthwise and widthwise slopes of the water surface, and the helical flow strength, were compared with those of the uniform 180° bend. The verification results of the model show that the numerical model can effectively simulate the flow field in the uniform bend. In addition, this research indicates that, in a convergent channel, the maximum velocity path at a plane near the water surface crosses the channel's centerline at about a 30° to 40° cross-section, while in the uniform bend, this occurs at about the 50° cross-section. The varying range of the water surface elevation is wider in the convergent channel than in the uniform one, and the strength of the helical flow is generally greater in the uniform channel than in the convergent one. Also, unlike the uniform bend, the convergent bend exhibits no rotational cell against the main direction of secondary flow rotation at the 135° cross-section.

Performance study for Francis-99 by using different turbulence models

The three-dimensional numerical investigation for turbine-99 at the best efficiency operation point, part load operation point and full load operation point was conducted by using the different turbulence models. By comparing the results of numerical simulation and experimental results, it was found that: there is a certain deviation between the numerical simulation results obtained by different turbulence models and experimental values, and the deviation increase with the reduction of output. Compared to other turbulence model, the result obtained by the standard k-e turbulent model has a relatively small difference with the experimental results. The main causes for the big difference between the numerical simulation and model test include two aspects: (1) the mesh generation and boundary conditions setting lead to differences between the research object and the actual model, (2) it is difficult to accurately simulate the unstable flow such as impact, flow separation and vortex in the turbine. Therefore, in the future actual flow pattern simulation, besides the reasonable choice of turbulence model, based on the actual flow characteristics, the boundary conditions and the simulation results will be amended to reduce the deviation between the numerical simulation and experimental results as much as possible.

Numerical simulation of blood flow and plaque progression in carotid–carotid bypass patient specific case

This study describes computer simulation of blood flow and plaque progression pattern in a patient who underwent surgical treatment for infected carotid prosthetic tube graft using carotid–carotid cross-over bypass. The 3D blood flow is governed by the Navier–Stokes equations, together with the continuity equation. Mass transfer within the blood lumen and through the arterial wall is coupled with the blood flow and is modelled by the convection–diffusion equation. Low-density lipoprotein (LDL) transport in lumen of the vessel is described by Kedem–Katchalsky equations. The inflammatory process is solved using three additional reaction–diffusion partial differential equations. Calculation based on a computer simulation showed that flow distribution in the left carotid artery (CA) was around 40–50% of the total flow in the right common CA. Also, the left CA had higher pressure gradient after surgical intervention. Plaque progression simulation predicted development of the atherosclerotic plaque in the position of the right common CA and the left internal CA. A novel way of atherosclerotic plaque progression modelling using computer simulation shows a potential clinical benefit with significant impact on the treatment strategy optimization.

Study of Pb2+ adsorption in a packed bed column of bentonite using CFD

ObjectivesIn this study, experiments and CFD (Computational Fluid Dynamics) simulations were conducted to investigate lead ion (Pb2+) adsorption in bentonite. MethodExperiments were carried out in a fixed bed column at 30°C,pH=4.0 and average particle diameter of 0.127mm. The influence of the flow rate on the breakthrough curves was examined with constant inlet concentration equal to 0.88meqL-1. The CFD technique was used for the simulation of flow patterns and ion concentration profiles inside the fixed bed column during the adsorption process. A 2D axisymmetric model based on Navier-Stokes and diffusion-convection equations was used for simulating the fluid phase. ResultsExperimental data obtained for different inlet flow rates and Pb2+ concentrations were used for validating the model. ConclusionThe CFD simulations predicted the experimental behavior of the fixed bed adsorption very well in all conditions under study.

Numerical simulation of flow patterns in the forebay and suction sump of Tianshan pumping station

Tianshan Pumping Station takes water from the Yellow River. A three-dimensional (3D) mathematical model of turbulence flow patterns in the forebay and suction sump was developed and a 3D turbulent flow simulation technique applied to numerical calculation of the flow pattern characteristics in both the original and rebuilt forebays of the pumping station. The numerical simulation results were analyzed and contrasted. The results showed that, with technical improvement, surface backflow was avoided, and bottom velocity in the forebay was increased while bottom velocity in the suction sump was unchanged. Because of this, there was no sediment deposition in the bottom of the forebay, and flow velocities in the forebay and suction sump were more evenly distributed.

ANALYSIS OF FLOODING DIRECTIONS OF THE 2011 EARTHQUAKE TOHOKU TSUNAMI

In contrast to many post-tsunami studies focusing on tsunami inundation heights, this study focuses mainly on tsunami flooding flow directions, which may have more direct impact on damages of structures. Based on tilted poles and trees in the inundated area, this study collected data of tsunami flow directions at Rikuzen-takata, Ootsuchi, and Naraha on the east coast of Japan. Numerical tsunami inundation model was then applied to each of these sites to investigate the relationship between simulated time-varying flow patterns and observed flow directions. Such link is essentially important to deepen our understandings on the dynamics of the inundation tsunami flow.

Numerical time-dependent 3D simulation of flow pattern and heat distribution in an ammonothermal system with various baffle shapes

A numerical analysis of an ammonothermal synthesis process for the bulk growth of nitride crystals was performed. The analysis includes the development of a thermal model for a lab-scale ammonothermal autoclave, which was validated by in situ temperature measurements and applied to tailor the temperature field inside the autoclave. Based on the results of the global thermal 2D simulations, a local 3D model was used to include convective phenomena in the analysis. Moreover, the influence of the baffle and different baffle shapes on the flow velocity was investigated. Fluctuations of the temperature as well as the flow velocities occur, indicating that 3D considerations are essential to accurately investigate the heat and mass transport in ammonothermal systems.