Fluid Flow Visualization Research Articles

Stable Algorithm Based On Lax-Friedrichs Scheme for Visual Simulation of Shallow Water

Many game applications require fluid flow visualization of shallow water, especially dam-break flow. A Shallow Water Equation (SWE) is a mathematical model of shallow water flow which can be used to compute the flow depth and velocity. We propose a stable algorithm for visualization of dam-break flow on flat and flat with bumps topography. We choose Lax-Friedrichs scheme as the numerical method for solving the SWE. Then, we investigate the consistency, stability, and convergence of the scheme. Finally, we transform the strategy into a visualization algorithm of SWE and analyze the complexity. The results of this paper are: 1) the Lax-Friedrichs scheme that is consistent and conditionally stable; furthermore, if the stability condition is satisfied, the scheme is convergent; 2) an algorithm to visualize flow depth and velocity which has complexity O(N) in each time iteration. We have applied the algorithm to flat and flat with bumps topography. According to visualization results, the numerical solution is very close to analytical solution in the case of flat topography. In the case of flat with bumps topography, the algorithm can visualize the dam-break flow and after a long time the numerical solution is very close to the analytical steady-state solution. Hence the proposed visualization algorithm is suitable for game applications containing flat with bumps environments.

Real-time evaluation of swallowing in patients with oral cancers by using cine-magnetic resonance imaging based on T2-weighted sequences

The aim of this study was to evaluate whether a new cine-magnetic resonance imaging (CMRI) technique might be useful for evaluating swallowing function in patients with different types of oral cancers by assessing 12 CMRI-related parameters. In total, 111 patients with oral cancers were evaluated. We examined whether visualization of fluid flow and determination of flow direction to the trachea or the esophagus were possible with CMRI. We evaluated the correlations between CMRI-related parameters and self-reported dysphagia scores as the status of dysphagia, T classification groups as tumor staging for preoperative patients, alterations in CMRI-related parameters between pre- and postoperative patients, and the degree of invasiveness of oral cancer surgery. We could judge the flow direction to the esophagus on CMRI in all 111 patients. Six CMRI-related parameters showed significant correlations with dysphagia status. Increases in CMRI-related parameters were significantly related to deterioration of swallowing status, as shown by a decrease in self-reported dysphagia scores, advances in the T classification, and degree of invasiveness of oral cancer surgery. The results of the present study suggest that CMRI can be used to directly visualize swallowing dynamics and objectively evaluate the swallowing complaints of patients with oral cancer.

Visualization of acoustically-assisted fluid flow in unconsolidated confined porous media

Acoustic techniques can deliver a high-power output in a short range, hence the application of acoustic excitation in conjunction with well stimulation and in-situ recovery methods may facilitate hydrocarbon production. In this work, an experimental apparatus is designed to directly vibrate pore fluids and visualize miscible- and immiscible-flood displacements in unconsolidated, confined porous media. A miscible-flood experiment is provided as an example, where iron oxide nanofluid is injected through a water-saturated sandpack, under both sonicated and silent conditions, to investigate how mechanical excitation influences the transport and retention of nanoparticles in porous media.

Visibility, Topology, and Inertia: New Methods in Flow Visualization.

In this article, we address three different topics in scientific visualization. The first part introduces optimization strategies that determine the visibility of line and surface geometry, such that a balance between occlusion avoidance and preservation of context is found. The second part proposes new methods for the visualization of time-dependent fluid flows, including the accurate depiction of Lagrangian scalar fields, as well as a new category of vortex identification methods. The third part introduces finite-sized particles as new application area for flow visualization, covering geometry-based methods, particle separation, topology, vortex corelines, and the determination of the origin of finite-sized particles.

Velocity Measurement of Fast Flows Inside Small Structures with Tagged MRI

Velocity is one of the most important parameters to study in complex fluid flow systems. Magnetic resonance imaging (MRI) is a non-invasive tool for quantitative visualization of fast fluid flows. Many of the flow studies by MRI measure the velocity of a fluid media using either phase encoding or time of flight (TOF) measurements. Until now, motion-sensitized SPRITE is the best method for the velocity assessment of very fast flows when the structure is large enough compared to flow displacement during the encoding time ($$t_{{\text{p}}}$$). However, when displacement during the encoding time becomes greater than the pixel size, velocity misregistration takes place. To detect the velocity with accuracy, we need to reduce the encoding time. There is a restriction on the encoding time reduction in motion-sensitized SPRITE: both the velocity encoding, and spatial encoding times take place simultaneously, causing longer encoding time. If these two steps are separated, it is possible to reduce the encoding time. In this paper, we demonstrate how this can be achieved by applying a TOF approach where the fluid is labeled by a spatially periodic modulation of the magnetization. The modulation part is performed when the liquid is still moving slowly, and the imaging part does not require the bipolar gradient to be switched on and off. This leads to a reduction of the encoding time and greater accuracy in the detection of the fast flow velocity.

Study on fluid flow and heat transfer in fluid channel filled with KKL model-based nanofluid during natural convection using FVM

PurposeA comprehensive study on the fluid flow and heat transfer in a nanofluid channel is carried out. The configuration of the channel is as like as quarter channel. The channel is filled with CuO–water nanofluid.Design/methodology/approachThe Koo–Kleinstreuer–Li model is used to estimate the dynamic viscosity and consider the Brownian motion. On the other hand, the influence of nanoparticles’ shapes on the heat transfer rate is considered in the simulations. The channel is included with the injection pipes which are modeled as active bodies with constant temperature in the 2D simulations.FindingsThe Rayleigh number, nanoparticle concentration and the thermal arrangements of internal pipes are the governing parameters. The hydrothermal aspects of natural convection are investigation using different approaches such as average Nusselt number, total entropy generation, Bejan number, streamlines, temperature fields, local heat transfer irreversibility, local fluid friction irreversibility and heatlines.Originality/valueThe originality of this work is investigation of fluid flow, heat transfer, entropy generation and heatline visualization within a nanofluid-filled channel using a finite volume method.

Fluid Dynamic Modeling and Flow Visualization of an Industrial Wet Chemical Process Bath

Simulating the fluid flow during a wet chemical process bath, allows for a deeper understanding of the flow conditions in the reaction basin. To validate the simulation, dye visualization as well as laser doppler velocimetry (LDV) and particle image velocimetry (PIV) were carried out for the first time in a transparent replica. Dye experiments led to a qualitative validation of the simulation model, as vortices and direction of rotation were detected in the basin. In summary, the repeated experiments show a good agreement with the simulation that there are areas in the basin where high relative standard deviations occur, mostly in areas with a very low velocity. The LDV velocity is higher compared to the theoretical velocity, while the simulation and PIV measurements match the theoretical value. The PIV measurements are in better agreement with the simulation, since the mean velocity in the ${z}$ -direction is 0.0039 m/s and 0.0033 m/s for the PIV and the simulation, respectively. The PIV results show a change in the velocity direction with time, which can also be seen in the simulation results. The PIV measurements therefore confirm the simulation results of a time-dependent change in the flow.

Elementary Pore Network Models Based on Complex Analysis Methods (CAM): Fundamental Insights for Shale Field Development

This paper presents insights on flow in porous media from a model tool based on complex analysis methods (CAM) that is grid-less and therefore can visualize fluid flow through pores at high resolution. Elementary pore network models were constructed to visualize flow and the corresponding dynamic bottomhole pressure (BHP) profiles in a well at reservoir outflow points. The pore networks provide the flow paths in shale for transferring hydrocarbons to the wellbore. For the base case model, we constructed a single flow path made up of an array of pores and throats of variable diameter. A passive ganglion (tracer) of an incompressible fluid was introduced to demonstrate the deformation of such ganglions when moving through the pores. The simplified micro-flow channel model was then expanded by stacking flow elements vertically and horizontally to create complex flow paths representing a small section of a porous reservoir. With these model elements in place, the flow transition from the porous reservoir fluid to the wellbore was modeled for typical stages in a well life. The dynamic component of the bottomhole pressure (BHP) was modeled not only during production but also during the drilling of a formation (with either balanced, underbalanced or overbalanced wellbore pressure). In a final set of simulations, the movement of an active ganglion (with surface tension) through the pore space was simulated by introducing a dipole element (which resisted deformation during the movement through the pores). Such movement is of special interest in shale, because of the possible delay in the onset of bubble point pressure due to capillarity. Capillary forces may delay the reservoir to reach the bubble point pressure, which postpones the pressure-drop trigger that would lead to an increase of the gas–oil ratio. The calculation of the estimated ultimate recovery (EUR) with an erroneous assumption of an early increase in the gas–oil ratio will result in a lower volume than when the bubble point delay is considered.

Using µPIV to Investigate Fluid Flow in a Pocketed Thrust Bearing

This article presents the results of an experimental and analytical investigation of the fluid flow in a pocketed thrust bearing. An experimental test rig was designed, developed, and used to visualize fluid flow in pocketed thrust bearings. Microparticle image velocimetry (μPIV) was used to measure fluid flow inside the pocket of a thrust bearing. The thrust bearings were constructed by gluing precision shim stocks to a flat BK7 glass disk in contact with a polished steel disk. The precision shim stock provides the desired pocket depth for the bearing. A polished steel disk in contact with the thrust bearing was driven by a motor in order to induce fluid flow within the pockets. μPIV was then employed to measure the shear-driven cavity flow and generate the quiver plots of the flow field. Three different lubricants were used at various speeds and a constant load to measure the effects of speed and viscosity on the flow out of the pocketed thrust bearing. In order to achieve the analytical aspect of this research, a model was developed to predict the film thickness, cavitation area, and pressure distribution generated within the bearing. The cavitation areas obtained from the model were compared with the experimental results. The results corroborate well. The calculated pressure and film thickness were then used to determine the 3D velocity profiles within the pocketed thrust bearing. The measured velocities obtained from the experimental images were compared to the analytical velocity fields. Comparing the measured velocities with the analytical model, the depth of the microparticles in the bearing pocket was determined. Using this approach, the μPIV-measured 2D velocity field was converted into a 3D velocity field, which illustrates the fluid motion inside a pocketed thrust bearing at various speeds and viscosities.

Simulation of continuous flows with discrete models

The vast majority of heat and power processes include the motion of significant amounts of gases and liq-uids. This makes it important and quite urgent to develop approaches for computer simulation and visualiza-tion of continuum flows in technological devices and pipelines. A whole set of new approaches to mathematical modelling of continuum flows has been recently developed. The most common one is using discrete mathematical models for these purposes. Discrete approaches can simplify modeling procedures in cases where traditional methods require complex time-consuming calculations. At the same time, correct-ness of description of various flow regimes by the discrete methods is often questioned. The second problem of the mentioned models is a large-scale transition from model discrete parameters to generally accepted macroscopic characteristics of flows. The purpose of this work is to determine continuous flow regimes that can be correctly described by certain models. The paper considers discrete dynamic models in the form of lattice gases. A continuum in this case is represented by a set of particles moving only in allowed directions. Despite certain limitations, there is solid evidence that lattice gases quite successfully describe a whole range of hydrodynamic phenomena, and the obtained results do not contradict the generally accepted views on the physical nature of continuum motion processes. The paper describes approaches that allow estimating flow parameters using generally accepted macroscopic indicators. It also studies possible application areas of lattice gas models using the motion of virtual particles on a spatial lattice (HPP and FHP models) and the model based on the discrete analogue of the Boltzmann equation (LBM model) to simulate and visualize continuum flows. The obtained data are in good agreement with the generally accepted results and do not contradict the provisions of classical hydrodynamics. The paper shows that the models considering particle collisions (HPP and FHP) are applicable to describing gas flows in laminar regimes. The LBM model should be considered to be more correct for simulation and visualization of real fluid flows.

Bi-directional integral pumping devices for dual mechanical seals: Influence of mesh type on accuracy of numerical simulations

A numerical study is conducted to simulate the performance of barrier fluid flow through a bi-directional dual mechanical seal with an integral radial pumping ring. Standard K-ε model is implemented as a turbulence model. Multiple Reference Frame approach is implemented to model the rotation of the pumping ring. The present study is a sequel to a previous companion work done in the area of visualization of barrier fluid flow. Improvements to the previous work depended on two aspects. First, a multi-block hybrid (tetra, prism and hexa) mesh is used where it is aimed to reduce numerical false diffusion by orienting the cells to be aligned with flow direction as much as possible. Second, expanding model’s boundaries to include inboard sealing faces. The numerical results are validated against Q-ΔP curves produced from experimental tests where an experimental setup is constructed, and appropriate instrumentation is employed to measure the pressure, temperature, and flow rate of the barrier fluid.Moreover, implementation of two spatial discretization schemes is illustrated to verify the numerical performance of each method. Second order Upwind and QUICK (Quadratic Upstream Interpolation for Convective Kinematics) schemes are used for the discretization of convective terms. The validity of implementation of each method is investigated since higher-order methods are known to be more computationally expensive but their accuracy are higher. The results by the hybrid mesh indicate that the use of the Second-order scheme provides more accurate prediction of Q-ΔP curves than the previous companion work. Moreover, the impact of using the QUICK scheme is the increased computational time while providing slightly more accurate Q-H curve relative to the second-order scheme.Finally, expanding model’s boundaries to include inboard sealing faces revealed that closed barrier fluid circulation takes place in the vicinity of the inboard sealing faces indicating poor renewal of the barrier fluid contained within this zone compared to the outboard sealing faces.

Numerical investigation of laminar compressible natural convection flow in asymmetrically and isothermally heated open-ended inclined channel

This study presents a numerical investigation of laminar compressible natural convection flow induced under high-temperature difference in an open-ended inclined parallel-walled channel heated isothermally and asymmetrically at the top wall (hot plate facing downwards) while the lower plate is considered adiabatic. The investigation is carried out with air (Pr=0.72) as the working fluid for a temperature difference of 110 °C from the ambient, over of range of modified Rayleigh number 6.2×101 to 1.6×104 and inclination of channel varying between 10 and 90° with respect to horizontal position. For the simulation, compressible governing equations without Boussinesq approximation is solved by employing new modified all-speed Roe scheme with matching preconditioning method, dual time-stepping technique and utilizing the modified Local One-dimensional Inviscid (LODI) relations suitable for compressible natural convection flow as non-reflecting boundary conditions at the inlet and outlet of the channel. Average Nusselt number based on inter-plate spacing increases with the increase of modified Rayleigh number and also with the increase of inclination from the horizontal position. This increase in average Nusselt number can be described by the variation of the level of thermal saturation inside the channel. Significant reduction in average Nusselt number is observed in the combined zone of lower angle of inclination and lower modified Rayleigh number. Visualization of fluid flow (temperature contour and velocity magnitude contour) indicates the existence of both fully developed flow and developing flow regime within the span of investigated modified Rayleigh number. Based on the investigation, a composite correlation between average Nusselt number and product of modified Rayleigh number and the sine of the angle of inclination considering as a single parameter is presented which can be conveniently used for designing of engineering application dealing with natural convection heat transfer under high-temperature difference.

CFD investigation of enhanced extra-heavy oil recovery using metallic nanoparticles/steam injection in a micromodel with random pore distribution

The present study simulated thermal enhanced oil recovery (steam and nanoparticles) for the first time using computational fluid dynamics. To better visualize fluid flow in the reservoir, a 2D micromodel generated by commercial grid generation tools was used as the porous medium. Four parameters that have a great impaction on the process were studied to determine the best combination of factors to attain maximum oil recovery. Type of nanoparticle, volume fraction of nanoparticles, diameter of nanoparticles and temperature of injected fluid were examined using the Taguchi method. All governing equations were solved in Fluent software based on finite volume. The numerical results were in a good agreement with the experimental results and the data shows that Al2O3 nanoparticles have the greatest potential for enhanced oil recovery in comparison with CuO and Fe3O4 nanoparticles. Decreasing the diameter of the nanoparticles and increasing their volume fraction in the base fluid and the temperature of the injected fluid improved oil recovery and a large amount of oil was produced from the porous medium. Injecting the nanofluid at an optimal level decreased the viscosity of the extra heavy oil from 35 to 25 Pa s.

Interactive obstruction-free lensing for volumetric data visualization.

Occlusion is an issue in volumetric visualization as it prevents direct visualization of the region of interest. While many techniques such as transfer functions, volume segmentation or view distortion have been developed to address this, there is still room for improvement to better support the understanding of objects' vicinity. However, most existing Focus+Context fail to solve partial occlusion in datasets where the target and the occluder are very similar density-wise. For these reasons, we investigate a new technique which maintains the general structure of the investigated volumetric dataset while addressing occlusion issues. With our technique, the user interactively defines an area of interest where an occluded region or object is partially visible. Then our lens starts pushing at its border occluding objects, thus revealing hidden volumetric data. Next, the lens is modified with an extended field of view (fish-eye deformation) to better see the vicinity of the selected region. Finally, the user can freely explore the surroundings of the area under investigation within the lens. To provide real-time exploration, we implemented our lens using a GPU accelerated ray-casting framework to handle ray deformations, local lighting, and local viewpoint manipulation. We illustrate our technique with five application scenarios in baggage inspection, 3D fluid flow visualization, chest radiology, air traffic planning, and DTI fiber exploration.

Simulations of a Single-Phase Flow in a Compound Parabolic Concentrator Reactor

This paper deals with the analysis and interpretation of flow visualization and residence time distribution (RTD) in a compound parabolic concentrator (CPC) reactor using computational fluid dynamics (CFD). CFD was calculated under turbulent flow conditions solving the Reynolds averaged Navier–Stokes (RANS) equation expressed in terms of turbulent viscosity and the standard k−ε turbulent model in 3D. A 3D diffusion-convection model was implemented in the CPC reactor to determine the RTD. The fluid flow visualization and RTD were validated with experimental results. The CFD showed that the magnitude of the velocity field remains almost uniform in most of the bulk reactor, although near and inside the 90° connectors and the union segments, the velocity presented low- and high-speed zones. Comparisons of theoretical and experimental RTD curves showed that the k−ε model is appropriate to simulate the nonideal flow inside the CPC reactor under turbulent flow conditions.

Design and construction of an apparatus to visualize incompressible fluid flow in several regimes

In this work, the design and construction of a didactic experimental equipment to visualize the fluid flow behavior in the laminar, transition and turbulent regimes is presented; as well as the ability to measure and display the respective Reynolds number (Re) of each flow; current educational equipments have limited or null capacity in this regard. The equipment was designed taking into account the basic laws of fluids such as mass, momentum and energy conservation. The analytical calculations were numerically validated using the finite element method (FEM), for which the Ansys software was used in its Ansys@ Parametric Design Language (APDL) and Workbench platforms. Solidworks tools for conceptual design and Stratasys Catalist for three dimension (3D) printing were used. Additionally, hardware was implemented for the step of measuring the flow velocity, temperature and Re calculation. The apparatus is a valuable resource in fluid flow visualization since it permits to read several fluid parameters immediately from a display.

Understanding Fish Linear Acceleration Using an Undulatory Biorobotic Model with Soft Fluidic Elastomer Actuated Morphing Median Fins.

Although linear accelerations are an important common component of the diversity of fish locomotor behaviors, acceleration is one of the least-understood aspects of propulsion. Analysis of acceleration behavior in fishes with both spiny and soft-rayed median fins demonstrates that fin area is actively modulated when fish accelerate. We implemented an undulatory biomimetic robotic fish model with median fins manufactured using multimaterial three-dimensional printing-a spiny-rayed dorsal fin, soft-rayed dorsal/anal fins, and a caudal fin-whose stiffnesses span three orders of magnitude. We used an array of fluidic elastomeric soft actuators to mimic the dorsal/anal inclinator and erector/depressor muscles of fish, which allowed the soft fins to be erected or folded within 0.3 s. We experimentally show that the biomimetic soft dorsal/anal fin can withstand external loading. We found that erecting the soft dorsal/anal fins significantly enhanced the linear acceleration rate, up to 32.5% over the folded fin state. Surprisingly, even though the projected area of the body (in the lateral plane) increased 16.9% when the median fins were erected, the magnitude of the side force oscillation decreased by 24.8%, which may have led to significantly less side-to-side sway in the robotic swimmer. Visualization of fluid flow in the wake of median fins reveals that during linear acceleration, the soft dorsal fin generates a wake flow opposite in direction to that of the caudal fin, which creates propulsive jets with time-variant circulations and jet angles. Erectable/foldable fins provide a new design space for bioinspired underwater robots with structures that morph to adapt to different locomotor behaviors. This biorobotic fish model is also a potentially promising system for studying the dynamics of complex multifin fish swimming behaviors, including linear acceleration, steady swimming, and burst and coast, which are difficult to analyze in freely swimming fishes.

Visualization of Fluid Flow Through Cracks and Microannuli in Cement Sheaths

Summary Cement-sheath integrity is important for maintaining zonal isolation in the well. The annular-cement sheath is considered to be one of the most-important well-barrier elements, both during production and after well abandonment. It is well-known, however, that cement sheaths degrade over time (e.g., from repeated temperature and pressure variations during production), but the link between leak rate and the cause of cement-sheath degradation has not yet been established. In this paper, we have studied fluid flow through degraded cement sheaths. The degree of degradation of the cement sheaths varied from systematically connected cracks to real microannuli. The leak paths, created by thermal-cycling experiments, were imported into a computational-fluid-dynamics (CFD) simulation software. The pressure drop over the cement sheath was used as a boundary condition, and the resulting pressure-driven flow was studied using methane gas as the model fluid. The Forchheimer equation was used to estimate the effective permeability of the cement sheaths with defects. Our results show that the pressure-driven flow is complex and greatly affected by the geometry of the flow paths. A nonlinear pressure-buildup curve was observed for all experimental cases, indicating that Darcy's law was not validated. For homogeneous microannuli, the pressure-buildup curve was linear. The estimated effective permeability for all cases was observed to be orders of magnitude larger than that of a good cement sheath.

Microfluidic Model Porous Media: Fabrication and Applications.

Complex fluid flow in porous media is ubiquitous in many natural and industrial processes. Direct visualization of the fluid structure and flow dynamics is critical for understanding and eventually manipulating these processes. However, the opacity of realistic porous media makes such visualization very challenging. Micromodels, microfluidic model porous media systems, have been developed to address this challenge. They provide a transparent interconnected porous network that enables the optical visualization of the complex fluid flow occurring inside at the pore scale. In this Review, the materials and fabrication methods to make micromodels, the main research activities that are conducted with micromodels and their applications in petroleum, geologic, and environmental engineering, as well as in the food and wood industries, are discussed. The potential applications of micromodels in other areas are also discussed and the key issues that should be addressed in the near future are proposed.

Heat flow visualization of a chemical compound isobutane (C4H10) past a vertical cylinder in the subcritical, near critical and supercritical regions

Supercritical fluids (SCF's) found to have a large number of applications in science and engineering field particularly in separation and purification, green technologies etc. The present research paper investigates the heatline visualization of unsteady free convection supercritical fluid flow over a vertical cylinder using Bejan's heat function concept by using isobutane as a model compound. A new thermodynamic equation has been obtained to calculate the volumetric thermal expansion coefficient (β) based on the Redlich-Kwong equation of state (RK-EOS), in order to determine the free convection properties of isobutane in supercritical fluid (SCF) region. In this model the thermal expansion coefficient is characterized as a function of compressibility factor, temperature and pressure. Crank-Nicolson type of implicit finite difference method is utilized to obtain the results in terms of the streamlines (ψ), isotherms (θ) and heatlines (Π) for the different values of reduced temperature and reduced pressure in the SCF region. The numerically calculated thermal expansion coefficient values are validated with existing experimental results. Numerical simulations are performed for isobutane in three regions namely, subcritical, near critical and supercritical regions. The unsteady boundary layer flow analysis shows that the streamlines are beginning from the leading edge to the far downstream, whereas the heatlines ends at a finite distance from the surface of cylinder. The non-dimensional values of heat function are closely associated with the overall heat transfer rate. The SCF flow analysis implies that in the vicinity of the hot cylindrical surface the heatlines are observed to be denser. Further, the deviation of streamlines, isotherms and heatlines from the hot cylindrical surface increases as reduced temperature and reduced pressure increases.