Laminar Flow Model Research Articles

Cavern development characteristics of pseudoplastic fluid in a stirred tank with dual-impellers

BackgroundIt is crucial to predict the cavern development and eliminate the cavern effect in time for achieving efficient mixing of pseudoplastic fluids. MethodsThe cavern developments of xanthan gum solutions (a typical pseudoplastic fluid) stirred by dual-impellers of perturbed six-bent-bladed turbine (6PBT) were researched numerically based on laminar flow model. Significant FindingsThe results showed that the values of the power consumption obtained by the numerical calculation agreed well with the data measured by the stirring experiment, which validated the laminar flow model established. The fluid rheology had little influence on the cavern shape and its development. The cavern produced by the double-layer impeller would gradually developed from the initial separation state to the overall cylindrical shape with the increase of the speed. When the upper and lower caverns were in state of separation, the changes of their height diameter ratio of the were no longer a constant value. After the integration of upper and lower caverns, the whole cavern first grew rapidly along the axial direction to the top liquid level, and then continued to expand along the radial direction. When the cavern volume ratio Rc reached 90%, it could be considered that the cavern effect was eliminated.

A review on rheological models and mathematical problem formulations for blood flows

A review on constitutive equations proposed for mathematical modeling of laminar and turbulent flows of blood as a concentrated suspension of soft particles is given. The rheological models of blood as a uniform Newtonian fluid, non-Newtonian shear-thinning, viscoplastic, viscoelastic, tixotropic and micromorphic fluids are discussed. According to the experimental data presented, the adequate rheological model must describe shear-thinning tixotropic behavior with concentration-dependent viscoelastic properties which are proper to healthy human blood. Those properties can be studied on the corresponding mathematical problem formulations for the blood flows through the tudes or ducts. The corresponding systems of equations and boundary conditions for each of the proposed rheological models are discussed. Exact solutions for steady laminar flows between the parallel plates and through the circular tubes have been obtained and analyzed for the Ostwald, Hershel-Bulkley, and Bingham shear-thinning fluids. The influence of the model parameters on the velocity profiles has been studied for each model. It is shown, certain sets of fluid parameters lead to flattening of the velocity profile while others produce its sharpening around the axis of the channel. It is shown, the second-order terms in the viscoelastic models give the partial derivative differential equations with high orders in time and mixed space-time derivatives. The corresponding problem formulations for the generalized rhelogical laws are derived. Their analytical solutions in the form of a normal mode are obtained. It is shown, the dispersion equations produce an additional set for the speed of sound (so called second sound) in the fluid. It is concluded, the most general rheological model must include shear-thinning, concentration and second sound phenomena

Improvement of electrical performance of Photovoltaic cell with incorporating nanofluid flow as cooling system

The present study is about the modeling of laminar flow of testing fluid within the sinusoidal wall in existence of V shaped fins. The heat absorption of testing fluid has been improved with loading nanoparticles and installing fins within the upper side of the pipe. Heat generation in various layers has been calculated and considered as the source term of conduction equations for each solid layer. The fluid regime within the pipe is laminar and equations have been solved in steady state form. The accuracy of the utilized numerical model has been tested based on data of absorber temperature for the previous article. Grid indecency has been examined and the best size of mesh was obtained. With installing fins, the performances of the system have been improved in both views of electrical (0.1%) and thermal (1.12%). Also, outputs showed that the efficacy of fins on thermal and electrical efficiencies for highest amount of inlet velocity (uin) is 14.30% and 39.75% greater than those of uin = 0.06. Increasing velocity can decrease the cell temperature about 7.4% and thermal performance increase about 17%.

Functional principles of the envelope characterized by the variable thermal resistance of the wall as a result of parietodynamic exhaust effect (PDE)

The paper presents the opaque envelope system in the endowment of inhabited buildings characterized by the use of the heat of the air discharged from the inhabited spaces, circulated through the space adjacent to the living environment / outdoor environment in order to reduce the need for heat / sensitive cold of the inhabited spaces (PDE). It is presented mathematical modeling of the processes of heat transfer and flow of indoor / outdoor air circulated through parallel vertical channels. The dimensions of vertical channel opening and air flows are based on the solutions of the property transfer equations associated with Model 1 (forced laminar flow) and Model 2 (globally representative model of both laminar flow and turbulent flow). Model 2 includes both laminar flow (space heating in cold season and cooling spaces in summer season hours with sun) and turbulent flow (cooling living spaces in summer season, hours of night – free cooling). A case study and the interpretation of the results obtained regarding the energy performance of the living space in relation to similar results associated with the conventional envelope is presented.

Flow Characteristics and Vortex Structure of Flow Across Micro Cylinders by Micro-PIV Measurement and CFD Simulation

The micro tube bank model is a commonly used structure in microelectro mechanical cooling systems. Flow across a micro tube bank is a basic benchmark for analyzing flow resistance and heat transfer capability. In this paper, the flow around a micro tube bank model was studied both experimentally and numerically. Micro-Particle Image Velocimetry technology was used to measure the flow field at different inlet flow rates. The laminar flow model, S-A model and standard k-ε model were used to calculate the flow field inside the micro tube bank model. By comparing the results from the three numerical models with the experimental results, there is a certain gap between them can be noted. However, it was found that the standard k-ε model is better than laminar model and S-A model in the comparison between numerical results and experimental results. In conclusion, the standard k-ε model is more suitable for the numerical calculation of the flow field around a micro scale tube bank model.

P78: Risk Assessment of Thrombus Formation in the left Ventricle during VAD Support using computational Models. “How simple is too simple?”

Background: Thrombus formation is a major complication in LVAD treatment, and is influenced by intraventricular blood flow dynamics. Many numerical studies have investigated left ventricular (LV) blood flow patterns with LVAD support using various assumptions which are needed to simplify the highly complex physiological processes for a computational environment. Until now, these various assumptions have not been investigated systematically. This study aimed to assess the effect of modelling assumptions on the risk assessment of thrombus formation in the LV during VAD support. Methods: A patient-specific LV and left atrium (LA) was modelled from CT data of a VAD patient. The impact of the turbulence model (laminar vs turbulent), fluid model (Newtonian vs Carreau approach vs Multiphase approach), model geometry (cylindrical LA vs segmented LA, absent MV vs present MV) and boundary conditions (continuous inflow vs periodic inflow) were evaluated systematically, resulting in eleven simulation set ups in total (Figure 1). They were compared quantitatively over 5 s simulation time by the difference of averaged velocities, residence time, washout, turbulent kinetic energy and computing time for the various simulation models. Results: Geometrical LA changes resulted in the biggest quantitative impact, with a 30.7% lower residence time with a cylindrical LA compared to the segmented LA. The comparison of a laminar and a turbulent flow showed a 26.8 % lower residence time in the laminar flow model compared to a model with turbulent flow. The most significant difference in computational time was found when comparing a Newtonian fluid model and a multiphase approach: The simulation with a multiphase approach took 81 core hours longer than the model with a Newtonian fluid model. Conclusion: The recommended model for achieving a low computing time with minimized loss of accuracy compared to current numerical models assumes a turbulent viscous model with Newtonian-modelled blood, a segmented left atrium, a mitral valve geometry, and pulsatile inflow.Figure 1. Simplification study: Steps and result.

Investigation of a novel Couette flow with cylindrical baffles

The high-precision measure instrument for flow velocity is essential for industrial applications because the high-precision velocity can well reflect the physical characteristic of the flow. A restricted laminar Couette flow with cylindrical baffles, using a synthetic heat conduction liquid, was designed to obtain a steady vortex flow and wider work scope, according to Couette flow and Suspension flow characteristics. The heat transfer mechanism was investigated with a laminar flow model by the Fourier law. The research indicates that the heat transfer enhancement is related to the Temperature Boundary Layer (TBL). The TBL is affected by the Velocity Boundary Layer (VBL). The TBL thickness and Nusselt number (Nu) have a dependent relationship. The Reynolds number (Re) and the gap between the baffle and plate wall (Δh/h) can further affect Nu. The vortex flow generated by Couette flow can significantly enhance the heat transfer performance by a double spiral structure, which can rapidly mix heat fluxes and make the temperature converge to uniform. There is a sensitive and stable relationship between flow velocity and heat transfer. Notably, it is linear when Δh/h or Re is small, which can be used to design a high-precision thermal flow velocity meter.

Design of a continuous device for ethoxylation reaction: The choice between micro and milli scale

A laminar flow model was developed to investigate the reaction kinetics of 1-dodecanol ethoxylation promoted by KOH, elaborating the data collected in microreactors. A generic laminar flow model was coded, and a sensitivity analysis was conducted highlighting the good flexibility of the model to simulate a wide range of conditions. Ethylene oxide diffusivity and liquid mixture viscosity were determined by applying existing correlations, carefully considering the change in viscosity with ethylene oxide conversion, temperature, and feed ethylene oxide/1-octanol ratio. The model was tested on literature data obtaining in every case good results. The obtained kinetic data were demonstrated to be in line with the ones obtained in separate investigations conducted in a fed-batch reactor, demonstrating that there was a real need in adopting the laminar flow reactor approach, as it allowed to retrieve of more precise information about the intrinsic kinetics of the ethoxylation reaction, when working with microreactors, compared with the ones obtainable with a plug-flow ideal fluid-dynamic model. The developed model was used to simulate the behavior of a milli-reactor (this device allows to reach sufficient productivity for industrial application) and it was forecasted the possibility to use continuous ethoxylation milli-reactors using fluid-dynamic conditions characterized by a high Reynolds number (>10000).

The application of laminar numerical wave tank for a heaving buoy hydrodynamics study in low-turbulence nonlinear waves

Numerical Wave Tanks (NWTs) allow for in-depth investigations into the hydrodynamics and wave responses of floating objects. Thus, they are widely used during the design phase of many offshore platforms and devices. Such problems often feature low turbulence, with wave propagation and wave-object interaction being the key features. In this paper, the merits of using a laminar flow model for a NWT with a free-to-heave buoy, subject to second order Stokes waves in a low sea state is investigated. The simulations are implemented using the interFoam solver, which is embedded in OpenFOAM. The time series of waves measured upstream and downstream of the buoy, and the buoy hydrodynamics are compared to analytical and experimental results for accuracy evaluations. It is shown that, due to the low turbulence level of the problem, the laminar approach can deliver more accurate results than turbulent models, such as Reynolds-averaged Navier-Stokes Simulation (RANS) or partially-averaged Navier-Stokes Simulation (PANS). Moreover, the simulation time of the laminar simulations is significantly shorter than to those of RANS and PANS.

A wall model for external laminar boundary layer flows applied to the Wall-Modeled LES framework

Wall-Modeled Large Eddy Simulation (WMLES) is a prominent technique for obtaining high-fidelity solutions of turbulent, high Reynolds number flows, with reasonably acceptable computational costs. However, for external flows, the very thin laminar boundary layer developing near the body leading edge imposes quite restrictive mesh resolution requirements, leading to prohibitively high computational costs for practical Reynolds numbers. We propose a wall-modeling approach for the laminar portion of the boundary layer in order to alleviate these costs by reducing the aforementioned mesh resolution requirements. The wall model is based on local self-similar solutions of the boundary layer, and is implemented in the same context of wall-stress models in the WMLES approach. A thorough assessment of the proposed wall model is performed in terms of the distribution of both pressure and skin friction coefficients along the surface, for a fully laminar flow around a NACA 0012 airfoil geometry, with a chord Reynolds number of Rec=5×103 and Mach number of M∞=0.5. Simulations are carried out to evaluate the effects of the wall model height on the solution. The influence of mesh refinement and mesh element distributions along the surface are also analyzed and discussed. The results obtained in the simulations using the proposed wall model are in good agreement with the reference solution, demonstrating the suitability of the model for external laminar flows.

Computational fluid dynamics simulation of bubble hydrodynamics in water splitting: Effect of electrolyte inflow velocity and electrode morphology on cell performance

Efficient management of oxygen gas bubbles evolving at the photoanode is important for a good overall performance of a photoelectrochemical (PEC) cell. The process of formation, detachment, coalescence and rise affects the bubble residence time at or near the photoanode. A reduced bubble residence time promotes easier electrolyte access to the photoanode surface, thereby enhancing the oxygen evolution reaction (OER) kinetics. In this work, computational fluid dynamics (CFD) simulations using laminar flow and phase-field model in COMSOL Multiphysics are conducted to study the gas bubble hydrodynamics for different bubble configurations, sizes, and bubble gaps. CFD results predict enhanced bubble rise in the presence of forced convection, i.e., some electrolyte inflow velocity (u≠0m.s−1). Experimental results using hematite as the model electrode also show a higher photocurrent density (ca. 4.33 mA.cm−2 at 2 V vs. RHE) for u = 0.1 m.s−1, compared to that without flow (3.5 mA.cm−2 at 2 V vs. RHE). This indicates improved access of electrolyte at the electrode surface and faster OER. Further, CFD simulations for electrode morphology effects show a reduced bubble adhesion for hydrophilic hematite nanorod arrays compared to planar photoanode, due to capillary wicking. The continuous contact film detaches and results in a reduced blockage of active sites at the bubble base, thereby enhancing the PEC performance for the nanorod arrayed morphology. Here too, experimental results show a four-fold increase in photocurrent density (ca. 0.1 mA.cm−2 at 1.5 V vs. RHE) and a 210 mV cathodic shift in onset potential for nanorods, compared to planar electrodes (0.025 mA.cm−2 at 1.5 V vs. RHE). A significant reduction in charge transfer resistance is observed for the former, implying better OER kinetics. The results obtained help in the understanding of transient processes involving O2 bubble hydrodynamics and electrolyte usage efficiency in a PEC reactor.

Numerical modeling of laminar and turbulent annular flows of power-law fluids in partially blocked geometries

The presence of cuttings bed in deviated wellbores has an undesirable effect on wellbore hydraulics by reducing the open flow area. In addition, pipe eccentricity affects the annular frictional pressure gradient under such configurations. The lack of practical correlations to account for the combined effects of cuttings bed and eccentricity on frictional pressure gradient of power-law fluids is the major motivation of this study. Thus, the effect of partially blocked eccentric annuli on frictional pressure gradient of power-law fluids is investigated. A numerical model is first developed to realize the laminar and turbulent annular flow of power-law fluids in eccentric configurations. The numerical solution of the governing equations is pursued using the finite difference method. The results of our numerical model are verified through comparisons with the published results of frictional pressure gradients in the literature. The numerical results indicate that with an increase in cuttings bed height the frictional pressure gradient can increase exponentially. Numerous simulation scenarios are considered for the flow of power-law fluids in partially blocked eccentric annuli. Then, the simulation results are fitted using regression analysis to obtain explicit correlations for the prediction of laminar and turbulent frictional pressure losses. The proposed correlations are essential for an accurate estimation of the annular frictional pressure gradient and equivalent circulating density, which ensures safe and optimized drilling operations.

Computational Study of Hemodynamic Field of an Occluded Artery Model with Anastomosis.

In this research work, the hemodynamic field of an occluded artery with anastomosis by means of computational simulation has been studied. The main objective of the current study is the investigation of 3D flow field phenomena in the by-pass region and the effect of the bypass graft to stenosis volume flow ratio on their formation. The anastomosis type was end-to-side with a 45° angle, while stenosis imposed a 75% area blockage of the aorta vessel and the total volume flow was 220 lt/h. The computational study of the flow field was utilized via a laminar flow model and three turbulence models (k-ε RNG, standard k-ω, and k-ω SST). Numerical results were compared qualitatively with experimental visualizations carried out under four different flow conditions, varying according to the flow ratio between the stenosis and the anastomotic graft. Comparison between computational results and experimental visualization findings exhibited a good agreement. Results showed that SST k-ω turbulence models reproduce better visually obtained flow patterns. Furthermore, cross-sectional velocity distributions demonstrated two distinct flow patterns down the bypass graft, depending on the flow ratio. Low values of flow ratio are characterized by fluid rolling up, whereas for high values fluid volume twisting was observed. Finally, areas with low wall shear stresses were mapped, as these are more prone to postoperative degradation of the bypass graft due to the development of subendothelial hyperplasia.

Numerical study of nonlinear flow and mass transfer through a channel filled with a porous medium using a hybrid heuristic paradigm

ABSTRACT The effects of mass transfer and chemical reactions on laminar viscous flow in a porous channel with moving or stationary walls are examined in this study. The mathematical model of the mass and flow transfer is in the form of a partial differential equation (PDE), a similarity transformation method used to convert the physical problem's governing partial differential equations (PDEs) into a group of nonlinear coupled ordinary differential equations (ODEs). The main accomplishment of the present study is the utilization of a precise and effective method based on artificial neural networks (ANNs) for the model of flow in a porous channel of a viscous fluid with a chemical reaction. To investigate the coupled nonlinear ordinary differential equations, a differential evolutionary (DE) is used for exploration to get optimal weights for the model, and then we use those optimal weights in interior point algorithms (IPA) for exploitation of the laminar viscous flow model in a porous channel with moving or stationary walls. Finally, the effects of Darcy number (Da), suction/injection parameter (α), Reynolds number (Re), and power-law index (m) influence are investigated in five different scenarios, each with four different cases. The outcomes of the hybrid of differential evolution and interior point algorithm (DE-IPA) are compared to the RK4 results. The statistical analysis (MAD, TIC, RMSE, and ENSE) is also performed to ensure that the proposed technique is stable and accurate.

Detection and analysis of coagulation effect in vein using MEMS laminar flow for the early heart stroke diagnosis

<abstract> <p>The primary objective of the research article is to describe the functionality of wrist watch which acts as a digital stethoscope to measure health constraints such as heart pulse through blood pressure. The second objective is the detection of blockages of an artery due to fatty, cholesterol-deposited, over a period when the blood is passing through due to stress and exercise, etc. Pressure and velocity are two inputs with their respective results of contrast and expansion of veins at the outputs. The major parameters in detecting the laminar flow are pressure and velocity. These parameters of a vein are analyzed by integrating valves in the vein. The movement of blood laminar flow in the vein is captured by a MEMS-based piezoelectric sensor by its functionality. The proposed design performance accuracy is estimated by modeling of vein's laminar flow when blood is circulating. The coagulation effect of the vein is used to measure heart stroke by placing MEMS along with the stent, as MEMS are tiny in size. The functionality of a digital Stethoscope works on the piezoelectric effect that generates an electrical signal when pressure is applied from the vein. The accuracy, functionality, and performance of the design can be analyzed by COMSOL multi-physics. Applications of MEMS include detection, prevention, and alert during the second heart stroke, and also used in the bionic eye and automotive electronics.</p> </abstract>

Characterizing pulsatile blood flow in a specific carotid bifurcation: insights into hemodynamics and rheology models

<abstract> <p>This study uses laminar and turbulent flow models to investigate the blood flow dynamics in a specific carotid bifurcation. Pulsatile boundary conditions and the rigid carotid artery wall are considered. Three viscosity models describe the non-Newtonian blood behavior. The Fluent solver and the finite volume method solve the equations. Results show a Poiseuille-like flow in the common carotid artery (CCA), unaffected by the flow regime, viscosity model, or boundary conditions. The branching zone exhibits a C-shaped stagnation zone with low velocity and wall shear stress due to the CCA widening and ICA/ECA curvature. Strong secondary flow is observed in the carotid sinus; the flow is directed towards the inner wall with higher velocity in the internal carotid artery. Discrepancies between viscosity models are pronounced in laminar flow, particularly with the natural boundary conditions. The non-Newtonian blood behavior is more apparent in the laminar flow of the external carotid artery, especially with the second set of boundary conditions.</p> </abstract>

Numerical comparison of laminar flow and turbulence models of hemodynamics based on pulmonary artery stenosis

Numerical comparison of laminar flow and turbulence models of hemodynamics based on pulmonary artery stenosis

Numerical comparison of laminar flow and turbulence models of hemodynamics based on pulmonary artery stenosis

Numerical comparison of laminar flow and turbulence models of hemodynamics based on pulmonary artery stenosis

Application of deep learning neural networks for the analysis of fluid-particle dynamics in fibrous filters

A novel hybrid data-driven framework was introduced in this study for the prediction of fluid-particle dynamics of submicron particles under hydrodynamic and Brownian forces in fibrous filters. The distribution of flow parameters was predicted by a high-resolution flow surrogate model based on a deep convolutional neural network (CNN) coupled with a Lagrangian particle tracking method based on the discrete phase model (DPM). The CNN-DPM model was applied to a group of several nonuniformly distributed fibers to calculate filtration efficiency. For CNN training, ground-truth data were obtained using a two-dimensional computational fluid dynamics (CFD) model for laminar incompressible flow. A simulation speedup of three orders of magnitude was obtained by CNN for predicting the velocity components and static pressure distribution within an error range of ±10%. The generalizability of CNN model was also confirmed for overlapped irregular fiber shapes and porosities out of the range of the training dataset with deviations in a range of ±20% in comparison with CFD results. The collection efficiency by CNN-DPM for small particle diameters with dp≤0.3μm was overestimated by approximately 3 % while agreeing well with CFD-DPM for larger particles. The errors of flow velocity predictions by CNN near the fibers added more randomness to the particle motion which was combined with the random Brownian motion of particles, consequently increasing the probability of the small particle hit number and filtration efficiency. The overall acceptable accuracy of the CNN-DPM was confirmed, which is suitable for fibrous filter design and optimization purposes that require thousands of simulations.

Prediction of submicron particle dynamics in fibrous filter using deep convolutional neural networks

This study developed a data-driven model for the prediction of fluid–particle dynamics by coupling a flow surrogate model based on the deep convolutional neural network (CNN) and a Lagrangian particle tracking model based on the discrete phase model. The applicability of the model for the prediction of the single-fiber filtration efficiency (SFFE) for elliptical- and trilobal-shaped fibers was investigated. The ground-truth training data for the CNN flow surrogate model were obtained from a validated computational fluid dynamics (CFD) model for laminar incompressible flow. Details of fluid–particle dynamics parameters, including fluid and particle velocity vectors and contribution of Brownian and hydrodynamic forces, were examined to qualitatively and quantitatively evaluate the developed data-driven model. The CNN model with the U-net architecture provided highly accurate per-pixel predictions of velocity vectors and static pressure around the fibers with a speedup of more than three orders of magnitude compared with CFD simulations. Although SFFE was accurately predicted by the data-driven model, the uncertainties in the velocity predictions by the CNN flow surrogate model in low-velocity regions near the fibers resulted in deviations in the particle dynamics predictions. These flow uncertainties contributed to the random motion of particles due to Brownian diffusion and increased the probability of particles being captured by the fiber. The findings provide guidelines for the development of data science-based models for multiphysics fluid mechanics problems encountered in fibrous systems.