FVM Method Research Articles

Numerical analysis of turbulent natural convection in the presence of wire-induced non-uniform magnetic field inside a porous medium

Turbulent natural convection of Fe3O4-water ferrofluid with Reynolds Averaged Navier-Stokes (RANS) based turbulence model of k−ω in the presence of wire-induced non-uniform magnetic field inside a porous medium is simulated, numerically. To discretize and solve the related equations the FVM method and SIMPLE algorithm are implemented. For applying the non-uniform magnetic field, two wires carrying electric currents have been installed below and above the enclosure. Simulations are implemented for different Rayleigh numbers (106≤Ra≤108), porosity number of (η=0.5and0.9), volume fractions of nanoparticles 0≤ϕ≤4%, magnetic field numbers 0≤MFN≤109. According to the results, in low Rayleigh number and high MFN, at the high-volume fraction of nanoparticles, applying a magnetic field optimally influenced transfer and Nusselt number. At high porosity numbers, low Ra numbers and ϕ=4%, the heat transfer rate improved by up to 17 %. However, at high Ra numbers and highϕ, applying the magnetic field reduces the Nusselt number by almost 12 %.

Influence of labyrinth clearance on the hydrodynamic performance of a high head Francis turbine

Abstract Francis turbines have a leakage loss from the corresponding labyrinth seals i.e., crown side and a skirt side labyrinth clearance. Therefore, the labyrinth clearance between the runner and turbine cover plays an important role in the hydrodynamic characteristics of the hydro turbine. Generally, the geometrical details of labyrinth clearance are not considered in the numerical model due to complexity involved in modelling and requirement of high computational power that may lead inaccurate prediction of performance of the turbine. In the present investigation, steady-state numerical simulations have been performed on a high head Francis turbine, under different operating conditions, ranging from part load to overload condition, to assess the influence of labyrinth clearance on the hydrodynamic performance of the turbine. FVM method (as discretization method) along with SST k-omega turbulence model has been adopted for computational modelling. The simulation results such as hydraulic efficiency and power output are validated with model test results which was done as per IEC 60193 standard and found satisfactory agreement. Further, the axial thrust force is also computed for different operating conditions and compared with model test results. Based on the simulation results, it has been found that the hydraulic efficiency of turbine with labyrinth clearance was found 0.4% - 1.1% lower than the turbine without labyrinth clearance. The influence of labyrinth clearance on the turbine performance is higher at part-load condition compared to other operating conditions. It is observed that the leakage loss is almost same for all loading conditions at a particular head and fall in the range of 0.61% - 0.81%. Further, the value of axial thrust increases with the increases in discharge value and value of maximum axial thrust was found as 203 kN at overload condition.

The influences of artery radii and stenosis severity on the thermal behavior of blood by employing Sisko and Lumen models: Numerical study

Artery stenosis occurs when blood vessels do not supply enough blood and oxygen due to blockage by a fatty mass called plaque. In this work, the influence of stenosis on the Nusselt number (Nu) for non-Newtonian blood flow is studied by the FVM method and using fluent software. Also, the artery is simulated based on the Lumen model. In this research, at first, it is assumed that stenosis severity increases as much as 20 %, 30 %, and 40 % of the internal cross-section area of the artery respectively while the radius is constant, then the stenosis severity is fixed at 40 %, and only radius of artery increases from 0.002 m to 0.0025, 0.0030, and 0.0035 m. The artery wall is affected by constant heat flux and Nusselt numbers in every stage as a significant parameter in each flow are calculated. It should be mentioned that the Nusselt numbers are achieved both in the direction of flow and perpendicular to one. The results show that an increase of stenosis severity from 20 % to 40 % and a decrease of the artery radius between 0.002 and 0.0035 m leads to Nusselt number enhancement due to acceleration of blood flow and increase of heat transfer while the maximum values of Nusselt number remain no change approximately. Therefore, influences of stenosis size on the thermal behavior of blood in the artery are not noticeable, and thermal risks are ignorable.

NUMERICAL SIMULATIONS OF BLOOD FLOW THROUGH LEFT VENTRICLE USING SPH AND FVM METHODS – A COMPARATIVE STUDY

This paper presents a comparative analysis of numerical simulations of blood flow through the left ventricle using SPH (LS-DYNA) and FVM (Ansys Fluent) solvers. Numerical simulations based on SPH and FVM methods can provide a more comprehensive understanding of cardiac blood flow patterns. In Fluent, left ventricle walls were modeled as boundary conditions with zero fluid velocity, while in the LS-DYNA software the walls were modeled with fixed particles. Boundary conditions were also prescribed on the appropriate regions (inlet, outlet, symmetry). In both programmes, inlet and outlet velocities were defined using table functions corresponding to the real cardiac cycle. For generating fluid flow in SPH, injection particles at mitral valve and deactivation planes at aortic semilunar valve were used. Numerical analysis results are given comparatively in both cases at the corresponding times. By comparing the results, it can be concluded that SPH can be efficiently used for the analysis of blood flow through the left ventricle. Although the modeling procedure, as well as the calculation itself, takes much longer to execute using SPH, this method offers possibilities such as studying FSI phenomena or tracking the movement of particles through the fluid domain.

Cooling a cavity equipped with a hot electrical element using nano-encapsulated phase change material /water: Study of mixed convection and natural convection

According to phase change materials (PCMs) operate at their phase change temperature, they can store a lot of latent heat energy without changing the temperature, so these materials are widely used in thermal storage tanks. The direct use of PCMs is not possible in all systems, therefore encapsulation of PCMs has been suggested by researchers. In the present work, the thermal performance of the natural and mixed convection flow inside a nested cylinder with a hot electrical element is investigated. Nano-encapsulated phase change material (PCMs) are mixed with the water-based fluid. Also, the effects of forced convection due to inner cylinder rotation along with natural convection are studied. Fluid flow, temperature distribution, melting zone of PCM nanocapsules, Nusselt numbers, and thermal performance are simulated using computational fluid dynamics by developing OpenFOAM solvers using C++ code. The governing PDE equations are solved in the FVM method and solved using the SIMPLE algorithm. The simulations are modeled for different Ra numbers (102−104), Reynolds numbers (0–20), and θf values. θf values correspond to the dimensionless melting temperature of the core of nanocapsules. This number depends on the temperature of the cold and hot sources and the phase change temperature of the core of NEPCMs. Based on the results, it is showed that there is an optimal number for θf, which is in the range of 0.3–0.5 in the lower Ra numbers (102), and θf=0.5 at upper Ra numbers (104). In the case of dominant conduction heat transfer mechanism, the presence of nanocapsules did not affect heat transfer. However, at a high Ra number, it was able to enhance Nusselt number by up to 13%. Also, at high Ra numbers (104), the rotation of the inner cylinder does not help to improve heat transfer.

Comparative analysis of numerical solutions of 2D unsteady dambreak waves using FVM and SPH method

Abstract This work presents a comparison of two-dimensional numerical solutions of unsteady free surface flow. This is a simulation of the dam-break wave with different configurations using based-mesh finite volume method and meshless smoothed particle hydrodynamics (SPH). Two well-known approaches, widely used in the computational fluid dynamics (CFD). These techniques have proven their robustness in the numerical treatment of such conservation laws. The main goal is to check the ability of the SPH method and the first order finite volume HLLC solver to reproduce the numerical solutions of the 2D shallow water equations. Based on many benchmark tests, one investigates the effect of the topographic variation along the x and y directions on behavior of the numerical solutions namely at the wet-dry front. The comparison between the simulated results, the analytical solutions and the experimental measurements shows a good correlation, although the finite volume approach remains more advantageous in terms of accuracy and the CPU time.

Influence of solar radiation and an electric force on nanofluid convection inside a porous sector cavity

Using novel numerical techniques, this paper estimates the effect of EHD force on ferrofluid treatment. Iron oxide additives of various nanoscale forms and dimensions are added to the operating fluid. Because the percentage of nanoparticles exceeds 0.06 and the slip velocity is disregarded, the features of the carrier fluid were modified using an empirical model. The left and bottom surfaces of the moving walls had the highest temperatures and voltages. A non-Darcy presumption was that the region was permeable. A combined FVM and FEM method was utilized to solve this issue. Due to the application of an electric force, the nanofluid is able to move more quickly, and two primary vortices combine to form a single, stronger vortex. As voltage increases, Nu increases by approximately 125.52%. Utilizing greater permeable medium results in a stronger wall collision and a 113.29% increase in Nu. Nu increases by approximately 3.69% when a nanoparticle with a greater shape factor than the sphere is utilized.

Investigating the thermal performance of nano-encapsulated phase change materials-water nanofluid in the presence of a heat source as applied in electronic devices

BackgroundGlobal warming and the human need for power resources in the last decades have highlighted the concerns related to energy saving for long-term applications. Thermal energy-saving systems are an important technique to overcome this issue. MethodsIn the present study, we aim to simulate the performance of a thermal energy-storing system with Nano-Encapsulated Phase Change Materials (NEPCMs) by Computational Fluid Dynamics (CFD). Free convection heat transfer through a square enclosure is numerically simulated, and a hot block is located at pisitions of the enclosure. The simulation is done with the FVM method and SIMPLE algorithm. The analyzed parameters are different Ra numbers (5 × 103 − 105), non-dimensional melting temperatures (0.1 ≤ θf ≤ 0.9), and NEPCM melting intensities (0.01 ≤ χ ≤ 0.03). Significant FindingsT The results revealed that the θf = 0.3 is corresponding to the optimum heat transfer rate, and it is independent of the Ra number. In the case with the highest heat transfer rate, adding NEPCMs to the based fluid caused the heat transfer to improve by 12.5%. Furthermore, in this θf number, uniform heat transfers through the cold walls of the enclosure. A low number of χ also revealed less Nusselt number. Increasing AR in high Ra number improves Nusselt number by 5%.

The influence of fluid-structure interactions 2-ways on dynamic characteristics of flexible tank

This paper investigates the influence of two-way fluid-structure interactions (FSI) on the dynamic characteristics of flexible storage liquid tanks. A coupled finite volume method FVM and finite element method FEM (FVM/FEM) was developed to simulate a flexible water tank subjected to seismic loading. FVM is used to simulate the fluid domain and FEM is used to capture the structural domain. The two-dimensional interaction equation is solved at the contact surface between the elastic tank wall and the fluid by tuning the relaxation parameter and convergence conditions. The model investigates the influence of considering two-way FSI on the dynamic characteristics of a tank flexible to a rigid tank wall. The results show that the frequency of flexible tank walls differs from that of rigid walls, especially the hydrodynamic pressure of liquid motion acting on the tank. A “threshold value” is revealed to distinguish flexible or rigid tanks. If the tank stiffness exceeds this threshold, then the thicker the tank is, the lower the hydrodynamic pressure. However, if the tank stiffness is less than this threshold, the thinner the tank is, the lower the hydrodynamic pressure. Further experiments on a fluid container under harmonic excitation are carried out using a shaking table to verify the dynamic behavior in comparison to numerical results. Good agreement is observed between numerical, analytical, published, and experimental data.

Fully resolved simulations of viscoelastic suspensions by an efficient immersed boundary-lattice Boltzmann method

An efficient immersed boundary-lattice Boltzmann method (IB-LBM) is proposed for fully resolved simulations of suspended solid particles in viscoelastic flows. Stress LBM based on Giesekus and Oldroyd-B constitutive equation are used to model the viscoelastic stress tensor. A boundary thickening-based direct forcing IB method is adopted to solve the particle–fluid interactions with high accuracy for non-slip boundary conditions. A universal law is proposed to determine the diffusivity constant in a viscoelastic LBM model to balance the numerical accuracy and stability over a wide range of computational parameters. An asynchronous calculation strategy is adopted to further improve the computing efficiency. The method was firstly applicated to the simulation of sedimentation of a single particle and a pair of particles after good validations in cases of the flow past a fixed cylinder and particle migration in a Couette flow against FEM and FVM methods. The determination of the asynchronous calculation strategy and the effect of viscoelastic stress distribution on the settling behaviors of one and two particles are revealed. Subsequently, 504 particles settling in a closed cavity was simulated and the phenomenon that the viscoelastic stress stabilizing the Rayleigh–Taylor instabilities was observed. At last, simulations of a dense flow involving 11001 particles, the largest number of particles to date, were performed to investigate the instability behavior induced by elastic effect under hydrodynamic interactions in a viscoelastic fluid. The elasticity-induced ordering of the particle structures and fluid bubble structures in this dense flow is revealed for the first time. These simulations demonstrate the capability and prospects of the present method for aid in understanding the complex behaviors of viscoelastic particle suspensions.

Investigations on effect of arrangement of fins on melting performance of vertical PCM enclosure (3D simulation using FVM methods)

Present investigation, effect of different forms of rectangular fins on melting performance of a vertical enclosure filled by with phase change material (PCM) was examined. Three individual fins were used instead of unit fin. The heat transfer surface was kept constant. The effect of location of fins as well as effect of length of fins and the distance of fins were considered as variant parameters. Firstly, placement of fins at lower half and upper half was examined. Secondly, effect of length of fins were examined. Finally, effect of vertical distance of fins was evaluated. Results presented that optimum melting efficiency was achieved when two of the three fins were placed in lower half. Through first step, case one, provided best performance which presented up to 23 percent improvement in overall melting time. At second step, case 10 had best performance and provided 30% improvement in melting time. Finally, at third step, case 13 had best melting performance. In this case, two of fins were positioned on lower half. lower and upper fins had the length of 40.5 and 10 mm. It is noteworthy that case 13 provided up 39% saved time for melting process in comparison with base case.

The thermal behavior of blood flow in the arteries with various radii and various stenosis angles using non-Newtonian Sisko model

In this work, the FVM method is employed to simulate blood flow behavior within stenosis arteries based on the non-Newtonian Sisko model by using UDF in Fluent. Stenosis is simulated in cone geometry, and influences of different angles of stenosis with different artery radii are studied on the Nusselt number and temperature of blood flow. It is observed that with increasing angles of stenosis and reducing internal radius, the artery is narrowed, which results in enhancement of Nusselt number of blood flow. Thus, the temperature of blood flow is reduced. Also, applying heat fluxes of q“ = 400 W/m2, q” = 800 W/m2, and q“ = 1000 W/m2 prepare temperature enhancement as much as 0.44 K, 0.89 K, and 1.15 K respectively which are important from a medical viewpoint. The maximum temperature is reported as much as 38.2 °C by applying heat flux of q” = 1000 W/m2, which is noticeable for the human body healthy, especially for the function of enzymes and other proteins of the body. Also, with increasing angles of stenosis and reducing internal radius, the artery is tightened and velocity of blood fluid is enhanced which affects blood circulation between tissues and the oxygenation process, temperature variation, and heat transfer alteration of blood flow within the human body. In reality, circulation of blood transfers heat between tissues, and the dimensions of the blood vessels are various, whenever more blood is needed in some vessels of the body due to more activity, these blood vessels expand to supply the required blood while other vessels tight to compensate it. Therefore, present mechanical research is applicable for medical science especially in surgical widening of a blocked or narrowed blood vessel.

Cooling a central processing unit by installing a mini channel and flowing nanofluid, and investigating economic efficiency

CPUs are widely used in many industries. These components require electrical energy for processing and generating heat due to their electrical resistance. On the other hand, they have a very high heat flux due to their small size and high energy consumption. Therefore, their cooling with new methods helps their performance a lot. In this study, water flow with Nano-encapsulated phase change material (NPCM) was simulated to cool an embedded CPU inside a mini channel. These NPCMs have a significant effect on heat transfer parameters due to their ability to phase change in their core. On the other hand, examining the exert economy broadens our horizons to choose an appropriate system in practical problem engineering. Numerical simulation by the FVM method was utilized to study the effects of Reynolds numbers, heat flux of CPU's surface, and volume fraction on the temperature distribution, the maximum temperature of CPU's surface, and economic efficiency. Evidence showed that increasing Reynolds number from 50 to 100 at zero volume fraction reduces the maximum temperature of the CPU's surface from 98.4to82.5°C. Also, mixing a 3% volume fraction of NPCM with pure water can decrease the maximum temperature of the CPU's surface by 2.27°C relative to pure water. Moreover, rising Reynolds number from 50 to 100 enhanced the net profit per unit transferred heat load (ηp) by 100 times.

Numerical analysis on heat transfer of parabolic solar collector operating with nanofluid using Eulerian two-phase approach

Parabolic trough solar collector (PTSC) is an effective solar harvesting system that can be combined to various systems with different working fluids. This research presents a novel investigation on a PTSC system in which nanofluids are used to transfer heat energy. CFD analysis is performed according to FVM method to complement the study. Syltherm 800 oil is used as the main operating fluid augmented with CuO nanoparticles to investigate thermal and hydrodynamic behaviors of the solar system comprehensively. To simulate the nanofluid the two-phase model and the single phase approach are applied. The results indicate that increasing the nanofluid volume concentration improves the coefficient of heat transfer, performance evaluation criteria and the collector thermal efficiency.

Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity

The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm. Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property. The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state. In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall. Moreover, the relationship between the energy wall and the heat transfer rate is payed attention, and the effects of the energy wall parameters including strength, thickness, and event location of energy wall and volume fraction are studied on the energy wall and heat transfer rate. According to the obtained results, adding NEPCM to the water enhances its heat transfer up to 48% in order to increase heat capacity of water-NEPCM mixture. Also, best heat transfer rate happens when the energy wall is at the center of the cavity. Moreover, a relation is presented for the thermal expansion coefficient of NEPCM, which considers the effects of the thermal expansion coefficient of the core and shell material.

Heat transfer enhancement in cold plate based on FVM method and field synergy theory

To optimize the overall heat dissipation performance of the straight channel of a cold plate for lithium battery in vehicles, we used the wavy channel to optimize the structure and uses the face-centered central composite design (FCCCD), which takes the overall thermal-hydraulic performance factor as the response to explore the interaction mechanism of the flow field and temperature field in wavy channel of the cold plate. When the amplitude of the wavy channel is 1 mm and the number of cycles is 4, the overall thermal-hydraulic performance will reach its maximum with an increase of 17.4 % relative to the straight channel. Then, for the coolant, we explored the heat transfer performance of the nanofluid. The heat transfer coefficient of the nanofluid with a volume fraction of 2 % is 117 % higher than that of pure water and does not cause a significant increase in pressure drop.

Numerical investigation of performance analysis of Triangular Solar air heater using Computational Fluid Dynamics (CFD)

Computational fluid dynamics based research is performed to investigate the thermal efficiency of triangular solar air heater (TSAH) passage. A systematic analysis of the device output parameters was carried out controlled under all test conditions including solar intensity, mass flow rate and air temperature at the inlet section. The glazing side of the triangular section is subjected to the solar intensity 746 W/m2. The three-dimensional TSAH model is developed and simulated using the FVM method with CFD code. The flow control equations have been solved with commercial ANSYS 14.5 software.A uniform triangular grid is generated according to the configuration using tetrahedron. The k-ε, RNG turbulence model with enhanced wall treatment function is used to solve the energy transport equations for turbulent flow. The optimal values of the geometric parameters are obtained on the basis of the performance index in the Reynolds number range from 2263 to 18103.It is observed the value of thermal efficiency increases with respect to velocity of air. It also increases the absorber and glass plate temperature.

Hydrodynamic analysis of a heat exchanger with crosscut twisted tapes and filled with thermal oil-based SWCNT nanofluid: applying ANN for prediction of objective parameters

Present study investigates hydrodynamic analysis of heat exchanger with crosscut twisted tapes and filled with thermal oil-based SWCNT nanofluid (NF). SIMPLE algorithm and FVM method are used. The heat transfer fluid enters the test section at Tin = 300 K in different flow velocities, which are related with Reynolds numbers 5000, 10,000, 15,000 and 20,000. For ensuring that the input flow to test section is always fully developed, the input part to length 2L is considered. It is also intended to ensure that the flow does not return to test section of the exit section of length L. Also, the test section has the constant temperature of Ts = 400 K. Different geometrical parameters of twisted tapes in heat exchanger are studied. The optimization is carried out due to fulfill the highest performance evaluation criterion (PEC index). Based on results, usage of twisted tapes has a sharp impact on thermal and hydraulic characteristics of heat exchanger and leading to swirling motion, which improve the heat transfer coefficient and augment the pressure drop (ΔP). Besides, usage of simple model is more efficient than crosscut model. Also, it is understood that the PEC index values always are more than 1.11, which means that employment of these turbulators is effective and positive with thermal–hydraulic viewpoint. The simple model (Case K and N = 8) is introduced as the most optimum model in this paper, and its PEC values for system filled with NF in ϕ = 0.8% at Re = 5000, 10,000, 15,000 and 20,000 are 1.37, 1.59, 1.78 and 1.93, respectively. The application of machine learning methods showed that the output parameters in the simulation of heat exchangers are well predicted. The accuracy of the developed neural network was such that the maximum error was below 1%.

FVM method based on K − ε model to simulate the turbulent convection of nanofluid through the heat exchanger porous media

The current study investigates the effect of the magnetic field on nanoparticle distribution and heat transfer rate. The natural convection of turbulent flow is simulated inside two half-cylinders heat exchanger. The cylinders are considered porous, and the boundary conditions are contemplated as constant flux and constant temperature. The simulation follows the k−ɛ turbulent model while utilizes the finite volume method for solving the governing equations. The effects of porous Rayleigh number (Rap), porosity number (η), magnetic number (Mn), and nanoparticle volume fraction (φ) on isothermal counters, nanoparticle distributions, and average Nusselt number are studied. The results outlined that adding nanoparticles declined the heat transfer rate in the absence of a magnetic field. At low Rayleigh numbers, the Nusselt number has a direct relation with Mn number and η, while at higher Ra numbers, although Nu number has a direct connection with η, it has a diverse relation with Mn number. Overall, the results highlighted that the heat transfer rate enhances in the presence of a magnetic field by adding nanoparticles.

Simulating electrohydrodynamics with smoothed particle hydrodynamics based on a charge-conservative approach

This paper presents an EHD model for SPH based on a charge-conservative approach. Compared with the leaky dielectric model, the EHD model used in this paper was charge conserved, since no term in the charge conservation equation was neglected. An implicit SPH formula for calculating the electric potential from the electrical properties of the previous time step was constructed, based on the electric potential Poisson equation and the charge conservation equation. The SPH formulas of the electric field and the charge density were also presented. To implement the EHD boundary condition accurately, a scheme, with two kinds of EHD boundary dummy particles, was developed. Both static and hydrodynamic numerical tests were conducted, and the accuracy of the proposed EHD model for SPH was verified by comparison with the results of analysis, the FVM method and the existing ISPH with the leaky dielectric model. This study provides an efficient method for simulating complex EHD problems with SPH.