Numerical Analysis Of Fluid Flow Research Articles

Numerical analysis of fluid flow due to mixed convection in a lid-driven cavity having a heated circular hollow cylinder

Mixed convection heat transfer in a lid-driven cavity along with a heated circular hollow cylinder positioned at the center of the cavity has been analyzed numerically. The present study simulates a realistic system such as air-cooled electronic equipment with a heat component or an oven with heater. A Galerkin weighted residual finite element method with a Newton–Raphson iterative algorithm is adopted to solve the governing equations. The computation is carried out for wide ranges of the Richardson numbers, cylinder diameter and solid fluid thermal conductivity ratio. Results are presented in the form of streamlines, isothermal lines, average Nusselt number at the heated surface and fluid temperature in the cavity for the mentioned parameters. It is found that the flow field and temperature distribution strongly depend on the cylinder diameter and also the solid–fluid thermal conductivity ratio at the three convective regimes.

Flow Structure and Heat Transfer Analysis in a Laminar Channel Flow with Built-in Side-by-Side Dual Triangular Prism

This paper presents the numerical analysis of fluid flow in a parallel plate channel having dual triangular prisms in side-by-side arrangement. The computational domain is considered two dimensional. The fluid flow is assumed to be incompressible, steady and laminar with constant thermophysical properties. The computations are performed for a Reynolds number of 100 and blockage ratio (b) of 0.25, where the blockage ratio (b) is the ratio of prism base to the channel height (b = B/H). The unstructured triangular grid is used for the computational domain. The results are compared with the channel having single triangular prism and plane channel. The channel walls are subjected to a constant wall temperature. Unsteady two-dimensional Navier Stokes and energy equations are solved numerically using a control volume method. The SIMPLE discretization algorithm is used for the convective terms in the solution equations. CFD software FLUENT 6.2 is used to simulate the fluid flow and temperature field. A preprocessor GAMBIT is used to generate the required mesh for the solver. Results illustrate that the Nusselt numbers on the channel walls are strongly modified by the vortices induced by the presence of triangular prisms. In the presence of triangular prisms, the average Nusselt number is 8.5% more as compared to plane channel and 4.5% as compared to channel having single prism at the same Reynolds number and blockage ratio.

Shape Optimization of a Segment Ball Valve Using Metamodels

This study presents the optimization design process of a segment ball valve that involves the reduction of the flow resistance coefficient and the satisfaction of the strength requirement. Numerical analysis of fluid flow and structural analysis have been performed to predict the flow resistance coefficient and the maximum stress of a segment ball valve. In this study, a segment ball valve incorporating the advantages of a ball valve and a butterfly valve has been devised. In general, ball valves are installed in a pipe system where tight shut off is required. Butterfly valves having smaller end-to-end dimension than ball valve can be installed in narrow spaces in a pipe system. The metamodels for the shape design of a segment ball valve are built by the response surface method and the Kriging interpolation model.

Numerical analysis of fluid flow through radial diffusers in the presence of a chamfer in the feeding orifice with a mixed Eulerian–Lagrangian method

This paper reports an experimentally validated numerical analysis of fluid flow through a radial diffuser comprising two concentric and parallel disks. The flow is supplied axially by a feeding orifice placed in the back disk and becomes radial after being deflected by the front disk. The main purpose of the study is to assess the effect of a chamfer at the exit of the feeding orifice. Due to the irregular flow geometry, a mixed Eulerian–Lagrangian method is employed to numerically solve the fluid flow. The model is validated by comparing the numerical results with experimental data for pressure distribution on the front disk, as a function of the gap between the disks and the Reynolds number. Results for pressure on the front disk and effective flow and force areas show that the flow is significantly affected by chamfer angles as small as 5°.

Numerical Analysis of Fluid Flow in a Compact Phase Separator~!2008-01-24~!2008-04-16~!2008-06-11~!

A compact separator consisting of two volutes (inlet and outlet) connected with a cylindrical chamber is pro- posed as a cost-effective alternative to conventional separators. The separator has a wide range of applications in the oil and gas industry. It has the advantages of being compact, free of the effect of motion on floating platforms, more tolerant to flow fluctuations and can be modularised in series to remove liquid or gas carry-over. In order to optimize the system performance a series of CFD simulations is programmed covering a wide range of inlet flows (phase mixing percentage). The starting point will be the CFD analysis of the liquid-gas flow, in various inlet flow patterns. The present paper pre- sents the results of the initial two-phase separation process simulation, carried out using the FLUENT commercial CFD code in terms of pressure, velocity and volume fraction distribution for both phases and all over the separator. The cross analysis of the results leads to a better understanding of the two-phase flow and separation inside each component and aids the research team to set up an experimental procedure up and proceed to the next step of the research programme.

Numerical analysis of fluid flow and heat transfer in pool of twin roll strip caster

Twin roll strip casting is regarded as a prospective technology offering many economic benefits. The control of fluid flow in the pool is, however, particularly difficult due to the high casting speed and small pool volume. In the present study, a three-dimensional mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in the pool using the finite difference method. The characteristics of transport phenomena in the pool of a twin roll strip caster using a wedge type melt delivery system were analysed by numerical simulation. The results show that it is desirable for the wedge melt delivery system to provide the uniformity of flow and temperature in the pool to maintain the casting process and improve the strip quality.

An experimental and numerical investigation of mixed convection from a heat generating element in a ventilated cavity

This study reports the results of an experimental and numerical investigation of mixed convection from a heat generating element in a ventilated cavity. Experiments were carried out for heaters of two different sizes, located centrally in a parallelepiped that has an air inlet and an outlet port. An induced fan at the outlet is used to create a flow, thereby facilitating studies in the complete mixed convection regime. After a detailed parametric study, correlations have been developed for the average Nusselt number and the maximum dimensionless temperature occurring in the heat generating element. Experiments have been backed up by a numerical analysis of fluid flow and heat transfer for a geometry that corresponds exactly to the one used for the experiments. The good agreement between the experiments and the numerical results confirms the adequacy of the two dimensional approximation and the turbulence closure model employed. Based on the numerical results, the position of the heat source was changed in order to improve the heat transfer performance and the experiments were repeated for this new position. Hence, a combined experimental and numerical investigation will significantly reduce the effort required to optimize the thermal performance in problems of this class.

Two-scale modeling in porous media: Relative permeability predictions

We present a numerical analysis of fluid flow through a porous medium with two distinct characteristic scales. The system considered is a monodisperse matrix with porosity ϕ and permeability Kpm with an embedded second phase, characterized by a phase content or saturation s and phase length scales Lϕ and Ls. Both two- and three-dimensional simulations are performed to compute the mobile fluid phase relative permeability kr,m and its dependence on s and Kpm. The relative permeability is found to vary as a power law of saturation, with a quasilinear behavior for low permeability, and increasing values of the exponent as Kpm increases. For media with low permeability, the linearity of kr,m is attributed to the drag force, whereas for high Kpm, the decrease of kr,m with s is due primarily to viscous forces. An analytical model for kr,m is also presented to aid the interpretation and to corroborate the simulation results. In the second part, in order to elucidate the role of the length scales on kr,m, simulations explicitly resolving both porous media and second-phase scales are performed. The relative permeability is found to drop rapidly when both scales are of the same order (Ls≈Lϕ) or when Ls<Lϕ. Three regimes (Darcy, Brinkman, Stokes) are consequently identified based on the length scales.

Numerical analysis of fluid flow and added mass induced by vibration of structure

The fluid flow induced by light-density, low-stiffness structures was treated as inviscid, incompressible irrotational and steady plane flow. On the basis of the dipole configuration method, a singularity distribution method of distributing sources/sinks and dipoles on interfaces of the structure and fluid was developed to solve the problem of fluid flow induced by the vibration of common structures, such as columns and columns with fins, deduce the expression of kinetic energy of the fluid flow, and obtain the added mass finally. The calculational instances with analytical solutions prove the reliability of this method.

Function and Performance of a Low Turbulence Inlet for Sampling Supermicron Particles from Aircraft Platforms

A low-turbulence, aerosol sampling inlet (LTI) has been developed for use on aircraft. The inlet makes use of boundary layer suction in a porous diffuser to slow the sample flow from aircraft air speeds near 150 m/s to velocities near 5 m/s without generating turbulence. The reduction of turbulence reduces losses of supermicron particles by turbulent deposition and permits the use of laminar flow calculations and well-understood drag formulations to accurately predict particle motion. Large particles are enhanced in the sample flow due to inertia. These enhancements are predicted with numerical analysis of fluid flow and integration of the equations of motion for the particles. The diffuser discussed in this article has been used in a number of field experiments, and the enhancement factors have been provided to the experimenters measuring aerosol downstream of the inlet. Some particles are doubtless lost in transport from the LTI to the aircraft fuselage. Estimates of those losses have also been made and...

Numerical analysis of fluid flow through a cylinder array using a lattice Boltzmann model

In this paper we present a detailed computational study of an incompressible Newtonian fluid flow across a periodic array of two-dimensional cylinders which is a simplest non-trivial representation of a porous media. A two-dimensional Lattice Boltzmann Method is used to solve the governing Navier–Stokes equation taking into account of viscous dissipation effects and influence of nonlinear fluid drag. Both the flow fields and the Darcy–Forchheimer drag coefficient as a function of the solid volume fraction are calculated for a wide range of flow Reynolds numbers. The predictions were compared with the results from conventional numerical and empirical models for verification. Apart from confirming that inertial effects can cause a significant deviation from Darcy's law for large velocities the results also show that the characteristics of the vorticity field vary considerably as the Reynolds number increases, which will have major implications to the transport of passive particulate substances within the pores and their removal rate.

Three-Dimensional Numerical Analysis of Fluid Flow and Heat Transfer in Wake with Positive Buoyancy (2nd Report, 3D Structure of Isothermal Wake)

The isothermal wake from a circular cylinder at the Reynolds number Re=300 was analyzed by a DNS computation, computed results were discussed, and features of 3 D motion were elucidated as follows : Qualitative features of the vorticities ωx, ωy with the upward direction and the horizontal directions and the velocity ω in the cylinder axis direction were revealed by an analogy of the vorticity ωz in the cylinder axis direction. The vortex dislocation was visualized in the farwake streaklines, had a band spectrum of time trace of the upward velocity, and was found to be resulted from the ω motion. A mechanism of the vortex dislocation was made clear by the ω motion which was different between the nearwake with fp=fwake and farwake with fp=2fwake, here fp is the dominant frequency and fwake is the wake frequency. The wave lengths of ωx and ωy were 1, i. e. the B mode oscillation, in the nearwake, and 2, i. e. the C mode oscillation, in the farwake. The 3D oscillation in the isothermal Karman vortex street at Re=300 was therefore composed of the B mode with the wave length 1 in the nearwake and the C* mode with both the length 2 and the vortex dislocation in the farwake.

Three-Dimensional Numerical Analysis of Fluid Flow and Heat Transfer in Wake with Positive Buoyancy (3rd Report, Positive Buoyancy Effect on 3D Structure)

The wake with positive buoyancy at the Reynolds number 300 and the Richardson number 0.3 of air was analyzed by the DNS computation, and revealed as follows : Positive buoyancy effects are that one is Effect I, that is, a decrease of the axial direction vorticity|ωz|, and the other is Effect II, that is, a decrease of the 3D motion, i. e. the vorticities |ωx|, |ωy| with the upward and horizontal directions, and the velocity |w| with the axial direction. Effect II is more dominant than Effect I.That is, the 3D motion moving right and left decreases remarkably, but the suppression of vortex street becomes weak. A space effect of Effect II is that the vortex dislocation becomes vague and a dislocation location becomes time-dependent. A time effect of Effect II is that the frequency of the 3D motion increases, the amplitude of the motion decreases, and the formation region length decreases. A space and time effect of Effect II is that the oscillation mode becomes the B mode with 1 of the wave length Λ, and 2fwake and 5fwake of the dominant frequency fp of the 3D motion in the nearwake, and the A* mode with 3 of Λ, 2fwake of fp, and the weak vortex-dislocation in the farwake, here fwake is the wake frequency.

A numerical analysis of fluid flow, heat transfer and solidification in the bending-type square billet continuous casting process

A numerical modeling system was developed which can simulate the transport phenomena of a bending type square billet continuous casting process. Fluid flow and heat transfer were analyzed with a 3-dimensional finite volume method (FVM) with the aid of an effective heat capacity algorithm for the solidification. For a complex geometry of the bending type billet caster, a body-fitted-coordinate (BFC) system was employed. The bent structure of the caster allows a recirculating flow to develop in the upper and outer-radius region and the main stream to shift toward inner radius. This causes the thinner solid shell in the inner radius region than in the outer one. Besides standard operation conditions, we have analyzed the results when casting speed, caster shape, and tundish superheat changes. Lower casting speed makes the solid shell thicker by reducing heat flux from the mold. In the vertical caster, solid shell thickness are more uniform than that in the bending-type in entire region. When superheat increases by 5°C, solid shell thickness at the mold exit becomes thinner by 1 mm.

Numerical analysis of fluid flow and heat transfer in periodic wavy channels

The two-dimensional steady and time-dependent fluid flow and heat transfer through periodic, wavy channels is numerically studied, for a fluid with a Prandtl number of 0.7, by means of an unstructured covolume method. The two geometrical configurations considered, a sinusoidal channel and an arc-shaped channel, are shown to provide little or no heat transfer augmentation, in comparison to a parallel-plate channel, in steady flow regimes at lower values of the Reynolds number. In addition, they both have higher pressure drop than that of the parallel-plate channel under fully developed flow conditions. For the unsteady regime, reached at about Re=175–200 for the sinusoidal channel, and Re=60–80 for the arc-shaped channel, both geometries exhibit a significant increase in the heat transfer rate, up to three times for the highest Reynolds number investigated. This increase is higher for the arc-shaped flow passage, but is accompanied by a higher friction factor than that of the sinusoidal channel.

3D Numerical Analysis of Fluid Flow and Heat Transfer in Wake with Positive Buoyancy. 1st Report, Formulation and Numerical Methodology.

First. a wake with positive buoyancy from a circular cylinder is formulated as a three dimensional and time dependent behavior of compressible fluid flow. Next, numerical methodology for the wake is obtained by employing the grid generation by solving the elliptic partial differential equations and by extending the HSMAC method to compressible fluid flow. As a result, in an isothermal wake, the above formulation and methodology becomes those for an incompressible fluid flow. The Strouhal numbers, time averaged drag coefficients, rms amplitudes of the lift coefficient, distribution of the vorticity with the cylinder axis direction, and streaklines obtained by the present computation at the Reynolds numbers 100 and 300 agree well with the previous studies. Furthermore, the time averaged mean Nusselt numbers obtained by the present computation at the Grashof numbers 0 and 490 and the Reynolds number 70 agree well with the previous studies. The present formulation and methodology are therefore validated.

Numerical Analysis of Fluid Flow and Heat Transfer in the Parallel Type Mold of a Thin Slab Caster.

The surface and internal defects in the continuously cast slab are closely related to the fluid flow conditions of the liquid steel in the continuous casting mold. Therefore, the control of the steel flow for example, by proper design of submerged entry nozzle and by optimum operating conditions, has become an important area for quality and productivity improvement. In this study, a three-dimensional numerical model for fluid flow and heat transfer analysis was employed and flow pattern and related phenomena in the parallel type thin slab mold were simulated together with a comparison with our previous study on the funnel type mold. The dependence of the flow on the shape of the SEN was illustrated for both straight and bifurcated nozzles. The bifurcated nozzle creates streamlines of two counter-rotating loops at each half of the mold similar to that of the funnel type mold with a bifurcated nozzle and produces a stabilized meniscus with a low surface velocity. The design of the nozzle port affects the velocity profile at the meniscus, heat transfer and accordingly the solidification process. An inclined bifurcated nozzle with a jet angle of 60° shows more stable velocity profile in the meniscus and more uniform distribution of solidified shell than the other port.

Numerical Analysis of Fluid Flow and Heat Transfer in the Funnel Type Mold of a Thin Slab Caster.

Thin slab casting is an emerging technology offering many economic benefits. In the case of a thin slab caster, the control of fluid flow in a mold is particularly difficult due to the high casting speed and large aspect ratio of the mold. In addition, the knowledge of the transport phenomena is important because melt delivery is directly related to the problems of non-uniform shell growth, surface turbulence and mold powder entrapment. In this study, a 3-dimensional mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in the funnel type mold using finite volume method based on the body fitted coordinate. The characteristics of transport phenomena in the mold of a thin slab caster were analyzed by numerical simulation. As a result of the simulation, the basic flow pattern could be characterized and the heat transfer calculations could accurately predict the areas where the mold is susceptible to cracking as a result of thermal stress. The predicted shell thickness showed good agreement with the measured thickness at the solidified shell of the break-out products.

Numerical Analysis of Fluid Flow and Heat Transfer in Molten Zinc Pot of Continuous Hot-dip Galvanizing Line.

A numerical model adopting a partially staggered grid system for the location of dependent variables has been developed to analyze the fluid flow and temperature distributions in a molten zinc pot of No. 2 CGL of POSCO Kwangyang strip mills. A control volume based finite difference procedure was employed to solve the conservation equations transformed by using the boundary-fitted-coordinate (BFC) system. The calculation results have shown that a change in the steel strip velocity has little influence on the overall flow pattern developed in the pot. The overall temperature distribution was rather uniform as predicted. However, charging cold ingots directly into the pot produced a non-uniform distribution of temperature. The local temperature fluctuations will promote the formation of intermetallic dross particles. It has been proposed that the non-uniform distribution of temperature could be reduced by selecting an appropriate channel inductor position as well as by optimizing the zinc ingot loading position.

Numerical Fluid Flow Analysis for Aerodynamic Response Characteristics of Tandem Circular Cylinders

The aerodynamic characteristics of tandem cables of cable-stayed bridges have become an increasingly serious problem with increments in span length. In order to reduce the construction cost and maintenance of cables, tandem cables have been adopted for cable-stayed bridges. These cables, however, have aerodynamic response characteristics such as wake-galloping. Therefore, a method to suppress wake-galloping in tandem cables is required. The purpose of this study is to investigate the characteristics of the wake-galloping phenomenon of tandem cables of cable-stayed bridges using numerical fluid flow analysis. The flow around the oscillating tandem circular cylinders modeled on tandem cables is calculated. The flow field is treated as an incompressible viscous flow. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to solve the flow field around the cylinders, and the three-step Taylor-Galerkin method, which is based on a fractional step finite element method, is adopted for discretization.