This paper looks into **numerical** **simulation** **of** **flow** and heat transfer in the annular tube. For various values **of** inlet velocities are specified values **of** heat transfer in the annular tube and along the full length **of** the heated tube. The effect **of** various simplified spacer geometries on heat transfer in the annular tube is also monitored.

6 Ler mais

England, the type **of** pool and weir and Denil fishways have been used widely (Beach, 1984). Pools and submerged orifice type fishway is not found like many other types **of** fishway. In Scotland, pools and submerged orifice type fishway and pool and weir fishway without openings and Borland fishway have been used successfully to pass Atlantic salmon. (Zarnecki, 1960) reported ability **of** Sea trout for passing from fishway. Pool and weir fishway for passing salmon is used in two dams on Vistula river in Poland, one **of** them with 10 meters height and other one with 32 meters height.Other publications by Sakowicz and Zarnecki (1962) reported that the type **of** pool and weir fishway was pleasant for salmon in west and east Europe. In Japan, approximately 1,400 fishways are from type **of** pool and weir. Factors affecting on fish swimming are not only velocity and depth **of** **flow**. Turbulance is either effective factor for fish swimming. Additional Turbulance can block the path **of** the fishway. Clay (1995) proposed a way to be identified the locations with high turbulence in fishway and how to determine their impact on fish behavior in fishway(Clay, 1995).

Mostrar mais
9 Ler mais

cooling, leaving a thin layer **of** liquid steel along the grain boundaries, which may later form embrittling precipitates. When liquid feeding could not compensate for the shrinkage due to solidiication, thermal contraction, phase transformation and mechanical forces, tensile stresses may be generated. When the tensile stresses are high enough to nucleate an interface from the dissolved gases, then a crack would form. In an actual CC-process, the instantaneous velocity **of** melt rests with the combined effect **of** Lorentz force, gravity and other factors acting on molten steel, and the low inluences the quality **of** castings in succession. The specific coupling relations between EM-ield and STP are shown in Fig. 5.

Mostrar mais
7 Ler mais

For VR = 1, the presence **of** a bacteria in the microchannels does not affect the overall fluid **flow** behaviour because the fluid in the microchannels is stagnated (null pressure difference be- tween entrance and exit). However, for VR = 100 the effects **of** bacteria presence on fluid velocity are visible (Figure 5.21b). Near the computed bacteria, in the gaps between the microchannel walls and the bacteria itself, the fluid elements are accelerated (due to decreasing space available for fluid to **flow**), which results on an increase **of** the local fluid velocity. When the average inlet veloc- ity is the same in both main channels, i.e. VR = 1, the fluid inside the microchannels is stagnated, and therefore the Péclet number is zero. Thus, diffusion governs the mass transfer along the micro- channels, as it is visible in the colour pattern from red, at the microchannel entrance, to blue, at the microchannel outlet (Figure 5.22). In the main channels, mass transfer occurs mainly by advec- tion. In Figure 5.23 one observes that, for VR = 100, mass transfer in the feed channel occurs by ad- vection. It was previously seen that for VR ≠ 1 the fluid flows from the feed channel to the waste channel. Therefore the mass transfer inside the microchannels is ruled by the hydrodynamic transport phenomena, i.e. diffusion does not have a significant effect when compared to advection. After the glucose reaches the end **of** the microchannels, mass transfer occurs mainly by diffusion in the waste channel due to the very low inlet velocity in the waste stream.

Mostrar mais
84 Ler mais

This DNS is used in conjunction with matrix-free instability analysis methods to compute the eigenvalues **of** the **flow** and their respective eigenfunctions. Regular matrix-forming methods would demand an enormous amount **of** memory to compute the **flow** modes, in the order **of** the squared total number **of** nodes in the domain multiplied by the number **of** variables, which would easily scale into terabytes **of** memory solely to store the required matrices (Theofilis 2011). This matrix-free method is based on the work **of** Eriksson and Rizzi (1985), who have implemented a method based on Arnoldi (1951) to find the most unstable or least stable modes **of** an inviscid **flow** around an airfoil.

Mostrar mais
13 Ler mais

The present work will focus on the **simulation** **of** **flow** in a conical helix tube with constant pitch and linear radius variation. In the literature, no work was found regarding simulations for this kind **of** helix. The complexity **of** the **flow** in helical tubes is a challenge even with the advent **of** CFD. Many problems persist that were not yet thoroughly studied, like the case **of** helical tubes with variable tube section, bifurcations, etc. Both from an analytical and a **numerical** perspective, the **flow** in helical tubes, still presents many challenges. In this work we obtained the **flow** profile for the case **of** a conical helix pipe. To accomplish this we applied the OpenFOAM software to solve numerically the Navier-Stokes equations, and used other software packages for pre- and post-processing.

Mostrar mais
69 Ler mais

Various gaps in the surface **of** the supersonic aircraft have a significant effect on airflows. In order to predict the effects **of** attack angle, Mach number and width-to-depth ratio **of** gap on the local aerodynamic heating environment **of** supersonic **flow**, two-dimensional compress- ible Navier-Stokes equations are solved by the finite volume method, where convective flux **of** space term adopts the Roe format, and discretization **of** time term is achieved by 5-step Runge-Kutta algorithm. The **numerical** results reveal that the heat flux ratio is U-shaped dis- tribution on the gap wall and maximum at the windward corner **of** the gap. The heat flux ratio decreases as the gap depth and Mach number increase, however, it increases as the attack angle increases. In addition, it is important to find that chamfer in the windward corner can effectively reduce gap effect coefficient. The study will be helpful for the design **of** the ther- mal protection system in reentry vehicles.

Mostrar mais
16 Ler mais

The current production **of** polymer matrix composites, is moving from a period in which the applications were mainly oriented to high value-added niches (aerospace and aeronautical etc.), To a phase in which are wanted less sophisticated applications and mass production in sectors such as automobiles and public goods. To ensure that the high-performance composite materials can spread in these fields, it is necessary to reduce production costs, to obtain finished materials and parts can be produced with constant quality and in an economical manner. Since currently the cost **of** processing accounts for about 60% on the cost **of** a piece **of** composite material, it is easy to identify the field where it is necessary to intervene. To reduce costs it is necessary face two major problems, the first is the reduction **of** waste, and the second is control **of** the process and its optimization. Currently there are few manufacturing processes **of** composite materials that allow full control **of** the process, and are exceedingly few data available to carry out this monitoring. During the production process **of** polymer matrix composites, occur several physic-chemical phenomena which include: chemical reactions, crystallization processes, heat exchange and **flow**. Therefore, to fully describe such a process, it is necessary first to make a complete characterization **of** materials and describe, at least phenomenologically the processes taking place. This study may be performed experimentally in the lab, creating behaviour patterns able to simulate the processes themselves. By operating this type **of** approach is possible in the production stage, optimize the processes being able to produce parts **of** consistent quality, with reduction **of** rejects and increase **of** production cost effective.

Mostrar mais
74 Ler mais

The prediction **of** ductile failure in metals still represents an important challenge for the **simulation** **of** rupture in structural components and for the design **of** both sheet and bulk metal forming processes. According to Kachanov (1986), large deformations in metals, which can induce the phenomenon **of** initiation and growth **of** cavities and micro cracks, has been studied in detail leading to the concept **of** ductile fracture. Pioneering work undertaken on the subject was carried out by McClintock (1968) and Rice and Tracey (1969), where the effect **of** the geometry **of** defects in a continuous matrix was taken into account in the study **of** ductile damage. Experimental evidence has shown that the nucleation and growth **of** voids and micro cracks, which accompany large plastic **flow**, causes a reduction **of** the elastic modulus, induces a softening effect in the material and can be strongly influenced by the level **of** stress triaxiality (McClintock, 1968; Rice & Tracey, 1969; Hancock & Mackenzie, 1976). The equivalent plastic strain at fracture and the level **of** stress triaxiality were initially employed to characterize material ductility in engineering applications (Bridgman, 1952; McClintock, 1968; Rice & Tracey, 1969; Johnson & Cook, 1985). A simple exponential expression for the evolution **of** the equivalent strain with stress triaxiality was established by McClintock (1968) and Rice and Tracey (1969) based on the analysis **of** void growth under hydrostatic loads, which is usually referred to as the two dimensional fracture loci. The work performed by Mirza et al. (1996) on pure iron, mild steel and aluminum alloy BS1474 over a wide range **of** strain rates confirmed the strong dependence **of** the equivalent strain to crack formation with the level **of** stress triaxiality.

Mostrar mais
314 Ler mais

In order to evaluate the waterborne performance **of** amphibious vehicle, based on Fluid Dynamics and principle **of** marine mechanics related knowledge, the resistances and viscous **flow** field **of** amphibious vehicle in different headway were numericaly simulated by solving Navier-Stokes equatlons with the k − ε turbulence model. we obtained the result **of** frictiona resistance coefficient 、 residual resistance coefficient and running resistance coefficient,thus we can calculate its total resistances. the reliability **of** computing methed was validated by comparing the calculation results with the test data.

Mostrar mais
4 Ler mais

Unfortunately, the world still depends on the fossil energy. As shown in Figure 2, as recent as in 2015, over 60% **of** the consumed energy was derived from oil and coal. Although the depletion **of** fossil resources is an issue that humanity must face by the end **of** this century, the environmental changes, such as global warm will affect the whole life directly on Earth. For example, the average sea level rises due to ice melting in the poles could submerge most **of** the coastal cities (Hansen, 2015) and it is known that a great part **of** the population **of** the world lives in such areas. Figure 2 also shows that the participation **of** other renewable energies has increased their share from 0.54% to 0.89% between 2005 and 2015. It represents an increase **of** almost 65%.

Mostrar mais
165 Ler mais

The turbulent mixture **of** coaxial turbulent jets in a confined and an unconfined configuration for diameter ratio less than 2 is applied in several devices such as engineering ejector, jets pumps, industrial burners, combustion chambers **of** jet engines and in particular, turbofan engines with or without afterburners with low bypass ratio. In sequence **of** this study we simulate computationally a 2D shear layer in a confined and unconfined configuration for diameter ratio less than 2 using the k - ε turbulent model, being compared afterwards the **numerical** data from computational **simulation** with experimental results. From this study no recirculation zone where found despite the high levels **of** turbulent kinetic energy with high values **of** shear stress between jets and between second jet and solid surface revealing good capabilities **of** computational **simulation** for this kind **of** **flow**. Multiple impinging jets aligned with a low velocity crossflow represent a subject **of** interest in several devices such as cooling **of** equipment, pollution dispersion and specialty VSTOL aircrafts with the capability **of** vertical take-off being a test case the F-35 aircraft when operating in VSTOL mode near ground. The present 3D computational **simulation** **of** multiple impact jets aligned with a low velocity crossflow for three velocity ratios show **numerical** data underdeveloped in comparison with experimental data despite the presence **of** ground vortex for the highest two velocity ratios.

Mostrar mais
109 Ler mais

Four racks, each capable **of** storing half a core, with 76 positions to place the Fuel Assemblies, compose the In Vessel Fuel Storage. In the CFD model, the different individual positions are represented with the porous media approach (as mentioned in 3.6.1, surrounding all the storing positions. The FA are inserted in the pipes **of** the IVFS and prevail until their residual heat has sufficiently decayed. It is assumed that all racks are fully occupied by the FA. Therefore, the same parameters are considered for both IVFS and FA rings porous media, as specified in section 3.6.1. The stored FA release some residual heat, making the IVFS an additional source **of** energy. Therefore, each FA has a uniform heat source in order to inject an extra 2MW in total. The loading and unloading **of** the assemblies to the IVFS is handled by two in-vessel fuel-handling machines, installed permanently in the reactor. Natural convection is also present, as the LBE is able to **flow** within the IVFS, contributing to cool down the FA. For this purpose, numerous holes are located in the cylindrical shell **of** the inner vessel, between the two plates **of** the IVFS casing. The IVFS was modelled with the Rehme Correlation and with a porosity **of** 0.44. The following figure 3.14 shows the porous media (IVFS) **of** the diaphgram in blue.

Mostrar mais
72 Ler mais

9 Ler mais

A comparison study has been carried out to investigate for performance enhancement **of** micro channel fins by modifying the secondary **flow** passage **of** the oblique fin micro channel. Thermal & **flow** performance is compared based on the performance index. The staggered pin fin geometry is able to thermally perform better with higher penalty **of** pressure drop. But the improved oblique fin geometry which is a variant **of** modified oblique fin geometry has shown a notable improvements in the performance. In the oblique fin micro channel the main **flow** branches out to the secondary **flow** with sharp angle leading to considerable pressure drop. The modification incorporated in the improved oblique fin geometry has helped the smooth entry and exit **of** secondary **flow** while ensuring the frequent boundary layer redevelopment leading to an enhancement in performance. The staggered pin fin is the best choice, if thermal performance alone considered as the criteria irrespective **of** the pumping power. Indicative heat transfer correlations have been developed using **numerical** **simulation**.

Mostrar mais
10 Ler mais

Then, the file nomadParam.txt guides NOMAD to another file which performs the evaluation **of** the trial points, designated by blackbox.sh. This file creates several subdirectories (based on a default case which exists on the same directory), where each evaluation will be performed. Moreover, it calls GMSH to read a geometry file and create the respective mesh. Next, it converts the mesh to OpenFOAM, edits boundary/initial conditions on each case and creates the domain where the objective function will be analyzed. Finally it calls another file, simula.sh. File simula.sh initializes OpenFOAM. After each iteration, OpenFOAM consults a file called scripttest.sh , which analyses the objective function results and verifies if the goal has been achieved. When the latter is true, OpenFOAM aborts and simula.sh returns the time value to NOMAD. Else, if the **simulation** lasts 1.5 seconds, the remaining % **of** cells which have not achieved a value for α = 0.5 ± 0.02 are added to the last time step and returned to NOMAD. This is done to try and establish a hierarchy amongst the cases which surpass 1.5 seconds, to make sure the search time for the optimum values is not affected.

Mostrar mais
100 Ler mais

For **numerical** simulations, a commercial code, Ansys®, was used. In the case under study, two different modules were used: fluid **flow** (Fluent) and structural (Structural). One **of** the great advantages **of** this program is the possibility **of** integrating different analyses and, therefore, using the results obtained from one **simulation** to the other. In this particular case, the pressure exerted by the fluid on the channel walls was used to determine the displacements and strains resulting from the pressure. The models used in **numerical** **simulation** were previously drawn in a CAD software called Solid- Works®. After obtaining the three-dimensional model in the CAD software, the model was converted to a parasolid extension. The geometries used in the simulations intend to reproduce the channel used in an experimental study **of** Rodrigues et al. [9], and it is presented in Fig. 1.

Mostrar mais
8 Ler mais

is used, then secondary flows are accurately simulated and the distribution **of** mean primary velocity and the wall shear stress are also accurately reproduced. But the main difficulty lies in the choice **of** the turbulence model. Thus, isotropic eddy viscosity models, like the standard k-ε model, are robust and economic but are incapable **of** producing secondary flows. Instead, the ARSM is being often used lately; it reasonably predicts secondary flows and is computationally economic compared to Direct **Numerical** **Simulation**, DNS, or more complex models (e.g. Large Eddy **Simulation**, LES). The present study simulates the uniform **flow** in compound channel for high relative depth (≈ 50%), using ANSYS CFX Computational Fluid Dynamics (CFD) code. For this purpose k-ε model, Shear Stress Transport (SST) model and Explicit Algebraic Reynolds Stress Model (EARSM) were employed. The k- ε model and SST model are isotropic models based on Boussinesq’s approximation and do not produce secondary flows, while EARSM is derived from the Reynolds stress transport equations and is able to simulate secondary flows caused by turbulence anisotropy . The main purpose **of** the study is comparison **of** the **numerical** results obtained by isotropic and anisotropic models with the experimental velocity results obtained by a Laser Doppler Velocimeter (LDV).

Mostrar mais
226 Ler mais

available in literature for this purpose, the one researchers have most widely used is the finite element method (FEM). To obtain reliable **numerical** results, how- ever, it is necessary to adopt a constitutive model capable **of** adequately representing the stress and strain relationships **of** the materials. It is also necessary to possess an appropriate computer program to simulate the construction process while also taking into account the coupling between **flow** and deformation.

8 Ler mais

Abstract: The aim **of** this research was to use experimental planning to collect data and also to establish a methodology to compare them with theoretical data, where both are associated to the dynamics **of** reduction in pollutants in a natural treatment system for wastewater. The experimental data were collected and evaluated from two **of** these systems, built according to Valentim & Amendola (1999) and Collaço (2001), at the Center **of** Mechanization and Agricultural Automation **of** the Agricultural Institute **of** Campinas, located in Jundiaí, SP, Brazil. These systems were rectangular in shape; one with crushed stone and another with chopped tires used as support bed to hold the plants, both with macrophyte species Typha sp. The theoretical data were obtained from a mathematical model, adapted to describe the physical process **of** subsurface **flow**. The **numerical** simulations using the implicit finite difference **numerical** method were carried out using MATLAB 6.1 software. The results **of** the comparative analysis between theoretical and experimental data are presented for the two types **of** support beds. Some coefficients and parameters were adjusted to characterize the constructed systems. The results obtained were analyzed and some conclusions about the physical process as well as those about the adequacy **of** the mathematical model were made.

Mostrar mais
6 Ler mais