This paper looks into numericalsimulationofflow 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.
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 offlow. 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).
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.
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.
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.
The present work will focus on the simulationofflow 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.
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.
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.
The prediction of ductile failure in metals still represents an important challenge for the simulationof 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.
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.
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%.
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 offlow. 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 simulationof 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.
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.
Numerical simulations of stationary laminar incompressible glycerine flow in a circular channel with aneurysm was performed in order to obtain the pressure distribution at the wall, these result being then used as boundary condition for a structural analysis of the wall channel. The calculations were performed in a commercial software using two different modules of Ansys®: Fluent and Structural. In the ﬁrst module the glycerine flow, commonly used as a blood analogue, was analysed inside a closed channel. For the second module it was also analysed the displacement and stress ﬁelds produced by the internal pressures obtained from fluid flow simulations. In the developed model it was considered that the material had a hyperelastic behaviour, and as a result it was used the stress-strain curve obtained experimentally for the PDMS material and implemented the constitutive model of Mooney-Rivlin.
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 numericalsimulation.
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.
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 numericalsimulation 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. , and it is presented in Fig. 1.
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 NumericalSimulation, 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).
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.
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.