Implementation of Computational Fluid Dynamics - Lab Report Example

Name University Professor Course Date Imрlеmеntаtiоn оf Cоmрutаtiоnаl Fluid Dynаmiсs 1.0Introduction Fluid dynamics is one of the important fields in engineering. It is both important in our lives and also in running of machines. Fluid therefore plays a significant role in ensuring that the machine moves efficiently. Fluid composed of air, water, oil and other liquids which we need daily. The study of fluids will help us understand the behavior of different fluids and what make them different from other fluids. Air and water which form fluids makes our body mass and the movement of air in the atmosphere ensures we have sufficient oxygen that we require to sustain our lives. At the same time 75% of out body is water and the movement of these fluids across our body system is important in improving our health. Fluids are therefore necessary in supporting carbon based life forms. To study biological system, it is only important to apply the knowledge of fluid dynamics. Fluids are important in transportation system and they greatly affect recreation and can also be used in entertainment. It is impossible for speaker sound to reach our ears without the movement of air and we cannot even breathe when there is no air. Based on the above findings engineers must have the knowledge of fluid behavior in order to examine different systems they come across. The purpose of this study is to investigate the behavior of different fluids with different densities, pressure and temperature. To determine the correct result, it is important to follow the correct procedure required when setting up simulation. The correct set up will be able to investigate the flow of two different fluids that have density and viscosity variations. It will also determine the flow of fluids with two different pressure conditions, fluids with two different Reynolds numbers and those with two different mach numbers. 1.1 CFD codes used In the examination of the flow rate of two different fluids through the pipes, it is important for the researcher to define the expected flow rate within the pipe and also to describe the behavior of these fluids under given conditions (Tomboulides et al, 2015). In all cases, it is vital to know the density of the fluid, its viscosity and temperature changes for the study to continue. It is also necessary to determine the length of the pipe, inlet and outlet diameter and the diameter of the main pipe. All these factors must be known in order to understand the behavior of two different fluids under the study. In these study only two multiphase simulation capabilities is applied to assess the flow rate and the general behavior of two different fluids in different conditions. STAR-CCM+ [4] code is used in this case to create a platform for advanced multiphase flow model to examine the behavior of two different fluids under analysis (Amicis, 2014). Another important code used in this study was Nek5000 which was mainly used to develop a platform for examining thermal fluids in order to determine the behavior of some fluids when there is an increase in temperature. 1.2 STARS-CCM+ This code is available in the market for different users. It is general purpose analysis software used in evaluating thermal and compressible/incompressible fluids flow. It allows for the use of generic polyhedral mesh and allow for the application of different approaches that can generate conformal computational meshes that are able to describe multifaceted geometries. It is also allows for the examination of Reynods average Navier Stocks modeling necessary for use in this study. Every simulation in this report employs  type RANS turbulence models. The results are obtained through the use of simple algorithm with the help of Rhie-Chow interpolation for speed to pressure coupling. The findings are then accelerated using algebraic multi-grid preconditioning. This code is able to generate second order accuracy in all its findings of spatial and chronological incident. The computations in this study are in their steady conditions and therefore appropriate result can be determined to explain the behavior of two different fluids under different conditions. 2.0 computational models The first step to take when analyzing the flow of fluids is to initially develop computational models. These models are developed independently using pre-processing method and selecting an appropriate strategy for the available codes. Sensitivity analysis was also done to verify the results obtained. 2.1 STARS-CCM+ In the creation of STAR-CCM+ model, it is possible to investigate the effects of different modeling decisions. This is because simulation of multiphase flows usually has numerous challenges. These challenges result from the availability of geometrical local variations that affects the flow structure. This is possible in helical coil in which low angle supports division of different phases. Boiling closure models are usually universal and mostly used for vertical pipe and therefore their use to support inclined pipe flows is not recognized by different users but for helical coil flows have not been tested virtually. When there is not sufficient information about temperature, velocity and density from relevant sources to be used for validation purposes, it is necessary to employ sensitivity analysis to find out parameters that need further analysis. 2.2 Computational Mesh Development The most important step is computing high quality computational mesh in this study. It has a number of functions which include the description of the flow of geometries. It should also be able to discretize the volume of all the closure models and solvers needed for use in this study. When developing helical coil model, two various approaches were used to evaluate it. The initial strategy was STAR-CCM+ which was mainly used to develop mesh that composed of volumetrically filled polyhedral core with a polygonal prismatic extrusion layer that covers the entire surface. The next was a block structured hexahedral mesh created through the use of directed meshing elements. Sensitivity analysis for STAR-CCM+ finite volume solution was conducted on the mesh structure to lodge an investigation for a single phase water flow which passes along helical coil. Its walls were not rough and heat was also not there to increase the temperature of the fluid. For it to work appropriately adiabatic condition was maintained as one of the assumptions needed for this study to proceed. The characteristics of the coolant was expected to have the same qualities as water at 50 K sub-cooling presumed for the helical coil boiling evaluation. The nest step followed was the development of a mesh that has a dense prismatic extrusion layers next to its walls in order to generate reference clarification for turbulent flow. To provide an accurate clarification in reference case, a low Reynolds number formulation of realizable RANS turbulence model was applied. It is not easy to identify its name but it has the capacity to provide limited capabilities to generate forecast of low Reynolds number evolution to commotion (Baglietto and Christon, 2013). For the model to work, it is important to have sufficient resolution in the computational mesh in order to provide solution to the boundary effect layer, with figures of the y+ parameter, the dimensionless border layer with a thickness, less than unity. B The y+ parameter is perceived as a thickness function for the initial cell and ordinary flow situation. The highest value for the mesh is indicated in the figure below as 0.8336 while the least value is 0.3143 and the mean value is 0.526. The forecasted velocity along the helical pipe is simply shown in the secondary flow pattern. The forecasted variation in pressure determined through the use of outlet is illustrated in figure 5 as shown below. It is absolutely right to use low Reynolds number model when carrying out simulation for single phase liquid flow case because it is able to provide perfect reference solution although it does not match with Eulerian-Eulerian formulation and a mesh with highly revolved boundary layer. It is explained that it is not suitable for Eulerian-Eulerian multiphase closure models. There are other alternative mesh structures that can be used for two- phased boiling flow simulation to reproduce similar single phase liquid flow as suggested in the case. These alternatives meshes are shown below Mesh a) is mainly uses polyhedral meshing for STAR-CCM+ and it used in setting prismatic extrusion layer, b) is used for maintaining the same mesh in right condition, c) is a block structure and it is the same as reference mesh although it has a coarser representation the close to wall region. Finally d) is the refined mesh specifically applied in the reference wall resolved low + simulation. The four meshes were used to complete the entire study for single phased flow conditions. They only used high Reynolds number formulation achievable turmoil model and all y+ two-layer hedge treatment which is observed to work better with coarse near wall mesh resolution. It is necessary to extract velocity profile only on the horizontal diameter by using all the four computational meshes as indicated in the figure below. The three alternative simulations that worked well with coarser meshes resulted into a steeper velocity slope although polyhedral mesh that has lengthened prismatic layer is more appropriate for the same purpose. The three simulations are also forecasted to generate slightly reduced pressure under helical coil stream tube. The findings of both standard STAR-CCM+ polyhedral mesh and the standard block-structured hexahedral are comparable because they generate the same results. The figure below show the evolution of predicted velocity profiles along the horizontal pipe diameter as coolant moves through the helix. The figure below also illustrates the expected velocity profile in the reference simulation using the high Reynolds number variant of the realizable k-epsilon turbulence model. Creation of S-Bends Geometry The creation of Sbend geometry is very simply but it require proper use of STAR-CCM+ during the creation period. It also requires the creation of new simulations. The new simulation should be saved in a disk with a specific file name S-bends. In the process the geometry will be formed through the application of 3D-CAD. In the activation of 3D-CAD, the geometry is right clicked and the new model is created and at the same time 3D CAD is activated. Creating the Geometry It is also not complicated to develop s-bends pipes geometry. A circle showing the inlet side need to be formed first and this is possible by developing a new sketch on YZ plane. This is achieved by right clicking the features YZ node then selecting develop sketch. Click sketch grid spacing in order to alter grid spacing to 0.0025m. The view normal to sketch plane button is clicked so that the sketch can come into view. This was achieved by using create circle tool to produce a sketch for a circle that has a radius of 0.01m. The sketch above is then removed by clicking on the exit and it provides the avenue for creating a pipe profile along its length. The second step is the creation of a new sketch on the same plane YZ and this is done using the same tool on 0.035m beginning at the origin and ends in x direction. Once it is completed, press exit and finally use center point circular arc tool to create an arc that has a radius 0.02m and to do this there must be three mouse clicks. The initial click must be located at 0.035m, 0.02m and this locates the centre point and the second should be located at a point 0.035, 0.00m and it is responsible for defining the start point and finally the third mouse should be at 0.035, 0.02m defining the end point. It is necessary to create a second arc to finish s-shapes and this require the use of center point circular arc tool. The points which must be marked are as shown below: Center: [0.075 m, 0.02 m]. Start point: [0.075 m, 0.04 m]. End point: [0.055 m, 0.02 m]. The final drawing for the s-pipes requires the drawing of a line at the start point [0.075 m, 0.04 m] and finally extends to 0.065 m in the positive x-direction The final skecth for s-pipes 3.0 Discussion 3.1 The behavior of pressure as a function of distance along the pipe for the different conditions The main pipe has 100 m3, 750kg/m3. This pipe is divided into two separate direction forming pipe A and pipe B. These two pipes have the same radii and pipe A is shorter in length than pipe B. The volumetric flow rate of the fluids in these two pipes is not greatly affected because what takes place in both pipes does not vary in terms of pressure significantly. The pressure at both branch is the same as explains by the below formula ΔPA =ΔPB. The pressure only reduces when there is an increase in the length of the pipe. The longer the pipe, the lower the pressure since the air or fluid flow in a longer distance according to the Hagen-Poiseuille equation which can be derived from laminar flow although it is similar according to turbulent flow. It is therefore observed that the length and flow rate of different fluids in pipe A and B are related according to the equation shown below. = When pipe A is three times longer than pipe B, fluids in pipe A will have to flow 75m3/h along pipe A more than pipe B. The difference in pressure will be there due to the availability of friction. The pressure will be the same when the pipes have the same lenghts because they will have the same friction which have an effect on pressure along the pipes. The longer pipe will have slightly lower pressure along the pipe (Santini and Ricotti, 2008). The fluid in a longer pipe will have a lower pressure and therefore the fluid flowing through it will have a lower flowrate than in a shorter pipe. The reduction in pressure in a longer pipe which also result into a decline in flowrate of fluid is caused by many factors but not friction only. The study is also conducted when pipe A is shorter than pipe B and both pipes have the same outlet pressure, all these pipes will generate equal drop in pressure although pipe A will have a higher flow rate. If the inlet and outlet pressure is fixed, the reduction in pressure is also observed to remain fixed and for that matter the flow rate in these two pipes containing different fluids adjust in order to balance the constraints. The reduction in pressure in a pipe depend on different factors such as friction, length of the pipe, internal diameter, fluid density, fluid viscosity and fluid temperature. In general, flow rate of different fluids along the pipe differs according to the length of the pipe. The pipe that has a longer length has alower flow rate than the pipe with a shorter pipe. 3.2 The behavior of velocity magnitude along the pipe for the different cases. Viscosity is the state of a fluid that makes its more resistant to flow. In my study two liquids with different viscosity were used to study its effect on the flow of a fluid through a pipe. Pipe A and pipe B were used (Yabuki and Nakabeppu, 2016). These two pipes have the same diameter and length in order to determine the effect of viscosity on the fluid flow. Pipe A contains honey while pipe B contained water. It is observed that fluid in pipe A has a lower flow rate as compared to fluid in pipe B. The result of my analysis showed that fluid in pipe A tends to cling on the surface than fluid in pipe B. Fluid in pipe A have a given internal friction than fluid in pipe B and therefore it flows slowly than fluid in pipe B. Fluid in pipe A tend to have cohesive forces between its molecules and this increases its ability to stick on the walls of the pipe than fluid in pipe B. It is therefore observed that a more viscous fluid be it honey, grease, oil or gas has a slower flow rate than a less viscous fluid because it sticks along the walls of the pipe than the way a less viscous fluid does. It is also determined that a more viscous fluid has a stronger coefficient of viscosity and therefore a more viscous fluid has a stronger velocity gradient because fluids closer to the wall of the pipe is stationary while a less viscous fluid has a weaker velocity gradient which allow fluids along the surface of the pipe to move slightly faster. The stationary layer of a more viscous fluid reduces the flow of the fluid above it. The flow rate of a viscous fluid is affected by either the length of the pipe, its diameter and pressure. It is also observed that more viscous fluid flow slowly in a pipe with a smaller diameter than a pipe with a larger diameter but not as compared to a less viscous fluid like water. A viscous fluid also flows more slowly in a narrow pipe than a larger pipe owing to the fact that they have the same pipe length and external pressure. When compared to a less viscous fluid, it flows much slowly under the same condition or nature of the pipe. 3.3 The behavior of temperature variation along the pipe for the different cases. Temperature changes affect flow rate of different fluids. The temperature is increased in one pipe than the other containing different fluids, the particles of that fluid move faster than the fluid whose temperature is low thereby spreading further apart from each other. The distance between each particle increases with the increase in temperature which reduces the cohesive forces. Because of this the fluid with a higher temperature will move more freely than the fluid with less temperature which reduces its viscosity. With the reduction in viscosity, the fluid will start to flow more easily than the fluid with a lower temperature that makes it to have a higher viscosity. The increase in temperature also reduces the density of fluids and this also makes it to flow faster than the fluid with low temperature which also is denser than heated fluids. Pressure is also affected by the increase in the level of temperature. When the temperature is increased for one fluid in one pipe, the pressure increases which make it to flow much faster than a fluid in the other pipe with low temperatures. In general, a warmer fluid flows faster because increase in temperature the movement of particles increases which reduces its viscosity thereby flowing faster. This is contrary to cooler fluids in a pipe (Tentner and Merzari, 2016). The movement of particles of such a fluid is slow and as a result it is more viscous than the other with higher temperatures. The same study was also conducted between gases and liquids. It is also determined that temperature also affect viscosity of gases also in the same manner it affect liquids. Based on gas theory gases are made up of tiny particles which are far apart and are in constant motion, the increase in temperature increases their motion which result into an increased friction. The increase in resistance reduces the flow of gases because of a stronger internal friction between the particles. When the temperature is increased, internal friction increases because the distance between its particles increases thus reducing its viscosity. Conclusion This report was very successful and all the expected results were determined using STARS-CCM+ which is able to determine the behavior of two different fluids flowing through a pipe of different lengths. The result showed that temperature affect the flow rate of a fluid since the increase in temperature increase the movement of particles thereby reducing viscosity of a fluid. The reduction in viscosity due to increase in temperatures increase it flow rate. It is also determined viscosity and increase in the length of pipe also increases the flow rate of a fluid. The result of this study is therefore very important in engineering in understanding the behavior of different fluids so as to use them for different purposes. Work Cited Amicis, A. Cammi, L.P.M. Colombo, M. Colombo, and M. E. Ricotti, “Experimental and numerical study of the laminar flow in helically coiled pipes,” Progress in Nuclear Energy 76 (2014) 206–215. Santini, A. Cioncolini, C. Lombardi, and M. Ricotti, “Two-phase pressure drops in a helically coiled steam generator,” International Journal of Heat and Mass Transfer 51 (2008) 4926–4939. Baglietto, and M. A. 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Bai, “Transient convective heat transfer in a helical coiled tube with pulsatile fully developed turbulent flow,” Int J Heat Mass Transfer 41 (1998) 2867–75. Read More