Implementation of Computational Fluids Dynamics in STARCCM+ Simulation - Coursework Example

Name: Instructor: Course: Date: Implementation of Computational Fluids Dynamics (CFD) in STARCCM+ simulation Introduction Simulation is a process of imitating real process operations over a given period. This process enables one to get the actual view of the system without one being practical in the field or carrying out the experiment. This report is about a simulation of the flow of fluids through an S bend pipe. However, the two fluids under study have different characteristics with the aim of studying their behavior as they move through the various sections of the pipe. Viscosity: the ability of a fluid to resist flow alongside density its weights per unit weight of water are the distinguishing characteristics of the two fluids. The first fluid has lighter density with lower viscosity compared to the second fluid which has a heavier viscosity. In studying these fluids, we also look at the relationships between the Reynolds number and the Mach numbers of the two fluids across different sections of the S-bend curve (Versteeg, p. 56). Mach number This refers to a dimensionless quantity comparing the ratio of fluid flow past a given boundary to that of the speed of sound. This can be given by the following equation Where c = speed of sound in the medium. M = Mach number. u = local flow velocity about the boundaries. Mach number is given by sixty-five percent if the speed of sound at subsonic level. At the supersonic level, the number is one hundred and thirty-five percent the speed of sound. The conditions for a given fluid are key determinants of the value of the Mach number. The number is usually used to determine the level through which any given fluid can be considered as being incompressible. The boundaries of the gas or fluid can be immersed in the medium or take the shape of a nozzle or a tunnel. A good example is in this case where the medium flows through an S type of bend. Because it's a ratio of two speeds, it has no dimensional units as they cancel out as shown in the first equation. If the Mach number is less than 0.3, then it means the fluid is isothermal with a quasi-steady type of flow. Such a flow is considered to be incompressible with very minimum compressibility effects being portrayed. Fluids have a similar behavior at specific Mach numbers despite the variations in their characteristics such as their density and degree of viscosity (Versteeg, p. 58). For the Mach numbers that are less than 0.8 the flow is characterized as being subsonic. Between 0.8 and 1.2, the flow is characterized as being transonic whereas from 1.2 to 1.5 the flow is characterized as a supersonic type of flow. The table below is a summary of the classification of the Mach numbers (Versteeg, p. 58). Reynolds number This refers to the ratio of the forces of inertia to that of the viscosity of the fluid as it flows which corresponding to the internal friction is caused by the different fluid velocities. In the case of an S bend curve, we see this effect being developed by introduction of fluid flow through it resulting in friction. The friction is the one than results to formation of the turbulent flow. The viscosity effect is responsible for neutralizing this effect as it gradually increases in the flow. Turbulence level is reduced because the kinetic energy is utilized by the viscous flow. The Reynolds number is critical when it comes to underlying the importance of the two forces in any fluid`s` flow. The number is essential in determining the particular point at which turbulence flow will take place in a fluid (Versteeg, p. 59). At lower Reynolds number the type of flow in the fluid is laminar. It is a smooth fluid flow under constant motion which is caused by the dominant viscous forces that use the kinetic energy of the fluid. High Reynolds number result into the turbulent flow with is more rapid and violent due to the high inertial forces characterized by the unused kinetic energy of the molecules. The following equation is a summary of the Reynolds number (Versteeg, p. 59). Where ρ = density of the fluid (kg/m3) L = linear dimension (m) u = velocity of the fluid (m/s) ν =fluid kinematic viscosity (m2/s). μ =fluid dynamic viscosity (Pa·s) Several factors can be used to define Reynolds number as it flows through a surface. They include fluids density, viscosity, velocity and its characteristic length. For a flow through an S bend pipe, the Reynolds number will be given by the following equation Where DH =pipe hydraulic diameter of the pipe (m). Q = volumetric flow rate (m3/s). A =cross-sectional area of the pipe (m2). υ = fluids mean velocity (m/s). μ = fluid dynamic viscosity (Pa·s) ν (nu) = kinematic viscosity (m2/s). ρ =fluid density (kg/m3). When the Reynolds number is less than 1000 the flow is laminar, when it goes above 200, the flow becomes turbulent therefore between 1000 to 2000 forms the transition period. The transition Reynolds numbers between this ranges are also known as the critical Reynolds numbers. The diagram below is an illustration of the boundary layer in fluid flow regarding the Reynolds number (Versteeg, p. 59). In this report the simulation software that has been used in the STARCCM+ program which allows one to create AutoCAD designs as well as create a simulation of the whole flow process of the fluid in the S bend pipe. The paper looks at the various steps through which the simulation was done as well as the behavior of different properties of the fluid (Versteeg, p. 59). Procedure The initial steps included familiarizing with the following features the STARCCM ++. The 3D Auto Card designing features as well as the other related visual features that are essential during the whole simulation process. Developing a 3D model of the pipe which was to be used later in the simulation process was the first step in the procedure. This was achieved by use of the AUTOCAD sub-component program for the STARCCM+ simulation program. The polyhedral mesh was then formed on the model. This was done about the flow direction in the pipe. The pipe had a labeled inlet and outlet openings (Versteeg, p. 65). During development of the geometry of the S-bend, the first step that was done was to draw a circle of diameter 0.01 meters. The next step was the development of the profile of the pipe. This was accomplished by use of two arcs of length seventy millimeters with a radius of forty millimeters. The profile was developed by joining of the two arcs with the line to come up with a complete line. The final points for the S-shaped figure are as follows Start points: [0.150 m, 0.08 m] and end points at [0.110 m, 0.04 m]. The complete S-shaped figure was then extruded with the aid of the sweep feature where the arc of the line formed the pathway through which the sweeping action took place this led to the development of the 3D figure as shown below (Versteeg, p. 65). The figure is an illustration of a swept S bends type of pipe, through which simulation of fluid flow will be carried out later in the experiment. The two faces of the model were identified and labeled according to one being the inlet with the other forming the outlet of the S-bend pipe. During conversion of the three dimension model to a geometric type of model, there are high chances of one confusing between the fluid inlet section and that of the outlet flow of the fluid. Hence there was the need to identify this sides to avoid confusion in the latter stages. With the help of the STARCCM+ program, a geometric model was developed with each of the inlet and outlet surfaces being assigned different boundaries to the geometric model. This step led to complete labeling of the inlet and outlet of the S-bend type as well as the volume of the fluid flowing through it at any given time. With the volume and cross, sectional dimensions of the pipe one can be able to easily carry out simulations relating to the different velocity, viscosity Reynolds number as well as the much number of fluids at different points. The final geometry scene was made by the simulation software with the inlets and outlets being specified correctly by the labels. The figure below shows the final geometric scene including its volumetric mesh which was developed by the end of this stage (Versteeg, p. 66). For our experimental requirements, we used inlet flow Reynolds number for the first fluid that was the lightest to be at 700. This was clear the flow was a laminar type, due to having a Reynolds number below 1000. The first fluid was kerosene used in our design while the second one was water at inlet Reynolds number of 1000. The physics models for the two fluids were defined before simulation of the process began. The respective flow velocities were predetermined to rhyme with the preset inlet Reynolds number of the two fluids (Versteeg, p. 67). Paraffin Scalar scene With a Reynolds number of 700 at the inlet section, the corresponding fluid pressure to achieve the number was found to be 0.0228. To be able to develop the scalar scene, the following coordinates were input into the system. The following corresponding coordinates were used to create the scalar scene [0.306, 2.0, 2.0] m/s. The fluid vectors that were decided for this scalar scene were as follows [2, 2 and 4]. Development of the scene was crucial in determining the properties of the paraffin as it flows through the planar section of the pipe. The obtained simulation in the process is as shown below (Versteeg, p. 80). Vector scene This is usually developed from the scalar scene of the simulation. In our simulation 950 iterations were made. This was essential in allowing the optimal convergence of values to allow for better accuracy and reliability of the results obtained. The vector scalar developed is as shown in the following figure (Versteeg, p. 85). Water Reynolds number The Reynolds number for the water at the inlet was found to be 979. To be able to have the fluid properties corresponding to this number the pressure of the flow at the inlet is 0.2128 Pascal's. When developing the scalar scene, the coordinates used were [0.350, 1.5, 1.5]. With the values of the fluid vectors being given as [1.5, 1.5 and 3].the final scalar simulation scene is as shown in the figure below (Versteeg, p. 86). Vector scene Convergence of values being critical in this type of simulation we settled for our number of iterations to be 1500 which ensured all possible points had converged. This increased the reliability and precision of the results obtained from the simulation. The vector scene is as shown in the figure below (Versteeg, p. 88). Discussion Task one The pressure variation in water was higher compared to the level in paraffin across different sections of the pipe. The paraffin has less viscous force than that of water. Therefore, the kinetic energy of the molecules is high allowing the fluid to flow at a faster velocity. As the fluid velocity increases, it has a corresponding decrease in the pressure of the fluid through various sections of the S-bend pipe. The water flowing in the pipe has higher viscous forces compared to paraffin. This high viscous force consumes most of the kinetic energy in the molecules as compared to paraffin. As a result with lower velocity, the water tends to exert more pressure through the tube when it flows. This is because the velocity of a flowing fluid is inversely proportional to its applied pressure. Comparing the two fluids one can conclude from the simulation that water was more incompressible as compared to paraffin. Despite a lower pressure at the inlet of water flowing pipe, the pressure steadily increased throughout the pipe compared to that of paraffin (Versteeg, p. 89). Task two For paraffin simulation, the Mach number that was initially high at 0.7 kept on increasing throughout the various section of the S-bend pipe. This was attributed to the high kinetic energy of its molecules that effectively overcame the viscous and frictional forces resisting its flow in the pipe. With high fluid velocity about the boundaries, there is a corresponding proportional increase in the value of Mach number since from the equation of Mach number the Mach number is directly proportional to the fluid velocity thereby becoming inversely proportional to the speed of sound (Versteeg, p. 89). The equation is summarized below Where c = speed of sound in the medium. M = Mach number. u = local flow velocity about the boundaries. The second fluid water has an initial lower Mach number compared to paraffin due to its lower initial fluid velocity. However, as it flows through the pipe the velocities increases leading to a corresponding proportional increase in the Mach number of the fluid. However during the process, the Mach number cannot be able to match the values of paraffin at different intervals as paraffin had averagely higher flowing velocity leading to a higher value of Mach number because the denominator in the equation which represents the speed of sound is constant (Versteeg, p. 89). Task three For paraffin simulation, the velocity increases at a faster rate along the various sections of the pipe. The behavior is because there is little friction forces between the fluid molecules and the boundary layers as well as minimum viscous forces that will inhibit the fluent flow of the liquid. As a result of the bends in the pipe the velocity is accelerated at a faster rate compared to that of paraffin. The other reason for its higher velocity is that it has a lower density allowing it to travel faster through the various sections of the pipe. The less dense the fluid, the less the resistance to its flow as compared to a denser fluid. Increased Mach number in the pipe at a faster rate meant there was a corresponding increase in the velocity of fluid flowing due to their direct proportionality relationship that is shown in the Mach numbers determination equation. However, for water, the velocity increased along the pipes, but it could not be compared to the rate at which the paraffin accelerated. This is attributed to the following factors. There were high viscous forces and frictional forces that produced more resistance to the flow of the fluid reducing its flowing velocity as compared to that of paraffin. Secondly, it has a higher density value of 1000 kg/ m3 compared to that of paraffin meaning it has more resistance to flow by its weight. Thirdly basing on the formula for determining the Mach number we realize that having a lower Mach number as compared to paraffin means its flowing velocity at different sections of the pipe will be lower concerning that of paraffin. Sound speed value was taken to be constant in the experiment (Versteeg, p. 90). Task four The temperature at the inlet of the paraffin was higher as compared to that of water. However, with time the velocity of the paraffin as it flows through the pipe increases at a higher rate compared to that of water. As a result, we realize less pressure is developed in the paraffin simulation through different sections of the pipe compared to that of water. The higher pressure developed in water simulation due to comparatively fewer velocity results to higher pressure in the pipe. Fluid pressure is directly proportional to its temperature, therefore the temperatures of the water simulation are higher at different sections of the pipe as compared to the temperatures of the different sections of the pipe (Versteeg, p. 90). Task five In the two simulations, we realize that there are significant differences in the properties of the inlet and outlet flows of the S-bend pipe as discussed above. The Mach number is higher in paraffin simulation compared to the value in the water simulation. This is attributed to the high value of the velocity of paraffin. The Reynolds number of water is higher than that of paraffin at various sections of the pipe because it's directly proportional to density and water has a higher density value compared to that of paraffin. The temperatures of the water simulations were higher due to the corresponding higher pressures in the simulation when compared to that of paraffin (Versteeg, p. 90). Conclusion The STARCCM+ is an essential tool when it comes to simulating the fluid flow dynamics in channels. In this experiment, the program enabled us to get the differences in flow properties of two fluids which had different velocities and densities through an S bend pipe. With simulation, it saves the time of one practically doing an experiment and collecting a lot of data and analysis as a similar model is easily developed at a click of the button. The two fluids used in the experiment had different properties when they flow through the pipe from Reynolds number, Mach number to the temperatures as discussed previously. Reference Versteeg, Henk Kaarle, and Weeratunge Malalasekera. An introduction to computational fluid dynamics: the finite volume method. Pearson Education, (2007):56-98. Read More