THE PRINCIPLE OF FLUID MECHANICS AND THE NUMERICAL PROCEDURE IN CFD
The project aimed at predicting and calculating the laminar flow of fluid in pipe using ANSYS fluent software. The ANSYS FLUENT software used finite volume method to stimulate the flow of fluid in a given pipe.
The problem given in this project is to stimulate and consider the fluid flowing through a circular pipe at a constant radius .And the parameter given for the pipe are as follow : L=8m,D=0.2,µ=2×10-3kg/Ms. The inlet velocity is to be constant over the cross section. The expected resultof the problem are velocity vector, velocity magnitude condition, pressure contour , velocity profile at the outlet and skin friction coefficient along the pipe wall.
The ANSYS fluent software is used to solve the problem given and the steps involve are, Building of Geometry, Creation of mesh, coefficient and Results.
The Geometry stage is where the parameter Land D given is inserted by drawing a rectangle on the XY-plane. Which V1=0.2m for the diameter and H2=8m for the length.
Under the creation of mesh the pipe wall is divided into 100 elements in the axial direction and 5 elements in the radial direction. This is done in order to predict and visualize the condition and fluid flow on each region of the pipe.
Each edge of the pipe named in order to assign boundary condition in FLUENT in later steps. Therefore the left side of the pipe named Inlet, The right side named outlet, the top side named pipe wall and the bottom side named centerline.
In conclusion, the flow of fluid for the velocity vector moved uniformly within the inlet region and gradually the flow of fluid developed continuously until it is full developed within the outlet.
Chapter two literature review explain the various past projects that have been done about stimulation and calculation involving laminar flow in a pipe using CFDANSYS FLUENT software package.
Chapter three give details on calculation modeling where Reynolds experiment and procedure followed have been analyzed.
Chapter four gives the details about the building of Geometry, Launching of design modeler, start creation sketch on XY plane with how to Dimensioning the rectangle. More so, the project discussed the Creation of Mesh where the pipe is divided into 100 elements in the axial direction and 5 elements in the radial direction with Edge sizing the specifying the number of division.
Chapter five explained the procedure of how to set the Boundary condition with the velocity inlet and centerline boundary condition and pipe wall boundary condition.
Chapter six shows the Result presentation of velocity vector at the outlet of the pipe with velocity magnitude contours which give the rough surface at first instance but by increasing the number of contour the result gives smooth surface at the inlet, are able to show the pressure contours which is plotted on a chart so location was created along the XY axis of the pipe outlet, where we further calculate for skin friction coefficient.
Chapter seven discussed the conclusion and recommendations made based on this project
1.2 PROJECT OUTLINE
1. Problem specification
2. Pre-Analysis and start up
3. Building of geometry
4. Creation of mesh
5. Physics set up of pipe flow
6. Numerical solution
7. Numerical result using CFD prost post
8. Verification and validation
1.3 Aim and Objectives of the Project are as follows:
To provide student with an understanding of the principle of fluid mechanics and the numerical procedure in CFD.
(1) To understand the fundamental of viscous incompressible flows, the fundamental of compressible flow and learn the basic of non-viscous potential flows.
(2) To be able to understand fluid dynamics principle and their application -.To be able to demonstrate competence in setting up computational fluid dynamic models, meshing, parameterization and post processing for some industrial important application. The technical competence in building and conducting CFD simulation is a skill which enhances employability.
(3) To be formulate and solve incompressible laminar flow in a Cartesian and polar coordinates.
(4) To be familiar with computational fluid dynamic with also demonstrate the use of ANSYS FLUENT code for solving two-dimensional laminar and turbulent flow
(5) To be familiar with stream function and potential function and elementary potential flows.
2.1 LITERATURE REVIEW
In a laminar flow there is no lateral mixing, thus all fluid elements keep their position relative to the cross-section of the pipe. In a laminar flow the velocity, pressure and other flow properties at each point in the fluid stay constant. Laminar flow is observed only where the flow conduit is relatively small, the fluid velocity is low and the viscosity is relatively high. Fluid flow can either he laminar or turbulent, depending on the value of the Reynolds number, which marks the ratio of the inertial force to the viscous force. If the viscous forces dominate the flow, the flow will be laminar. On the other hand, if the inertial forces dominate the flow, the flow will be turbulent. Laminar flow is a smooth streamlined flow where the fluid layers pass over one another like a deck of playing cards. It is characterized by diffusion and a low value of convection. Lamina flow, for specific cases, can be solved as an exact solution of the Navier Stokes equations. A clear example is blood flow through capillaries, where the velocity is very low and viscosity dominates the flow. Turbulent flow, on the other hand, is highly irregular and often called ‘chaotic’ . For some given initial conditions it is difficult to predict what the flow will he after a stipulated period of time. The longer the time period the more inaccurate the prediction w ill be. This is exactly why weather prediction is subject to uncertainty. Even with the most powerful supercomputers of today it is impossible to accurately predict turbulent flow for a large scale with a high enough resolution. This is because of the nonlinearity of the advection terms in the Navier Stokes equations. Reynolds (1883) was the first to propose a criterion for differentiation between laminar and turbulent flows in his lassie dye visualization Re=DV P and suggested a critical value of Re2 1 00 for the upper limit of laminar flow. In a second paper (Reynolds. 1895) he showed by time-averaging the Navier-Stokes equations that new extra convection terms appeared in turbulence which have the units of stress and are therefore called Reynolds stresses. Considerable effort has been expanded in the last hundred and thirty years to understand the process transition. “The problem is simple in concept and yet the origins of the observed turbulent motion remain largely mysterious despite more than century of research” (Mullin and Peixinho, 2006). The literature on the transition is vast, prompting Herbert (1988), a well-known author, to note that “different reviews on shear-flow instability may have little in common and a zero-overlap of cited literature. This curious fact illustrates the many facets of the overall problem. The multitude of views. concepts. and methods, and the need to remain open minded. It also grants me the right to present my own view supported by a selection of references that I know is far from complete”. We will therefore not even attempt a survey of the
present literature but will concentrate on some developments directly relevant to the topic of this paper. Kerswell (2005) noted that all experimental and theoretical evidence points to the fact that he laminar flow state (which exists potentially for all flow rates) is linearly stable to any infinitesimal disturbance..