# CFD solving techniques (how to use CFD)
Techniques for approximating the partial differential or integral equations. There is always loss of information during discretisation and this is the major part of CFD.
Spectral Methods, Boundary Element Methods BEM, Particle Methods
Two aspects of discretisation
Geometry: Grid, Mesh, Particles
Model: all mathematical operators(d/dx) to arithmetic operators on grid points
Grid generation: Popular Techniques
The derivative transformations
Matrices and Jacobians
Grid Generation (for finite difference calculations)
Mesh Generation (for finite volume calculations)
Unstructured meshes, Cartesian meshes
Analyse and Solve
Lax-Wendroff Technique: This is an explicit, finite difference menthod. applicable to time and space marching solutions, especially hyperbolic equations
Maccormack’s Technique: applicable to time and space marching solutions, especially hyperbolic equations
Crank-Nicolson Technique: applicable to time and space marching solutions, especially parabolic equations
Relaxation Technique: applicable to elliptic equations
Alternating-Direction-Implicit(ADI) Technique: applicable to time and space-marching solutions, hyperbolic and parabolic equations
The pressure correction technique: application to elliptic, parabolic and hyperbolic equations
FLUENT Learning Modules
The following tutorials show how to solve selected fluid flow problems using ANSYS Fluent. The tutorial topics are…
Intro to FEA
For every physical phenomenon there are governing equations that can be converted to codes(approximations).
The core idea is transforming simple PDEs into simple difference equations.
FVM, FDM, FEM are representations of governing equations(approximations)
What does Ansys do?
- Internally, codes are written for governing equations.
- Geometry is divided into elements(meshing)
- Governing equations are then solved for parameters(pressure, stress, deformation) at each centre/node.
- These are then sent for post-processing(plotting velocity-pressure, stress-deformation distributions)
What is Workbench?
It’s a platform of solvers.
Meshing: Ansys meshing tool
Global settings: Sizing of the whole domain, setting problem physics
meshing methods: prisms, hexagonal, mesh assembly
finer mesh -> better efficiency but greater computation time
Mesh Convergence/ mesh independent solution
we refine the mesh till the variation in numerical results becomes under acceptable range(5%).