CFX-10 Introduction Lecture 1

CFX-10 Introduction Main Steps in CFD Analysis Geometry Meshing Physics Definition Solver Post-processing

Main Steps in CFD Analysis Step 1: Geometry DesignModeler or Import from CAD create a solid representing the fluid flow region Step 2: Meshing CFX-Mesh, CFX-TurboGrid or ICEM create a volume mesh using the solid Step 3: Physics Definition CFX-Pre define physical models, material properties and boundary conditions Step 4: Solver CFX-Solver Manager solve equations and produce a solution Step 5: Post-processing CFX-Post analyze and visualize the solver results

Step 1: Geometry DesignModeler or CAD

Geometry Create or Import the geometry Domain in which the governing equations will be solved and solution obtained ANSYS DesignModeler can be used to create geometry Results in one or more bodies Not required if the mesh is imported from a separate application

CFX-Mesh, ICEM or CFX-TurboGrid Step 2: Meshing CFX-Mesh, ICEM or CFX-TurboGrid

Meshing Mesh Generation Process of generating finite volumes or elements CFX can accept meshes with elements that are hexahedral, tetrahedral, prismatic (wedges), pyramids or any combination Surface mesh and volume mesh make up the mesh Meshes can be created in a different session or imported from another meshing utility

Step 3: Physics Definition CFX-Pre

Import Mesh into CFX-Pre The mesh defines the fluid domain(s) to be solved Mesh Tab imports and manages grids Each imported mesh is stored as a Mesh Assembly Import Mesh Transform Mesh Assembly Delete Mesh Assembly Edit Render Options for Selected Regions View Mesh Statistics for Selected Regions

Create Toolbar To define your simulation, follow the toolbar from left to right Some items are optional, depending on your simulation Hold the mouse over each icon to see what it does

Create Toolbar In the simplest cases, the following items are required after importing the mesh 1. Domains 3. Solver Control 2. Boundary Conditions 4. Write Solve File

Create Toolbar Create a Coordinate Frame – if the default coordinate frame is not sufficient Define the Simulation Type – steady state (default) or transient Create a Domain – define properties of fluid, solid and/or porous domain(s) Create a Subdomain – if you need to apply sources within a domain Create a Source Point – if you need to apply a point source within a domain Create a Boundary Condition – define what’s happening at the boundaries Create a Domain Interface – for periodicity and to connect multiple domains Define the Global Initial Conditions – initial conditions for all domains Define the Mesh Adaption Criteria – to adapt the mesh as the solution progresses Define the Solver Control Criteria – the parameters that control the Solver Output Control and Monitor Points – the files the Solver outputs Write Solver File – write a file and proceed to the Solver

Domains Define the regions in which the equations are solved Fluid, solid and porous regions Pick the fluid(s) or solid materials Select the physical models: Turbulence and Heat Transfer model Buoyancy Multiphase models Combustion and Radiation models Particle Tracking ……

Boundary Conditions Boundary Conditions are needed to completely specify (or close) the problem Required on all external surfaces of geometry Boundary values can be constants or CEL expressions A Default Boundary Condition is applied to external surfaces which have not been explicitly defined created automatically for each domain All mesh regions are available in CFX-Post, not just Boundary Conditions

Boundary Conditions There are 5 general types of boundary conditions INLET: allow flow into the domain only OUTLET: allow flow out of the domain only OPENING: allow flow in and out of the domain WALL: no flow, normal velocity is zero SYMMETRY: flat surface specifying plane of symmetry

Solver Control Control of the CFX-5 Solver is undertaken by the use of Solver Parameters, set on the Solver Control form Convergence Control maximum number of iterations timescale selection Advection Scheme Convergence criteria MAX or RMS residual conservation target

Write Solver File CFX-Pre writes out a “Definition” (.def) file to run in the Solver Contains everything needed (mesh and physics) to run the simulation. CFX-Pre stores mesh data in the “Geometry, Topology and Mesh” (.gtm) file and physics in the .cfx file Keep these files to re-open simulations in CFX-Pre

Step 4: Solver CFX-Solver Manager

Solver Solve the governing equations Set the flow solver options Iteratively solve the governing equations as a batch process Obtain convergence

Solver Manager The Solver Manager is primarily used to: start a new calculation, or set up multiple runs restart a calculation from an earlier solution examine the problem information set up parallel runs monitor residuals, global balances, monitor points, expressions, etc.

Step 5: Post-processing CFX-Post

CFX-Post Examine results, either in graphical or numerical format

CFX-Post Provides capability to quantify and visualize results Typical Post functionality involves creating Locator Objects (Points, Lines, Slice Planes, etc.) plotting Visualization Objects (Contours, Vectors, etc.) on locators evaluating expressions on locators exporting data for further external analysis CFX-Post also includes turbomachinery specific post-processing tools

CFX-Post: Visualization

Main File Types in CFX CFX-Pre CFX-Solver CFX-Post CFX-Pre case (.cfx) & GTM (.gtm) file CFX Results File (.res) CFX Definition File (.def) Other mesh files CFX-Pre CFX-Pre case (.cfx) & GTM (.gtm) file CFX Definition File (.def) CFX-Solver CFX Solver Output file (.out) CFX Results File (.res) CFX Definition File (.def) CFX GTM File (.gtm) CFX-Post

Practical Sessions Practical 1: Duct Bend A simple example to take you through the stages of setting up and running a model and then visualising the results Practical 2: Duct Bend With Vanes Include heat transfer and turning vanes (thin surfaces) in the above example.