TS/CV/DC CFD TeamTS/CV/DC CFD Team

A Brief Introduction to CFDA Brief Introduction to CFD

Sara C. Eicher

CERN, CH

Alice

Outline of PresentationOutline of Presentation

•• What is CFD?What is CFD?

•• CFD StructureCFD Structure

•• Planning StrategyPlanning Strategy

•• Errors and Uncertainties Errors and Uncertainties

•• CFD Solving StepsCFD Solving Steps

Sara C. Eicher

What is CFD?What is CFD?

•• Solution of fluid dynamics problems by means of a computer Solution of fluid dynamics problems by means of a computer

based simulationbased simulation

Sara C. Eicher

ATLAS

ALICE

GLOBE

What is CFD?What is CFD?

•• Solution of fluid dynamics problems by means of a computer basedSolution of fluid dynamics problems by means of a computer based simulationsimulation

•• Set of partial differential equations describing conservation laSet of partial differential equations describing conservation laws for ws for transport of mass, momentum, energytransport of mass, momentum, energy

•• Components of a Numerical Simulation:Components of a Numerical Simulation:

Sara C. Eicher

CFD

Mathematical Model

Discretisation Method

Coordinate System

Computational Mesh

Approximations

Solution Method

Convergence Criteria

CFD StructureCFD Structure

Sara C. Eicher

•• CFD code consists mainly of three modules:CFD code consists mainly of three modules:

•• But firstly plan your analysisBut firstly plan your analysis

-- PrePre--processor processor –– problem formulation and mesh constructionproblem formulation and mesh construction

-- Solver Solver –– solution of the discretised governing equations solution of the discretised governing equations

-- PostPost--processor processor –– analysis and display of resultsanalysis and display of results

Planning StrategyPlanning Strategy

Sara C. Eicher

1. State clearly the objective of the study: 1. State clearly the objective of the study: what are the required what are the required results and degree of accuracy (engineering quantities, performaresults and degree of accuracy (engineering quantities, performance, nce, overall overall behaviourbehaviour, etc), etc)

2. What conditions are known? 2. What conditions are known? ((freestreamfreestream conditions, overall conditions, overall geometry configuration, etc)geometry configuration, etc)

3. Choose suitable computational model: 3. Choose suitable computational model: decide domain decide domain representation and boundary conditions to apply; can we use 2D orepresentation and boundary conditions to apply; can we use 2D or 3D, r 3D, what grid topology is most suited, etc)what grid topology is most suited, etc)

4. Get values for appropriate physical parameters 4. Get values for appropriate physical parameters (density, (density, viscosity, etc)viscosity, etc)

5. Choose suitable physical models: 5. Choose suitable physical models: is the flow is the flow inviscidinviscid, laminar or , laminar or turbulent, steady or unsteady, incompressible or compressible; iturbulent, steady or unsteady, incompressible or compressible; is heat s heat transfer, combustion, particle transport important?transfer, combustion, particle transport important?

PrePre--ProcessorProcessor

Sara C. Eicher

•• Geometry Geometry ModellingModelling

•• Mesh GenerationMesh Generation

•• Physical ModelsPhysical Models

•• Boundary ConditionsBoundary Conditions

•• Setup of Solution MethodSetup of Solution Method

ALICE

PrePre--ProcessorProcessor

Sara C. Eicher

•• Geometry Geometry ModellingModelling

•• Mesh GenerationMesh Generation

•• Physical ModelsPhysical Models

•• Boundary ConditionsBoundary Conditions

•• Setup of Solution MethodSetup of Solution Method

ALICE

PrePre--ProcessorProcessor

Sara C. Eicher

•• Geometry Geometry ModellingModelling

•• Mesh GenerationMesh Generation

•• Physical ModelsPhysical Models

•• Boundary ConditionsBoundary Conditions

•• Setup of Solution MethodSetup of Solution Method

ALICE

SolverSolver

•• Input FilesInput Files

•• CalculationCalculation

•• Running TimesRunning Times

•• Monitoring Calculation Monitoring Calculation

ProgressProgress

Sara C. Eicher

PostPost--ProcessorProcessor

•• Results Manipulation and DisplayResults Manipulation and Display

•• Further AnalysisFurther Analysis

•• Report FindingsReport Findings

Sara C. Eicher

Errors and UncertaintiesErrors and Uncertainties

•• ModellingModelling ErrorsErrors

•• Discretisation or Numerical ErrorsDiscretisation or Numerical Errors

•• Iteration or Convergence ErrorsIteration or Convergence Errors

•• RoundRound--off Errorsoff Errors

•• Problem UncertaintiesProblem Uncertainties

•• User ErrorsUser Errors

•• Code ErrorsCode Errors

Sara C. Eicher

CFD Solving StepsCFD Solving Steps

Sara C. Eicher

GEOMETRY SETUP2D/3D MESH GENERATION

PHYSICAL MODELSBOUNDARY CONDITIONSMATERIAL PROPERTIES

ANALYSIS CONTROL PARAMETERS

CALCULATIONCONVERGENCE MONITORING

EXAMINE RESULTSDISPLAY DATA

FURTHER ANALYSIS

START

END

NO

YES

PREPROCESSOR

SOLVER

POSTPROCESSOR