CFD: What is it good for?

Transcription

1 CFD: What is it good for? Tom O Mahoney TNO Fluid Dynamics

2 Introduction to CFD

3 CFD - Computational Fluid Dynamics Computational the using of computers to simulate the physics of fluids Fluid Either gas or liquids Dynamics changes in time Usually CFD is used to refer to the simulation of fluid dynamics using finite volume methods (described in next slide) and not more reduced or simplified models

4 Computational Fluid Dynamics finite volume methods Take the simulation area and divide it up into small cells / boxes (called volumes) just like in FEM (but for where the fluid is) On the boundaries of the whole area say what the fluid is doing Say under what conditions the fluid starts Use the principles of conservation of mass, momentum and energy to determine how the fluid changes with time Mass Momentum - in Energy Mass Momentum - out Energy + change

5 What makes a CFD person? Knowledge of fluid dynamics Equations of motion Dominant forces for the situation at hand Knowledge of numerical methods Accuracy, stability of numerical algorithms Numerical treatment of physical models Knowledge of the programs / CFD software FLUENT, StarCCM+, CFX, OpenFoam, Xstream, Comsol CAD and meshing software

6 First application Internal flows in turbomachinery Large-Eddy Simulation of Ingestion of Hot Annulus Gas in Turbine Rim Seals

7 Rolls-Royce - Trent 1000 Bypass Fan Low pressure turbine Intermediate pressure turbine Intermediate pressure compressor High pressure compressor Combustion chamber High pressure turbine

8 What is the problem? Temperatures in the turbine are very high ( ºC) The higher the temperature the more efficient the turbine But the temperature is higher than the melting point of the metal!! Metal has to be cooled, reduce thermal stress because the mechanical stress is already high (12,000-15,000rpm) Plane doesn t fall out of the sky! (the turbine last longer without having to be maintained / replaced)

9 Simulation of a turbine cavity for a jet engine Stationary Rotating

10 The actual CFD domain Stationary Rotating The cavity region between the discs

11 Setting the boundary conditions Inlet NGV Hot flow Rotor Blade Outlet Ingress flow Egress flow STATIONARY PART ROTATING PART TURBINE DISC Inlet Cool flow Too much ingestion has severe detrimental effect on turbine disc life

12 Results - turbulence Frames at same time but position changes in flow direction

13 Results - ingestion Model name Large-Eddy Simulation Unsteady RANS Two different models give very different answers

14 Second application Multiphase flows in process machinery Slug flow in a pipe with bends

15 Shell - Process installation There are lots of pipes

16 Experiments at TNO Sharp bend Water / air system Measuring pressure along the pipe Measuring force on the bend Visualise flow regime

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19 Creating a CFD mesh

20 Results volume fraction of water It is very difficult to model the fast changing interface using CFD

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22 Results effect on the pipe structure Also calculate the displacement or bending of the pipe

23 Result comparison of forces Blue is the experiment and red the simulations

24 CFD: Do it - yourself CFD with open source software OpenFoam

25 Download and install Ubuntu This is best

26 Run a terminal Type the commands in Useful commands: ls list directory contents mkdir make directory cd <name> - go to <name> cd../ - go down a directory rm <name> remove a file rm r <name> - remove folder cp <name> <new-name> - copy file

27 Download and install OpenFoam (and parafoam) Follow these steps in an Ubuntu terminal

28 Go to a tutorial directory and run a case A case directory has folders 0, system and constant All tutorials are set up so that you should be able to create the mesh: Type blockmesh <enter> And then to run the solver Type icofoam <enter> Finally open the results in paraview: Type parafoam <enter> Note: the solvers vary, could be simplefoam, pisofoam etc.. Note also: some tutorials don t work like this, best to look in the incompressible folder

29 Look at results in parafoam

30 That s CFD in a nutshell