1
2
6
5
4
3

Previous: Physical model set-up Up: Computation set-up Next: Numerical solution parameters

This is an automatically generated documentation by LaTeX2HTML utility. In case of any issue, please, contact us at info@cfdsupport.com.

Computation set up

 
  • Computation parameters are stored in dictionary system
  • File controlDict controls whole computation
  • Print the file on the screen:
    # cat $FOAM_RUN /pitzDaily/system/controlDict

     

    application     simpleFoam;

startFrom       startTime;

startTime       0;

stopAt          endTime;

endTime         2000;

deltaT          1;

writeControl    timeStep;

writeInterval   100;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;

functions
{
    #includeFunc streamlines
}
  • The block named functions in the rest of controlDict file will be discussed later on and for now can be erased.
  • Detailed description of controlDict file is in section [*]

     

OpenFOAM Training by CFD Support,   CFD SUPPORT,   info@cfdsupport.com    +420 212 243 883      © CFD support, s.r.o., Sokolovská 270/201, 190 00 Praha 9, Czech Republic

6
2
1
5
4
3

Next: Alternative formulation Up: Turbomachinery CFD Solver Previous: Center of mass of   Contents   Index

Water turbines - notes on calculations

Figure [*] represents a physical setting of a turbine casing with respect to a dam. Let us denote by $ \color{white} h$ the head, i.e. the difference between heights of water levels in front of the dam and at the back of it. Vertical distance between the center of mass of the inlet surface of volute and the high water level is denoted by $ \color{white} h_{In}$. Vertical distance between the center of mass of the outlet surface of draft tube and the low water level is denoted by $ \color{white} h_{Out}$. Finally, vertical distance between the centres of mass of inlet and outlet surfaces is denoted by $ \color{white} h_{IO}$.
11 1

Figure: General water turbine sketch. Physical setting of a turbine casing with respect to a dam. Water levels indicated.

We can see there are several simple relations among quantities just defined

12 1
13 2
14

To simplify calculations we usually considers water an incompressible fluid with no phase changes possible and we solve the well known equations, the conservation laws the fluid obeys.

Coservation of linear momentum is expressed by the Navier-Stokes equation. In this case (incompressible fluid, steady state) it can take the form

15
where $ \color{white} \vec{U}$ is a velocity field, $ \color{white} \nu$ kinematic viscosity, $ \color{white} \varrho$ density, $ \color{white} p$ pressure field and $ \color{white} \vec{f}$ is a force density of a gravitational field, given by ([*]). Conservation of mass is expressed by the continuity equation. In this case it takes the simple form
16
It remains to discuss boundary conditions for the equations mentioned above. For we usually do not know the inlet velocity field, we are about to prescribe pressure field for both inlet and outlet surface. At the inlet surface a total pressure is known and it is equal to hydrostatic one. With the use of formula ([*]) we can write
18
where $ \color{white} \vec{r}_{0,H}$ is a position vector of an arbitrary point of the high water level (plane). Since total pressure is defined as a sum of static and dynamical pressure
19
we can, by means of this definition ([*]) and formula ([*]), express $ \color{white} p$ at the inlet
21 1

At the outlet the situation is a little bit complicated. After the flow (with high total pressure) exits the draft tube it mixes with water (with low total pressure) surrounding the draft tube. We usually take simplifying steps and assume the static pressure of exiting flow equals the hydrostatic pressure of surrounding water, i.e. we write

22 1
where $ \color{white} \vec{r}_{0,L}$ is a position vector of an arbitrary point of the low water level. Described steps correspond to real physical setting. In a task like this we need to know not only the $ \color{white} h$, but even $ \color{white} h_{In}$ (optionally $ \color{white} h_{Out}$), i.e. a position of the turbine with respect to the high or low water level. Quantity $ \color{white} h_{IO}$ can be obtained from the given turbine casing geometry, of course.
Subsections
6
2
1
5
4
3

Next: Alternative formulation Up: Turbomachinery CFD Solver Previous: Center of mass of   Contents   Index

OpenFOAM Training by CFD Support,   CFD SUPPORT,   info@cfdsupport.com    +420 212 243 883      © CFD support, s.r.o., Sokolovská 270/201, 190 00 Praha 9, Czech Republic
1
2
6
5
4
3

Previous: blueDyMSolver – transient, incompressible Up: TCFD Solvers Next: redDyMSolver – transient, compressible
This is an automatically generated documentation by LaTeX2HTML utility. In case of any issue, please, contact us at info@cfdsupport.com.

redSolver - steady state, compressible

TCFD solver for steady state, compressible fluid flow is called redSolver. It was gradually developed during the time from the rhoSimpleFoam solver. In any matters the redSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, it can use MRF method, limits for variables can be specified and many other changes have been done.

OpenFOAM Training by CFD Support,   CFD SUPPORT,   info@cfdsupport.com    +420 212 243 883      © CFD support, s.r.o., Sokolovská 270/201, 190 00 Praha 9, Czech Republic