Hallo Jack.
In dem "Fundamentals-Tutorial" (sollte auch auf
C:\Programme\Solidworks2008\Cosmos\Floworks\lang\english\docs als PDF
vorliegen) ist in dem Kapitel 22 bei den Validation Examples ein
schönes Beispiel zus sehen.
Kavitation entsteht meistens als Folge von Strömungsablösung bzw.
Strömungsabriss.
Mit Floworks kann man nun den Bereich, in dem Kaviation ENTSTEHT,
sichtbar machen.
Mögliche Gegenmassnahmen (im Ventilbau)
- Veränderung der Geometrie "Störkante"
- Einbringen eines Strömungswiderstandes und dadurch Erhöhung
des Druckniveaus auf ein unkritisches Niveau.
Hinsichtlich der Berechnung selbst hier noch ein paar Info's aus
der Knowledge-Base:
Cavitation
Cavitation is a common problem for many engineering devices in which the main working fluid is in liquid state. The deleterious effects of cavitation include: lowered performance, load asymmetry, erosion and pitting of blade surfaces, vibration and noise, and reduction of the overall machine life. Cavitation models used today range from rather crude approximations to sophisticated bubble dynamics models. Details about bubble generation, growth and collapse are important for the prediction of a solid surfaces erosion, but are not necessary to estimate the performance of a pump, valve or other equipment. In COSMOSFloWorks an engineering model of cavitation is employed to predict the extent of cavitation and its influence on the performance of the analyzed device.
Recommendations
If your analyze a flow of water in some points of which the local static pressure may fall below the liquid's vapour pressure at the local ambient temperature causing cavitation or if a localized boiling of water may occur in the water flow due to intense heating, it is recommended to select the Cavitation option in the Fluids dialog box of the Wizard or General Settings.
Cavitation area growths slowly during calculation and there is a risk that the calculation will stop before the cavitation area develops completely. To avoid this, always specify Global Goal of Average Density and increase the Analysis interval on the Finish tab of the Calculation Control Options dialog box up to 2.5 travels. Also make sure that the other finish conditions do not cause the calculation to stop before goals are converged. The easiest way to ensure that is to select If all are satisfied in the Value cell for the Finish conditions on the Finish tab of the Calculation Control Options dialog box.
To see the cavitation areas you can select density or the volume fraction of vapour as the parameter for visualization.
Limitations and Assumptions
The model has the following limitations/assumptions:
Cavitation is currently available only for incompressible water (when defining the project fluids you should select Water SP from the list of Pre-Defined liquids); cavitation in mixtures of different liquids cannot be calculated.
The properties of the non-condensable gas are set to be equal to those of air.
The temperature and pressure in the phase transition areas should be within the following ranges: T = 277.15 - 583.15 K, P = 800 - 107 Pa.
If the calculation has finished or has been stopped and the Cavitation option has been enabled or disabled, the calculation cannot be resumed or continued and must be restarted from the beginning.
The Cavitation option should not be selected if you calculate a water flow in the model without flow openings (inlet and outlet).
The model does not describe the detailed structure of the cavitation area, i.e parameters of individual vapour bubbles.
The fluid region where cavitation occurs should be well resolved by the computational mesh.
The parameters of the flow at the inlet boundary conditions must be such that the volume fraction of liquid water in the inlet flow would be at least 0.1.
Roland
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