POLYFLOW - Trajectories for a transient flow in a deforming domain?
How can one obtain and display particle trajectories for a time-dependent flow calculated on a deforming domain? A typical situation of relevance can be found e.g. for the flow around a rotating screw.
A short cook book for a POLYDATA session in order to calculate traectories...
In a new POLYDATA session, after reading the mesh file, create a new task and select
- MIXING task
- Time dependent problem
This will lead to a main menu for a MIXING task, where several attributes have to be specified.
- Identify the flow domain
- Select the appropriate boundary type (inflow, outflow, or non-penetrable border)
- Definition of the velocity field. This will open a menu as shown in the image Trajectories_Figure_1 below. Here, select:
* Continuous transient flow for a linear interpolation in time
* Automatic selection of result files
* Modify the time step [enter here the time step of the transient simulation - Note that the transient simulation must have been performed with a constant time step]
* Modify the prefix of the result file [enter here the relative path and name of the `res` files to be read - note that the browser is not available here!]
* Modify the number of result files
* Modify the first result file ID [it may differ from 1]
- For the generation of material points, select the entries or the whole domain in accordance with the physics involved and type of statistics. For example, the generation zone can be a box or the whole flow domain for a transient flow in a closed domain, while it can be the inlets for a transient flow through an open domain.
- Parameters for the tracking
* Modification of TMAX: this is the upper-limit for time integration; in other words the tracking of a particle trajectory will be performed until TMAX or until the corresponding particle has left the domain through an exit.
* Modification of VNORMAX: this value is used for scaling purposes; a reasonable order of magnitude should be given.
- Storage of the results. This will open a menu as shown in the image Trajectories_Figure_2 below. Here select storage of the calculated results vs. time or displacement according to the physics of the flow and the type of analysis to be performed. Accordingly, the value of the time step or displacement has to be entered.
At this point, the POLYDATA session can be terminated, and the data file can be saved.
Before running POLYFLOW for the calculation of trajectories, it may be interesting to make sure that they will be created in a format that can be displayed in FieldView. For this, add the keyword FVPARTICLES in the .p3rc file to be invoked when calling POLYFLOW.
The example 37 from the Examples manual describes a complete session dedictaed to a 2D transient flow on a moving domain. Other examples can be examined.