## Ansys Products

Discuss installation & licensing of our Ansys Teaching and Research products

#### Discrete Phase Model Settings (Steady State)

• Andrew Roberts
Subscriber
Hi,

I am looking at this:

• I wondered if you could tell me the equivalent timestep and number of timesteps (unsteady settings) for the tracking parameters, if I set max. number of steps = 50,000 and step length factor = 5 (steady settings)?
Alternatively:
• What is the meaning of the step length factor = 5? Is it the same as a maximum cell-based Courant number = 0.2?
• What is the meaning of max number of steps - is this like the number of timesteps where the timestep is the one limited by the maximum cell-based Courant number?
• Rob
Ansys Employee

It's all covered in the User's Guide and/or Theory Manual. Basically, those settings are to govern how many times (maximum) the particle trajectory & position are checked/updated per cell and in total. The Numerics are also responsible for the number of times it's checked per cell to make the calculation more efficient: I suggest not messing with most of those without a good understanding of what they mean.

• Andrew Roberts
Subscriber

If it is checking like Courant Number: what is the timestep that would be used? (is this set to unity) - I couldn't find the answer in the guides. So the particle is checked N times (step length factor) according to the ratio of the cell velocity and cell size only?

• Rob
Ansys Employee

More or less, the trajectory (using the above panel) would be checked up to 5 times in a cell, probably less if accuracy control determines not much is happening.  https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/flu_ug/flu_ug_sec_discrete_use_oview.html

After 50,000 checks the parcel would be shown as incomplete if still in the domain.

• Andrew Roberts
Subscriber

So, it doesnt have synchronous physical time, in other words it is possible for the particles to exist at different points in time within the same domain?

Step length factor = Number of Lagrangian steps per Eulerian step (cell size)

Physical Lagrangian time (seconds) could be anything between 1 and 50,000 x (velocity/cell size) x step length factor

• Rob
Ansys Employee

With steady the total trajectory is what is seen. The particle has a flight time, and can exchange mass/energy/momentum with the cells. Hence the volume fraction limitations.