Currently, I am using the MPPIC method to simulate coal gasification. I noticed that in the “Confusion about the CPL control method”, there are two options: “maximum” and“average”. I would like to know the differences between them and how to choose between the two. By the way, my fluidized bed is in a pneumatic conveying regime.
When specified, the CFL number is used to compute the time step at which the PIC loop is marching in time. Each parcel has a different velocity, but we can only have a common time step for all particles. We basically compute the CFL for each parcel, compare it with the specified CFL number and scale the time step to match the specified CFL. The options are to scale the time step based on either the maximum or average CFL number among all particles. Using the maximum i smore restrictive (smaller time step) but guarantees all particles will have a CFL less than or equal to the specified CFL. The average option allows the local CFL to be larger than the specified one. This can be appropriate if a few parcels move very fast in a dilute region.