Fluent meshing
 

Hello
I'm new with ansys and CFD.
And i'm trying to do a flow simulation with fluent+fluent meshing.

Question1:
I want to know is there anyway to know/calculate how to choose meshing parameters (like facesize, body-size values or something like smooth transition and number of boundary layers etc.)for a specific geometry?

More detailed description:
For example
My geometry is a direct perfusion bioreactor which the scaffold(a porous zone) is embedded in it.(attached picture)
In this case
The porous zone is where the greatest gradient occurs and the most important area in this simulation.So i decided to do a face mesh on whole faces + a body mesh on the porous zone but i don't know what will be the proper size (target mesh size).so i just picked 1 for face-size and 0.0005 for the porous body.
As you can see there is no logic and knowledge behind my choices .
So i will be really really grateful if someone explain this or introduce a good source (video, tutorial, book,...) to learn.
Link of the picture of my geometry (front cross section) :https://ibb.co/gvVwQ6H

Question 2:
Is there anyway to know that what is the optimum/maximum cell numbers in a mesh inorder to avoid system (loptop) crash?

Software information:
Ansys fluent with meshing 2021 R2
Hardware information:
Intel core i7 (4th), 8

Thanks in advance

To make a suitable mesh you want probaly know characteristic size of phenomena you are tryuing to simulate.

so the mesh size should be small enough to represent these phenomena.
Models are you going to use plays significant role either, for example heat transfer from fluid to wall:
1. In case you want to accurately get boundary layer -> usually you want refine mesh alot near the wall to have several finite volume per thickness of boundary layer
2. On the other hand you may use one wall treatment model -> in that case finite volume could be bigger that the thickness of boundary layer

Optimal mesh is a mesh small enough to represent your model with a certain accuracy (which is defined by you)
Max number of finite volumes depends on avaliable RAM and time you have to spend on computation.

Experiences are matter
 

Hi, Tara
In addition to dear Alexander's answer, It depends on the essence of the phenomena for example simulating an ignition in a combustion chamber is different from a simple flow over a plate, So you have to rich to these orders with experience in your related field.
All the best,
Arash