[Rana abdo]

If i have a rough solid plate geometry with length 1.5 m having micron peaks and vallys on it how can i mesh the micron peaks and vallys without having too many cells i choose a mesh size of 0.0001 m but i need to capture even the smallest peak and vally is there another way of meshing such geometry
I am using ansys fluent meshing.

[flotus1]

You can not explicitly simulate roughness with such a difference in length scales.
Depending on what you are interested in, either decrease the extent of your simulation model. Or look into wall roughness modeling for turbulence.