Imagine drilling a large diameter hole in two passes - pilot hole & hole opening.
When you drill the pilot hole you will end up with a large size difference between the ID of the pilot hole, and the ID of the previous casing string.

How to optimise flow rate in this scenario to ensure good hole cleaning?

High flow to satisfy uphole velocity inside casing is likely to over-pressure the pilot hole. Optimal flow inside the pilot hole is likely to be insufficient to lift cuttings inside the casing section.

I would like to hear form you what solutions you would come up with, and what practices you have come across to deal with this situation (e.g. retievable liner casing, parasite strings, bleed off subs, modified fluid rheology, drill string design, etc.).

Thanks for your input!