[Shamoon Jamshed]

I am doing a research in separated flows for which the candidate geometry is Backward facing step. I am using Fluent solver and I have to do Z-DES or Hybrid RANS/LES. I have made the grid well-refined in the separated region and defined it as zone 1 and the far-field and upper regions as Zone2.

The problem is with "How to define Interface?" I have right now defined interface using a line (I am using 2d geometry right now) and created interface. This interface asked me the options of (coupled wall, matching and mapped) of which I selected matching. Initially I ran RANS all over the two zones and after convergence I switched to DES with k-omeg SST. Then I selected WMLES for zone 1. I am considering zone1as LES zone.

Questions
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1. Is this my whole approach correct?
2. Before you switch to DES you need to initialize velocity flow-field, how can I define it only in Zone 2. Right now Fluent is not asking me to do any thing in zone 2 only, its just initializing all over.