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Please don't use the Eulerian multiphase with DPM as the particles won't see the secondary phase(s). DDPM does that, but you probably don't need that.
For a steady flow and transient particle we assume the flow is altered by the particles (if interaction is on as you have set) but we move the particles with time. It's to save computational time, and you need to check carefully to ensure the particles reach a pseudo steady state. Read the theory guide - the maths will either make you sleep or explain everything!