convection terms
 

Hello ~!
I am modeling a high speed electric motor with a internal two blades.
This model includes turbulence model for blades.
My problem is decreasing calculation time.
I am using Realizable k-e model, and segregated flow.
I don't want to change mesh cell number(#18,000,000)
To decrease calculation time, I thought Changing convection term, 1st order at initial to 2nd order at final. But I wondering this will be reasonable for solution accuracy and It is okay for my problems....
, Are there any Idea? please help me...........

I think there is no problem if you run with 1st order and then change it to second order.