# Simulating a rotary blade: Geometry Subtraction in sliding mesh vs moving frame

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 December 30, 2021, 08:58 Simulating a rotary blade: Geometry Subtraction in sliding mesh vs moving frame #1 New Member   Sardar Join Date: Dec 2021 Posts: 4 Rep Power: 3 (Chances are this is a question more fitting the geometry and meshing forum, but I decided otherwise.) I am somehow new to the fluent. and am trying to simulate a rotary impeller in a mixing tank. I have two zones: "tank_body" and the "rotary_zone". I can see online that two methods are available: first "moving/soliding mesh" and, second "moving frame." Q1. Online videos suggest that when sliding mesh is chosen, the rotor volume should be subtracted from the surrounding rotary zone. But what about the moving frame method? It looks like if the frame method is chosen,the blades' volume is NOT subtracted from the "rotary zone", apparantly because the blades are going to be given a zero rotational velocity with respect to the moving frame surrounding the blades. Q2. Can I NOT subtract the blade volumes from the rotary zone, and at the same time use the moving mesh method? Thanks. Any help is very much appreciated as I am single-handed and working for a tight deadline.

 December 31, 2021, 10:33 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,111 Rep Power: 60 If we're talking about the same tank with an impeller in it and nothing else, the geometry and mesh for both methods are the same. Only when you try to model systems of parts do things become different, because then you have regions of moving things and regions of not-moving things to worry about. You always have to subtract the impeller. You are doing CFD, having a mesh of the solid doesn't get you anywhere. SardarMech likes this.

 Tags frame motion, rotor blade, sliding mesh method