This is my first post here. Please kindly help me with this issue.
I am doing a simulation of an axial compressor of a gas turbine engine. It is the gas turbine used in a power plant, hence it is huge and high air mass flow rate around 340 kg/s and hence the flow inside is a sonic flow.
I have chosen the Mixing Plane method to model my problem. Therefore I only need one blade from each stage. There are 6 stages (rotor + stator) hence total number of blade is 12 blades + 1 IGV blade.
However, since the problem of interest is very similar to the Mixing Plane tutorial provided by ANSYS FLUENT.
Normally, there exists a small gap between the rotor blade tip and its outer casing (rotor tip clearance). However, such gap does not exist in the geometry provided in the FLUENT tutorial. The rotor blade is basically connected to rotor hub and rotor shroud at its root and tip, respectively.
In setting the boundary conditions for each of these walls;
Cell zone condition >>> rotor is defined as one separated zone that rotates (rotating/moving frame of reference) while stator is another separated zone but is fixed in space (inertial frame of reference)
Boundary conditions >>> rotor blade and rotor hub are walls which rotate. So, they are defined as stationary walls (with respect to the rotating frame of reference) This totally makes sense to me.
The problem arises when setting up the boundary condition for the rotor shroud (or the outer casing). Of course, in the real compressor, this wall is NOT rotating and fixed in space. The tutorial suggests defining it as a moving wall with respect to the ABSOLUTE frame and set the rotational velocity at 0 rpm. This way, the rotor shroud will be fixed in space >>> which totally makes sense to me, again.
However, thinking about the actual geometry (the 3D cad) given, the rotor blade tip is connected to the rotor shroud..... but in setting up the boundary conditions for them, rotor is rotating, while the shroud (which is connected as the same entity) is not allowed to moved. How does this happen? It does not make any sense to me. Could you kindly clarify this to me?