a small question about rotating frame
 

hi，developers and users:

I find a paragraph in your AIAA paper which describe the rotating frame in SU2.

5. Rotating frame and Arbitrary Lagrangian-Eulerian (ALE) formulations

When simulating fluid flow about certain aerodynamic bodies that operate under an imposed steady rotation, including many turbomachinery, propeller, and rotor applications, it can be advantageous to transform the system of flow equations into a reference frame that rotates with the body of interest.19,20,29 With this transformation, a flow field that is unsteady when viewed from the inertial frame can be solved for in a steady manner, and thus more eciently, without the need for grid motion.


You mentioned in the last a steady rotating simulation don't need grid motion.
However, in the rot_caradonna_tung rotating testcase you provide, in the config file:

------------------------ GRID DEFORMATION PARAMETERS ------------------------%
%
% Kind of deformation (NO_DEFORMATION, HICKS_HENNE, PARABOLIC, NACA_4DIGITS,
% DISPLACEMENT, ROTATION, FFD_CONTROL_POINT,
% FFD_DIHEDRAL_ANGLE, FFD_TWIST_ANGLE,
% FFD_ROTATION, FFD_CAMBER, FFD_THICKNESS, FFD_VOLUME)
DV_KIND= FFD_TWIST_ANGLE
%
% Marker of the surface in which we are going apply the shape deformation
DV_MARKER= ( quad_blade, tri_blade )



Why grid deformation still needed?

Tanks in advance.


Jin

Hi Jin,

You are looking at two quite separate things.

To solve rotating problems, SU2 has implemented the flow equations in the rotating coordinate frame. This formulation, which looks quite like the original flow equations but with additional source terms to account for fictional forces (centrifugal, Coriolis) allows for the steady state solution of problems with a fixed rate of rotation. This is useful for helicopter rotors, propellers, wind turbines, etc.

The option values you are looking at in the config file are related to grid deformation for the purpose of design. A typical problem that these values are used for is for finding the shape of an airfoil to minimize drag at a given lift. SU2 runs successive cases attempting to find such an optimal shape, and as the shape of the airfoil changes it is necessary to deform the grid to match the new shape.

Hope this helps,
Aniket