I guess in the end it amounts to the same as having ALE on the entire domain, but you can do a combination of changing the inflow and adding fictitious forces on the flow. In this way you account for the accelerations explicitly using forcing terms (as opposed to ALE where you get the same "implicitly"). I guess it works, but you might get quite high accelerations further away from the axis. I remember we tried it at some point but I am unsure of the outcome. Philipp On 2018-08-21 17:30, [email protected] wrote:

Hi Harry,

One simple approach is to use ALE but to have the entire domain pitch,

thus preserving your mesh structure.

That would properly account for all the accelerations in your non inertial

domain.

The slightly tricky part would be to determine what BCs you need. �You

need to be careful about changing the character of the BCs (e.g., from inflow

to outflow) �in the middle of a computation because that changes which quantities

are prescribed and which are unknown. � Perhaps one approach would be

to have a circular domain with 3/4 of it Dirichlet and 1/4 being outflow (i.e.,

Neumann for velocity).

hth,

Paul

------------------------------------------------------------------------ *From:* Nek5000-users <[email protected]> on behalf of [email protected] <[email protected]> *Sent:* Tuesday, August 21, 2018 9:43:56 AM *To:* [email protected] *Subject:* [Nek5000-users] Rotating computational domain Hello Neks,

I am an undergraduate student new to Nek and I am working on a simulation studying dynamic stall in a dynamically pitching airfoil.� I want to do a pitch and hold simulation at low Reynold's number (Re = 12000) where I rotate the entire computational domain up to about 50 degrees AOA and then hold at 50 degrees, with steady inflow ux = 1.� I would like to rotate the domain about the z axis, which passes through the quarter chord location of the airfoil profile (modified NACA 0012).

Because of the steep AOA, I would like to stay away from pitching the airfoil within the stationary domain with ALE to avoid too much mesh deformation.� To this end, I have been scouring documentation to try and find a method of applying a rotational mesh velocity to the entire domain about the z axis while keeping the flow within the domain at ux = 1.� I am feeling very stuck.� Others have suggested applying a Coriolis force to the flow, but I don't really see how this would simulate rotation of the entire domain.� It seems to me that simulation of a Coriolis force would be acceptable to correct the flow field to always be ux = 1 inside a rotating domain, but I don't see how that would apply a mesh velocity anywhere.

Are there any examples where an entire computational domain is rotated that I can look at, or has anybody done similar work who can point me in the right direction?

Regards, -Harry

_______________________________________________ Nek5000-users mailing list [email protected] https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users

Hi Paul and Phillip, I have validated my model at constant AOA and am now returning to my pitch and hold scenario to do some work. I definitely think the ALE formulation applied to the entire domain is the way to go, but I'm feeling a little confused about the "mv" boundary condition. In the mv_wall example, the "mv" boundary condition is applied to the section of the wall that is moving, so in my mind it follows logically that to have the entire domain pitch about the z axis, the entire domain would need the "mv" condition. This doesn't seem possible while preserving my inlet and outlet BCs. I understand that for ALE to work appropriately, we need to match the normal component of fluid velocity to that of the mesh velocity at any boundary. Does this apply also to the inlet and outlet, or only internal fluid boundaries such as my airfoil? I am also looking at the mv_cyl and ocyl/ocyl2 examples, but these are in rea/re2 format and I cannot look at the element boundary conditions (forgive me, I'm still learning terminology so some of what I say is not 100% accurate). While looking through the example files, I see that the logical switch "ifusermv" is assigned in "usrchk" in some of the examples, and in one of the "usrdat" subroutines in others. I don't really appreciate the difference, is there one? I am building my mesh in ANSYS Fluent, and then converting the mesh to ASCII .rea format with mshconvert2, and then extruding to 3D and converting to rea/re2 format with n2to3. Before, I would scroll to the bottom of the .msh file and add Nek5000 BC flags to each boundary (i.e. adding an _W to wall, _O to outlet, and _v to inlet) before converting to .rea format, and this would successfully apply boundary conditions. However, when attempting to insert the _mv boundary condition on my wall, the boundary conditions in the .rea file are unchanged. Is there a better/more appropriate way to assign the "mv" BC when converting a mesh? On Tue, Aug 21, 2018 at 11:30 AM <[email protected]> wrote:

Hi Harry,

One simple approach is to use ALE but to have the entire domain pitch,

thus preserving your mesh structure.

That would properly account for all the accelerations in your non inertial

domain.

The slightly tricky part would be to determine what BCs you need. You

need to be careful about changing the character of the BCs (e.g., from inflow

to outflow) in the middle of a computation because that changes which quantities

are prescribed and which are unknown. Perhaps one approach would be

to have a circular domain with 3/4 of it Dirichlet and 1/4 being outflow (i.e.,

Neumann for velocity).

hth,

Paul

------------------------------ *From:* Nek5000-users <[email protected]> on behalf of [email protected] <[email protected]> *Sent:* Tuesday, August 21, 2018 9:43:56 AM *To:* [email protected] *Subject:* [Nek5000-users] Rotating computational domain

Hello Neks,

I am an undergraduate student new to Nek and I am working on a simulation studying dynamic stall in a dynamically pitching airfoil. I want to do a pitch and hold simulation at low Reynold's number (Re = 12000) where I rotate the entire computational domain up to about 50 degrees AOA and then hold at 50 degrees, with steady inflow ux = 1. I would like to rotate the domain about the z axis, which passes through the quarter chord location of the airfoil profile (modified NACA 0012).

Because of the steep AOA, I would like to stay away from pitching the airfoil within the stationary domain with ALE to avoid too much mesh deformation. To this end, I have been scouring documentation to try and find a method of applying a rotational mesh velocity to the entire domain about the z axis while keeping the flow within the domain at ux = 1. I am feeling very stuck. Others have suggested applying a Coriolis force to the flow, but I don't really see how this would simulate rotation of the entire domain. It seems to me that simulation of a Coriolis force would be acceptable to correct the flow field to always be ux = 1 inside a rotating domain, but I don't see how that would apply a mesh velocity anywhere.

Are there any examples where an entire computational domain is rotated that I can look at, or has anybody done similar work who can point me in the right direction?

Regards, -Harry _______________________________________________ Nek5000-users mailing list [email protected] https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users

-- Harry E. Werner IV Secretary Clarkson University SCUBA Club *Cell:* (716) 570-4023