[Nek5000-users] mixed Velocity BC's

[nek5000-users at lists.mcs.anl.gov]

Hi Andrew,

At present, this can be done with Pn-Pn-2, which allows
specification of traction boundary conditions.

One issue is that an arbitrary surface is fundamentally different 
than an aligned one because the constraints U.n = 0 and U.t_i = tau_i
couple the components of U=(u,v,w), meaning that these velocity
components must be solved in a single Helmholtz solve instead of
as 3 independent ways.   The stress formulation takes care of this.
It should be possible to do this in the Pn-Pn formulation as well,
but we're not there yet.  One possibility might be to use a high-order
explicit prescription of the boundary condition. (I'd have to think
about that a bit...)

Paul



On Fri, 31 Dec 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Ultimately I'd like to be able to do this on any general surface.  Basically, impose a slip velocity in the streamwise direction with a specified gradient (so w_y=0 and u_y=const in a y-plane), no penetration in the wall-normal (v=0).
>
> Thanks,
> Andrew
> On Dec 31, 2010, at 9:29 AM, nek5000-users at lists.mcs.anl.gov wrote:
>
>>
>> Hi Andrew,
>>
>> On what type of surface do you want this?  (z plane?, y plane?...?)
>>
>> Also, if y-plane, wouldn't it be:
>>
>>   v=0
>>   w_y = 0
>>   u_y = const
>>
>> ?
>>
>> (Or am I totally missing what you're trying to do ?)
>>
>> Cheers,
>>
>> Paul
>>
>>
>> On Thu, 30 Dec 2010, nek5000-users at lists.mcs.anl.gov wrote:
>>
>>> Howdy Neks,
>>>
>>> Has anyone tried or know how to implement a mixed velocity BC?  Such
>>> as v=w=0 and du/dy=const?
>>>
>>> Thanks
>>> Andrew
>>>
>>> --
>>> Andrew Duggleby, Ph.D. '01
>>> Assistant Professor
>>> Department of Mechanical Engineering
>>> Texas A&M University
>>> College Station, TX  77843-3123
>>>
>>> 109 Engineering Physics Building
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