# Alternative boundary treatment on cell-centered scheme

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 3, 2013, 10:12 Alternative boundary treatment on cell-centered scheme #1 Member   Dokeun, Hwang Join Date: Apr 2010 Posts: 71 Rep Power: 7 Dear all I used ghost cell concept for euler solver but confused how can I compute gradient of flow properties at boundary face for viscous flux. Because I need gradients of velocity and Temperature at ghost cell for face centered properties, but I have no idea about this. For your understanding I'd like to use modified gradient described in Blazek's Is there any alternative or breakthrough?

July 3, 2013, 11:35
#2
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 1,612
Rep Power: 23
Quote:
 Originally Posted by dokeun Dear all I used ghost cell concept for euler solver but confused how can I compute gradient of flow properties at boundary face for viscous flux. Because I need gradients of velocity and Temperature at ghost cell for face centered properties, but I have no idea about this. For your understanding I'd like to use modified gradient described in Blazek's Is there any alternative or breakthrough?

In a FV method is quite natural to prescribe the flux at a boundary. FOr example

mass:
zero flux on a not-permeable wall, prescribed flow rate on inflow, etc

momentum:
zero convective flux a not-permeable wall, prescribed flux for fixed flow rate. The diffusive flux is imposed such that the velocity on a boundary is prescribed, for example, at first order, a normal derivatives of the velocity on a wall is
mu*du/dy|wall -> mu * (u(wall+1) - u(wall-1))/(2*dy) = mu*u(wall+1)/dy

temperature:
quite natural if you have adiabatic or fixed heat flux q = -k*Grad T

and so on ...

July 11, 2013, 09:59
#3
Member

Dokeun, Hwang
Join Date: Apr 2010
Posts: 71
Rep Power: 7
Quote:
 Originally Posted by FMDenaro In a FV method is quite natural to prescribe the flux at a boundary. FOr example mass: zero flux on a not-permeable wall, prescribed flow rate on inflow, etc momentum: zero convective flux a not-permeable wall, prescribed flux for fixed flow rate. The diffusive flux is imposed such that the velocity on a boundary is prescribed, for example, at first order, a normal derivatives of the velocity on a wall is mu*du/dy|wall -> mu * (u(wall+1) - u(wall-1))/(2*dy) = mu*u(wall+1)/dy temperature: quite natural if you have adiabatic or fixed heat flux q = -k*Grad T and so on ...
Dear FMDenaro.

Thank you for your kind reply with example.

I guess I understood your explanation. But I'd like to be checked the thought below and get some more about boundary condition.

Quote:
 Supersonic inlet [gradients are zero]Inviscid flux directly obtained on boundary Viscous flux needs only care about heat conduction terms, Supersonic outlet[gradients are zero]Inviscid flux directly obtained on boundary Viscous flux needs only care about heat conduction terms, Inviscid wallInviscid flux need only care about pressure at wall Viscous wallViscous flux needs only care about heat conduction terms, Subsonic inletInviscid flux use (*) Viscous flux ?? Subsonic outletInviscid flux use (*) Viscous flux ?? (*)'Three-Dimensional Unsteady Euler Equations Solution Using Flux vector Splitting'. AIAA Paper 84-1552
I have no idea how can I dealing Viscous flux for subsonic inlet/outlet.

How can I implement viscous flux for subsonic boundary condition?

Thank you in advance

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post rietuk STAR-CCM+ 8 February 27, 2013 05:50 ARC Open Source Meshers: Gmsh, Netgen, CGNS, ... 0 February 27, 2010 11:56 AB CD-adapco 4 October 28, 2004 13:04 Confused. Main CFD Forum 9 August 29, 2003 13:54 vineet kshirsagar Main CFD Forum 1 January 13, 2002 02:46

All times are GMT -4. The time now is 01:13.

 Contact Us - CFD Online - Top