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Boundary layers mesh

Posted Feb 23, 2012, 1:40 p.m. EST MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Microfluidics, Mesh Version 4.3 3 Replies

Mohamed Zanaty
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Hello all,

My main question is related to "Boundary layers" in meshing for laminar flow physics?
As I understand, Boundary layers are needed when we got a high velocity gradient touching our moving surface. This is the case for turblent flow. But, for laminar flow, why do we need boundary layers in the mesh ?
Does the automatic generation of boundary layers by COMSOL mesher means that we need the these layers for our simulations or I could simply remove it from my mesh?

Thanks in advance
Regards,
Mohamed
3 Replies Last Post Oct 10, 2012, 7:36 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 23, 2012, 3:03 p.m. EST
Hi

boundary layers are interesting along all boundaries across which you have strong gradients, particularly for diffusion type equations. Even in laminar flo, along a no-slip boundary you have a rather strong gradient of the velocity, ending at U=0 on the boundary. Therefore COMSOl always proposesby defult boundary layers, for the CFD on such no-slip (and perhaps many others haven checked all cases) boundaries. And this also in laminar flow.

Personally I use boundary layers also in HT transient analysis between material with very different heat diffusiviies, or along boundaries with constant T, where I have a very different initial condition in the material (again essentially for transient solver cases, far less critical for steady state solving))

--
Good luck
Ivar
Hi boundary layers are interesting along all boundaries across which you have strong gradients, particularly for diffusion type equations. Even in laminar flo, along a no-slip boundary you have a rather strong gradient of the velocity, ending at U=0 on the boundary. Therefore COMSOl always proposesby defult boundary layers, for the CFD on such no-slip (and perhaps many others haven checked all cases) boundaries. And this also in laminar flow. Personally I use boundary layers also in HT transient analysis between material with very different heat diffusiviies, or along boundaries with constant T, where I have a very different initial condition in the material (again essentially for transient solver cases, far less critical for steady state solving)) -- Good luck Ivar
Gareth Ward
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Posted: 1 decade ago Oct 10, 2012, 5:57 a.m. EDT
Does anyone have any suggestions for joining a boundary layer mesh to a regular tetrahedral mesh. I have an acoustics model which contains a narrow pipe where the thermoacoustics model is implemented but is mostly free space. The boundary mesh seems sensible for modelling the interaction of fluid with a boundary layer but it won't mesh with the remaining space.

Alasdair
Does anyone have any suggestions for joining a boundary layer mesh to a regular tetrahedral mesh. I have an acoustics model which contains a narrow pipe where the thermoacoustics model is implemented but is mostly free space. The boundary mesh seems sensible for modelling the interaction of fluid with a boundary layer but it won't mesh with the remaining space. Alasdair
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 10, 2012, 7:36 a.m. EDT
Hi
Often a boundary layer goes all the way out to the outer edge of your model (to the in-out-lets), if you need to continue the mesh from there for another physics, you might get around by using a mesh "convert" (to tri) on the in-out-let boundaries, or you might use assembly mode but that is rahter heavy to define all the pairs

--
Good luck
Ivar
Hi Often a boundary layer goes all the way out to the outer edge of your model (to the in-out-lets), if you need to continue the mesh from there for another physics, you might get around by using a mesh "convert" (to tri) on the in-out-let boundaries, or you might use assembly mode but that is rahter heavy to define all the pairs -- Good luck Ivar

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