[pankos]

Could someone to tell me what boundary conditions must be put at flat plate problem for laminar boundary layer?

I have solved the problem with below boundary conditions but i see a problem (incresment of density) at left lower corner at which connect the left boundary with symmetry plane.

Left boundary: specify: pressure, all velocities
upper boundary: same of left
right boundary: all gradients are zero
left lower (x<0): symmetry
right lower (x>0): viscous wall

[cfdnewbie]

sounds like you are overspecifying the lower left boundary, or you are having accuracy issues. a rise in density at that point means that you have created a stagnation point there, which is due to your flow coming from an Euler (symmetry wall) to a Navier Stokes (viscous) wall!

[panou]

No, i do not refer at stagnation point at connection of symmetry and wall but at start of symmetry plane (at left lower corner of domain).
As i see , some information of domain arrive here and after increse the density except of reflection of information.

[cfdnewbie]

Originally Posted by panou

No, i do not refer at stagnation point at connection of symmetry and wall but at start of symmetry plane (at left lower corner of domain).
As i see , some information of domain arrive here and after increse the density except of reflection of information.

Well, still, if you get a stagnation point (an unphysical one), you should check how the code sets the boundary conditions. Are they set twice at the point? Maybe there's a conflict, it sounds like you are over-constraining the flow there, e.g. what happens to the density in the symmetry BC routine?