I am an aerospace Engg student.I have to simulate flow past two buildings in tandem arrangement.i m using standard k-epsilon model.flow in coming in through one face where velocity-inlet condition is specified.in other 4 sides of the domain is specified as outflow B.C.in the walls the standard wall function is activated.i have taken around 9 lakhs os hexahedral cells.the domain dimensions are 20x12x8.the building dimensions are 0.5x0.5x1 & 0.5x0.5x2.the under relaxation factors r 0.7 for pressure & 0.3 for momentum.i m using steady segregated solver for 3d. the problem is that after say 500 or 100 iterations the residuals start to oscillate & reverse flow through the outflow boundary takes place, though initially they monotonically decreases.can u suggest any remedy? Swagata

Hi Swagata,

Rather than declaring outflow consider using pressure outlet. This should fix the problem.

Regards

Rajit