Very large diag coeff matrix=removed value?
 

Hi,

I'm trying to solve the flow past a square cylinder using the fractional step. For the poisson eqn (or momentum), I need to do something abt the cells occupied by the square cylinder.

One of my mtd is to make the coefficient of the diagonal coefficient of those cells very big hence their values will never change.

Another way is to restructure the system of equations to exclude the cylinder's cells. Hence, for a simple 3X3 (9) cells, we will orginally get a 9X9 matrix to be solved. If the centre cell is removed, we will get a 8X8 matrix instead.

I tried the 2 mtds and found that the answers are different. Should that be so? And is the second mtd a better one for the square cylinder problem?

Thanks in advance