backward facing step

Hi dear all;

I am modeling fluid flow in backward facing step by finite volume formulation of LBM. But I have some problems with flow configuration.

I set Reynolds number as Re=(2U_aveH)/nu. where H is inlet channel high and U_ave is mean velocity at the inlet. (also expansion ratio is 2 and nu=(C_s^2)/3=Tau/3). but my results differ from previous valid results. i.e. the length of primary flow reattachment is smaller in specific Re number. also the 2nd reattachment appear in lower Re number (about 250 instead of 380) furthermore its length is not the same as previous results.

Can anyone direct me?