Laminar. transient forced convection problem over a 2D backward facing step (BFS) at an inlet Reynolds number (Re) of 400 is investigated numerically using OpenFOAM. To increase the Nusselt number (Nu) along the bottom wall. active flow control is applied by zero-net-mass-flux (ZNMF) combinations of suction and injection through three thin slits which are placed on the top. https://chefesquipmenters.shop/product-category/bowls/