I am working on a flow model with a fan inlet and multiple outlet slots all located on the cover to a tank. The fan blows air down into the tank, and a gas mixture is expelled through the slots. The slots are set up with the Environmental Pressure boundary condition. Due to vortexing, air is drawn back into the tank through the slots. The initial conditions are set up such that there is gas inside the tank, and pure air outside. Since pure air is drawn in through the slots during vortexing, the gas concentration inside the tank drops too quickly. The vortexing is expected, so I don't really want to add longer ducts to try to eliminate it as it would add resistance and could skew the results.
Is there a way that I can set up the slots so that air can not reenter through them? It would be like a check valve with zero pressure required to open and zero pressure drop across the valve.