So, in order to apply "slip" and "atmospheric pressure" BC's at my top patch and "neglect" the air-water interaction I must extend my domain in the vertical direction?, also u said that the cavity length maybe is not a problem but I feel that these phenomena are very unphysical as I expect longer cavity's for much faster flows (bigger Reynolds number at the inlet patch), also does anyone know where can I get more information about BC's for k, epsilon, and omega for this type of situations?, Thanks for ur help!