A contained gravity current using openfoam
 

Hello everyone :)
i am doing my master thesis on reproducing a lab experiment of a contained gravity current using lock exchange concept. i am struggling in applying the k epsilon model as it is not giving me reasonable results at all using twoliquidmixingfoam solver.
my model is follow:
the lock separates the the ambient and lock fluids equally with 225 cm in length and 16 cm depth with different in density around 64 kg/m3. all boundaries are walls with noSlip condition for velocity except the upper boundary with slip condition as actually it is open air face in reality.
when using mesh size 1cm*1cm and i use wall function boundary conditions for k, epsilon, and nut the flow is damping so fast when using turbulent diffusion equals to zero. and when using alphatab equals to 1 the flow seems like it is not moving but after a while the alpha of the lock fluid starts to diffuse, like it is kind of mixing without any flow motion!! i dont know if it is clear or not but i cant interpret it to be honest.
so my questions are:
1. yplus at some point on the lower boundary approaches low values less than 1, so how to deal with such a situation ?
2. if the near wall region is not resolved sufficiently, it will cause any problems for the mean flow velocity like dissipating the mean kinetic energy and the flow will damp so more fast?

Reynolds number is around 49000 with mean velocity 0.31 m/sec