Can anyone give me a clear definition on y+ and negative cell volume.

Ashok

y+ is the adimensional normal distance from de wall

y+ = f(rho, mu, tao_w, y)

rho, density (kg/m^3) mu, viscosity (kg/s*m) tao_w, shear strain in the wall (kg/s^2*m) y , normal distance from de wall (m)

y+ = sqrt(rho*tao_w)*y/mu

for example the transition from de sub-viscous layer to the logaritmic velocity profile near the wall is when y+ is near 11

if you want to define the sub-viscous layer you need y+ for the first node close 1,

if you want to use wall function, maybe with y+ for the first node close to 20 is ok

A negative cell volume is not good, you need to check the mesh, I don't now how fluent calculate the negative volume but I sure that it's wrong.

good luck happy new year