When at a velocity inlet I decide to use 'Intensity and Hydraulic Diameter' as the Turbulence Specification method ...

What does the Intensity value mean ? If I change the intensity from 5% to 10% how is it going to affect my solution?

Turbulent intensity is measure of fluctuation in average velocity due to tubulence in flow, and is written as:

TI = sqrt((u'^2+ v'^2+w'^2)/3)/Uinf

These are time averaged velocity . this value would have influence on boundary layer...

This means that how much fluctuation you're assuming at the inlet/outlets....

If use high value then it would have effect of convergence, use it deligently to get converged solution.... solve at 5% and compare the results at 10%, check your output variable, how it changes.... this would depend on mesh density....

Get convergence with low disturbance and increase the disturbance if required....

thank you ashu. that certainly helps