Hello Ramya,
The design max tip speed of the IEA Wind 15-MW is 95 m/s. At standard atmospheric conditions, that is already a Mach number of about 95/340 = 0.279. So, it is quite reasonable that the relative velocity of the incoming flow at the tip can exceed Mach 0.3, especially in the floating case where we have seen some rotor over-speeds in the controller sometimes.
Hope that helps,
Garrett