Rotating blades like this should never go beyond the critical Mach number where local airflow on the blade upper surface reaches Mach 1.0 (about Mach 0.8ish).

Rotating blades like this should never go beyond the critical Mach number where local airflow on the blade upper surface reaches Mach 1.0 (about Mach 0.8ish). The shockwaves that form are attached to the surface and like to shift around with slight changes in conditions, which cause awful vibrations. I'd expect the blades to be braked in some way to never exceed critical Mach number.