For example, some wind tunnels are powered using flywheels (c.f. high enthalpy wind tunnel F4 from ONERA in France is using a 15 tons flywheel to get the neces

For example, some wind tunnels are powered using flywheels (c.f. high enthalpy wind tunnel F4 from ONERA in France is using a 15 tons flywheel to get the necessary power).