FASTER THAN SOUND

Dominion, Volume 26, Issue 220, 13 June 1933, Page 3

FASTER THAN SOUND

Speed of Turbine Blades

If you could sit on the end of one of the low-pressure blades of a modern high-capacity steam turbine when it was in operation, and someone exploded a firecracker behind you. it wouldn’t scare you in the least. Indeed, you’d never even hear it, for you would be going so fast the sound would never reach you. Such blades in some of the larger turbines travel at the rate of 13.8 miles per minute; considerably faster than the speed of sound in air! says a writer in “Power Plant Engineering” (Chicago). •’Waturally, when travelling at this speed, anything that may strike the blades, particles of water or solid matter, causes terrific erosion. Even gases; a rotor operating at this speed in air at ordinary pressures would heat to a red heat in a short time because of the friction of the air. A small stream of water directed across the path of the blades, it is said, will wear them through in a matter of minutes.

“In practice, of course, these blades travel practically in a vacuum. The steam which keeps them moving travels at speeds only slightly higher, so that the relative speed between blade and steam is small. But, even so, if there are impurities in the steam, or if water particles are present, the blades are subject to erosion, and, In practice, this constitutes one of the serious problems. “This question of turbine-blade erosion is one with which all power-plant operators are concerned.

“In steam turbines, the problem Is to keep water away from the blades, but in hydraulic turbines we want to keep the water in contact with the blades as much as possible. Well, at Hoover Dam they will have plenty of water to work with, the whole Colorado River, in fact. Work on this stupendous project is proceeding rapidly, and the construction of the power plant has now been started.”