They bolt the blades to a heavy-duty table that vibrates faster than the eye can see. The setup subjects the blades to acceleration forces approaching 10 g, double what a racecar driver might experience when making a turn at a motorway.
The high-pitched whine in the video below, for example, is caused by a 20-inch blade made from a nickel super-alloy vibrating hard enough to displace the tip by up to a few inches for more than a million cycles.
Why is GE being so hard on this blade? Subjecting new components to extreme vibration helps designers make sure they will be able to handle extreme conditions.
Bert Stuck, general manager for GE’s power generation engineering component and development testing, says the test is meant to ensure that the part will be reliable in any situation a customer might experience.
Eventually, the team vibrates the blade to the point of failure. A pass in this test is equal to a break in the precise spot where engineers calculated it would be.
Vibration is just one of the many tests that Stuck’s team performs on newly designed components, before moving on to testing entire compressors and turbines.
(GE recently opened the world’s largest dedicated turbine test bed in Greenville. Since the test bed is not connected to the grid, it can do things to turbines that could otherwise destabilize or damage the power network.)
“We test [blades] to failure so we can determine what the design margins actually are, and make sure they match what we predicted,” Stuck says.
GE’s 9HA turbine is the world’s largest and most efficient gas turbine. It’s currently being tested in Greenville.