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Thermal Gradient Testing

The Issue

The flow path or outer flow annulus of a gas turbine engine experiences continuous temperature changes. This results from the work done during compression and from the energy added during combustion and expansion of gases through the turbine stages. These flow path temperatures determine the metal temperatures of each disk rim.

Simultaneously, the secondary flow systems tend to maintain disk bore temperatures at more constant levels to prevent excessive rim growth and lowering of the disk material properties.

Why It Matters

At the mid stages of the high compressor, rim temperatures become high enough relative to the bores to create significant radial thermal gradients. These gradients induce thermal hoop stresses that become a significant percentage of the overall disk stress.

In the extreme case, the thermal stresses induced in a high pressure turbine disk rim can override the hoop stresses caused by rotation. In the case of drum rotors, axial thermal gradients exist along with the radial gradients of the individual stages, which tends to add bending stresses at critical welded or bolted interfaces.

What You can Do

By conducting spin tests at a temperature that simulates the stress state a component would be exposed to under operating conditions, test data is more valid and useful than for spin tests conducted at ambient temperature.

For these reasons, spin testing of any hot section disk should include testing with the proper radial thermal profile applied, either as a constant gradient or synchronized with speed.

How Test Devices Can Help

Test Devices has experience and expertise applying both radial and axial gradients through multi zoned ovens with heating and cooling capability at each zone. In addition, other data, such as radial growth and strain measurements, can be taken to validate structural models under both rotational and thermal gradient conditions.

This combination of test features offers the best approximation of the operational gas turbine environment, making Test Devices Thermal Gradient Testing an ideal component of a turbine engine development program.

NEW: Thermal Mechanical Fatigue Testing

Test Devices has run a successful demonstration test of Thermal Mechanical Fatigue (TMF) testing, which synchronizes the temperature gradient with engine speed in real time. Compared to constant gradient testing, TMF creates a more realistic test environment by simulating operating conditions to a much higher degree.