Dynamic Spin Testing
Dynamic spin testing is a technique to investigate the behavior of blades on turbines or compressor rotors under the effect of strong centrifugal load. The body load on blades affects their resonance properties, corresponding modeshapes, and damping properties.
Dynamic spin testing puts a bladed rotator through the CF loads while exciting them at specified frequency – Simulating the loading condition the blades will actually see in service, then measures how it responds. A dynamic spin test can generate the data to characterize the blade dynamics properties, perform comparative assessment of damper designs, and study the details of how a blade (or a blade slot) accumulates damages. Test Devices by SCHENCK performs this work in Hudson, Massachusetts using patented dynamic spin rigs technology (DSR) developed in house. Ultimately a full characterization of bladed rotor behavior will require a module level test the component and subassembly level test such as DSR can be a more expeditious and economical tool for engineers to perform preliminary validation of the design changes or new concept before committing to a more time consuming and expensive step.
Bladed rotors for aero-propulsion systems, such as jet engine rotors, are designed to optimize the performance while minimizing the weight – The tension between designing a robust structure while using the least amount of material drives inherent challenges in designing cutting-edge aerospace components.
In blade dynamics and high cycle fatigue regime, many rotating parts and blade failures are caused by accumulation of thousands or millions of cycles that accumulates at the frequency of blade resonance, which the damage can accumulate rapidly and cause catastrophic failures – This is an important distinction from LCF damages which accumulate over much longer period of time driven by the engines operating cycles.
DSR is one of the most complex tests we offer in our services. The level of technologies and expertise involved in reproducing a controlled test environment, with advanced instrumentation to observe the part behavior throughout sets apart the dynamic spin test from a more conventional spin tests (spin testing services).
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What a Dynamic Spin Test Measures
In addition to typical spin test data (speed, drive shaft vibration, spin pit and test rotor temperatures), dynamic spin testing requires a layer of specialized data measurements to characterize the blade and disk dynamic behaviors – At minimum this type of testing will involve blade tip-timing system (BTT) and rotor strain gages. The BTT is a non-contact instrumentation which measures the variation in the timing of blade tip pass due to their dynamic response and derives the resonance frequency and the response level. The rotor mounted strain gages are often used as reference data to validate the BTT measurements and the FEA based results.
The missions for dynamic spin tests vary depending on customers’ needs, but below are the typical set of results using the DSR capabilities:
- Characterization of dynamic responses such as blade resonance frequencies, mode shapes, damping, mistuning and other properties.
- High cycle fatigue testing to establish the endurance limits and validate a Goodman diagram against measured behavior rather than analysis alone
- Combined HCF and LCF cycling within one program, so interaction effects between the two damage mechanisms are captured
- Crack propagation studies to track how a flaw grows once it has started
- Blade tip growth and deflection measurement at speed to confirm running clearances
In many cases because these objectives overlap, one test article can often can be used to generate several of these results, giving DSR approach a tangible cost and schedule advantage over other methods.
Tooling, Arbors, and Program Control
Almost every dynamic spin test requires customized spin tooling and exciter system setup. We offer engineering services to design necessary test hardware, select test instrumentations and perform analyses to reduce the risk and ensure successful test outcomes.
Work is performed under an AS9100 and ISO9001 certified quality management system, with ITAR registration in place for defense and controlled programs. That applies whether the article is a jet engine disc, a rotor for high speed electric motors, a commercial space component, or an additively manufactured part with no established fatigue history. If you are still deciding which evaluation your program needs, our guide to choosing the correct spin testing service is a good starting point. Ask an Expert about your test objectives, or submit a Request for Quote for pricing and scheduling on your dynamic spin testing program.
