Spherical Fixture for Turbine Blade Modal Testing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The use of rectangular fixtures for modal testing of turbine blades is suboptimal due to their low natural frequencies, which can interfere with the testing of blades, leading to inaccurate determination of natural frequencies and mode shapes.
Innovation Solution
A generally spherical fixture is used to retain the blade in a fixed-free configuration, with a blade retaining portion and attachment portions, including a slot, set screw, and pusher plate, to minimize interference by having higher natural frequencies than rectangular fixtures of the same composition and mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular fixtures are used for modal testing, then the fixture structure is simple and easy to manufacture, but the natural frequencies of the fixture are low which interferes with blade testing accuracy
Solution Approach 1:
The patent applies spheroidality by replacing the conventional rectangular fixture with a spherical fixture. The spherical geometry fundamentally changes the fixture's vibrational characteristics, raising its natural frequencies above the blade's natural frequencies. This eliminates frequency interference and enables accurate modal testing, while the spherical shape maintains manufacturing feasibility through standard machining processes.
2Device complexity
If rectangular fixtures are used, then the fixture design is conventional and simple, but the fixture natural frequencies interfere with blade modes leading to inaccurate testing
Solution Approach 1:
The spherical fixture design replaces complex rectangular geometry with a simpler spherical form that inherently provides higher natural frequencies. This geometric transformation resolves the interference between fixture and blade modes, improving testing reliability without significantly increasing design complexity.
3Measurement precision
If a spherical fixture is used, then the natural frequencies of the fixture are higher and do not interfere with blade testing, but the fixture design and manufacturing become more complex
Solution Approach 1:
The spherical geometry, while different from conventional rectangular designs, actually simplifies certain aspects of the fixture design by providing uniform stress distribution and simplified mounting interfaces. The manufacturing process remains feasible through standard spherical machining operations, making the increased design complexity acceptable given the significant improvement in measurement precision.
Data Source
AI summary
Systems and methods for modal testing of blades. A method for modal testing of a blade comprises providing a generally spherical fixture for retaining the blade in a fixed-free configuration. The method includes using an excitation device for exciting the blade while the blade is retained within a blade retaining portion of the fixture. The method comprises using a measurement device to measure a response of the blade to the excitation. The fixture includes an attachment portion configured for the securement of the excitation device to the fixture.