Numerical and Experimental Study on the Modal Characteristics of a Rotor Test Rig

Verena Heuschneider, Florian Berghammer, Manfred Hajek

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations

Abstract

A Mach scaled 85 kW rotor test rig for the investigation of Dynamic Stall on highly loaded helicopter rotor blades up to a diameter of 1.80 m and a tip speed up to 220 m/s is built at the Institute of Helicopter Technology, Technical University of Munich. The current state is the complete assembly of the drive train components including the engine cradle, wind tunnel adaptor, rotor shaft, and bearings as well as strain gauge load cells. To ensure a safe entry into service and operation at the nominal rotor speeds between 40 and 50 Hz, we develop a numerical finite element model of the test rig structure in order to study its dynamic characteristics. The numerical analysis results show critical eigenmodes at 44.21 and 54.98 Hz, modes 5 and 6. By means of a complementary experimental modal analysis on the steel frame structure natural frequencies, mode shapes, and damping characteristics of the critical modes are identified. The measurement results for three different excitation points and their synthetization prove the identification of ten eigenmodes between 0 and 70 Hz, which mainly emerge from the wind tunnel adaptor. Modes 6 and 7 have eigenfrequencies that are in and critically close to the nominal speed range, 46.97 and 54.88 Hz. They match with the numerically calculated eigenfrequencies but show different mode shapes, as the Modal Assurance Criterion (MAC) values for the comparison of numerical and experimental model convey. As closer investigations show, the numerical eigenfrequencies have a tendency to higher values from the fifth mode onwards.

Original languageEnglish
Title of host publicationTopics in Modal Analysis and Testing, Volume 8 - Proceedings of the 38th IMAC, A Conference and Exposition on Structural Dynamics, 2020
EditorsBrandon Dilworth, Michael Mains
PublisherSpringer
Pages315-321
Number of pages7
ISBN (Print)9783030477165
DOIs
StatePublished - 2021
Event38th IMAC, A Conference and Exposition on Structural Dynamics, 2020 - Houston, United States
Duration: 10 Feb 202013 Feb 2020

Publication series

NameConference Proceedings of the Society for Experimental Mechanics Series
ISSN (Print)2191-5644
ISSN (Electronic)2191-5652

Conference

Conference38th IMAC, A Conference and Exposition on Structural Dynamics, 2020
Country/TerritoryUnited States
CityHouston
Period10/02/2013/02/20

Keywords

  • Experimental modal analysis
  • Finite element model
  • Impact excitation
  • Modal Assurance Criterion
  • Rotor test rig
  • Structural dynamics

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