An integral damping approach has been studied for the trailing edge blowing (TEB) fan to reduce fan blade vibrations. The TEB fan is a unique technology demonstrator that was designed and fabricated at the NASA Glenn Research Center for testing in Glenn’s 9- by 15-Foot Low-Speed Wind Tunnel. The rotor blades are constructed of a composite core with two 16-ply composite outer skins (or shells). The integral damping concept consists of a thin layer of viscoelastic material (VEM) embedded within the outer skins to significantly damp the primary bending and torsion vibration modes. Air is blown out of slots near the trailing edges of the TEB fan blades to fill in the wakes downstream of the rotating blades. This leads to a reduction in the rotor-stator interaction (tone) noise caused by the interaction of wakes with the downstream stators. The TEB fan will demonstrate a 1.6-EPNdB (effective perceived noise decibel) reduction in tone noise through wake filling. Furthermore, the reduced blade row interaction will decrease the possibility of forced-response vibrations and enable closer spacing of blade rows, thus reducing engine length and weight.
The viscoelastic material patch, approximately 0.005 in. thick, replaces the composite material of the blade skin at a selected location of the blade. The patch includes a barrier film to protect the VEM during the curing process. The location, shape, and size of the VEM patch have been varied to optimize the damping without reducing the strength of the blade. Finite-element models of the integral damped fan blade were created to analytically predict the damping, structural strength, vibration mode, and frequencies, and to optimize the VEM patch location, shape, and size. Four sets of blades with different levels of damping were analyzed, fabricated, and tested. The testing validated the structural analysis and demonstrated the feasibility of the integral damping approach. The optimally damped blade, which had a VEM patch size of 29 percent of the blade surface, had a resonant blade vibration amplitude that was 1.5 to 3.3 times less than that of an undamped blade.
TEB fan blade with embedded VEM damping patch.
Long description of figure.
The research described here was performed under a grant to Dr. John Kosmatka (University of California, San Diego) in collaboration with Glenn researchers. This work was supported by the Quiet Aircraft Technology Project, Dr. Joseph Grady, manager.
Ma, Zhixin; and Kosmatka, John: Structural Analysis of an Integral Damped Reduced Weight Fan Blade. Structural Systems Research Report, SSRP-04/09. Final Report submitted to NASA Grant NCC3-902, Aug. 2004.
Glenn contact: Dr. Milind A. Bakhle, 216-433-6037, Milind.A.Bakhle@nasa.govLast updated: October 11, 2006
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