Comparison of SEA Predictions and Shuttle Fuel Pipe Responses – An Investigation of Fatigue Crack Growth using Acoustic Excitation

This paper describes how, in 2002, cracks in the Main Propulsion System (MPS) Feed Lines Flow Liners were discovered in the Space Shuttle Orbiter vehicles. The flow liner is used to contain the main engine liquid fuel (oxygen/hydrogen) across a flexible bellows located in a gimbal section of the pipe. The pipe itself carries cryogenic fluid from the fuel tanks located in the External Tank (ET) to the Shuttle main engines that are located on the Orbiter. The high fluid velocities in the pipe generate large amplitude vibrations in the flow liner and it is suspected that the vibration amplitudes are sufficient enough to generate fatigue cracks in the liner. There are two flow liners per gimbal assembly (upstream and downstream). The gimbal assembly is located just upstream of the low-pressure fuel pump. There is also a gimbal assembly on the oxidizer side, but no cracks have been found on those flow liners. The liner’s purpose is to shield a bellows from flow, eliminating the possibility of flow induced vibration of the bellows. Each flow liner has a series of slots located near the weld line for cleaning purposes. The cracks have been found at the edges of these slots. Hot fire tests of the Space Shuttle main engines have been performed with instrumented flow liners. These tests showed large amplitude oscillations in the range of 900 to 3500 Hz. These oscillations are caused by fluid/structure interaction and are the theorized source of the cracks (high-cycle fatigue). Because of the excessive time and resources required for hot-fire engine tests, the ability to duplicate the oscillations in an acoustic lab would greatly aid in the investigation of the crack phenomena. This will allow for detailed studies of the vibration characteristics at a fraction of the time and cost. Typically, mechanical shakers are used to drive mechanical structures. However, mechanical stinger attachments were thought to cause distortions to the normal modal patterns. Therefore, Boeing suggested that acoustic excitation might be able to drive the liner to levels where fatigue crack growth could occur. In order to investigate this idea, a preliminary analysis of the flow liner response to was used to determine the feasibility of this approach.

Language

  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; References; Tables;
  • Pagination: pp 347-354
  • Monograph Title: Noise-Con 04. The 2004 National Conference on Noise Control Engineering

Subject/Index Terms

Filing Info

  • Accession Number: 01054190
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Jul 16 2007 6:05PM