Spring loaded poppet valves are widely used in gas turbine Fuel Pump and Metering Units (FPMU) as a means of pressure control.  These valves often employ a piston-cylinder type poppet guide for its simplicity and cost-efficiency reasons.  In a recent investigation of external fuel leaks, cavitation damages were discovered in a small deadheaded cavity of a filter bypass valve, which was created by the axial clearance between the piston’s tip and cylinder’s drill point.  Experiments using high bandwidth pressure sensors were designed to survey pressures in the cavity and in the surrounding of the valve.  Ten prototype valves were designed and manufactured in order to cover a range of diametric clearances between the pistons and cylinders, as well as the cavity volumes.  These prototypes were tested in two similar FPMUs but with different gear widths over a range of pump speeds, flow rates, and fuel temperatures that were derived from a turbofan application.  Data showed that there were severe pressure fluctuations in the cavity and that their amplitudes were several times greater than those of flow ripple in the surrounding of the valve.  Static pressure constantly fell below the local vapor pressure of the fuel, which would lead to cavitation.  Spectral analyses of the test data showed that the peaks of the cavity pressures and flow ripple aligned perfectly with the harmonics of gear tooth passing frequencies.  No other peaks of significant magnitudes were observed at other frequencies.  Computing individual cavity pressure-to-flow ripple amplitude ratios from all test conditions and overlaying them on a single plot revealed an apparent resonant frequency around which that ratio reached as high as 8.  In an attempt to find the source of this frequency, the cavity-guide system was modelled as an ideal Helmholtz resonator.  The computed fundamental Helmholtz resonance frequency (HRF) agreed with the observed resonant frequency in the cavity.  An increase in the clearance shifted this frequency to a higher value.  A decrease in the fuel temperature shifted this frequency to a smaller value.  Both were expected behaviours of a Helmholtz resonator.  These findings led to a venting solution of the deadheaded cavity by placing an appropriately sized through hole.  Back-to-back testing with unvented prototypes showed stark improvements of the vented solution.  The amplitudes of pressures in the vented cavity were much more comparable to those of the flow ripple.  The ranges of maximum and minimum pressures in the vented cavity were no more than those of the flow ripple whereas the unvented valves showed ranges that were at least as twice as greater.  Static pressure no longer fell below the vapor pressure in the vented valves, effectively eliminating a source of cavitation damage.     


Acoustic Amplification of Flow Ripple and Cavitation Damage in an Aerospace Fuel System Component

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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