Correlation Measurements of Airplane Fuselage Vibrations

The vibrations of the skin and stiffeners of an airplane fuselage have been measured in a region where the excitation is predominantly that due to the turbulent boundary layer, at Mach numbers 0.78, 0.6, and 0.45. The data have been analyzed to assess the relative importance of standing and running waves, and to determine the spatial coherence of the vibration field. In the longitudinal, or stream, direction, the broad-band correlation shows running wave characteristics, which depend on the aircraft velocity and cabin pressurization. The convection velocities are not necessarily the same as the broad-band convection velocities for the pressure field, but there is evidence of a coincidence-type condition at M=0.6. The correlation scale in the longitudinal direction is much larger than that in the circumferential direction, where there is no significant correlation between adjacent panels separated by a longitudinal stiffener. Cross power spectral density measurements have been used to determine spatial coherence and convection velocity at particular frequencies, for comparison with the broad-band data.