The coherence lengths underneath a turbulent boundary layer were measured in flight at several positions on an aircraft. It 'was found that the coherence length scales with the boundary layer thickness, except for one measurement position where the boundary layer was believed to be disturbed by the vicinity of the wing. A comparison of the data with the models by Corcos and Efimtsov showed an underprediction of the values. However good applicability of the Efimtsov-theory was found when fitted to the measured data. A variation of flight speed and flight altitude showed no considerable change in the coherence length parameters. Variation of interior sound level is therefore not ascribed to a variation of coherence length, but rather to a variation of other parameters.
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