Drivers of Jet-flap interaction noise: The thrust vs. shear layer difference velocity experiment

Abstract

The fundamentals of jet-flap interaction (JFI) are not fully known. One of the open questions is the search for the velocity scaling similarity parameter. While the scaling exponent is known to be n=5...6 from static JFI experiments (single-phase), the two-phase flight ops JFI problem produces more than one suitable flow parameter candidate. Promising scaling parameters are thrust velocity and shear layer (S/L) difference velocity. These two velocity parameters are played out against one another in order to force a definitive experimental result. The changes in build length due to using different operational parameters are calculated. The experimental parameter room is limited by max velocity limits of wind tunnel air and pressurized air (volumetric limit or sonic jet velocity), by quasi-static velocity ratio (for closed-circuit wind tunnel) and either upper limit of JFI effect or velocity profile type (here strong normal velocity profiles). The derived experiment is tailored to force a definite result wrt. thrust or S/L velocity. If this experiment does not give a clear result, JFI scaling cannot be easily modelled. A next step could be for example the measurement of downwash-velocities, i.e. flow properties which are more complex to determine and may require a build-dependent model.