Abstract
For jet-powered VTOL aircraft, the principal sources of nearfield noise are the direct and ground-reflected noise of the jet exhaust, the aerodynamic noise from wall jet formed by the deflected exhaust flow and the noise of the impinging jet. These principal sources are considered and several of their basic characteristics for VTOL jet noise are established. Emphasis is placed on the change in acoustic power and near-field levels due to their combined effect. A prediction method for near-field noise of VTOL jets is then outlined in the form of additive corrections to apply to near-field levels for the undeflected jet. These corrections have a maximum value of about 15–20 dB in the range of typical resonance frequencies for flight vehicle skin panels. However, these additive corrections vary substantially with frequency and elevation of the vertically directed nozzle. The approximate trend in these variations is illustrated based on the results of model studies. [This work was supported by the Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, Ohio.]
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