Parametric Study of the Flutter Stability of a Swept-Back Half-Wing with Engine Nacelle in Subsonic Flow.

Abstract

A parametric investiagation of the aeroelastic flutter stability behaviour of a swept-back half-wing with a pylon-mounted engine nacelle in inviscid subsonic flow is performed. The equations of motion, and therefrom the aeroelastic stability equations, are derived in terms of generalized coordinates in modal form, applying the Rayleigh-Ritz method with assumed mode functions. Two specific mode shapes - a fundamental wing bending mode together with each of three different engine nacelle pitching modes - are combined individually to compose a binary flutter system with two degrees of freedom. For the computation of the motion-induced unsteady (generalized) airloads, a panel technique is used for both the wing and the engine nacelle that is replaced by an annular wing. For a configuration representative of modern large transport aircraft, numerical results are presented for a variety of systematic parameter variations and Mach numbers. Thereby, for each binary combination of mode shapes, special emphasis is placed on the effects of the frequency ratio of the respective modes and the location of the wing torsional node lines of the various engine pitching modes, together with the effects of the motion-induced unsteady airloads on the engine nacelle.