Amplification and amplitude limitation of heave/pitch limit-cycle oscillations close to the transonic dip

• Published in: Journal of fluids and structures 2006-05, Vol.22 (4), p.505-527
• Main Authors: Dietz, G., Schewe, G., Mai, H.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fluid dynamics; Flutter; Fundamental areas of phenomenology (including applications); General theory; Limit-cycle oscillations; Physics; Solid mechanics; Structural and continuum mechanics; Supercritical airfoil; Transonic dip; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...)
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2006.01.004

Recent results from flutter experiments of the supercritical airfoil NLR 7301 at flow conditions close to the transonic dip are presented. The airfoil was mounted with two degrees-of-freedom in an adaptive solid-wall wind tunnel, and boundary-layer transition was tripped. Flutter boundaries exhibiting a transonic dip were determined and limit-cycle oscillations (LCOs) were measured. The local energy exchange between the fluid and the structure during LCOs is examined and leads to the following findings: at supercritical Mach numbers below that of the transonic-dip minimum the presence of a shock-wave and its dynamics destabilizes the aeroelastic system such that the decreasing branch of the transonic dip develops. At higher Mach numbers the shock-wave motion has a stabilizing effect such that the flutter boundary increases to higher flutter-speed indices with increasing Mach number. Amplified oscillations near this branch of the flutter boundary obtain energy from the flow mainly due to the dynamics of a trailing-edge flow separation. A slight nonlinear amplitude dependency of the shock motion and a possibly occurring boundary-layer separation cause the amplitude limitation of the observed LCOs. The impact of the findings on the numerical simulation of these phenomena is discussed.