A Parameter Study of Transonic Airfoil Flutter and Limit Cycle Oscillation Behavior

Kholodar, Denis B.; Thomas, Jeffrey P.; Dowell, Earl H.; Hall, Kenneth C.

doi:10.2514/6.2002-1211

Cited by 10 publications

(13 citation statements)

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“…The amplitude ratio at flutter increases from 0.72 at M ∞ = 0.55 to about 0.9 at transonic Mach numbers. Similar behaviour was observed by Kholodar et al 6,7 for the amplitude ratio at flutter at an ω h /ω α of 0.8 for the NACA64A010A airfoil. (Here ω h /ω α = 0.70.)…”

Section: B Mach Number Variation In Inviscid Flowsupporting

confidence: 70%

“…This is also depicted in Figure 14, which shows the phase difference versus the amplitude ratio. From Figure 13 Upon comparing the results obtained here with the Mach number variations performed by Kholodar et al, 6,7 it is noted that they observed, at an ω h /ω α of 0.8, unstable LCOs (up to 7…”

Section: B Mach Number Variation In Inviscid Flowmentioning

confidence: 76%

“…Studies of the bifurcation behaviour of LCO solutions caused by aerodynamic non-linearities are rare [5][6][7][8][9][10][11][12] and to the author's knowledge, only two of these studies have found subcritical bifurcations. Kholodar et al 6,7 have found subcritical bifurcations of the NACA64A010A airfoil in inviscid flow using the harmonic balance (HB) method, whereas Balajewicz and Dowell 12 observed subcritical bifurcation behaviour for the NACA0012 airfoil in inviscid flow (also using the HB method). Furthermore, Kholodar et al 6,7 are, to the author's knowledge, the only researchers that systematically studied the effect of Mach number and structural parameter variations.…”

Section: Introductionmentioning

confidence: 99%

“…Kholodar et al 6,7 have found subcritical bifurcations of the NACA64A010A airfoil in inviscid flow using the harmonic balance (HB) method, whereas Balajewicz and Dowell 12 observed subcritical bifurcation behaviour for the NACA0012 airfoil in inviscid flow (also using the HB method). Furthermore, Kholodar et al 6,7 are, to the author's knowledge, the only researchers that systematically studied the effect of Mach number and structural parameter variations. They observed that there is a high sensitivity of the LCO behaviour with respect to Mach number and uncoupled natural structural frequency ratio, especially in the transonic regime.…”

Section: Introductionmentioning

confidence: 99%

“…The mass ratio had a less significant impact on the LCO bifurcation behaviour. However, Kholodar et al 6,7 did not analyse the LCO bifurcation behaviour and its corresponding source (the aerodynamic forces) in detail. Why does a certain bifurcation behaviour establish itself?…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Bifurcations of limit-cycle oscillations of a two degree-of-freedom airfoil caused by aerodynamic non-linearities

Rooij

Nitzsche

Dwight

2017

58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

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Flutter is usually predicted using linearised theory. In reality, flutter is always non-linear and might already occur below the linearly predicted flutter boundary. Whether this is the case for limit-cycle oscillations (LCOs) caused by aerodynamic non-linearities is not known, since these LCOs can only be predicted using expensive wind-tunnel tests or coupled Computational Fluid Dynamics (CFD)-Computational Structural Mechanics (CSM) simulations. However, it is important to know whether a sufficiently large disturbance can already cause LCOs below the flutter boundary predicted from linearised theory. Furthermore, since structural properties and the flow conditions will vary, it is necessary to study the resulting variations of the Hopf bifurcation behaviour of the LCO solutions near the flutter point. In this work viscous and inviscid transonic flows are considered. The LCO bifurcation behaviour was found to vary significantly when the uncoupled structural natural frequency ratio and the location of the elastic axis are changed. When the non-linearity is relatively weak, a change in the Hopf bifurcation type might result. A Mach number variation in inviscid flow showed that the effective flutter boundary might significantly deviate from that predicted using linearised theory. For both the structural parameter variations and the Mach number variation, LCOs were observed below the linearly predicted flutter boundary. At the nominal structural parameters, the amplitude-dependent behaviour of the phase of the lift was found to be responsible for the type of bifurcation of the LCO solution that occurs. Inspection of the local force distributions at various pitch amplitudes showed that the motion of the shock wave on the lower surface is responsible for the behaviour of the phase of the lift and hence for the bifurcation behaviour of the LCOs observed in this work.

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Section: B Mach Number Variation In Inviscid Flowsupporting

confidence: 70%

Section: B Mach Number Variation In Inviscid Flowmentioning

confidence: 76%