By using a combined analytical-computational methodology, a unified modelling of aerodynamic indicial functions covering the incompressible, subsonic compressible, transonic, and supersonic flight speed regimes is presented. The procedure is carried out in conjunction with a computational fluid dynamic analysis. For a plunging-pitching airfoil, selected unsteady aerodynamic load expressions have been supplied, and appropriate procedures enabling one to obtain these loads via the indicial function approach have been presented. While a single indicial function is needed to describe the aerodynamic loads in the incompressible flight speed regime, for cases where the compressibility effects play a dominant role, four indicial functions are needed. Having in view the usefulness of indicial functions towards determination of unsteady aerodynamics loads in both time and frequency domains, and implicitly for aeroelastic response and flutter predictions, the advantages of their implementation and use appear evident. Comparisons and validations of the aerodynamic model against numerical, analytical, and experimental results are presented, and pertinent conclusions are drawn.Keywords: linear/non-linear indicial aerodynamic functions, incompressible and compressible flight speed regimes, two-degrees-of-freedom airfoil aerodynamics JAERO88
This paper discusses modeling, simulations and experimental aspects of active aeroelastic control on aircraft wings by using Synthetic Jet Actuators (SJAs). SJAs, a particular class of zero-net mass-flux actuators, have shown very promising results in numerous aeronautical applications, such as boundary layer control and delay of flow separation. A less recognized effect resulting from the SJAs is a momentum exchange that occurs with the flow, leading to a rearrangement of the streamlines around the airfoil modifying the aerodynamic loads. Discussions pertinent to the use of SJAs for flow and aeroelastic control and how these devices can be exploited for flutter suppression and for aerodynamic performances improvement are presented and conclusions are outlined.
Nomenclature b= half-chord length, m C L , C M = lift and moment coefficients in concentrated form; Eq.(1) C Lα , C Mα ; C Lq , C Mq = lift and moment coefficients caused by a change in the angle of attack and in the pitch rate, respectively; Eq. (6) C lα = lift-curve slope, 1/rad h, α = plunging displacement (m) and the twist angle (rad) about the pitch axis, respectively L , M = unsteady lift per unit length, N/m, and moment per unit length, N, respectively q = pitch rate about the reference axis (≡ 2bα/U ∞ = 2α ) t, τ = time variable (s) and its dimensionless counterpart (≡ U ∞ t/b), respectively U ∞ = freestream speed, m/s ρ ∞ = air density, kg/(m s 2 ) ς = parameter denoting dependence on prior motion history φ L , φ M = aerodynamic indicial lift and moment functions in concentrated form; Eqs. (2) and (3) φ α , φ Mα ; φ q , φ Mq = indicial functions in concentrated form; Eq. (6) ω, k = circular and reduced frequencies (≡ ωb/U ∞ )
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