Gust Load Alleviation: Identification, Control, and Wind Tunnel Testing of a 2-D Aeroelastic Airfoil

Abstract

One important element in the progression of aircraft environmental impact reduction is to reduce their overall weight (without impacting other consumption-oriented performance index, such as drag). In addition to the numerous work conducted in material and structural engineering, from a control viewpoint, this challenge is strongly connected to the need of the development and assessment of dedicated load control strategies in response to gust disturbances. Indeed, the load factors due to gust are considered as a sizing criteria during the aircraft conception steps and require specific verification according to the certification process. To this end, a dedicated experimental research program based on Wind Tunnel (WT) campaigns has been carried out. More specifically, the paper contributions are twofold: (i) to identify the gust load effect using two different versatile frequency-domain techniques, namely the Loewner interpolation and a modified subspace approach, and (ii) to design and implement an active closed-loop control to alleviate the gust main effect. The entire procedure is validated in a wind tunnel setup , involving a gust generator device and a 2D aeroelastic airfoil, for varying configuration travelling from sub to transonic airflow and varying angles of attack, emphasizing the effectiveness and robustness of the overall approach.

Vortical Gusts: Experimental Generation and Interaction with Wing

“…The problem of a harmonic gust has also been examined experimentally and numerically. The typical method [23,24] of creating such gusts is to pitch vanes upstream of the test section to yield transverse gusts or to open and close shutters downstream of the test section [25] to create an oscillating freestream. The use of a small number of vanes [26,27] can create distinct vortices, which yield a transverse velocity far from the vortices.…”

Structured linear fractional parametric controller H<inf>∞</inf> design and its applications

“…Nevertheless, the approach quickness should be exploited in further developments. Following previous experimental results discussed in [4,21,22], on-going work will implement this strategy on a real aircraft during flight experiments.…”

Identification of parametric models in the frequency-domain through the subspace framework under LMI constraints

“…n p to obtain A(p). 3) Build the matrices Λ and Λ aug according to (15) and get the matrix C(p) 4) Solve the least square problem given in (16) to get the matrices B(p) and D(p)…”

“…It is then interesting to use Algorithm 2 with a stability constraint since the system is known to be stable. This is a common problem when identifying a parametric model on the basis of noisy experimental data (see [15]). Poles of the parametric model identified using Algorithm 1 (blue points) or Algorithm 2 with a stability constraint (red points) for p = 0.1k, k = 1 .…”

“…. N p a) Build the data matrices W and G as in(6) b) Compute O (j) qfollowing(7)and (8) c) Compute the matrices Ω j , ∆ j , Λ j as in(12) d) Compute the transformation matrix T j according to[3] 2) Build the matrices Ψ, ∆ aug , Γ and Λ aug according to(15) and get the matrices A(p) and C(p) of the parametric model given in (2) 3) Solve the least square problem given in(16) to get the matrices B(p) and D(p) In practice, if one does not want the matrices B and D to be parameter-dependant, the key is to adapt the least square problem given in Equation(16), in this case, B(p) = B 0 and/or D(p) = D 0 .…”