Gust alleviation is very important to a large flexible aircraft. A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust. Based on the proper orthogonal decomposition method, a reduced order modeling of gust loads was proposed. And then the open-loop and closed-loop reduced order state space model for the transonic aeroelastic system was developed. The static output feed back control scheme was used to design a simple multiple-in multiple-out (MIMO) gust alleviation control law. The control law was demonstrated with the Goland+ wing model with four control surfaces. The simulation results of different discrete gusts show the capability and good performance of the designed MIMO controller in transonic gust alleviation.

A reduced-order-model-based multiple-in multiple-out gust alleviation control law design method in transonic flow

This paper presents the implementation of gust modeling capability in the CFD code FUN3D. The gust capability is verified by computing the response of an airfoil to a sharp edged gust. This result is compared with the theoretical result. The present simulations will be compared with other CFD gust simulations. This paper also serves as a users manual for FUN3D gust analyses using a variety of gust profiles. Finally, the development of an Auto-Regressive Moving-Average (ARMA) reduced order gust model using a gust with a Gaussian profile in the FUN3D code is presented. ARMA simulated results of a sequence of one-minus-cosine gusts is shown to compare well with the same gust profile computed with FUN3D. Proper Orthogonal Decomposition (POD) is combined with the ARMA modeling technique to predict the time varying pressure coefficient increment distribution due to a novel gust profile. The aeroelastic response of a pitch/plunge airfoil to a gust environment is computed with a reduced order model, and compared with a direct simulation of the system in the FUN3D code. The two results are found to agree very well.

/pdf/development-verification-and-use-of-gust-modeling-in-the-4bp8ujjaor.pdf

Development, Verification and Use of Gust Modeling in the NASA Computational Fluid Dynamics Code Fun3d

The increased flexibility of long endurance aircraft having high aspect ratio wings necessitates attention to gust response and perhaps the incorporation of gust load alleviation. The design of civil transport aircraft with a strut or truss-braced high aspect ratio wing furthermore requires gust response analysis in the transonic cruise range. This requirement motivates the use of high fidelity nonlinear computational fluid dynamics (CFD) for gust response analysis. This paper presents the development of a CFD based gust model for the truss braced wing aircraft. A sharp-edged gust provides the gust system identification. The result of the system identification is several thousand time steps of instantaneous pressure coefficients over the entire vehicle. This data is filtered and downsampled to provide the snapshot data set from which a reduced order model is developed. A stochastic singular value decomposition algorithm is used to obtain a proper orthogonal decomposition (POD). The POD model is combined with a convolution integral to predict the time varying pressure coefficient distribution due to a novel gust profile. Finally the unsteady surface pressure response of the truss braced wing vehicle to a one-minus-cosine gust, simulated using the reduced order model, is compared with the full CFD.

/pdf/developing-an-accurate-cfd-based-gust-model-for-the-truss-2s38eao6u7.pdf

Developing an Accurate CFD Based Gust Model for the Truss Braced Wing Aircraft

Aeroelastic Analysis Using FUN3D-Based ROM Simultaneously Subject to Gust and Control Surface Deflections

The responses of a NACA0012 airfoil and a large-aspect-ratio wing, subjected to gust excitation about high mean angles of attack, close to stall, are presented here. Reynolds-averaged Navier–Stokes...

Gust Response at High Angles of Attack

A general unsteady CFD/Aeroelastic code, ZEUS, is enhanced with arbitrary discrete gust profile analysis capability. Typical type of discrete gust profile such as one-minus-cosine gust is easily defined in the ZEUS input, and the sharp edge gust and any other type of gust can be simply defined using the table input format. The aerodynamic response under the sharp edge gust combined with the Proper-Orthogonal-Decomposition (POD) method allows us develop a compact and efficient reduced-order model (ROM), which can be used to rapidly predict pressure coefficient solutions on the aerodynamic surface under any type of discrete gust profile other than the sharp edge gust. The gust ROM developed at the pressure efficient level makes it independent of the structural model, and readily applicable for the framework of Dynamic Flight Simulation (DFS) tool which combines a flight dynamics model with an add-on aeroelastic model in a Matlab/Simulink environment. The AGARD 445.6 wing configuration is used as a numerical example to demonstrate the present gust ROM methodology. It has been shown that the gust ROM with the convolution law and POD method is proper over various Mach numbers considered.

http://enu.kz/repository/2011/AIAA-2011-2041.pdf

A Compact CFD-Based Reduced Order Modeling for Gust Analysis

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A Compact CFD-Based Reduced Order Modeling for Gust Analysis