172,000 research outputs found
Gust response: a validation experiment and preliminary numerical simulations
No full textIn this paper the experimental setup and first results for a gust generator experiment will be presented. The experiment was carried out in the transonic wind-tunnel
facility in Goettingen (DNW-TWG). The first goal of the experiment was to answer the question, whether it is possible to induce an unsteady flow field with a rigid moving profile as a gust generator. Furthermore the main objective of the experiment was the understanding of the physical phenomena of an impacting gust on an elastic structure. For that purpose a new set-up has been constructed and built, which allows the investigation of two subsequent airfoil-models in the flow of the wind tunnel. The first airfoil is active and should produce a generic gust. The second model located downstream is passive and responds to the unsteady
load changes induced by the moving active profile. For a first investigation, amplitudes and frequencies were varied as well as the vertical position of both airfoils relative to each other. The experiment was conducted to deliver a comprehensive data base for validating the DLR in-house fluid-structure-interaction software “PyCSM” which has been developed for aeroelastic simulations in time domain.
In order to support the experiment in the preparation phase, fluid-structure-interaction simulations in time domain have been carried out. These simulations mainly show the response amplitudes expected for the passive wing. For that purpose the DLR TAU Code for the calculation of the steady and unsteady aerodynamic loads and a finite element shell
model have been used
The effect of wavy leading edges on aerofoil-gust interaction noise
No full textHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil–gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (?g) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA/?g and the noise reduction is significant for LEA/?g?0.3. The present results also suggest that any two different cases with the same LEA/?g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1.0?LEW/?g?1.5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise
High-order computations on aerofoil-gust interaction noise and the effects of wavy leading edges
No full textHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges on aerofoil gust interaction (AGI) noise. The present study is based on periodic velocity dis-turbances predominantly in streamwise (x-) and vertical (y-) directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. The perturbed velocity components of the present gust model do not vary in the spanwise (z-) direction. In general, the present results show that wavy leading edges lead to reduced AGI noise. Under the current incident gusts, it is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (?g) is the most important factor for the reduction of AGI noise. It is observed that AGI noise reduces with increasing LEA/?g, and significant noise reduction can be achieved for LEA/?g?0.3. The present results also suggest that any two different cases with the same LEA/?g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1.06LEW/?g 61.5. In addition, it is found that the beneficial effects of wavy leading edges are maintained for various angles of attack and aerofoil thicknesses. Also, wavy leading edges remain effective in reducing AGI noise for gust profiles containing multiple frequency components. It is discovered in the current research that wavy leading edges result in in-coherent response time to the incident gust across the span, which causes a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise
An adaptive aeroelastic control approach using non linear reduced order models
No full textA systematic approach to the model order reduction of high fidelity coupled fluid/structure/flight dynamics models and the subsequent control design is described. It uses information on the eigenspectrum of the coupled-system Jacobian matrix and projects the system through a series expansion onto a small basis of eigenvectors representative of the full-model dynamics. A nonlinear reduced order model is derived and is exploited for a worst case gust and adaptive control design. The investigation focuses on a flight control design based on the model reference adaptive control scheme via the Lyapunov stability approach. The novelty of this paper is two-fold. Firstly, it uses a single nonlinear reduced model for parametric worst case gust search. Secondly, it is shown that it makes feasible an implementation of a complex control methodology for a large nonlinear system. The adaptive controller is able to alleviate gust loads for a three degrees-of-freedom aerofoil and for an unmanned aerial vehicle. An investigation for the adaptation parameters is performed and their effect on control input actuation and aeroelastic closed-loop response is discussed
Robust Control Synthesis for Gust Load Alleviation from Large Aeroelastic Models with Relaxation of Spatial Discretisation
No full text04/03/14 meb. Ok to add, authors retain copyright.This paper introduces a methodology for the design of gust load control systems directly from large aeroelastic models with relaxation of spatial discretisation. A convenient state-space representation of the vortex-panel unsteady aerodynamics suitable for control synthesis is presented. This allows a full understanding of the dynamics of the linearized vortex aeroelastic model and is suitable for control system design. Through the use of robust controllers, large reductions in loading could be achieved. Comparisons are also made between robust and classical control methods. It further demonstrates that controllers synthesized from models of coarse spatial discretizations and of an order of magnitude smaller in size were capable of rejecting disturbances on fully converged models, with performances comparable to expensive higher order controllers developed from full models
Predictive Control for Alleviation of Gust Loads on Very Flexible Aircraft
No full text11/03/14 meb. Author retains copyright as beforeIn this work the dynamics of very flexible aircraft are described by a set of non-linear, multi-disciplinary equations of motion. Primary structural components are represented by a geometrically-exact composite beam model which captures the large dynamic deformations of the aircraft and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-eld around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be about a nonlinear reference state, is performed to yield relatively high-order linear time-invariant state-space models. Subsequent reduction of these models using standard balanced truncation results in low-order models suitable for the synthesis of online, optimization-based control schemes that incorporate actuator constraints. Predictive controllers are synthesized using these reduced-order models and applied to nonlinear simulations of the plant dynamics where they are shown to be superior to equivalent optimal linear controllers (LQR) for problems in which constraints are active
Numerical analyses of discrete gust response for a flexible aircraft
No full textBased on Navier-Stokes equations and structural and flight dynamic equations of motion, dynamic responses in vertical discrete gust flow perturbation are investigated for a supersonic transport model. A tightly coupled method was developed by the subiteration between aerodynamic equations and dynamic equations of motion. First, under the assumption of rigid-body and single freedom of motion in the vertical plunging, the results of direct-coupling method are compared with the results of quasi-steady model method. Then gust responses for the one-minus-cosine gust profile are analyzed with two freedoms of motion in plunging and pitching for the rigid and flexible airplane configurations. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved
Tests of a Gust-alleviating Flap in the Gust Tunnel
No full textTests were made to determine the effectiveness of a long-period dynamically overbalanced flap in reducing airplane accelerations due to atmospheric gusts. For two gust shapes, one gust velocity, one forward velocity, and one wing loading, a series of flights was made with the flap locked and was then repeated with the flap free to operate. The records were evaluated by routine methods. The results indicate that the flap reduced the maximum acceleration increment 39 percent for a severe gust but with a representative gust shape (a sharp-edge gust), the reduction was only 3 percent. The results also indicate that the flap tended to reduce the longitudinal stability of the airplane. Computations made of the effectiveness and the action of the flap were in good agreement with the experimental results
Optimization of a Composite Wing Subject to Multi Constraints
No full textIn this thesis, an investigation has been carried out into a minimum weight optimization analysis of a composite wing with multi design constraints under both static and dynamic loadings. The study includes the influence of a morphing leading edge on the wing stiffness and gust load reduction by employing a passive gust alleviation device at the wing tip.
The design process started from a generic study of optimal structure against buckling for three typical types of reinforced skin panel structures including stiffener panel, sandwich and grid panel. The optimal design in terms of buckling performance and structural efficiency were compared. The study then focused on the optimal design of stiffened skin panels for a particular wing. Parametric studies on optimal design for isotropic stiffened panels were carried out in which practical design constraints were introduced. The optimal design method was further extended to composite stiffened skin panels. Optimal designs were obtained within a compression distributed load range from 500 N/mm to 5250 N/mm and a symmetric balanced layup with 0˚, 90˚, and ±45˚ plies. Based on the study, the modelling and optimal design method for composite stiffened panels was applied to a composite wing box for its upper surface panel design. The initial composite wing box was designed to achieve a minimum weight. Gradient based optimization method was applied in the analysis with practical design constraints. The results indicate that the effect of leading edge morphing on the overall wing structural stiffness is negligible. It has been shown that the weight of the upper surface of the wing box structure can be reduced by 19.8% from its initial design.
Optimal design of a passive gust alleviation device (PGAD) mounted at the wing tip was then investigated. Based on the dynamic analysis of the 3D wing FE model in different flight and payload cases, a method and program was developed to create a dynamically equivalent beam model. Gust response of the optimized wing model was computed for a wide range of frequencies in accordance with the CS-25. Next, a parametric study of the key design variables of the PGAD was carried out to determine the optimal design parameters for minimum gust loading. The results have shown that the gust response can be reduced by 15% by using a 1m long PGAD for a conventional aircraft wing and yet reduce 50% tip displacement with 37.2% bending moment at wing root for a flying wing concept aircraft wing with 1.6m long PGAD mounted at the wing tip.
The results of the investigation contribute to knowledge in the following aspects. It provides an evaluation of the structural efficiency of three typical types of stiffened panels against buckling prevention. The research also provided an optimal design method for composite stringer stiffened panels by combining theoretical and practical design constraints. It made possible for the first-time a numerical evaluation of the novel PGAD as applied to a large aircraft
Integrated Aeroelastic Measurements of the Periodic Gust Response of a Highly Flexible WIng
No full textThe aeroelastic response of a highly flexible wing to periodic gust excitation is determined experimentally. The integrated optical measurement approach that is applied provides combined measurements of the structural response of the wing and the unsteady flow field around it. The aeroelastic loads acting on the wing are derived from these measurements using physical models and validated against force balance measurements. It is observed that both structural and aerodynamic responses to a periodic gust excitation of a given amplitude depend strongly on the frequency of the gust. The obtained data set of results provides a complete description of the aeroelastic response that is suited as a reference for the development of aeroelastic simulation models.AerodynamicsAerospace Structures & Computational Mechanic
- …
