11:00
Low/high order methods 2
Chair: Lorenz Tichy
11:00
30 mins
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Gust response analysis of supersonic aircraft based on three-dimensional piston theory
Chen Song, Changchuan Xie, Chenyu Liu, Yang Meng
Abstract: Though the influence of atmosphere disturbance (gust) on low-speed aircraft has been studied a lot since the disintegration of the Helios Prototype, the gust load on supersonic vehicles still needs further discussion, along with efficient analysis methods. On the other hand, with the development of hypersonic glide vehicles, the assembly of warhead and booster usually has a lower basic frequency than supersonic fighters and therefore, is more sensitive to atmosphere disturbance, which makes it necessary to analyze the gust response of supersonic aircraft.
In this paper, first-order piston theory is applied in the local frame of 3-D aero mesh to calculate the unsteady aerodynamic force caused by elastic vibration and gust, which could be written into matrix form using modal coordinates and interface interpolation method, where and are aerodynamic damping and stiffness respectively. Integrate the aerodynamic model into the structural dynamics, and the aeroelastic dynamic equation could be formed, with the notation :
where are the generalized mass, damping, and stiffness matrixes of the structure.
In most research, the ODE is solved by numerical methods like Ruuge-Kutta methods though semi-analytical solution exists: , with . To justify the proposed method and semi-analytical solution, the dynamic response of a simple wing model under 1-cos gust is calculated by both the proposed method and ZAERO at Ma 3.0:
(a)
Fig. (a): Diagram of the wing model
(b): Acceleration of monitor point
(b)
In conclusion, the gust response analysis based on three-dimensional piston theory has great consistency with commercial software, yet the proposed method could be applied to high-resolution 3-D mesh. The analytical solution gives almost identical results to Runge-Kutta with 1/20 of the time spent, which makes it practical to analyze complex objects.
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11:30
30 mins
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Development of a nonlinear FSI method for simulation of airfoil flutter with and without impact absorbers
Michael Pitzal, Johann Groß, Patrick Kopper, Andrea Beck, Malte Krack
Abstract: The motivation for this work originates from an experimental campaign of an aero-elastically unstable NACA 0010-65 airfoil. Two configurations of the elastically suspended uniform wing were considered, one without and one with impact absorbers. In the former configuration limit cycle oscillations (LCO) saturated by nonlinear aerodynamic forces occurred, as well as coexisting solutions on different amplitude levels for the same flow velocity. In the latter, the impacts dissipate enough energy to significantly reduce (or almost annihilate) the vibration level in the analyzed flow velocity range.
In this work we present a nonlinear FSI method, which accurately predicts both LCO and flutter suppression by impact absorbers in accordance with measurements. To this end, strong coupling between fluid and structural dynamics is established in time domain, which is required to capture the complex vibration regimes. The computational domains are still treated separately, such that the proposed method is conceptually not restricted to any particular choice of CFD or structural dynamics solvers as well as modelling approaches.
For this particular case, we obtain the fluid dynamics using 2-dimensional Euler equations, solved by Discontinuous Galerkin Spectral Element Method framework FLEXI (written in FORTRAN). The mechanical system (implemented in MATLAB) is described by rotational and stroke motions of the airfoil while the contact interaction of impact absorbers with the airfoil is approximated using the Hunt-Crossley model. Data exchange between the two computational domains is realized via Python.
To modern aircraft, wing flutter denotes one of the major design constraints. This work contributes to accurate prediction of wing LCO and development of effective flutter suppression devices, which are indispensable for the increase of engineering design space and, thus, efficiency of future aircraft.
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12:00
30 mins
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Efficient and high-precision nonlinear static aeroelastic load analysis method based on vortex lattice method acceleration
Zou Zhicheng, Xie Changchuan, An Chao, Yang Lan, Zhu Lipeng, Ni Zao
Abstract: High-precision CFD/CSD coupling aeroelastic load analysis is an effective way to solve the nonlinear aeroelastic problem of flexible wings. In order to improve calculation efficiency while ensuring calculation accuracy, a nonlinear static aeroelastic load analysis method accelerated by vortex lattice method is proposed in this article. Vortex lattice method is adopted to achieve a faster convergence both in the iteration of static aeroelastic analysis and trimming process. An RBF-based mesh deformation tool with greedy algorithm is used to realize fast and accurate mesh deformation during the iterations. The numerical model of a commercial aircraft with very flexible wing is investigated by the traditional aeroelastic load analysis method and the accelerated method. Compared with the traditional method. The proposed accelerated method can significantly improve the calculation efficiency while ensuring the high precision.
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