Full Aircraft Configurations Research Articles

천음속 버펫 발단 예측을 위한 새로운 정상 접근 방법

A new steady approach has been developed to predict the transonic buffet onset of a high speed aircraft. In this paper, the flow is assumed to be steady for the buffet onset. The present study involves the analysis of a distinct change in the variation of various static aerodynamic parameters. These distinct changes indicates the onset of transonic buffet. Among the various aerodynamic parameters considered in this study, the variation in the center of pressure has shown to provide a clearest indicator of transonic buffet onset. This new steady approach can be applied to predict the transonic buffet onset for airfoils with shock induced separation bubble and for large swept wings with small aspect ratios. Good agreements have been obtained compared with unsteady wind tunnel buffet test data. Based on the results obtained the new steady approach, it can be newly suggested that the distinct slope changes of the center of pressure curve can be used as an indicator of buffet onset for the steady experimental method on a full aircraft configuration.

조종면 강제 조화운동을 고려한 비선형 플러터 비행시험 모사

본 연구에서는 천음속 미소교란 방정식을 이용하여 조종면의 강제 조화 운동을 고려한 전기체 형상에 대하여 천음속/초음속 비선형 플러터 특성을 파악할 수 있는 정밀 해석 시스템을 개발하였다. 본 시스템에는 충격파의 비선형 특성을 고려하기 위해 전산구조동역학, 유한요소해석 및 전산유체역학 기법을 동시에 연계하여 적용하는 연계시간 적분법을 도입하였다. 복잡한 전기체 형상에 대한 효과적인 격자생성을 위해 자체 자동격자 생성프로그램이 개발되었다. 천음속과 초음속 속도 영역에서 전기체 항공기에 대한 정적/동적 공탄성 특성을 고찰하였으며, 시간 영역에서 조종면 강제 조화운동에 대한 플러터 비행시험 시뮬레이션 결과들을 제시하였다. In this study, transonic/supersonic nonlinear flutter analysis system of a complete aircraft including forced harmonic motion pf control surfaces has been effectively developed using the modified transonic small disturbance (TSD) equation. To consider the nonlinear effects, the coupled time marching method (CTM) combining computational structural dynamics (CFD) has been directly applied for aeroelastic computations. The grid system for a complex full aircraft configuration is effectively generated by the developed inhouse code. Intransonic and supersonic flight regimes, the characteristics of static and dynamic aeroelastic effect has been investigated for a complete aircraft model. Also, nonlinear flutter flight simulations for the forced harmonic motion of control surfaces are practically presented in detail.

EULAIR: a novel finite–element–based Cartesian grid Euler flow solver that does not require cut–cell geometric information at solid boundaries

We describe the theoretical foundations and associated numerical algorithm of a new method for the solution of compressible flows, using Cartesian grids (CGs). A unique feature that distinguishes this method from other CG approaches is its treatment of solid boundaries and their corresponding boundary conditions. Starting with a standard finite–element–method formulation based on the method of weighted residuals, we show that it is possible to treat the boundary in a manner that makes it unnecessary to determine its intersection with the surrounding CG. This feature is of great significance both algorithmically and numerically, for it eliminates complex topological operations hitherto considered essential in CG methods. In this new method, we require only a determination of the grid cells that envelop a series of known integration points on the body surface, which is a trivial problem for a CG. The resulting pseudo–finite–element formulation leads to a very robust numerical algorithm and computer code (EULAIR). We show the results of calculations performed on two–dimensional bodies and aerofoils to demonstrate the power of this new technique. The Euler equations have been solved in all these cases. However, the method is applicable to any partial differential equation that may be analysed by a CG approach. A computer code applying the three–dimensional formulation to solve flows around full aircraft configurations is currently under intensive development.

Implicit time-accurate solutions on unstructured dynamic grids

In this paper an unstructured multigrid algorithm is used as an iterative solution procedure for the discrete equations arising from an implicit time discretization of the unsteady Euler equations on tetrahedral grids. To calculate unsteady flows due to oscillating boundaries, a novel grid movement algorithm is introduced in which an elliptic equation with a non‒linear diffusion coefficient is used to define the displacement of interior grid nodes. This allows large grid displacements to be calculated in a single step. The multigrid technique uses an edge‒collapsing algorithm to generate a sequence of grids, and a pseudo‒time‒stepping smoother. On the coarser grids, no grid motion is used. Instead, surface normals are rotated consistently and transfer/interpolation weights are based on the time‒averaged grid co‒ordinates. A 2D NACA0012 test case is used to validate the programme. 3D results are presented for the M6 wing and a full aircraft configuration. © 1997 John Wiley & Sons, Ltd.

Effects of modal symmetry on transonic aeroelastic characteristics of wing-body configurations

To study accurately the transonic aeroelastic characteristics, it is important to model the full aircraft configuration, including asymmetry. Recently, an accurate method of computing unsteady transonic flows on full-span wing-body configurations was developed using the transonic potential flow theory. In this work, the method is further developed to account for the aeroelasticity of full-span wing-body configurations. This is accomplished by simultaneously integrating the unsteady aerodynamic forces and modal structural equations of the wing-body configurations. To validate the method, aeroelastic computations are made for a wing-body configuration with a rectangular wing. The aeroelastic responses of this configuration are correlated with the responses of a similar isolated wing. The comparisons are favorable. Aeroelastic computations associated with symmetric and antisymmetric modes are also made to study the influence of modal asymmetry on responses. This new development is further illustrated by computing the aeroelastic characteristics of a typical fighter aircraft. The results from this study will be useful in accurately computing the transonic flutter boundaries of aircraft, including those associated with asymmetric modes.