Steady Aerodynamic Forces Research Articles

Homogeneous Parametric Modeling of Airloads

This work proposes two parametric modeling strategies for steady aerodynamic forces. We point out that airloads are homogeneous and introduce a parametrization based on spherical harmonics and a neural network. The parametrization using spherical harmonics enables an analogue of frequency-based truncation and a variation on the Singular Value Decomposition (SVD), constituting an orthogonal decomposition of the modeled airloads. Since neural networks are universal function approximators, the model based on this allows for more flexible parametrizations, including actuations and model inversions. Both parametrization strategies are showcased for model identification and reduction purposes, highlighting their strengths and weaknesses.

Verification of a Body Freedom Flutter Numerical Simulation Method Based on Main Influence Parameters

The body freedom flutter characteristics of an airfoil and a fly wing aircraft model were calculated based on a CFD method for the Navier–Stokes equations. Firstly, a rigid elastic coupling dynamic model of a two-dimensional airfoil with a free–free boundary condition was derived in an inertial frame and decoupled by rigid body mode and elastic mode. In the fluid–solid coupling method, the rigid body was trimmed by subtracting the generalized steady aerodynamic force from the structural dynamic equation. The flutter characteristics were predicted by the variable stiffness method at a fixed Mach number and flight altitude. Finally, validation of the predicted body freedom flutter characteristics was performed through a comparison of theoretical solutions based on a Theodorsen unsteady aerodynamic model for airfoil and experimental results for a fly wing aircraft model. The mechanism of the influence of the bending mode stiffness and the position of the center of gravity on the body freedom flutter characteristics were briefly analyzed.

T-tail flutter simulations with regard to quadratic mode shape components

It is known that the dynamic aeroelastic stability of T-tails is dependent on the steady aerodynamic forces at aircraft trim condition. Accounting for this dependency in the flutter solution process involves correction methods for doublet lattice method (DLM) unsteady aerodynamics, enhanced DLM algorithms, unsteady vortex lattice methods (UVLM), or the use of CFD. However, the aerodynamic improvements along with a commonly applied modal approach with linear displacements results in spurious stiffness terms, which distort the flutter velocity prediction. Hence, a higher order structural approach with quadratic mode shape components is required for accurate flutter velocity prediction of T-tails. For the study of the effects of quadratic mode shape components on T-tail flutter, a generic tail configuration without sweep and taper is used. Euler based CFD simulations are applied involving a linearized frequency domain (LFD) approach to determine the generalized aerodynamic forces. These forces are obtained based on steady CFD computations at varying horizontal tail plane (HTP) incidence angles. The quadratic mode shape components of the fundamental structural modes for the vertical tail plane (VTP), i.e., out-of-plane bending and torsion, are received from nonlinear as well as linear finite element analyses. Modal coupling resulting solely from the extended modal representation of the structure and its influence on T-tail flutter is studied. The g-method is applied to solve for the flutter velocities and corresponding flutter mode shapes. The impact of the quadratic mode shape components is visualized in terms of flutter velocities in dependency of the HTP incidence angle and the static aerodynamic HTP loading.

Study on the safety of operating high-speed railway vehicles subjected to crosswinds

A coupled vehicle-track dynamic model is put forward for use in investigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as a nonlinear multi-body system, and the ballasted track is modeled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic response and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that crosswinds at attack angles of 75° to 90° with respect to the forward direction of the vehicle have a great influence on the safety of operating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, i.e., the safest, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.

Co-simulation of High-speed Train Fluid-structure Interaction Based on the Equilibrium State

In order to achieve the co-simulation between train aerodynamics and vehicle-track coupling dynamics in crosswind,a fast and high-efficiency equilibrium state method is presented.Firstly,vehicle-track coupling dynamics responses to steady aerodynamic forces and train aerodynamics under steady attitude state are solved alternatively ignoring track irregularity.The equilibrium state is obtained by judging convergence criterion.The static forces of train in equilibrium state are loaded to the model of vehicle-track coupling dynamics and the responses of high-speed train are calculated.The fluid-structure dynamics of a high-speed train are simulated under the case that the velocity of crosswind is 13.8 m/s and running speed of train is 350 km/h.The differences in aerodynamic forces and safety indexes calculated with equilibrium state method,alternative co-simulation and off-line simulation are compared.The results show that there is little difference in results calculated with equilibrium state method and alternative co-simulation;however,the calculation efficiency of equilibrium state method is much higher than that of alternative co-simulation.

G1101 風洞実験用空気軸受型3分力ロードセルの開発研究(GS11 物体まわり流)

An air suspended load cell, which is available to measure steady aerodynamic forces on the spinning golf ball in the wind tunnel flow, has been developing during these five years. The characteristic to measure two components of forces as drag and side ones had already been accomplished with sufficient accuracy. However, the performances of the lift force direction had not been achieved by the influences of atmospheric pressure changes. The sufficient accuracy has accomplished, in this study, mainly by two improvements of the light-weight of ball supporting unit and the cancellation mechanism of atmospheric pressure variations. The lift force on highly spinning golf ball in the wind tunnel flow are measured and compared with the results of gauge type load cell.

Numerical method of static aeroelastic correction and jig-shape design for large airliners

In this paper, a coupled CFD-CSD method based on N-S equations is described for static aeroelastic correction and jig-shape design of large airliners. The wing structural flexibility matrix is analyzed by a finite element method with a double-beam model. The viscous multi-block structured grid is used in aerodynamic calculations. Flexibility matrix interpolation is fulfilled by use of a surface spline method. The load distributions on wing surface are evaluated by solving N-S equations with a parallel algorithm. A flexibility approach is employed to calculate the structural deformations. By successive iterations between steady aerodynamic forces and structural deformations, a coupled CFD-CSD method is achieved for the static aeroelastic correction and jig-shape design of a large airliner. The present method is applied to the static aeroelastic analysis and jig-shape design for a typical large airliner with engine nacelle and winglet. The numerical results indicate that calculations of static aeroelastic correction should employ tightly coupled CFD-CSD iterations, and that on a given cruise shape only one round of iterative design is needed to obtain the jig-shape meeting design requirements.

Investigation on influence factors of buffeting response of bridges and its aeroelastic model verification for Xiaoguan Bridge

A time-domain procedure for analyzing buffeting responses of bridges is presented and implemented in ANSYS, formulated taking into account the self-excited forces, aerodynamic admittance functions (AAFs) and the coherence of buffeting forces. The buffeting forces simulated based on the span-wise coherence of buffeting forces and also considering the aerodynamic admittance functions, together with the steady aerodynamic forces are applied as external loads to the structural model to analyze the buffeting responses in time domain. In order to account for self-excited forces, elemental aeroelastic stiffness and aeroelastic damping matrices for spatial beam elements are derived following the quasi-steady theory and are incorporated in buffeting analysis through the user-defined Matrix27 element in ANSYS. The procedure is applied to the Xiaoguan Bridge, China, during the longest double cantilever stage of construction. The wind tunnel tests of four typical bridge section models are performed to measure the aerodynamic parameters of the bridge including the steady aerodynamic coefficients and aerodynamic admittance functions. The bridge aeroelastic model testing is also carried out, and coherence functions of buffeting forces are derived from the measured buffeting forces. The measurement results of the displacements and internal forces are compared with those obtained from the analytical predictions. The influence factors, including aeroelastic effect, aerodynamic admittance functions and coherence of buffeting forces, are studied in some detail. It is shown the present method inclusive of above factors gives much closer predictions of buffeting responses to the experimental results.

회전익 표면의 정상하중에 의한 소음의 방사특성

회전하는 물체의 표면에 걸리는 정상하중에 의해 발생되는 소음을 이론적으로 해석하여 그 방사특성을 분석하였다. 해석의 편의성을 위해, 물체의 표면에 걸리는 힘은 표면 전체에 고루 분포된 분산하중이 아닌 한 점에 집중된 점하중으로 표현하였고, 소음계산은 엄밀한 Lowson의 하중소음식을 사용하였다. Lowson 식의 각 항들을 수학적으로 보다 자세하게 구분하여 각 항들이 가지는 물리적 특성에 대해 논의하였다. 회전각속도를 변화시켜가며 단일 점하중에 의해 발생되는 소음의 방사특성을 근거리 및 원거리에서 조사하였고 그에 대한 이론적 근거를 제시하였다. 또한 거리에 따른 음압의 크기를 조사하여 근거리와 원거리에서의 음압감소비율 및 회전각가속도의 역할에 대해 논의하였다. 마지막으로, 점하중의 개수가 증가될 때 소음이 오히려 감소하는 현상을 설명함과 더불어 소음저감의 방안과 그 한계점 및 향후 연구주제에 대하여 논의하였다. Loading noise generated by steady aerodynamic force exerted on the rotating body surface is theoretically analyzed and its radiation characteristics is examined as a fundamental research of helicopter rotor noise. For simplicity, the force exerted on each blade is not distributed but concentrated at one point and the noise is evaluated by using Lowson' exact formula with a discussion of the physical meaning of each term in the formula. For a single point force rotating with various angular frequencies, we investigated the radiation characteristics and theoretically explained the physical behavior at near and far-field. By investigating the amplitude of acoustic pressure with various distances, we observed the different decreasing ratio at near- and far-field with the discussion of the effect of acceleration of angular frequency. Finally, the phenomenon that the noise level is reduced everywhere as the number of blade increases is explained with the suggestion of a noise reduction idea, the limitations of this study, and the future research topics.

Direct frequency domain calculation of open rotor noise

Fig. 1 Typical curved waverider (——) and a caret wing (-) and the supporting shock waves: 7 = 1.4; A/o>= 10; a = 25 deg.; fto = 0.1; 62=-2 References ^essiter, A. F., Lift of Slender Delta Wings According to Newtonian Theory, AIAA Journal, Vol. 1, No. 4, 1963, pp. 794-802. Hemdan, H. T., and Hui, W. H., Unsteady and Steady Aerodynamic Forces of Slender Delta Wings According to Newtonian Theory, Canadian Aeronautics and Space Journal, Vol. 23, No. 4, 1976, pp. 238-251. Malmuth, N. D., Three-Dimensional Perturbations on Hypersonic Wedge Flow, AIAA Journal, Vol. 2, No. 8, 1964, pp. 1383-1389. Hui, W. H., Supersonic and Hypersonic Flow with Attached Shock Waves over Delta Wings, Proceedings of the Royal Society of London, Series A, Vol. 325, 1971, pp. 251-267. Hemdan, H. T., Waverider Configurations According to Thin Shock-layer Theory, Acta Astronautica, Vol. 21, No. 8, 1990, pp. 571-582.

Ground vehicles in high cross winds part III: The interaction of aerodynamic forces and the vehicle system

This is the final part of a three-part paper that draws together previous work on ground vehicles in high cross winds, and sets up a consistent analytical framework for discussion of the various wind-induced problems, Part I considered steady aerodynamic forces and moments; Part II then considered unsteady aerodynamic effects. This paper uses the data and methods of the first two papers to look at the various wind-induced problems of ground vehicles in cross winds-vehicle suspension excitation, vehicle overturning and wind-induced course deviations-and considers the interaction of the aerodynamic forces and moments with the vehicle/driver system.

Ground vehicles in high cross winds part I: Steady aerodynamic forces

Ground vehicles in cross winds suffer from a variety of wind-induced effects that if they are to be described and predicted, require aerodynamic force and moment data. Part I of this paper has considered the steady aerodynamic forces and moments on ground vehicles in high cross winds. This paper considers the unsteady aerodynamic forces in the frequency, amplitude and time domains and sets them in a consistent analytical framework. Part III will go on to consider the interaction between the applied aerodynamic forces and the dynamics of the vehicle system.

Ground vehicles in high cross winds part II: Unsteady aerodynamic forces

Ground vehicles in cross winds suffer from a variety of wind-induced effects that if they are to be described and predicted, require aerodynamic force and moment data. Part I of this paper has considered the steady aerodynamic forces and moments on ground vehicles in high cross winds. This paper considers the unsteady aerodynamic forces in the frequency, amplitude and time domains and sets them in a consistent analytical framework. Part III will go on to consider the interaction between the applied aerodynamic forces and the dynamics of the vehicle system.

On wake-induced vibration of a conductor in the wake of another via a 3-D finite element method

Bundled conductors exhibit a phenomenon known as wake-induced vibration, or, in power-line parlance, subspan vibration. The wake-induced vibration is caused by the steady aerodynamic force field, generated by the wake of the windward conductor, in which the leeward conductor lies. Two-dimensional formulations of this problem have been thoroughly studied. In the present paper this problem is treated three-dimensionally via a finite element method developed at the National Research Council, Ottawa, Canada. Discrepancies between 2-D and 3-D results lead one to question the validity of 2-D model representation for the 3-D physical reality. However, it remains to be seen whether or not the 3-D numerical results can be substantiated experimentally.