Rectangular Flat Plate Wing Research Articles

Examination and Prediction of the Lift Components of Low Aspect Ratio Rectangular Flat Plate Wings

An investigation of the lift components present over low aspect ratio rectangular wings is presented. Wing aspect ratios ranging from 0.5 to 3 are examined using published experimental results and analytic analysis methods. The methods are based on the fundamental decomposition of Polhamus; that is, lift is attributed to a potential flow lift component coupled with a vortical lift component stemming from the leading and side edges of the flat plate wing. The analysis suggests a low sensitivity to Reynolds numbers spanning three orders of magnitude and brings into doubt the realization of a leading edge vortex lift component for wings with unswept leading edges under steady state conditions. The analytic prediction method of Purvis is shown to provide close accord with all experimental data sets when lift contributions caused by a leading edge vortex are excluded.

On the lift curve slope for rectangular flat plate wings at moderate Reynolds number

The lift coefficient for a flat plate at low angles of attack is obtained experimentally for various aspect ratios (AR ​= ​1, 2, 4, 8) and moderate Reynolds numbers (Re ​= ​40 ​× ​103 to Re ​= ​200 ​× ​103). The variation of the lift coefficient with the angle of attack in the pre-stall region is consistent with a linear slope approximation. We consider that this slope is a function of both the aspect ratio and Reynolds number. In this research, we provide a correlation that can predict the lift slope value with an average error of less than 5%. This correlation captures the idea of Prandtl’s finite wing theory and extends its application for any Reynolds number. The same correlation is tested against other literature experiments providing very accurate results even outside our range of measured AR and Re.

Comparison of Rotating and Translating Wings: Force Production and Vortex Characteristics

Experiments were conducted on a rectangular flat plate wing at high incidence to compare the force production and leading-edge vortex location and strength as a function of time for eight sets of wing kinematics: rectilinear and rotational pitch and surge, with fast and slow accelerations. The primary differences observed in the force histories were between the pitch and surge cases, and they occurred during the acceleration or pitching portions of the motions. The force histories were found to be similar between the rectilinear and rotational cases. The leading-edge vortex trajectories in the rectilinear cases were found to be similar when compared on a new time scale , related to the integrated leading-edge-normal velocity. The vortex trajectory of the rotational cases matched those of the rectilinear cases until the leading-edge vortex in the rotational case settled into a position attached to the wing. Circulation values of the leading-edge vortex for all cases were found to collapse when plotted versus and scaled by the instantaneous leading-edge-normal velocity. The results demonstrate a successful collapse of both vortex quantities and force production using only leading-edge kinematics.

Passive control of roll oscillations of low-aspect-ratio wings using bleed

A passive flow control method, which uses bleed from a slot near the wing tip, has been shown to attenuate self-excited roll oscillations of a low-aspect-ratio (AR = 2) rectangular flat plate wing. This method was found to be successful across the whole range of angle of attack and better than previous active flow control methods. The effectiveness of the slot strongly depends on its location and width. For effective slot geometries, the tip vortex becomes less coherent, almost eliminating the roll oscillations. Nonlinear interactions between the shear layers shed from the tip and the slot, as well as between the shear layer and the counter-rotating vortex may act as excitation, which can modify the response of the self-sustained oscillator. When the slot is located too close to the tip, there is rapid merging of the shear layers and less interaction, and the slot loses its effectiveness. Also, when the slot is narrow, there is insufficient bleed, resulting in less effective attenuation. Force measurements revealed that this technique can be used as an effective method to suppress roll oscillations without sacrificing and possibly improving aerodynamic performance.

Attenuation of Self-Excited Roll Oscillations of Low-Aspect-Ratio Wings by Using Acoustic Forcing

Attenuation of self-excited roll oscillations of low-aspect-ratio wings using acoustic excitation was studied in a wind tunnel. For a rectangular flat-plate wing with an aspect ratio of 2, roll oscillations can be completely suppressed, and the onset of the roll oscillations can be delayed with external acoustic excitation. Similar results were also obtained for wings with two different airfoil profiles. Velocity measurements indicated that acoustic excitation could restore a symmetric vortex flow over the free-to-roll wings, thus eliminating the self-excited roll oscillations. The effect of excitation is most noticeable for the side of the wing that sees a larger effective angle of attack due to the rolling motion. Acoustic excitation energizes the shear-layer instabilities and results in reattachment or smaller separated flow region closer to wing surface, thus in turn suppressing the roll oscillations.

Investigation of Computational Non-Linear Aeroelastic Response of High Aspect Ratio Wing

Aircrafts with high aspect ratio wings are most eligible candidates for high altitude and long endurance flights. Such wings show a non-linear deformation behavior because of structural geometric non-linearity. In the present study both linear and non-linear static aeroelastic behaviors of a high aspect ratio rectangular flat plate wing are analyzed using a simplified approach. The main emphasis lies in the tremendous change of lift distribution on the flexible high aspect ratio wing when large deflections are incorporated in the static aeroelastic analysis. The computational static aeroelastic simulations are performed in the finite element method based commercial software ANSYS-14. The aerodynamic load is calculated using the strip theory. Since the aero-load changes with the twisting deformation hence a user defined script is written using ANSYS parametric design language (APDL). The computationally achieved divergence velocity results are compared with the analytical results. The results of parametric study at different flight load conditions and angles of attack have highlighted the role of geometric nonlinearities in both bending and twisting deformations. The impact of follower pressure forces on the aeroelastic response is also investigated.

A lift formula applied to low-Reynolds-number unsteady flows

A lift formula for a wing in a rectangular control volume is given in a very simple and physically lucid form, providing a rational foundation for calculation of the lift of a flapping wing in highly unsteady and separated flows at low Reynolds numbers. Direct numerical simulations on the stationary and flapping two-dimensional flat plate and rectangular flat-plate wing are conducted to assess the accuracy of the lift formula along with the classical Kutta-Joukowski theorem. In particular, the Lamb vector integral for the vortex force and the acceleration term of fluid for the unsteady inertial effect are evaluated as the main contributions to the unsteady lift generation of a flapping wing.

Active Control of Self-Induced Roll Oscillations of a Wing Using Synthetic Jet

Active control of self-excited roll oscillations of a rectangular flat plate wing with an aspect ratio of two was studied experimentally in a wind tunnel, using synthetic jet excitation near the leading edge. It was found that, by activating the synthetic jet excitation at an optimum frequency of St = 1, large amplitude roll oscillations could be attenuated and the onset of the oscillation can be delayed by up to Δαmax = 3.5° for extremely small values of momentum coefficient. High frame-rate Particle Image Velocimetry (PIV) measurements revealed a strong resonance between the synthetic jet excitation and shear layer instabilities. The resonance energizes the shear layer separated from the leading edge and results in a local flow field that is more typical of lower wing incidence, thus effectively suppressing roll oscillations.

Thin-Wing Vibration Control Using Flexible Fins

This paper describes thin-wing vibration control using an array of small flexible rectangular polymer fins attached near the leading edge on the upper wing surface to manipulate unsteady flow structures. Dynamic aeroelastic deformation of a rectangular flat-plate wing and motions of the fins relative to the wing are measured by using a high-speed videogrammetric system in a low-speed wind tunnel. The major vibration modes of the baseline wing and the wing with the fins are extracted. It is found that wing vibration particularly near the dominant first torsion mode is considerably suppressed by the flexible fins interacting with highly unsteady separated flows in the ranges of the freestream velocities and angles of attack. Global velocity measurements indicate that the fins significantly reduce the unsteadiness of the separated flow on the wing. The physical mechanisms behind the vibration suppression with the flexible fins are explored based on the analysis of the measured data.

Lift Enhancement for Low-Aspect-Ratio Wings with Periodic Excitation

In an effort to enhance lift on low-aspect-ratio rectangular flat-plate wings in low-Reynolds-number post-stall flows, periodic injection of momentum is considered along the trailing edge in this numerical study. The purpose of actuation is not to reattach the flow but to change the dynamics of the wake vortices such that the resulting lift force is increased. Periodic forcing is observed to be effective in increasing lift for various aspect ratios and angles of attack, achieving a similar lift enhancement attained by steady forcing with less momentum input. Through the investigation on the influence of the actuation frequency, it is also found that there exists a frequency at which the flow locks on to a time-periodic high-lift state.

Effect of Tip Vortices in Low-Reynolds-Number Poststall Flow Control

We numerically investigate the application of steady blowing to three-dimensional stalled flows around low-aspect-ratio rectangular flat-plate wings at a Reynolds number of 300. The objective of this study is to explore techniques to enhance lift by directly modifying the dynamics of the wake vortices. Out of various combinations of forcing location and direction considered, we identify two configurations that provide significant lift enhancement. In these cases, actuation appears to strengthen the tip vortices for increased downward induced velocity upon the leading-edge vortices. This in turn moves the low-pressure core directly above the top surface of the wing to greatly enhance lift.

직사각형 평판 날개의 날개짓과 비틀림 운동에 대한 비정상 VLM 공력 해석

The unsteady vortex lattice method is used to model twisting and flapping motions of a rectangular flat plate wing. The results for plunging and pitching motions were compared with the limited experimental results available and other numerical methods. They show that the method is capable of simulating many of the features of complex flapping flight. The lift, thrust and propulsive efficiency of a rectangular flat plate wing have been calculated for various twisting angles and reduced frequency with an amplitude of flapping angle(20°). And the effects of the twisting on the aerodynamic characteristics of the flapping wing are discussed by examination of their trends.

1617 極低アスペクト比矩形翼の全迎角空力特性と流れ構造 : 第 2 報 : 翼近傍流れと後流構造

1617 極低アスペクト比矩形翼の全迎角空力特性と流れ構造 : 第 2 報 : 翼近傍流れと後流構造

1404 極低アスペクト比矩形翼の全迎え角空力特性とその流れ構造に関する研究

1404 極低アスペクト比矩形翼の全迎え角空力特性とその流れ構造に関する研究

Chordwise Divergence of Rectangular Flat Plate Wings at Supersonic Speeds

Chordwise Divergence of Rectangular Flat Plate Wings at Supersonic Speeds