Rectangular Airfoil Research Articles

Numerical Simulation and Flow Display of Bionic Alula on Rectangle Airfoils

Some birds have small wings (Alula) in the middle of their main wings. These small wings will tilt upward when the bird flies at a high attack angle to maintain a stable flying posture. This paper explores the lift effects of bionic Alula on rectangular airfoils with different aspect ratios through numerical simulation and flow display experiments. According to the numerical simulation, Alula can increase the rectangular airfoil lift coefficient by a maximum of 24% when the airfoil aspect ratio is 2. By comparing simulation results with flow display results, the low-pressure area generated by Alula and the merge of the Alula vortices with the airfoil tip vortices mainly contribute to the lift enhancement.

Numerical aerodynamic of the rectangular wing concerning to ground effect

Numerical aerodynamic of the rectangular wing is presented regarding to the ground effect. Clark-Y wing section is selected for the present calculations. The Reynolds-averaged Navier-Stokes (RANS) equations solver of the ANSYS-CFX software is employed with a realizable k-e turbulent model. The numerical results lift and drag of the rectangular airfoil at ground effect are verified with the experimental data. Pressure distribution and velocity contour and turbulent intensity at the trailing edge of the airfoil are presented and discussed.

Three-dimensional vortex structure using phase-averaged stereoscopic PIV for an oscillating airfoil

A quasi-steady-state approach to the prediction of fluid forces acting on an insect wing leads to errors that suggest that flight is impossible. However, because biological flight does occur, the effect of unsteady fluid forces must be important to flight. The propulsive forces of these animals are related to unsteady fluid forces accompanied with the movement of vortices. Therefore, unsteady fluid forces must also be considered when estimating the propulsive force of swimming the front crawl and the flat scull technique in synchronized swimming. The purpose of this study was to investigate the effect of a three-dimensional airfoil shape on three-dimensional vortex structure for a high reduced frequency. The vortex structure and its behavior for a discoid airfoil were investigated. Furthermore, the vortex structure of the discoid airfoil was compared with that of a rectangular. The vortical flow fields were measured in the wake of the discoid airfoil using a stereoscopic particle images velocimetry technique. The three-dimensional vortex structure was depicted by plotting iso-vorticity surface calculated from the reconstructed velocity data. Compared with the rectangular airfoil, a strong vortex exists over a prolonged period of time in the wake of the discoid airfoil.

2차원 평판날개에서의 Tripwire가 공력에 미치는 영향

In this paper, we experimentally investigated the effects of attached cylindrical tripwires on the aerodynamic performance. The research was carried out with a simple two-dimensional (2-D) rectangular airfoil fabricated from thin flat-plate aluminium, with elliptical leading and trailing edges. Tripwires of varying widths and thicknesses, and attack angles of <TEX>$-5^{\circ}{\sim}20^{\circ}$</TEX> were used to investigate the aerodynamic characteristics (e.g. lift and drag forces) of the airfoil. We found that attaching the tripwires to the lower surface of the airfoil enhanced the lift force and increased the lift-to-drag ratio for low attack angles. However, attaching the tripwires to the upper surface tended to have the opposite effects. Moreover, we found that attaching the tripwires to the trailing edge had similar effects as a Gurney flap. The aerodynamic characteristics of the flat-plate airfoil with tripwires can be used to develop passive control devices for aircraft wings in order to increase their aerodynamic performance when gliding at low attack angles.

A numerical study of the effects of a winglet on airfoils

The purpose of this research is to investigate the effects of a winglet on aerodynamic noise of an airfoil. For simplicity, Reynolds Averaged Navier-Stokes equations combined with Realizable turbulence model are used to solve the turbulent flow. In order to verify the accuracy of flow field analysis, a uniform flow past a three-dimensional rectangular airfoil is analyzed and tracks the center line of the tip vortex. The agreement between the simulated and measured center line is good. For the sound field analysis, the flow induced noise around a rectangular airfoil is computed by the Broadband Noise Source (BNS) model. Proudman's formula was used to evaluate acoustic power per unit volume of aerodynamic noise. This study focuses on the sound power of aerodynamic noise generated by tip vortex when the flow passes through an airfoil and an airfoil with winglet. In order to understand the effects of the winglet on the aerodynamic noise, the different winglet characteristics are investigated and discussed. It is found that with a winglet the dynamic coefficient is improved and the generated sound power is also reduced by about 5.4 dB in this study.

Modelling of Cascade Fin Aerodynamics Near Stall using Kirchhoff's Steady-state Stall Model

Nonlinear longitudinal aerodynamics associated with cascade fins at high angles of attack near stall has been modelled using Kirchhoff's formulation. Grid fins are a relatively recent development in guided missile technology. In this paper, a new category of grid fins, nomenclatured as cascade fins, has been proposed. In cascade fin design, an appropriate selection of gap-to-chord ratio and the number of planar members lead to desired stall angle and acceptable overall lift coefficient, respectively. Kirchhoff's steady-state stall model has been validated on wind tunnel data generated for Cascade fins having rectangular airfoil cross-section. National Wind Tunnel Facility (NWTF) of IIT, Kanpur, was used to generate the wind tunnel data consisting of the variation of lift coefficient with angle of attack. The cascade fins were tested to generate the data by varying gap-to-chord ratio and number of planar fins. The cascade fins with rectangular cross-section were tested with and without end plates. Kirchhoff's steady-state stall model was applied to wind tunnel data of cascade fins for modelling flow separation point and maximum likelihood method was used to estimate the parameters characterising stall characteristics. The effects of end plates, variation of number of fins and gap-to-chord ratio on parameter estimation were also studied. It has been observed that Kirchhoff's steady-state stall model could advantageously be applied to model nonlinear aerodynamics associated with cascade fins at high angle of attack. Defence Science Journal, 2011, 61(2), pp.157-164 , DOI:http://dx.doi.org/10.14429/dsj.61.481

Comparison of Wing Characteristics at an Ultralow Reynolds Number

The hydrodynamic characteristics of 20 wings of different airfoil shape were measured at Re = 4 X 103. Each wing had an aspect ratio At of 7.25. Comparison of the measured wing characteristics showed that hydrodynamic characteristics of a wing with a rectangular airfoil can be improved by either a camber of 5%, a sharp leading edge, or proper corrugation

Trailing Vortex Wake Growth Characteristics of a High Aspect Ratio Rectangular Airfoil

The growth characteristics of trailing vortex wakes are investigated in a towing tank. The wakes from a lifting rectangular NACA 0012 airfoil with an aspect ratio of 8 are studied up to 1400 chords downstream. The circulation Reynolds number ranged from 4 x 10 3 to 4 x 10 4 . Digital particle image velocimetry is used to measure the velocity field in the cross-stream plane from which vorticity is calculated. The vortex pair is observed to be very stable and long-lived, showing little decay in the circulation of the individual vortices. The vorticity, however, diffuses over time within the cores of the vortices.

B232 翼端で発生する後曳き渦の渦核断面の回転に関する研究

This paper describes trailing vortices formed at wing tips of a rectangular airfoil (NACA63012), whose aspect ratio is unity. Our attention is paid on rotating motion of a core of the vortex portion located near trailing edge. Rotation of the core was definitely observed by systematic measurement using smoke wire method. Numerical simulation of the rotating motion for an elliptical shape was also made by 2-D discrete vortex method. The result of the simulation agreed considerably well with that of the experiment. Also, we tried to measure peak velocity of the outer boundary of the core, which can be noticed from smoke profile. The circulation of the vortex in the downstream direction was approximately evaluated from the peak velocity by assuming core shape in a reasonable way.

Trailing vortex wake growth characteristics of a high aspect ratio rectangular airfoil

The growth characteristics of trailing vortex wakes are investigated in a towing tank. The wakes from a lifting rectangular NACA 0012 airfoil with an aspect ratio of 8 are studied up to 1400 chords downstream. The circulation Reynolds number ranged from 4 x 10 3 to 4 x 10 4 . Digital particle image velocimetry is used to measure the velocity field in the cross-stream plane from which vorticity is calculated. The vortex pair is observed to be very stable and long-lived, showing little decay in the circulation of the individual vortices. The vorticity, however, diffuses over time within the cores of the vortices.

Water Tank Study of the Decay of Trailing Vortices

Underwater towing experiments were carried out with a rectangular airfoil of aspect ratio 5.3 at 4° and 8° angles of attack and at chord-based Reynolds numbers between 2.2 x 10 5 and 7.5 x 10 5. Tangential velocity measurements in the downstream region between 100 and 1000 chord lengths indicate rates of vortex decay proportional to r 7/8 at 8°, whereas previous flight tests show that the decay rate approaches £~ 1/2 far downstream. The observed behavior is explained in terms of an analytical solution that includes time dependence of the turbulent eddy viscosity, VT ~ tm. It shows that, for m > 0, an isolated turbulent vortex decays faster than t~1/2. In this case, the decay is accompanied by increasing vr, or levels of turbulence, which corresponds to turbulent nonequilibrium flow. The special case of vortex decay with equilibrium flow (m = 0) leads to the well-known decay rate 2. Since, in towing tank experiments at low Reynolds number, turbulent vortex decay may occur predominantly in nonequilibrium, it is doubtful that such tests correctly predict the late stage of decay of aircraft trailing vortices, when turbulence is the only dissipating mechanism.

A general solution for the rectangular airfoil in supersonic flow

The potential on a rectangular airfoil due to an arbitrarily prescribed motion at its surface is obtained by an operational solution of the linearized equations and subsequent comparison with the known solution in steady flow. It is shown that the result can be extended to more general planforms with the aid of the Lorentz transformation. Other methods of solution are noted.

A note on my paper: A general solution for the rectangular airfoil in supersonic flow

A note on my paper: A general solution for the rectangular airfoil in supersonic flow

The oscillating rectangular airfoil at supersonic speeds

The pressure distribution on a quarter infinite, zero thickness airfoil having a prescribed distribution of downwash (on the wing only), which exhibits a harmonic time dependence, is determined by a Fourier transform solution of the linearized, potential equation for supersonic flow. The solution is effected with the aid of the Wiener-Hopf technique and leads to a Green’s function, which may be expressed either as a finite, definite integral or as an expansion in powers of a dimensionless frequency parameter. It is shown that the results are applicable to the calculation of the forces and moments on rectangular airfoils of effective aspect ratio ( A cot ⁡ θ A\cot \theta , where θ \theta is the Mach angle) greater than unity. It appears that the force and moment coefficients of practical interest may be expressed in terms of known functions, including certain integrals which have been calculated for the two-dimensional, oscillating airfoil. The extension of the two-dimensional results to rectangular wings for which the prescribed downwash is constant along the span is particularly simple. The extension of the results for harmonic time dependence to the step function (Heaviside) case is indicated.

Investigation of the Wing-Wake Frequency with Application of the Strouhal Number

The present paper consists of two parts. The aim of the first part is to record the results of calculation of the Strouhal Number in two-dimensional flow behind an infinite plate, an infinite circular cylinder, and an infinite airfoil. The results obtained are compared with those from previous tests, and sometimes a fair agreement is obtained. The most important conclusions are as follows: (1) In general the Strouhal Number is not a constant. (2) The Strouhal Number in the wake behind a body with sharp edges is approximately constant. (3) The Strouhal Number in the wake behind a circular cylinder is constant only below the critical Reynolds Number. Above the critical Reynolds Number some assumptions permit one to conclude that as a first approximation the Strouhal Number is a linear function of the Reynolds Number. (4) When the wake behind an airfoil consists of vortex rows, the value of the Strouhal Number behind the airfoil, referred to the projection of the airfoil on the direction perpendicular to the direction of the flow, may be assumed as a constant. In the second part of this paper the results of some tests in a wind tunnel in twoand three-dimensional flow are presented. The following bodies were tested: (a) Airfoil in two-dimensional flow. (b) Airfoil of finite length. (c) Airfoil with flap in two-dimensional flow. (d) Airfoil with flap of finite length. The purpose of the tests was to find and to compare the values of the Strouhal Number behind the above-mentioned bodies. The results of the tests proved tha t : (a) When one refers the value of the Strouhal number of any airfoil in two-dimensional flow, with or without flaps, to the projection of the airfoil on the direction perpendicular to the direction of the airflow, the values of the Strouhal Number are within the limits of the values given by other investigators. (b) The frequency in the wake behind the center span of a rectangular airfoil of finite length is not affected by the tip vortexes. (c) The graph of frequency versus velocity appears to be a straight line but it is difficult to see whether it always passes through the origin of coordinates, although a slight tendency is visible. Blenk obtained straight lines passing through the origin, but his results do not agree with results obtained by Abdrashitov.

Effect of Dive Brakes on Airfoil and Airplane Characteristics

Effect of Dive Brakes on Airfoil and Airplane Characteristics