Planar Wing Research Articles

Extinction of interacting nonpremixed flames and existence of stationary retreating edges in twin-jet counterflow

A two-dimensional ‘twin-jet counterflow’ burner, in which two opposing streams from two double-slit nozzles form a counterflow, has been utilised to investigate the effect of the interaction of nonpremixed flames on extinction behavior. Results show that owing to the existence of unique petal-shaped flames, the extinction boundary for the cross-stream arrangement can be extended appreciably, as compared with that for the conventional counterflow arrangement, through the interaction of the curved sections of the interacting flames. The stationary petal-shaped flames had four flame edges, consisting of two retreating edges with negative edge speed in the direction toward the burnt gas region and two propagating edges with positive edge speed in the direction toward the unburned mixture. The OH-PLIF images of the petal-shaped flames demonstrated a strong concentration interaction between the two curved flame sections. Hysteresis in the transition between the petal-shaped flame and the curved flame having planar wing sections were observed. The representative propagation speed of the retreating edges of the petal-shaped flames correlated reasonably with maximum flame luminosity. The extinction characteristics of the retreating edges can be described in terms of the local Karlovitz number, which accounted for the local characteristic reaction time.

Numerical and Experimental Analysis of a Generic Fan-in-Wing Configuration

The present investigation focuses on assessing the predictive capabilities of state-of-the-art computational fluid dynamics for a generic fan-in-wing configuration by comparison with experimental data. The objective is to reproduce a short take off and landing or a transition-flight situation without ground effect. A rotating fan is placed in the wing plane, inside of the wing's rear part and close to the root section. The obtained experimental data include force measurements, surface pressure measurements, flowfield mapping using particle image velocimetry and wool-tufts visualization. A structured mesh of the entire configuration with minimum geometrical simplifications is used to perform unsteady Reynolds-averaged Navier-Stokes computations. The area surrounding the rotor blades is set up as sliding mesh to simulate the rotation. Because of the abrupt deflection of the flow by the fan, an unsteady recirculation area is generated above the rotor blades resulting in a highly distorted inflow. The blocking of the freestream by the jet exiting the fan's nozzle creates a back pressure affecting the internal aerodynamics. The jet rolls up in a counter-rotating vortex pair with considerable impact on the wing's aerodynamic performance. Time-averaged unsteady results over one fan revolution show a good agreement with the experimental data. The major turbulence phenomena are well predicted by the simulation.

Experimental investigation of the aerodynamic characteristics of generic fan-in-wing configurations

AbstractThis experimental investigation concentrates on the aerodynamic behaviour of a generic fan-in-wing configuration. The effects of the fan(s) on the flow circulation in a short take-off and landing or a transition flight condition without ground effect are evaluated. A wind-tunnel model has been constructed and tested to quantify the aerodynamic effects. Force measurements, surface pressure measurements, stereo-particle image velocimetry and wool tufts flow visualisation are performed. Different fan-in-wing configurations with the fans rotating in the wing plane, one fan either at the rear or front part of the wing and two fans are compared to the closed wing without fans set as reference. A fan placed near the trailing edge improves significantly the lift coefficient due to a jet flap effect on the wing lower side combined with enhanced suction on the wing upper side. The jet exiting the nozzle rolls up in a counter rotating pair of vortices affecting significantly the wing behaviour.This experimental investigation constitutes also a useful database for further CFD comparison.

On the vein-stiffening membrane structure of a dragonfly hind wing

Aiming at exploring the excellent structural performance of the vein-stiffening membrane structure of dragonfly hind wings, we analyzed two planar computational models and three 3D computational models with cambered corrugation based on the finite element method. It is shown that the vein size in different zones is proportional to the magnitude of the vein internal force when the wing structure is subjected to uniform out-of-plane transverse loading. The membrane contributes little to the flexural stiffness of the planar wing models, while exerting an immense impact upon the stiffness of the 3D wing models with cambered corrugation. If a lumped mass of 10% of the wing is fixed on the leading edge close to the wing tip, the wing fundamental frequency decreases by 10.7%∼13.2%; if a lumped mass is connected to the wing via multiple springs, the wing fundamental frequency decreases by 16.0%∼18.0%. Such decrease in fundamental frequency explains the special function of the wing pterostigma in alleviating the wing quivering effect. These particular features of dragonfly wings can be mimicked in the design of new-style reticulately stiffening thin-walled roof systems and flapping wings in novel intelligent aerial vehicles.

1609 流体構造連成により引き起こされる昆虫羽ばたき飛行のピッチング運動に関する3次元数値的研究(OS16-3 生物・生体工学に関する流れ,オーガナイズドセッション)

In this study, we evaluated the lift force generated by the crane-fly's flapping wing with the passive pitching using the three dimensional finite element method for the fluid-structure interaction. The torsional flexibility of the wing was modeled as the spring attached to the wing plane. In the computational simulation, the model wing kept the high angle of attack during the flapping translation and rotated quickly upon the stroke reversal without any aid for the pitching motion. The generated lift force was comparable to the insect's weight. Our result strongly suggests that the pitching motion can be passive in the cranefly's flapping flight.

Vortex structure of separated flows on model wings at low freestream velocities

Flow past model wings is experimentally investigated in a subsonic wind tunnel at large angles of attack at which the laminar boundary layer separates near the leading edge of the wing (flow stall). The object of the study was the flow structure within the separation zone. The carbon-oil visualization of surface streamlines used in the experiments showed that in the separation zone there exist one or more pairs of large-scale vortices rotating in the wing plane. Certain general properties of the vortex structures in the separation zone are found to exist, whereas the flow patterns may differ depending on the model aspect ratio, the yaw angle, and other factors.

Semiperiodic screening of a rotating plane wing

The lift force created by the transverse rotation of a plane screened wing at different speeds and angles of inclination of the screen is considered. The experimental data satisfy the self-similarity condition.

Effects of Nonlinearities on Subsonic Aerodynamic Center

A refined mathematical definition for the aerodynamic center of a wing or complete airplane is presented, which allows for inclusion of the trigonometric and aerodynamic nonlinearities. From this definition, analytical relations are developed for both the axial and vertical positions of the aerodynamic center at any angle of attack, independent of whether or not the nonlinearities are included. Results show that, when all nonlinearities are included, the position of the aerodynamic center can change with angle of attack. Because the traditional approximation provides only a fixed axial coordinate, this analysis provides two additional pieces of information about the aerodynamic center, that is, its vertical coordinate and its movement. Two examples are presented, which separate these two effects. The first example uses computational fluid dynamics to show that, when the effects of the nonlinearities are combined with wing sweep at high angles of attack below stall, the aerodynamic center of a planar wing moves significantly aft and below the wing. The second example, which uses an approximate closed-form solution for two lifting surfaces, emphasizes the importance of knowing the vertical position of the aerodynamic center and shows that, in the absence of sweep, its movement with angle of attack is slight.

On the natural frequencies and mode shapes of dragonfly wings

A base-excitation modal testing technique is adopted to measure the natural frequencies and mode shapes of dragonfly wings severed from thoraxes. The severed wings are glued onto the base of a shaker, which is capable of inducing translational motion in the lateral direction of the wing plane. Photonic probes are used to measure the displacement history of the shaker base and the painted spots of the wing simultaneously. A spectrum analyzer is employed to calculate the frequency response functions, from which the natural frequencies and the associated mode shapes of the wing structure can be extracted. Our experimental results show that the fundamental natural frequency of dragonfly wings is in the order of 170 Hz when it is clamped at the wing base. The average flapping frequency 27 Hz of dragonflies is about 16% of the fundamental natural frequency. At this frequency ratio, the inertial force of the wing is negligible compared to the elastic force. In other words, the wing deformation during flapping flight is solely due to the balance between the external aerodynamic force and the elastic force of the wing structure. The wing structures are generally lightly damped, with damping ratio in the order less than 5%.

Robust evolutionary algorithms for UAV/UCAV aerodynamic and RCS design optimisation

One of most important challenges in Unmanned (Combat) Aerial Vehicles (UCAV) is improvement of survivability and that can be achieved by well designed aerodynamic and Radar Cross Section (RCS) shapes. The aerodynamic efficiency aims to providing a short distance take-off, long endurance and better maneuverability. In addition, the stealth property is one of the essential requirements to complete diverse missions and ensure the survivability of UAVs. This paper explores the application of a robust Evolutionary Algorithm (EA) for aerofoil sections and wing plan form shape design and optimisation for the improvement of aerodynamic performance and the reduction of Radar Cross Section. The method is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing and asynchronous evaluation. Results obtained from the optimisation show that utilising the designing transonic wing aerofoil sections and plan form in combination with evolutionary techniques improve the aerodynamic efficiency. It is shown that this optimisation procedure produced a set of shock-free aerofoils and achieved supercritical aero-diamond wings. Results also indicate that the method is efficient and produces optimal and Pareto non-dominated solutions.

Fly like a Bird

This paper discusses the development of a new aircraft based on a bird's flying principle. As currently envisioned, the ultra-slim vehicle would be unmanned, solar-powered, and made of strong, lightweight materials. Rather than a metal framework covered by riveted plates and hydraulically actuated parts, the plane's body and wings would consist of a plastic-like material called an ionic polymer-metal composite, which deforms when exposed to an electric field. If the voltages are applied just right, the material can be made to flap like a wing. On top of the composite wings would be paper-thin sheets of photovoltaic material and lithium-ion batteries, layered on by thin-film deposition. Energy efficiency is the largest benefit in this project. The solid-state aircraft would have many potential uses; gathering scientific data, relaying communications, and surveying terrain are but a few.

Design Optimization of Shielding Effect for Aircraft Engine Noise

The present study is a technical report of the multi-objective design optimization of the two-dimensional shielding effect for the reduction of aircraft engine fan noise. The design optimization has been performed for the simplified cross section of aircraft with fuselage and plane wing. Two objective functions are considered for minimizing the sound pressure level at the side and the bottom locations relative to the fuselage, where standard measuring locations are defined by International Civil Aviation Organization. Those values are evaluated by using the linearized Euler equations. Since a wing, which is defined as a plate without thickness, is assumed as a V-tail wing, it is described by using the length and cant angle relative to the fuselage. The kriging-based response surface model is selected as an optimizer for the reduction of optimization cost. As a result, it is revealed that engine fan noise described by a monopole sound source is reduced by the shielding effect. Moreover, there is no tradeoff between two objective functions, i.e., the sound pressure levels at the side and the bottom measuring locations can be simultaneously reduced. As it is better that the wing length is as long as possible, the cant angle is essential for the shielding effect to reduce engine fan noise.

Numerical simulation of insect flight

In the non-inertial coordinates attached to the model wing, the two-dimensional unsteady flow field triggered by the motion of the model wing, similar to the flapping of the insect wings, was numerically simulated. One of the advantages of our method is that it has avoided the difficulty related to the moving-boundary problem. Another advantage is that the model has three degrees of freedom and can be used to simulate arbitrary motions of a two-dimensional wing in plane only if the motion is known. Such flexibility allows us to study how insects control their flying. Our results show that there are two parameters that are possibly utilized by insects to control their flight: the phase difference between the wing translation and rotation, and the lateral amplitude of flapping along the direction perpendicular to the average flapping plane.

Experimental study of aerodynamic behavior in wind tunnels with ornithopter and plane models

There are similarities between planes and birds. In fact aerodynamics bases are the same. In order to make some comparisons, this paper presents two series of experiments: one in a wind tunnel with an ornithopter model for measurements of aerodynamic forces with flapping wings. The wing movement has two degrees of freedom flapping around the longitudinal axis of the model and feathering around the wing axis. Measurements of aerodynamic forces: lift and drag in static case averaging values during many cycles of movement and in dynamic case have been performed. The other part of the paper concerns velocity and turbulence measurements on a metal plane wall jet in a wind tunnel with and without a rough surface, with and without acoustic vibrations in order to simulate a plane wing. Aerodynamic characteristics have been obtained in all cases.

Experimental Investigations on the Ground Effect Characteristics of the U-shaped and V-shaped Wing Designs for the Aero-Train

This paper describes the investigations on the aerodynamic characteristics of a U-shaped and V-shaped wing in ground effect. The lift, drag, side force, and rolling moment were measured in a low turbulance wind tunnel, using a 6-component balance. The flow over the upper surface was visualized by the tuft method. The results obtained were as follows : The U-shaped and V-shaped wing had an almost equivalent lift-to-drag ratio compared to a planar wing. This was due to the dihedral angle of U-shaped and V-shaped wing, resulting in a decrease of the induced drag. While separation only occurred on the V-shaped wing at an attack angle of 6 degree, a higher lift-to-drag ratio of the U-shaped wing was obtaind at attack angle of 4 and 6 degree. With both wings, an almost equal restoring force and an even higher restoring moment were obtained than with a conventional box shaped wing. Thus, the U-shaped and V-shaped wing offer a more suitable wing configuration for the Aero-Train than a conventional wing does.

Polynomial series expansion for optimisation of wing plane structures in idealised critical flutter conditions

AbstractA numerical procedure, which utilises polynomial power series expansions for the optimisation of multipanel wing structures in idealised critical flutter conditions, is introduced and developed. It arises from the Rayleigh-Ritz method and employes trial polynomial describing functions both for the flexural displacement and for the thickness variation over the multipanel surface. An idealised structural plate model, according to the Kirchhoff’s theory, together with a linearised supersonic aerodynamic approach, are supposed. The classical Euler-Lagrange optimality criterion, based on variational principles, has been utilised for the optimisation operations, where by imposing the stationary conditions of the Lagrangian functional expression, a nonlinear algebraic equations system is obtained, whose solution is found by an appropriate algorithm. By utilising an iterative process it is possible to reach the reference structure critical conditions, with an optimised thickness distribution throughout the multipanel surface. The final part of the work consists in searching the minimum weight of the multipanel planform wing structure with optimised thickness profilevsthe flutter frequency, considered as a variable imput parameter, for fixed flutter speed and equal to the critical one of the reference uniform structure.

Big macrocyclic assemblies of carboranes (big MACs): synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units

The macrocyclic compound, [1,2-C 2B 10H 10-1,4-C 6H 4-1,7-C 2B 10H 10-1,4-C 6H 4] 2 ( 5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)- ortho-carborane. The X-ray crystal structure of 5·C 6H 6·6C 6H 12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic C s and local C 2 v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D 2 h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol −1 higher in energy than the C 2 v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful.

Free stream turbulence effect on the flow structure over the finite span straight wing

Flow visualization tests have been performed to examine the structure of the near-wall flow over a low-aspect ratio straight wing installed at various angles of attack b and chord Reynolds number Re_c = U c/v = 1.76 ×10^5 . The experiments were carried out at two free-stream turbulence levels, b = 0.1% and b = 1%, the latter one having been achieved using a baffling grid. To visualize the flow, termochromic cholesteric liquid crystals and digital processing of video images were used. At the low turbulence level and b = 27°, a flow stall on the lee side of the wing was observed, with a pair of large-scale vortices rotating in the wing plane. Simultaneously, no vortex structures were observed on the windward wing surface. It was found the flow patterns on either side of the wing significantly changed with increasing free-stream turbulence level. A separation bubble appeared near the leading edge on the lee side of the airfoil at b = 1%, and large-scale stationary longitudinal vortices originated over the wing windward surface. The number and sizes of the longitudinal structures were found to be dependent on the angle of attack.

Temperature measurements in steady axisymmetric partially premixed flames by use of rainbow schlieren deflectometry.

We focus on the utility of rainbow schlieren as a tool for measuring the temperature of axisymmetric partially premixed flames (PPFs). Methane-air PPFs are established on a coannular burner. The flames involve two spatially distinct reaction zones, one in an inner premixed region that has a curved tip and a spatially planar wing portion and another that involves an outer nonpremixed zone in which intermediate species burn in air. Schlieren images are found to visualize clearly these PPF characteristics through light deflection by steep refractive-index gradients in the two reaction zone fronts. The temperature distributions of two flames established at fuel-rich mixture equivalence ratios of phi(r) = 1.5 and 2.0, with bulk-averaged velocities, Vreac = 60 cm s(-1) and Vair = 50 cm s(-1), are inferred from color schlieren images, and a measurement error analysis is performed. Errors arise from two sources. One lies in the process of inferring the temperature from the refractive-index measurement by making assumptions regarding the local composition of the flame. We have shown through simulations that the average temperature deviations due to these assumptions are 1.7% for the phi(r) = 1.5 flame and 2.3% for the phi(r) = 2.0 flame. Another source involves the local uncertainty in the measurement of the transverse ray displacement at the filter plane that is used to determine the refractive index and thereafter the flame temperature. We have ascertained that a maximum error of 4.3% in the temperature determination can be attributed to this local measurement uncertainty. This investigation demonstrates the capability of the schlieren technique for providing not only qualitative displays of the PPFs but also full-field-of-view temperature measurements that are accurate, spatially resolved, and nonintrusive.

A Limiting Solution for Flow Past a Delta Wing in the Presence of Supercritical Flow Regions

The flow past a planar delta wing is studied for strong interaction between the boundary layer and the outer supersonic flow. An analytic investigation is carried out using the “Newtonian” passage to the limit in which the specific heat ratio tends to unity and the Mach and Reynolds numbers to infinity. Possible flow regimes are classified for various wing aspect ratios. For determining the supercritical-subcritical flow transition line an analytic expression, correct to the second approximation, is obtained for flow past a cold wing with a fairly large aspect ratio in which the transverse boundary-layer flows are insignificant.