Showing papers on "Lift-induced drag published in 2020"

High aerodynamic lift from the tail reduces drag in gliding raptors.

Abstract: Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.

Aeroelastics Flight Dynamics Coupling Effects of the Semi-Aeroelastic Hinge Device

Abstract: A recent consideration in aircraft design is the use of folding wingtips, with the aim of enabling higher-aspect-ratio aircraft with less induced drag but also meeting airport gate limitations. Thi...

Dynamics of viscoelastic fluid in a rotating soft microchannel

Abstract: In this study, we numerically investigate the effects of rotational forces, viz., centrifugal force and Coriolis force, on the flow dynamics of a viscoelastic fluid in a polymeric layer grafted microchannel. The viscoelastic fluid is represented by the Oldroyd-B model, and the effect of viscoelasticity on the underlying transport is studied. A numerical procedure consistent with the finite difference method is used to solve the system of partial differential equations. The numerical model takes into consideration, among many others, the drag effects of the “soft layer” and the transiences in the flow dynamics leading to the steady state. The complex interplay between the effect of rotational forcing and the presence of the soft layer is observed to lead to vital conclusions that could improve the design of many lab-on-a-compact disc based microfluidic devices. In addition, the effect of elasticity on the flow dynamics in the presence of rotational forces and soft layer induced drag force is studied. The in-house numerical code employs the finite difference numerical scheme to discretize the equations and consequently solves the obtained system of linear algebraic equations using the Gauss–Seidel iterative scheme. By demonstrating the velocity profiles, we discuss the effect of the various rheological parameters on the underlying transport feature. Finally, the effect of the rotation on the net throughput is studied extensively.

Variable cant angle winglets for improvement of aircraft flight performance

Abstract: Traditional winglets are designed as fixed devices attached at the tips of the wings. The primary purpose of the winglets is to reduce the lift-induced drag, therefore improving aircraft performance and fuel efficiency. However, because winglets are fixed surfaces, they cannot be used to control lift-induced drag reductions or to obtain the largest lift-induced drag reductions at different flight conditions (take-off, climb, cruise, loitering, descent, approach, landing, and so on). In this work, we propose the use of variable cant angle winglets which could potentially allow aircraft to get the best all-around performance (in terms of lift-induced drag reduction), at different flight phases. By using computational fluid dynamics, we study the influence of the winglet cant angle and sweep angle on the performance of a benchmark wing at Mach numbers of 0.3 and 0.8395. The results obtained demonstrate that by adjusting the cant angle, the aerodynamic performance can be improved at different flight conditions.

A Novel Control Allocation Method for Yaw Control of Tailless Aircraft

Abstract: Tailless aircraft without vertical stabilisers typically use drag effectors in the form of spoilers or split flaps to generate control moments in yaw. This paper introduces a novel control allocation method by which full three-axis control authority can be achieved by the use of conventional lift effectors only, which reduces system complexity and control deflection required to achieve a given yawing moment. The proposed method is based on synthesis of control allocation modes that generate asymmetric profile and lift induced drag whilst maintaining the lift, pitching moment and rolling moment at the trim state. The method uses low order models for aerodynamic behaviour characterisation based on thin aerofoil theory, lifting surface methodology and ESDU datasheets and is applied to trapezoidal wings of varying sweep and taper. Control allocation modes are derived using the zero-sets of surrogate models for the characterised aerodynamic behaviours. Results are presented in the form of control allocations for a range of trimmed sideslip angles up to 10 degrees optimised for either maximum aerodynamic efficiency (minimum drag for a specific yawing moment) or minimum aggregate control deflection (as a surrogate observability metric). Outcomes for the two optimisation objectives are correlated in that minimum deflection solutions are always consistent with efficient ones. A configuration with conventional drag effector is used as a reference baseline. It is shown that, through appropriate allocation of lift based control effectors, a given yawing moment can be produced with up to a factor of eight less aggregate control deflection and up to 30% less overall drag compared to use of a conventional drag effector.

Analytic and computational analysis of wing twist to minimize induced drag during roll

Abstract: Geometric and/or aerodynamic wing twist can be used to produce a lift distribution that results in a rolling moment. A decomposed Fourier-series solution to Prandtl’s lifting-line theory is used to...

Control Authority of a Camber Morphing Flying Wing

Abstract: Flying wings achieve their roll, pitch, and yaw controllability exclusively through spanwise variations of lift and drag due to the lack of an empennage. Instead of using conventional control surfa...

Analysis of aerodynamic characteristics using the vortex lattice method on twin tail boom unmanned aircraft

Abstract: This study focuses on analysis the aerodynamic characteristics of the LSU 05-NG aircraft in a relatively shorter time with sufficient results to provide an overview of aircraft characteristics. The method used is the Vortex Lattice Method (VLM) on XFLR5 software. VLM models an aircraft surface into infinite number of vortices to calculate lift curve slope, induced drag and force distribution. In this study, VLM was used to calculate aerodynamic parameters which include CL, CD, CM, CL with respect to CD, and L/D. The results showed that VLM can provide good results for the prediction of the lift coefficient. As for the drag coefficient, VLM used the assumption that fluid flow is inviscid so only induced drag is calculated. This also impacted the results of L/D analysis using VLM. Simulation results for the value of L/D results showed that the VLM simulation on XFLR5 has a higher magnitude than the results of the simulation with CFX.

On the Design of Aeroelastically Scaled Models of High Aspect-Ratio Wings

Abstract: Recently, innovative aircraft designs were proposed to improve aerodynamic performance. Examples include high aspect ratio wings to reduce the aerodynamic induced drag to achieve lower fuel consumption. Such solution when combined with a lightweight structure may lead to aeroelastic instabilities such as flutter at lower air speeds compared to more conventional wing designs. Therefore, in order to ensure safe flight operation, it is important to study the aeroelastic behavior of the wing throughout the flight envelope. This can be achieved by either experimental or computational work. Experimental wind tunnel and scaled flight test models need to exhibit similar aeroelastic behavior to the full scale air vehicle. In this paper, three different aeroelastic scaling strategies are formulated and applied to a flexible high aspect-ratio wing. These scaling strategies are first evaluated in terms of their ability to generate reduced models with the intended representations of the aerodynamic, structural and inertial characteristics. Next, they are assessed in terms of their potential in representing the unsteady non-linear aeroelastic behavior in three different flight conditions. The scaled models engineered by exactly scaling down the internal structure suitably represent the intended aeroelastic behavior and allow the performance assessment for the entire flight envelope. However, since both the flight and wind tunnel models are constrained by physical and budgetary limitations, custom built structural models are more likely to be selected. However, the latter ones are less promising to study the entire flight envelope.

Minimising induced drag with weight distribution, lift distribution, wingspan, and wing-structure weight

Abstract: Because the wing-structure weight required to support the critical wing section bending moments is a function of wingspan, net weight, weight distribution, and lift distribution, there exists an optimum wingspan and wing-structure weight for any fixed net weight, weight distribution, and lift distribution, which minimises the induced drag in steady level flight. Analytic solutions for the optimum wingspan and wing-structure weight are presented for rectangular wings with four different sets of design constraints. These design constraints are fixed lift distribution and net weight combined with 1) fixed maximum stress and wing loading, 2) fixed maximum deflection and wing loading, 3) fixed maximum stress and stall speed, and 4) fixed maximum deflection and stall speed. For each of these analytic solutions, the optimum wing-structure weight is found to depend only on the net weight, independent of the arbitrary fixed lift distribution. Analytic solutions for optimum weight and lift distributions are also presented for the same four sets of design constraints. Depending on the design constraints, the optimum lift distribution can differ significantly from the elliptic lift distribution. Solutions for two example wing designs are presented, which demonstrate how the induced drag varies with lift distribution, wingspan, and wing-structure weight in the design space near the optimum solution. Although the analytic solutions presented here are restricted to rectangular wings, these solutions provide excellent test cases for verifying numerical algorithms used for more general multidisciplinary analysis and optimisation.

Numerical Investigation of Influence of Diverse Winglet Configuration on Induced Drag

Abstract: In this study, numerical calculations were conducted over 3D wing surface with varying winglet configuration and their modifications to understand effect of wingtip device on induced drag formation. NACA0012 airfoil was used for all configurations due to availability of experimental lift and drag data. Lift, drag and pressure coefficient were calculated with SST turbulence model at the Reynolds numbers of 6 × 106 and were compared with experimental data to validate the simulation accuracy of numerical approaches. The winglet with different relative angle with wing surface was designed, and numerical calculation was performed with commercial software COMSOL. The winglets attached to the wingtip were divided into 3 different categories such as single winglet up or down sloping, split winglet up and down sloping. To see normal wingtip vortex, conventional wingtip was simulated together with winglet in all cases. Pressure coefficient for the midline section of the wing is in a good agreement with the experimental data, but pressure coefficient at the tip section is very different. Maximum size of vortices was observed for the case of winglet 45° up sloping with the surface, but with the increasing winglet angle with the surface, size of vortex decreases. Results indicate that wingtip vortex formation was reduced considerably at the angle of attack relative to wing surface starting from 90° and considering only lift and pressure coefficients, up-sloping winglet can be considered to be more efficient than down sloped one and maximum efficiency increased between 4 and 6%.

Preliminary Take-Off Analysis and Simulation of PrandtlPlane Commercial Aircraft

Abstract: The present paper deals with the take-off performance analysis of PrandtlPlane aircraft. The PrandtlPlane is a Box-Wing configuration based on Prandtl’s “Best Wing System” concept, which minimizes the induced drag once wingspan and lift are given. The take-off dynamics is simulated implementing the non-linear equations of motion in a numerical tool, which adopts a Vortex Lattice Method solver to evaluate the aerodynamics characteristics taking also ground effects into account. The take-off analysis is performed for both a PrandtlPlane and a reference monoplane, with the aim of comparing the performance of the two different architectures. The preliminary results show the potential advantages of the PrandtlPlane, such as runway length reduction and improved passenger comfort.

Vorticity Confinement and TVD Applied to Wing Tip Vortices for Accurate Drag Prediction

Abstract: The vorticity confinement (VC) method was used with total variation diminishing (TVD) schemes to reduce possible over-confinement and applied to tip vortices shed by edges of wings in order to predict induced drag using far-field integration. The optimal VC parameter was determined first by application to 2-D vortices and then to tip vortices shed by a 3-D wing. The 3-D inviscid simulations were post-processed using the wake-integral technique to determine lift-induced drag force. Dependence of the VC parameter on the flight Mach number and the angle of attack was evaluated. Grid convergence studies were conducted for 2-D vortices and for induced drag generated by 3-D wing. VC was used with TVD minmod and differentiable flux limiters to evaluate their effect on the VC method. Finally, the VC approach was combined with the Reynolds stress equation turbulence model, and the results were compared to experimental data of tip vortex evolution.

Box Wing and Induced Drag: Compressibility Effects in Subsonic and Transonic Regimes

Abstract: Prandtl introduced the best wing system or Box Wing a century ago and showed its exceptional lift-induced drag performance with respect to wing systems having the same wingspan and lift (Prandtl, L...

Drag reduction and flow structures of wing tip sails in ground effect

Abstract: The hydrodynamics and flow structures of a base wing slotted with tip sails in proximity to the ground were studied experimentally in order to investigate the flow control efficiency of wing tip sails in ground effect. The experiment was conducted in a towing tank at a Reynolds number 1.5×105. The lift and drag forces were measured by a transducer, the velocity fields of the wing tip vortices were measured using a time-resolved particle image velocimetry system (TR-PIV). The tip-sails and ground clearance were both effective in reducing the total drag, the lift coefficients of the tip-sails wings were increased as compared with that of a base wing. The lift-drag ratios of the tip-sails wings were improved obviously in a range of angles of attack from 2° to stalling angle. The tip-sails played more important role in unwinding the concentrated wing tip vortices at higher angle of attack, the intensity of the tip vortices were much weaker than that of the base wing. The development of the wing tip vortices was suppressed as well due to the inhibition of the ground, the downwash speed was reduced and the induced drag was decreased.

Experimental validation of numerical decambering approach for flow past a rectangular wing

Abstract: Experimental investigation on two rectangular wings with NACA0012 and NACA4415 profiles is performed at different Reynolds numbers to understand their aerodynamic behaviours at a high α regime. In-...

Computational fluid dynamics based winglet design and analysis of GL-1 glider

Abstract: Winglet is one of the effective devices that installed in wing tip to reduce induced drag which is the second largest contribution of drag especially in low-speed aircraft. The largest contribution of induced drag is from wingtip vortices. On previous study, GL-1 was not employing by winglet and the aerodynamic efficiency LD was 27 or corresponding to 11.7 km maximum range. However, that value was below from conceptual design result which is 30 or equal to 13.7 km maximum range. The objective is to improve aerodynamic efficiency LD of GL-1 glider 30 by introducing the winglet. The problem is determining winglet geometry that could reach design target. So, study of parametric method is conducted including winglet height study, sweep angle study, and taper ratio study. To produce desired aerodynamic characteristic from winglet, computational fluid dynamics method with solving Reynold Averaged Shear Stress coupled with Shear Stress Transport and Gamma-Theta transition model is used. After utilizing winglet to GL-1, CL increased by 3.4106 percent, CD reduced by 3.2068 percent, and aerodynamic efficiency LD. increased by 6.8366 percent the maximum range has increased from 11.7 to 12.5 km.

Optimization and Design of a Subsonic Aircraft Lifting System with the View to Minimize Induced Drag

Abstract: The optimization of the aerodynamic load distribution (circulation G) has been performed along the span of the complex lifting system, which provides the minimum induced drag. Optimization computations have been conducted for a set of aerodynamic configurations. Aerodynamic design has been performed by an example of a closed, optimized, biplane-type lifting system relating to the category of nonconventional configurations.

Comprehensive Optimization of the Unmanned Tilt-Wing Cargo Aircraft With Distributed Propulsors

Abstract: The unmanned tilt-wing cargo aircraft using distributed propulsors is an emerging aircraft significantly different from traditional types. This paper proposes an aerodynamic, propulsion, noise, weight integrated optimization design method for this new aircraft. The method consists of several functional modules specially developed or adjusted targeting the aircraft’s characteristics, such as the boundary state analysis, propeller/rotor oblique inflow analysis, waked wing analysis, propeller/rotor noise evaluation, multi-state wing mass analysis, multi-objective genetic algorithm optimization. It comprehensively considers the impact of various complex factors on the optimization results, such as the impact of distributed propulsors on the wing aerodynamics, the effect of wingtip propellers on the induced drag reduction, the coupling between wing aerodynamics and structure, the propeller/rotor aerodynamics optimization, and noise control. With the proposed method, it is possible to directly translate the top-level design requirements into the design scheme with the optimal specific system performance (such as the lowest delivery cost and highest delivery efficiency) at the very initial aircraft design stage, thereby greatly shortening the development cycle. A case study was presented. The results show that the introduction of distributed propulsors can increase the delivery efficiency by 28.2% and reduce the delivery cost by 15%; suppressing the wingtip vortices using propellers can increase the wing lift-drag ratio by 5.43%-6.65%; the slipstream generation efficiency and thrust efficiency are significantly different between different distributed propulsor schemes. To maximize the overall efficiency, it is necessary to balance between the slipstream generation efficiency and the overall thrust efficiency when optimizing the tilt-wing cargo aircraft.

Comparison of Flow-Solvers: Linear Vortex Lattice Method and Higher-Order Panel Method with Analytical and Wind Tunnel Data

Abstract: Two induced drag analysis techniques, Vortex Lattice Method (VLM) and panel method are renowned for inviscid aerodynamic computations and are widely used in the aerospace industry and academia. To demonstrate the applicability of potential flow theory and to establish an extensive correlation of linearized, attached potential flow-solver codes for estimating lift and induced drag, a generic rectangular wing planform is analyzed. Due to a wide range of applicability in conceptual design, the two solvers are compared for accuracy, computational time and input controllability to find an optimum solver that can predict inviscid aerodynamics accurately and efficiently but with the least amount of time. VLM-based code is founded upon the Laplace equation. It approximates a three-dimensional wing into a two-dimensional planform, making it apposite for moderate aspect ratio and thin-airfoil aircraft. A modified VLM is used that takes a suction parameter, calculated analytically, as an input to capture three-dimensional leading-edge thrust and vortex lift effects. On the contrary, the higher-order panel method takes the complete wing surface and changes the wake orientation to model modified flow to better predict the effects of downwash. These codes, allow computation in both subsonic and supersonic regimes, as they include Prandtl-Glauert compressibility correction. The rectangular wing is generated with an identical number of panels and networks for coherent comparison. Distinguishable pre-processing techniques are utilized and similar boundary conditions and flow conditions are maintained over the surfaces that are then given to solvers. The induced drag polar is plotted and compared with wind tunnel and analytical data.