Showing papers on "Vortex lattice method published in 2020"
TL;DR: A new self-adaptive meta-heuristic based on decomposition is specifically developed for this many-objective optimisation problem for an unmanned aerial vehicle (UAV) posed with 6 objective functions: take-off gross weight, drag coefficient, take off distance, power required, lift coefficient and endurance subject to aircraft performance and stability constraints.
76 citations
TL;DR: In this article, the nonlinear vortex lattice method (NVLM) is adopted to compute the aerodynamic loads of two small-scale wind turbines, which can be applied to a wide range of operating conditions.
23 citations
TL;DR: The proposed method can be used to solve the aeroelastic response problems of wings containing geometric nonlinearities and is suitable for predicting the nonlinear flutter speed and calculating the gust responses of a large-aspect-ratio wing in time domain.
21 citations
TL;DR: A method for frequency-limited balancing of the unsteady vortex-lattice equations is introduced in this article, which results in compact models suitable for computational-intensive applications in load analysis.
Abstract: A method for frequency-limited balancing of the unsteady vortex-lattice equations is introduced that results in compact models suitable for computational-intensive applications in load analysis, ae...
15 citations
03 Jul 2020
TL;DR: In this article, an added layer of the coupling technique was introduced to predict rotor blade heat transfer using the BEMT and UVLM, and the new approach implements the viscous coupling of the two methods from one hand and introduces a link to a new airfoil CFD-determined heat transfer correlation.
Abstract: Calculating the unsteady convective heat transfer on helicopter blades is the first step in the prediction of ice accretion and the design of ice-protection systems. Simulations using Computational Fluid Dynamics (CFD) successfully model the complex aerodynamics of rotors as well as the heat transfer on blade surfaces, but for a conceptual design, faster calculation methods may be favorable. In the recent literature, classical methods such as the blade element momentum theory (BEMT) and the unsteady vortex lattice method (UVLM) were used to produce higher fidelity aerodynamic results by coupling them to viscous CFD databases. The novelty of this research originates from the introduction of an added layer of the coupling technique to predict rotor blade heat transfer using the BEMT and UVLM. The new approach implements the viscous coupling of the two methods from one hand and introduces a link to a new airfoil CFD-determined heat transfer correlation. This way, the convective heat transfer on ice-clean rotor blades is estimated while benefiting from the viscous extension of the BEMT and UVLM. The CFD heat transfer prediction is verified using existing correlations for a flat plate test case. Thrust predictions by the implemented UVLM and BEMT agree within 2% and 80% compared to experimental data. Tip vortex locations by the UVLM are predicted within 90% but fail in extreme ground effect. The end results present as an estimate of the heat transfer for a typical lightweight helicopter tail rotor for four test cases in hover, ground effect, axial, and forward flight.
13 citations
TL;DR: In this paper, numerical simulations of the flow-induced vibration of a sheet by considering geometrical nonlinearity and wake shedding from the trailing edge are presented. And the relationship between material damping, flapping behavior, boundary conditions, and energy harvested from the fluid is investigated.
12 citations
TL;DR: A novel hybrid unmanned aerial vehicle (UAV) capable of transitioning between VTOL, hover, and efficient (fixed-wing type) forward flight is developed, subject to various aerodynamic and geometric constraints.
11 citations
TL;DR: It is concluded, that propeller induced flow effects have a significant contribution in flight dynamic modeling for vehicles with large propeller diameter to wingspan ratio, with improved 6-DOF equations of motion with a contribution of advance ratio of 22% or more.
Abstract: In this research effect of propeller induced flow on aerodynamic characteristics of low aspect ratio flying wing micro aerial vehicle has been investigated experimentally in subsonic wind tunnel. Left turning tendencies of right-handed propellers have been discussed in literature, but not much work has been done to quantify them. In this research, we have quantified these tendencies as a change in aerodynamic coefficient with a change in advance ratio at a longitudinal trim angle of attack using subsonic wind tunnel. For experimental testing, three fixed pitch propeller diameters (5 inch, 6 inch and 7 inch), three propeller rotational speeds (7800, 10800 and 12300 RPMs) and three wind tunnel speeds (10, 15 and 20 m/s) have been considered to form up 27 advance ratios. Additionally, wind tunnel tests of 9 wind mill cases were conducted and considered as baseline. Experimental uncertainty assessment for measurement of forces and moments was carried out before conduct of wind tunnel tests. Large variation in lift, drag, yawing moment and rolling moment was captured at low advance ratios, which indicated their significance at high propeller rotational speeds and large propeller diameters. Side force and pitching moment did not reflect any significant change. $\frac {L}{D}$ at trim point was found a nonlinear function of propeller diameter to wingspan ratio $\frac {D}{b}$ , and propeller rotational speed. Rate and control derivatives were obtained using unsteady vortex lattice method with propeller induced flow effect modeled by Helical Vortex Modeling approach. In this research, we have proposed improved 6-DOF equations of motion, with a contribution of advance ratio $J$ . It is concluded, that propeller induced flow effects have a significant contribution in flight dynamic modeling for vehicles with large propeller diameter to wingspan ratio, $\frac {D}{b}$ of 22% or more.
11 citations
TL;DR: The results indicated that wingspan morphing is better than wing sweep morphing to harness better aerodynamic advantages with favorable flight stability characteristics, however, extension in wingspan beyond certain limits jeopardizes the advantages.
Abstract: Morphing aircraft are the flight vehicles that can reconfigure their shape during the flight in order to achieve superior flight performance. However, this promising technology poses cross-disciplinary challenges that encourage widespread design possibilities. This research aims to investigate the flight dynamic characteristics of various morphed wing configurations that can be incorporated in small-scale UAVs. The objective of this study was to analyze the effects of in-flight wing sweep and wingspan morphing on aerodynamic and flight stability characteristics. Longitudinal, lateral, and directional characteristics were evaluated using linearized equations of motion. An open-source code based on Vortex Lattice Method (VLM) assuming quasi-steady flow was used for this purpose. Trim points were identified for a range of angles of attack in prestall regime. The aerodynamic coefficients and flight stability derivatives were compared for the aforementioned morphing schemes with a fixed-wing counterpart. The results indicated that wingspan morphing is better than wing sweep morphing to harness better aerodynamic advantages with favorable flight stability characteristics. However, extension in wingspan beyond certain limits jeopardizes the advantages. Dynamically, wingspan and sweep morphing schemes behave in an exactly opposite way for longitudinal modes, whereas lateral-directional dynamics act in the same fashion for both morphing schemes. The current study provided a baseline to explore the advanced flight dynamic aspects of employed wing morphing schemes.
8 citations
22 Apr 2020
TL;DR: In this paper, the authors used the Vortex Lattice Method (VLM) on XFLR5 software to model an aircraft surface into infinite number of vortices to calculate lift curve slope, induced drag and force distribution.
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.
7 citations
TL;DR: It is demonstrated that the presence of propellers can influence the aeroelastic stability of a Very Flexible Aircraft.
Abstract: This work investigates the propeller’s influence on the stability of High Altitude Long Endurance aircraft, incorporating all resultant loads at the propeller hub, propeller slipstream, and gyroscopic loads. Such effects are usually neglected in the aeroelastic simulation of HALE aircraft. For that goal, a previously developed framework, which couples a geometrically nonlinear structural solver with an Unsteady Vortex Lattice method (uVLM) for lifting surfaces and a Viscous Vortex Particle (VVP) method for propeller slipstream, was employed to generate time-data series. Also, a method, based on a combination of Proper Orthogonal Decomposition and system identification, to extract dynamic information (frequencies, damping, and modes) of the aircraft from a time-series signal is proposed and successfully tested for a purely structural case, for which reference data is available. The method is then applied to investigate the stability of aeroelastic cases. The results demonstrate that the presence of propellers can influence the aeroelastic stability of a Very Flexible Aircraft.
01 Mar 2020
Abstract: This paper describes a methodology to predict the aerodynamic behaviour of an Unmanned Aerial System. Aircraft design and flight dynamics modelling are mainly concerned with aerodynamics, and thus its estimation requires a high level of accuracy. The work presented here shows a new non-linear formulation of the classical Vortex Lattice Method and a comparison between this methodology and an experimental analysis. The new non-linear Vortex Lattice Method was performed by calculating the viscous forces from the strip theory, and the forces generated by the vortex rings from the vortex lifting law. The experimental analysis was performed on a reduced scale wing in a low speed wind tunnel. The obtained results were also compared to those obtained from semi-empirical methods programmed using DATCOM and our Fderivatives new in-house codes. The results have indicated the accuracy of the new formulation and showed that an aerodynamic model obtained with the aerodynamic coefficients predicted with this method could be useful for flight dynamics estimation.
01 Aug 2020
TL;DR: The present investigation addresses two key issues in aerodynamic performance of a propeller–wing configuration, namely linear and nonlinear predictions with low-order numerical models and produced induced drag distribution that behaves as expected.
Abstract: The present investigation addresses two key issues in aerodynamic performance of a propeller–wing configuration, namely linear and nonlinear predictions with low-order numerical models. The develop...
01 Sep 2020
TL;DR: The preliminary results show the potential advantages of the PrandtlPlane, such as runway length reduction and improved passenger comfort.
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.
01 Mar 2020
TL;DR: In this paper, a geometrically exact vortex lattice method and panel method are presented to deal with aerodynamic load computation for nonlinear static aeroelastic problems.
Abstract: Geometrically exact vortex lattice method and panel method are presented in this paper to deal with aerodynamic load computation for geometrically nonlinear static aeroelastic problems. They are co...
TL;DR: In this article, a non-planar Unsteady Vortex Lattice Method (UVLM) is proposed for estimating vertical acceleration and in situ EDR value from Quick Access Recorder (QAR) flight data.
Abstract: Inducing civil aviation aircraft to bumpiness, atmospheric turbulence is a typical risk that seriously threatens flight safety. The Eddy Dissipation Rate (EDR) value, as an aircraft-independent turbulence severity indicator, is estimated by a vertical wind-based or aircraft vertical acceleration-based algorithm. Based on the flight data of civil aviation aircraft, the vertical turbulence component is obtained as the input of both algorithms. A new method of computing vertical acceleration response in turbulence is put forward through the Unsteady Vortex Lattice Method (UVLM). The lifting surface of the target aircraft is assumed to be a combination of wing and horizontal tail in a turbulent flight scenario. Vortex rings are assigned on the mean camber surface, forming a non-planar UVLM, to further improve the accuracy. Moreover, the neighboring vortex lattices are placed as close as possible to the structural edge of control surfaces. Thereby, a complete algorithm for estimating vertical acceleration and in situ EDR value from Quick Access Recorder (QAR) flight data is proposed. Experiments show that the aerodynamic performance is computed accurately by non-planar UVLM. The acceleration response by non-planar UVLM is able to track the recorded acceleration data with higher accuracy than that of the linear model. Different acceleration responses at different locations are also obtained. Furthermore, because the adverse effects of aircraft maneuvers are separated from turbulence-induced aircraft bumpiness, the new acceleration-based EDR algorithm shows better accuracy and stability.
TL;DR: In this paper, the generalized aerodynamic force (GAF) matrix is derived for the Unsteady Vortex Lattice Method (UVLM) without the assumption of out-of-plane dynamics.
27 Dec 2020
TL;DR: The 3D Panel Method has an accuracy that is close to CFD with a shorter time, however, it requires 400 while CFD 1210 seconds with results that are not much different as mentioned in this paper.
Abstract: This research focuses on calculating the force distribution on the wings of the LSU 05-NG aircraft by several numerical methods. Analysis of the force distribution on the wing is important because the wing has a very important role in producing sufficient lift for the aircraft. The numerical methods used to calculate the lift force distribution on the wings are Computational Flow Dynamics (CFD), Lifting Line Theory, Vortex Lattice Method, and 3D Panel Method. The numerical methods used will be compared with each other to determine the accuracy and time required to calculate wing lift distribution. Because CFDs produce more accurate estimates, CFD is used as the main comparison for the other three numerical methods. Based on calculations performed, the 3D Panel Method has an accuracy that is close to CFD with a shorter time. 3D Panel Method requires 400 while CFD 1210 seconds with results that are not much different. While LLT and VLM have poor accuracy, however, a shorter time is needed. Therefore to analyze the distribution of lift force on the wing it is enough to use the 3D Panel Method due to accurate results and shorter computing time.
TL;DR: The results of traditional aerodynamic analysis and the flexible flight dynamics modeling including the effects of structural motion for a flexible wing unmanned aerial vehicle are shown, providing a useful model for dynamics system identification and in-flight aeroelastic testing.
06 Apr 2020
TL;DR: Experimental investigation on two rectangular wings with NACA0012 and NACA4415 profiles was performed at different Reynolds numbers to understand their aerodynamic behaviours at a high α regime as mentioned in this paper.
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-...
22 Sep 2020
TL;DR: In this paper, the authors explore the initial design space for composite kites, focusing on the configuration of the bridle line system and its effect on the aeroelastic behaviour of the wing.
Abstract: In this work we explore the initial design space for composite kites, focusing on the configuration of the bridle line system and its effect on the aeroelastic behaviour of the wing. The computational model utilises a 2D cross sectional model in conjunction with a 1D beam model (2+1D structural model) that captures the complex composite coupling effects exhibited by slender, multi-layered composite structures, while still being computationally efficient for the use at the initial iterative design stage. This structural model is coupled with a non-linear vortex lattice method (VLM) to determine the aerodynamic loading on the wing. In conjunction with the aerodynamic model, a bridle model is utilised to determine the force transfer path between the wing and the bridles connected with the tethers leading to the ground station. The structural model is coupled to the aerodynamic and bridle models in order to obtain the equilibrium aero-structural-bridle state of the kite. This computational model is utilised to perform a design space exploration to assess the effects of varied load introduction to the structure and resulting effects on the kite.
01 Jan 2020
TL;DR: A novel approach for attitude control of swept wing unmanned aerial vehicles (UAVs) is presented, involving the use of only differential wing sweep and rudder deflection, and shows that the nonlinear mapping achieves decoupling of the roll and pitch movement, but performance is limited by the inertia of the moving wings.
Abstract: A novel approach for attitude control of swept wing unmanned aerial vehicles (UAVs) is presented, involving the use of only differential wing sweep and rudder deflection. An analytic aerodynamic model of the aircraft based on simple sweep theory is derived in a first step. The prediction of a vortex lattice method is then compared to the initial model. Based on the body moment analysis of the two models, design constraints and a control structure are proposed and implemented on a small scale UAV with variable sweep wings. The control structure involves a cascaded PID controller with a nonlinear mapping from controller output to sweep angles. The obtained simulation results show that simultaneous bank and elevation inputs can be tracked successfully by the attitude controller. Tracking of step inputs and dynamic inputs in the roll direction using only wing sweep is demonstrated in flight tests. The results show that the nonlinear mapping achieves decoupling of the roll and pitch movement, but performance is limited by the inertia of the moving wings.
01 Jan 2020
TL;DR: In this article, a generic rectangular wing planform is analyzed 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, and the two methods 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.
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.
TL;DR: In this paper, a bio-inspired nano rotor is carried out to improve the rotor propulsive performance by considering the influence of induced drag and wake vortex distortion on aerodynamic forces.
06 Jan 2020
TL;DR: A research of a new type of twin-body asymmetric flying-wing aircraft (TAFA) and two kinds of simulations are conducted to prove the effectiveness of its flight performance.
Abstract: Twin-body aircraft has the advantages of heavy load and long voyage, which make it suitable to execute the task. However, it also has some problems such as high-strength mid-wing requirement and no usable airport in the practical application. In order to solve these problems and promote twin-body aircraft’s adaptability, this paper conducts a research of a new type of twin-body asymmetric flying-wing aircraft (TAFA). Two kinds of simulations (CFD and VLM) are conducted to prove the effectiveness of its flight performance. The results show that the flight performance of TAFA is the best among the four different kinds of plane that can perform the same tasks.
TL;DR: In this article, the authors investigated the stern fin as a proposed solution for improving the poor course stability of a ship-shaped offshore structure in towing operation by creating a practical approach, where the fin's hydrodynamic lift coefficient was predicted by the vortex lattice method.
01 Jan 2020
TL;DR: In this paper, a configuration of an airfoil typical section where the flap is considered as a Nonlinear Energy Sink (NES), which adds zero mass and has a cubic stiffness was presented.
Abstract: Recent studies on nonlinear passive absorbers present high control efficiency for broadband frequency range with low added mass. This work presents a configuration of an airfoil typical section where the flap is considered as a Nonlinear Energy Sink (NES), which adds zero mass and has a cubic stiffness. An aeroelastic test-bench was created and characterized for linear and nonlinear structural configurations and tested in a subsonic wind-tunnel experimental campaign. The strongly nonlinear hardening stiffness is obtained by using linear springs and geometric nonlinearities. For the nonlinear tests, several Limit Cycle Oscillation (LCO) and subcritical and supercritical Hopf bifurcations were observed. Numerical analysis was also carried out for both linear and nonlinear cases using: Unsteady Vortex Lattice Method (UVLM) and Theodorsen theory (both low fidelity), Euler (medium fidelity) and Reynolds-Averaged Navier Stokes (high fidelity) methods. The numerical methods present good agreement, within the limits of each approach, and correspond with the experimental data. Using the NES, a gain of flutter speed is reached compared to the linear flap restoring force configuration.
01 Jan 2020
TL;DR: A methodology for aerodynamic optimization of UAV with VTOL capabilities and the design of the T - shaped stabilizer was achieved by utilizing analytical methods while the Vortex Lattice Method, DATCOM and CFD were used for verification purposes.
Abstract: This paper presents a methodology for aerodynamic optimization of UAV with VTOL capabilities. Aircrafts such as these usually fly at low speeds and due to that low Reynolds numbers are to be expected. The friction drag is highly dependent on the quality of the production process so unless special measures are undertaken, high friction drag coefficients could drastically influence overall performance of the aircraft. Changes of the geometrical parameters influence not only the induced drag of the wing, but also the distribution of the base drag due to sensitivity to changes of the Reynolds numbers. In order to determine the optimal geometrical parameters of the wing, a code for wing performance analysis was written. All necessary factors were calculated by utilizing the Glauert's solution of the Prandtl's equation for multi-segmented wings. By including experimental data of numerous airfoils optimized for low Reynolds numbers, the base drag distribution, along with the induced drag of the wings were calculated for a wide range of angles-of-attack. The obtained results are presented through diagrams and the methodology for the selection of the highest efficiency wing is described. The design of the T - shaped stabilizer was achieved by utilizing analytical methods while the Vortex Lattice Method, DATCOM and CFD were used for verification purposes.
06 Jan 2020