Showing papers on "Vortex lattice method published in 2019"

Multimodality in Aerodynamic Wing Design Optimization

Abstract: The application of gradient-based optimization to wing design could potentially reveal revolutionary new wing concepts. Giving the optimizer the freedom to discover novel wing designs may increase ...

Takeoff and Performance Trade-Offs of Retrofit Distributed Electric Propulsion for Urban Transport

Abstract: While vertical takeoff and landing aircraft have shown promise for urban air transport, distributed electric propulsion on existing aircraft may offer immediately implementable alternatives. Distri...

Vortex-Sheet Representation of Leading-Edge Vortex Shedding from Finite Wings

Abstract: A characteristic feature of flows past many oscillating airfoils and wings is the leading-edge vortex (LEV). Although considerable progress has been made in the low-order modeling of LEV formation ...

Prediction of Noise from Low Reynolds Number Rotors with Different Number of Blades using a Non-Linear Vortex Lattice Method

Abstract: The demand of micro air vehicles (MAV) with multiple rotors is increasing in both military and civil applications because of their versatility on various missions. However, the use of MAVs for some missions still has limited success because of their noise pollution. One of the main noise sources is aeroacoustic sound produced by the low Reynolds number flows around the rotors. There have been many previous studies about small-scale rotor systems of MAVs during the past decades, but they mainly focused on investigations of the aerodynamics rather than the acoustics. Several studies considering the acoustics have started recently. However, only steady loading forces computed by using Blade Element Momentum Theory (BEMT) were considered in the previous studies, and the noise from unsteady flow phenomena were not taken into account. The main objective of the current study is to investigate the noise mechanisms and further to find ways to reduce the noise levels in unsteady low Reynolds number flows. A Non-linear Vortex Lattice Method (NVLM) is used to simulate the unsteady low Reynolds number flow and model the corresponding noise sources. The tonal components of far-field noise is predicted by using an acoustic analogy based on Ffowcs Williams-Hawkings (FW-H) equations. These numerical methods are applied to low Reynolds number propeller and rotor cases, and validated upon experimental data. Then, they are used to investigate the influence of the number of blades on both aerodynamic and aeroacoustic performance and provide further insight into prominent sources of noise.

Propeller Effects on the Response of High-Altitude Long-Endurance Aircraft

Abstract: An enhanced nonlinear aeroelastic-coupled-flight dynamics framework that enables the investigation of propeller aerodynamics and inertial effects on the response of a very flexible aircraft is pres...

Surrogate Modelling for Wing Planform Multidisciplinary Optimisation Using Model-Based Engineering

Abstract: Optimisation is aimed at enhancing aircraft design by identifying the most promising wing planforms at the early stage while discarding the least performing ones. Multiple disciplines must be taken into account when assessing new wing planforms, and a model-based framework is proposed as a way to include mass estimation and longitudinal stability alongside aerodynamics. Optimisation is performed with a particle swarm optimiser, statistical methods are exploited for mass estimation, and the vortex lattice method (VLM) with empirical corrections for transonic flow provides aerodynamic performance. Three surrogates of the aerodynamic model are investigated. The first one is based on radial basis function (RBF) interpolation, and it relies on a precomputed database to evaluate the performance of new wing planforms. The second one is based on an artificial neural network, and it needs precomputed data for a training step. The third one is a hybrid model which switches automatically between VLM and RBF, and it does not need any precomputation. Its switching criterion is defined in an objective way to avoid any arbitrariness. The investigation is reported for a test case based on the common research model (CRM). Reference results are produced with the aerodynamic model based on VLM for two- and three-objective optimisations. Results from all surrogate models for the same benchmark optimisation are compared so that their benefits and limitations are both highlighted. A discussion on specific parameters, such as number of samples for example, is given for each surrogate. Overall, a model-based implementation with a hybrid model is proposed as a compromise between versatility and an arbitrary level of accuracy for wing early-stage design.

Discrete Adjoint Approach for Nonlinear Unsteady Aeroelastic Design Optimization

Abstract: Presented is a discrete adjoint approach for computing nonlinear unsteady aeroelastic geometric design sensitivities, which can subsequently be used for nonlinear unsteady aeroelastic geometric des...

Fast Multipole Accelerated Unsteady Vortex Lattice Method Based Computations

Abstract: The authors present an accelerated aerodynamic computational model derived from the integration of the fast multipole method (FMM) with the unsteady vortex lattice method (UVLM) based aerodynamic m...

Nonlinear vortex lattice method for stall prediction

Abstract: The stall behavior of an empennage is a crucial and conditioning factor for its design. Thus, the preliminary design of empennages requires a fast low-order method which reliably computes the stall behavior and which must be sensitive to the design parameters (taper, sweep, dihedral, airfoil, etc.). Handbook or semi-empirical methods typically have a narrow scope and low fidelity, so a more general and unbiased method is desired. This paper presents a nonlinear vortex lattice method (VLM) for the stall prediction of generic fuselage-empennage configurations which is able to compute complete aerodynamic polars up to and beyond stall. The method is a generalized form of the van Dam algorithm, which couples the potential VLM solution with 2.5D viscous data. A novel method for computing 2.5D polars from 2D polars is presented, which extends the traditional infinite swept wing theory to finite wings, relying minimally on empirical data. The method has been compared to CFD and WTT results, showing a satisfactory degree of accuracy for the preliminary design of empennages.

Static Aeroelastic Characteristics of Morphing Trailing-Edge Wing Using Geometrically Exact Vortex Lattice Method

Abstract: A morphing trailing-edge (TE) wing is an important morphing mode in aircraft design. In order to explore the static aeroelastic characteristics of a morphing TE wing, an efficient and feasible method for static aeroelastic analysis has been developed in this paper. A geometrically exact vortex lattice method (VLM) is applied to calculate the aerodynamic forces. Firstly, a typical model of a morphing TE wing is chosen and built which has an active morphing trailing edge driven by a piezoelectric patch. Then, the paper carries out the static aeroelastic analysis of the morphing TE wing and corresponding simulations were carried out. Finally, the analysis results are compared with those of a traditional wing with a rigid trailing edge using the traditional linearized VLM. The results indicate that the geometrically exact VLM can better describe the aerodynamic nonlinearity of a morphing TE wing in consideration of geometrical deformation in aeroelastic analysis. Moreover, out of consideration of the angle of attack, the deflection angle of the trailing edge, among others, the wing system does not show divergence but bifurcation. Consequently, the aeroelastic analysis method proposed in this paper is more applicable to the analysis and design of a morphing TE wing.

The Effects of Wing Mass Asymmetry on Low-Speed Flight Characteristics of an Insect Model

Abstract: Wing asymmetries can be found in real insects and flapping-wing micro air vehicles. This paper investigates some characteristics, including the trim conditions, power requirements and passive open-loop dynamics of an insect model with the asymmetry in wing mass in low-speed flight. The motion of the insect model is obtained through a simulation framework that couples an unsteady vortex-lattice method and a multibody dynamics code. The results show that a heavier wing has to be moved with a larger stroke amplitude to compensate for the wing mass asymmetry. The power required by the heavier wing is also found greater. Moreover, we can observe the asymmetries in lateral dynamics while comparing dynamic responses due to rightward and leftward gust disturbances.

Numerical Prediction of Hydroelastic Performance of the Flexible Propeller

Abstract: In this work, the numerical method for the prediction of unsteady behavior of the flexible propeller is presented. First, we use the boundary element method based on the lifting surface theory to solve the hydrodynamic problem around the flexible propeller and employ the finite element method (FEM) program for an analysis of the structural response. The FEM is formulated with 20-node isoparametric elements for the analysis of the structural response, and then results from two different methods are well arranged through the carefully designed interface scheme. In addition, we carry out dynamic analysis of the specific flexible propeller and validate the results by comparing them with the existing numerical data.

Analytical Evaluation of Box Wing Aircraft Aerodynamic Characteristics at Early Design Stages

Abstract: The first-approach techniques for analytical evaluation of the airfoil shape and calculation of the aerodynamic coefficients for a box-wing aircraft are suggested. The reliability of the calculation results was estimated using FLZ code (the vortex lattice method). The comparison showed satisfactory convergence of coefficients for the clean configuration and some discrepancy for the take-off and landing configuration.

Prediction of Aerodynamic Noise Radiated from a Small Multicopter Unmanned Aerial Vehicle using Acoustic Analogy

Abstract: The rotor interaction phenomenon occurs frequently in unmanned aerial vehicles (UAVs) with multi-rotor configuration. In this study, we investigated the rotor interaction effects of a small-size quadcopter UAV on the aerodynamic performance and acoustic characteristics. The numerical simulation of DJI Phantom 2 model in the hover flight condition was conducted using the nonlinear vortex lattice method (NVLM) with the vortex particle method (VPM) and acoustic analogy based on the Farassat-1A formula. NVLM can consider the nonlinear aerodynamic characteristics that are mainly associated with viscous and low Reynolds number effects by incorporating airfoil look-up table and vortex strength correction. VPM is well suitable for simulating complex wake structures of quadcopter UAV because maintaining the connectivity between adjacent vortex particles is not required. Calculations for an isolated rotor were compared against measurements to validate the predicted results, including thrust force and tonal noise at 1st blade passing frequency (BPF). The calculations for a quadcopter configuration show that the average thrust coefficient decreases and thrust coefficient begins to fluctuate dramatically due to severe rotor interaction. In addition, the sound pressure level of the quadcopter is much higher than that of the isolated rotor and a significant difference in noise directivity between the quadcopter and isolated rotor is clearly captured. It is observed that unsteady loading introduced by rotor interaction leads to a considerable increase in noise. This study is a preliminary study to the aeroacoustic problem in multicopter UAV. The discussion in this work gives scope for further research on noise reductions of multicopter UAV by controlling a separation distance between the rotors.

Influences of airfoil profile on lateral-directional stability of aircraft with flying wing layout

Abstract: The purpose of this study is to analyze influence of airfoil profile on lateral-directional flying quality of flying wing aircraft. The lateral-directional stability is always insufficient for aircraft with the layout due to the absence of vertical stabilizer. A flying wing aircraft with double-swept wing is used as research object in the paper.,The 3D model is established for the aircraft with flying wing layout, and parametric modeling is carried out for airfoil mean camber line of the aircraft to analyze lateral-directional stability of the aircraft with different camber line parameters. To increase computational efficiency, vortex lattice method is adopted to calculate aerodynamic coefficients and aerodynamic derivatives of the aircraft.,It is found from the research results that roll mode and spiral mode have a little effect on lateral-directional stability of the aircraft but Dutch roll mode is the critical factor affecting flying quality level of such aircraft. Even though changes of airfoil mean line parameters can greatly change assessment parameters of aircraft lateral-directional flying quality, that is kind of change cannot have a fundamental impact on level of flying quality of the aircraft. In case flat shape parameters are determined, the airfoil profile has a limited impact on Dutch roll mode.,Influences of airfoil profile on lateral-directional flying quality of aircraft with double-swept flying wing layout are revealed in the thesis and some important rules and characteristics are also summarized to lay a theoretical basis for design of airfoil and flight control system of aircraft with the layout.

Cloth Simulation Algorithm Based on the Mass-Spring Model and the Non-planar Vortex Lattice Model

Abstract: With the development of computer technology, the simulation of fabrics has been widely used in many aspects of production and life. This paper focuses on the physical performance of a specific fabric under a quasi-steady-state flow field, which more realistically restores the movement of the fabric in low-speed airflow. It is combined the quasi-steady-state mechanical model based on aerodynamic theory with the classical structural mechanics model of cloth. By cyclically calculating the displacement and deformation of the cloth dot at different times, the cloth motion animation can be obtained. The experimental results show that through the combination with the Mass-Spring Model and the Non-planar Vortex Lattice Method, the fabric simulation effect with third dimension can be obtained.

Unsteady aerodynamics investigation of deploying tandem-wing with different methods:

Abstract: In the rapidly deploying process of the unmanned aerial vehicle with folding wings, the aerodynamic characteristics could be largely different owing to the effects of deformation rate and the aerod...

Analysis of wake surfing benefits using a fast unsteady vortex lattice method

Abstract: The computer simulation framework Flexit is used to analyse the fuel economy benefit of aircraft wake surfing. Wake surfing involves multiple aircraft flying in close formation during cruise conditions to reduce overall induced drag and improve overall fuel efficiency. The aircraft fly in echelon such that the kinetic energy lost in vortices generated by the lead aircraft can be partially recovered by the following aircraft flying in regions of the wake where induced velocities have an upwardly directed vertical component. We build on recent theoretical and flight test work by developing a medium fidelity methodology using Flexit for predicting potential performance benefits of wake surfing. We present results from a specific systematic parametric study that corresponds to a series of recent flight tests with two C-17 transport aircraft to demonstrate the methodology and predict the fuel savings that can be obtained by different arrangements of aircraft in a wake surfing formation. The predictions are compared with the flight test data and the trends observed in our simulations agree with the trends of the full scale tests.

CFD Based Determination of Longitudinal Static and Dynamic Stability Derivatives of Twin Boom UAV

Abstract: Static and dynamic stability derivatives known as aero model are important numbers used in preliminary design of a vehicle and often used in engineering flight simulator. These measure how much change in forces and moments acting on the vehicle when there is a small change in flight condition parameters such as angle of attack, altitude and speed. Increasing the capability of computational fluid dynamics (CFD) method in solving complex unsteady flow around complex geometry, it can be used for determining dynamic stability derivatives of the vehicle which was often conducted in wind tunnel requiring higher cost and quite complex mechanism measurement device. The paper presents the determination of longitudinal static and dynamic stability derivatives of the designed UAV using computational fluid dynamics method and Fourier analysis. For obtaining dynamic stability derivatives, the UAV model have to move in either the single periodic vertical movement or single pitch rotation or in both combination of them with sines or cosines function. The unsteady flow solution around the moving vehicle are then obtained by solving Reynolds averaged navier-stokes equations. The results of unsteady aerodynamic forces and moments of the UAV are then analyzed using Fourier method to yield static and dynamic stability derivatives. Based on the results show that the designed UAV has good longitudinal dynamic stability agreement compared to vortex Lattice method. It fulfills the requirement for the UAV to have longitudinal stability in terms of pitching moment with the rate of angle of attack and pitch rate.