Computational aeroelastic analysis of wings based on the structural discontinuous Galerkin and aerodynamic vortex lattice methods

An original computational framework for the aeroelastic analysis of wings featuring general transverse section is developed. The framework is based on the coupling between a novel discontinuous Galerkin structural model and an aerodynamic vortex lattice method, which is implemented in both the planar and non-planar version. The structural model, which constitutes the novelty of the present work, allows generalized kinematics and is thus able to capture higher-order structural deformation modes. With respect to other more used structural representations, the discontinuous Galerkin approach is based on the use of discontinuous basis functions and suitably-defined boundary terms to enforce the inter-element continuity and boundary conditions. Such features naturally enable high-order accuracy, ease of parallelization and, specifically for this work, straightforward coupling with the vortex lattice method. The framework is validated through benchmark tests, providing favourable matching with reference literature data

Aeromechanics of Coaxial Rotor Helicopters using the Viscous Vortex Particle Method

Coaxial rotor helicopters are a candidate for the next generation of rotorcraft due to their ability to achieve high speeds without compromising hover performance. Coaxial rotors are designed to offload the retreating side of the rotor in high speed flight to delay the effects of reverse flow and blade stall which limit the speed of conventional single main rotor helicopters. The proximity of the two rotors induces periodic blade passage effect loads and unsteady rotor wake interactions absent in single rotor configurations. Coaxial rotors employ stiff composite hingeless blades to prevent the possibility of blade strike. At high speeds, the coaxial rotor operates at reduced RPM to avoid the drag penalty on the advancing blade tip. This combination of rotor lift distribution, periodic blade passage effect, unsteady rotor wake interaction, combined with stiff hingeless blades and reduced rotor RPM implies that a coaxial rotor system requires a specialized aeromechanical analysis. The goal of this dissertation is to develop a comprehensive aeromechanical analysis capable of modeling the aeroelasticity of stiff hingeless counter-rotating blades and the complex rotor-wake interactions present in a coaxial rotor system. The rotor wake is modeled with the Viscous Vortex Particle method, a grid free approach for calculating vortex interactions over long distances. The spanwise blade loading in attached flow is obtained from a computational fluid dynamics based rational function approximation unsteady aerodynamic model. The ONERA dynamic stall model is extended to capture three dimensional effects due to flow separation. The combination of the viscous vortex particle method with reduced order models for spanwise loading captures the unsteady coaxial rotor loads with computational efficiency. Trim procedures are developed to determine control inputs for a coaxial rotor to maintain equilibrium in hover and forward flight. In forward flight, two different trim conditions are considered: trim with propulsor off, and trim at level attitude. The two trim conditions have a significant impact on the vibratory hub loads, rotor inflow distribution and the aeroelastic stability. A unique aspect of the coaxial rotor is that its stability in both hover and forward flight are governed by equations with periodic coefficients. Therefore, a periodic aeroelastic stability analysis based on Floquet theory is applied. A new graphical method is developed to identify coupling between the blade modes of the two rotors. The aeromechanical formulation is applied to a rotor resembling the Sikorsky X2TD coaxial helicopter. In hover, the rotor experiences 8/rev blade passage loads due to oscillations in the blade bound circulation induced inflow. Increasing the collective pitch increases the coupling between the flap and lag modes of the blade. The aerodynamic interactions lead to an inter-rotor coupling of the first flap modes. In forward flight, the effects of trim condition, advance ratio, lift offset, and separated wake on the hub loads, inflow distribution and aeroelastic stability are examined. The results indicate that the aeroelastic stability of the lag mode is reduced in forward flight at a level attitude compared to hover. This study provides an improved physical understanding of the aeroelastic interactions in coaxial rotors. The work presented in this dissertation has the potential to facilitate design and development of future high-speed coaxial rotorcraft.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163227/1/punsingh_1.pd

Experimental investigation of UAV rotor aeroacoustics and aerodynamics with computational cross‑validation

The study provided a base of comparison of known computational techniques with different fidelity levels for performance and noise prediction of a single, fixed-pitch UAV rotor operating with varying flight parameters. The range of aerodynamic tools included blade element theory, potential flow methods (UPM, RAMSYS), lifting-line method (PUMA) and Navier–Stokes solver (FLOWer). Obtained loading distributions served as input for aeroacoustic codes delivering noise estimation for the blade passing frequency on a plane below the rotor. The resulting forces and noise levels showed satisfactory agreement with experimental data; however, differences in accuracy could be noticed depending on the computational method applied. The wake influence on the results was estimated based on vortex trajectories from simulations and those visible in background-oriented schlieren (BOS) pictures. The analysis of scattering effects showed that influence of ground and rotor platform on aeroacoustic results was observable even for low frequencies

Helicopter Performance Analysis by means of a free-wake method

Analisi della scia e della distribuzione della velocità indotta dovuta al rotore di un elicottero usando il metodo del vortice libero. Simulazione dei rotori Caradonna-Tung e Carpenter e dell'intero elicottero H135

Aeronautical engineering: A continuing bibliography with indexes (supplement 232)

This bibliography lists 422 reports, articles, and other documents introduced into the NASA scientific and technical information system in October, 1988

Aeronautical engineering: A continuing bibliography with indexes (supplement 262)

This bibliography lists 474 reports, articles, and other documents introduced into the NASA scientific and technical information system in Jan. 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

A survey of free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle

The objective of this paper is to analyze free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle (UAV). Free software is the best choice when the reduction of production costs is necessary; nevertheless, the quality of free software may vary. This paper probably does not include all of the free software, but tries to describe or mention at least the most interesting programs. The first part of this paper summarizes the essential knowledge about UAVs, including the fundamentals of flight mechanics and aerodynamics, and the structure of a UAV system. The second section generally explains the modelling and simulation of a UAV. In the main section, more than 50 free programs for the design, analysis, modelling, and simulation of a UAV are described. Although the selection of the free software has been focused on small subsonic UAVs, the software can also be used for other categories of aircraft in some cases; e.g. for MAVs and large gliders. The applications with an historical importance are also included. Finally, the results of the analysis are evaluated and discussed—a block diagram of the free software is presented, possible connections between the programs are outlined, and future improvements of the free software are suggested. © 2015, CIMNE, Barcelona, Spain.Internal Grant Agency of Tomas Bata University in Zlin [IGA/FAI/2015/001, IGA/FAI/2014/006

AEROELASTIC SIMULATION OF WIND TURBINES USING FREE VORTEX METHODS AND STRATEGIES FOR ACCELERATING THE COMPUTATION

This dissertation integrated the free vortex method code Wake Induced Dynamics Simulator (WInDS), which was developed by Sebastian et al., into the open source and widely-used software FAST. A range of computational strategies including paral- lelization and Treecode algorithms are used to increase the computational efficiency of the software. Full aero-hydro-servo-elastic simulations with free vortex method are conducted, which focus on an in-depth study on the influence of the aeroelasticity of the wind turbine and platform motions on the unsteadiness of the aerodynamics, and the comparison of aeroelastic responses of two floating wind turbine concepts. This dissertation also applies long short-term memory (LSTM) architecture for fast wind power prediction