Mechanical and Aerospace Engineering Faculty PublicationsCopyright (c) 2016 Utah State University All rights reserved.
http://digitalcommons.usu.edu/mae_facpub
Recent documents in Mechanical and Aerospace Engineering Faculty Publicationsen-usThu, 13 Oct 2016 13:36:45 PDT3600Propulsion Theory of Flapping Airfoils, Comparison with Computational Fluid Dynamics
http://digitalcommons.usu.edu/mae_facpub/105
http://digitalcommons.usu.edu/mae_facpub/105Tue, 11 Oct 2016 13:37:19 PDT
It is shown that the time-dependent aerodynamic forces acting on a flapping airfoil in forward flight are functions of both axial and normal reduced frequencies. The axial reduced frequency is based on the chord length, and the normal reduced frequency is based on the plunging amplitude. Furthermore, the time-dependent aerodynamic forces are related to two Fourier coefficients, which are evaluated here from computational results. Correlation equations for these Fourier coefficients are obtained from a large number of grid- and time-step-resolved inviscid computational-fluid-dynamics solutions, conducted over a range of both axial and normal reduced frequencies. The correlation results can be used to predict the thrust, required power, and propulsive efficiency for airfoils in forward flight with sinusoidal pitching and plunging motion. Within the range of parameters typically encountered in the efficient forward flight of birds, results obtained from the correlation equations match the computational-fluid-dynamics results more closely than do those obtained from the classical Theodorsen model.
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Doug F. Hunsaker et al.A Numerical Vortex Approach to Aerodynamic Modeling of SUAV/VTOL Aircraft
http://digitalcommons.usu.edu/mae_facpub/104
http://digitalcommons.usu.edu/mae_facpub/104Thu, 18 Feb 2016 14:15:35 PST
A numerical lifting line method, coupled with a numerical blade element method, is presented as a low computational cost approach to modeling slipstream effects on a finite wing. This method uses a 3D vortex lifting law along with known 2D airfoil data to predict the lift distribution across a wing in the presence of a propeller slipstream. The results are of significant importance in the development of an aerodynamic modeling package for initial stages of vertical take-off and landing (VTOL) aircraft design. An overview of the algorithm is presented, and results compared with published experimental data.
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Doug F. HunsakerPost Stall Behavior of a Lifting Line Algorithm
http://digitalcommons.usu.edu/mae_facpub/103
http://digitalcommons.usu.edu/mae_facpub/103Thu, 18 Feb 2016 14:15:33 PST
A modified lifting line algorithm is considered as a low-cost approach for calculating lift characteristics of wings above stall. The model employs a numerical lifting-line method utilizing the 3D vortex lifting law along with known 2D airfoil data to predict the lift distribution across a wing. This method is expected to be of significant importance in the design of tail-sitter vertical take-off and landing (VTOL) aircraft where the aircraft experiences stall conditions during important flight maneuvers. The algorithm is presented, and results compared with published experimental data.
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Doug F. HunsakerEvaluation of an Alternate Incompressible Energy-Enstrophy Turbulence Model
http://digitalcommons.usu.edu/mae_facpub/102
http://digitalcommons.usu.edu/mae_facpub/102Thu, 18 Feb 2016 14:15:31 PST
A concise overview of turbulence modeling challenges is presented along with developmental concerns of traditional turbulence models. An alternate energy- enstrophy turbulence model developed by Dr. Warren Phillips is given followed by plans for closing the new model and evaluating the subsequent closure coefficients. This paper is effectively an overview of a PhD dissertation proposal and includes only a brief description of the project outline.
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Doug F. HunsakerApplication of a Coordinate Transformation and Discretization Method for Computational Fluid Dynamics
http://digitalcommons.usu.edu/mae_facpub/101
http://digitalcommons.usu.edu/mae_facpub/101Thu, 18 Feb 2016 14:15:29 PST
An overview of the computational methods implemented in a two-dimensional laminar flow solver is presented. The methods discussed include coordinate transformations making the code capable of solving flow in non-rectilinear domains, a discretization method implemented in the computational domain, and a pressure- coupling method which is used to enforce the continuity equation. Results of the numerical solver for laminar flow are presented and discussed.
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Doug F. HunsakerA One-Dimensional Finite-Difference Solver for Fully-Developed Pipe and Channel Flows
http://digitalcommons.usu.edu/mae_facpub/100
http://digitalcommons.usu.edu/mae_facpub/100Thu, 18 Feb 2016 14:15:27 PST
An algorithm is developed to solve the fundamental flow cases of fully-developed turbulent flow in a pipe and in a channel. The algorithm uses second-order finite-difference approximations for nonuniform grid spacing and is developed in such a way as to easily facilitate the implementation of several two-equation, Reynolds- Averaged-Navier-Stokes turbulence models. Results are included for the Wilcox 1998 k-ω model.
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Doug F. HunsakerA Numerical Lifting-Line Method Using Horseshoe Vortex Sheets
http://digitalcommons.usu.edu/mae_facpub/99
http://digitalcommons.usu.edu/mae_facpub/99Thu, 18 Feb 2016 14:15:24 PST
A numerical method based on the original lifting- line theory of Prandtl is developed which includes the influence of horseshoe vortex sheets. The method is an attempt at developing a higher-order method than previous delta-function methods of the same type. The definition of a horseshoe vortex sheet singularity is introduced and the velocity induced at an arbitrary point in space by the singularity is developed. No closed-form solution for this induced velocity was found for points not collinear with the bound portion of the singularity. Additionally, the velocity induced along the bound portion of a horseshoe vortex sheet with sweep is indeterminate. The singularity was used to develop a numerical method capable of predicting the aerodynamic forces and moments on a system of lifting surfaces. The method gives results within the accuracy of other similar methods, but requires higher grid refinement and more computation than previous methods.
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Doug F. HunsakerPerspectives on UAV Airframe Design
http://digitalcommons.usu.edu/mae_facpub/98
http://digitalcommons.usu.edu/mae_facpub/98Thu, 18 Feb 2016 14:15:21 PST
A perspective on how unmanned airframes may be efficiently and quickly developed as the UAV industry grows.
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Doug F. HunsakerOptimization of Flapping-Flight Using Numerical Lifting-Line Analysis
http://digitalcommons.usu.edu/mae_facpub/97
http://digitalcommons.usu.edu/mae_facpub/97Thu, 18 Feb 2016 14:15:18 PST
Progress in modeling and optimization of efficient flapping-flight aircraft.
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Doug F. HunsakerA Fundamental Approach to Modeling Flapping Flight
http://digitalcommons.usu.edu/mae_facpub/96
http://digitalcommons.usu.edu/mae_facpub/96Thu, 18 Feb 2016 14:15:15 PST
A viable approach to the modeling and development of efficient flapping-flight unmanned systems.
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Doug F. HunsakerDesign of 'Iris', a Small Autonomous Surveillance UAV
http://digitalcommons.usu.edu/mae_facpub/95
http://digitalcommons.usu.edu/mae_facpub/95Thu, 18 Feb 2016 14:15:13 PSTJennifer Boyce et al.A Lifting-Line Approach to Estimating Propeller/Wing Interactions
http://digitalcommons.usu.edu/mae_facpub/94
http://digitalcommons.usu.edu/mae_facpub/94Thu, 18 Feb 2016 14:15:10 PST
A combined wing and propeller model is presented as a low-cost approach to first-cut modeling of slipstream effects on a finite wing. The wing aerodynamic model employs a numerical lifting-line method utilizing the 3D vortex lifting law along with known 2D airfoil data to predict the lift distribution across a wing for a prescribed upstream flowfield. The propeller/slipstream model uses a blade element theory combined with momentum conservation equations. This model is expected to be of significant importance in the design of tail-sitter vertical take-off and landing (VTOL) aircraft, where the propeller slipstream is the primary source of air flow past the wings in some flight conditions. The algorithm is presented, and results compared with published experimental data.
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Doug F. Hunsaker et al.A Numerical Blade Element Approach to Estimating Propeller Flowfields
http://digitalcommons.usu.edu/mae_facpub/93
http://digitalcommons.usu.edu/mae_facpub/93Thu, 18 Feb 2016 14:15:08 PST
A numerical method is presented as a low computational cost approach to modeling an induced propeller flowfield. This method uses blade element theory coupled with momentum equations to predict the axial and tangential velocities within the slipstream of the propeller, without the small angle approximation assumption common to most propeller models. The approach is of significant importance in the design of tail-sitter vertical takeoff and landing (VTOL) aircraft, where the propeller slipstream is the primary source of air flow past the wings in some flight conditions. The algorithm is presented, the model is characterized, and the results (including the results of coupling the propeller model with a lifting-line aerodynamic model) are compared with published experimental data.
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Doug F. HunsakerOptimization of Iris, a Small Autonomous Surveillance UAV
http://digitalcommons.usu.edu/mae_facpub/92
http://digitalcommons.usu.edu/mae_facpub/92Thu, 18 Feb 2016 14:15:05 PSTDoug F. Hunsaker et al.Estimating the Subsonic Aerodynamic Center and Moment Components for Swept Wings
http://digitalcommons.usu.edu/mae_facpub/91
http://digitalcommons.usu.edu/mae_facpub/91Thu, 18 Feb 2016 14:15:04 PST
An improved method is presented for estimating the subsonic location of the semispan aerodynamic center of a swept wing and the aerodynamic moment components about that aerodynamic center. The method applies to wings with constant linear taper and constant quarter-chord sweep. The results of a computational fluid dynamics study for 236 wings show that the position of the semispan aerodynamic center of a wing depends primarily on aspect ratio, taper ratio, and quarter-chord sweep angle. Wing aspect ratio was varied from 4.0 to 20, taper ratios from 0.25 to 1.0 were investigated, quarter-chord sweep angles were varied from 0 to 50 deg, and linear geometric washout was varied from -4.0 to +8.0 deg. All wings had airfoil sections from the NACA 4-digit airfoil series with camber varied from 0 to 4% and thickness ranging from 6 to 18%. Within the range of parameters studied, wing camber, thickness, and twist were shown to have no significant effect on the position of the semispan aerodynamic center. The results of this study provide improved resolution of the semispan aerodynamic center and moment components for conceptual design and analysis.
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W. F. Phillips et al.Pitch Dynamics of Unmanned Aerial Vehicles
http://digitalcommons.usu.edu/mae_facpub/90
http://digitalcommons.usu.edu/mae_facpub/90Thu, 18 Feb 2016 14:15:01 PST
Dynamic stability requirements for manned aircraft have been in place for many years. However, we cannot expect stability constraints for UAVs to match those for manned aircraft; and dynamic stability requirements specific to UAVs have not been developed. The boundaries of controllability for both remotely-piloted and auto-piloted aircraft must be established before UAV technology can reach its full potential. The development of dynamic stability requirements specific to UAVs could improve flying qualities and facilitate more efficient UAV designs to meet specific mission requirements. As a first step to developing UAV stability requirements in general, test techniques must be established that will allow the stability characteristics of current UAVs to be quantified. This paper consolidates analytical details associated with procedures that could be used to experimentally determine the pitch stability boundaries for good UAV flying qualities. The procedures require determining only the maneuver margin and pitch radius of gyration and are simple enough to be used in an educational setting where resources are limited. The premise is that these procedures could be applied to UAVs now in use, in order to characterize the longitudinal flying qualities of current aircraft. This is but a stepping stone to the evaluation of candidate metrics for establishing flying-quality constraints for unmanned aircraft.
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W. F. Phillips et al.Smooth-Wall Boundary Conditions for Dissipation-Based Turbulence Models
http://digitalcommons.usu.edu/mae_facpub/89
http://digitalcommons.usu.edu/mae_facpub/89Thu, 18 Feb 2016 14:14:59 PST
It is shown that the smooth-wall boundary conditions specified for commonly used dissipation-based turbulence models are mathematically incorrect. It is demonstrated that when these traditional wall boundary conditions are used, the resulting formulations allow an infinite number of solutions. Furthermore, these solutions do not enforce energy conservation and they do not properly enforce the no-slip condition at a smooth surface. This is true for all dissipation-based turbulence models, including the k-ε, k-ω, and k-ζ models. Physically correct wall boundary conditions must force both k and its gradient to zero at a smooth wall. Enforcing these two boundary conditions on k is sufficient to determine a unique solution to the coupled system of differential transport equations. There is no need to impose any wall boundary condition on ε, ω, or ζ at a smooth surface and it is incorrect to do so. The behavior of ε, ω, or ζ approaching a smooth surface is that required to force both k and its gradient to zero at the wall.
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W. F. Phillips et al.Application of an Energy-Vorticity Turbulence Model to Fully rough Pipe flow
http://digitalcommons.usu.edu/mae_facpub/88
http://digitalcommons.usu.edu/mae_facpub/88Thu, 18 Feb 2016 14:14:56 PST
Based on a more direct analogy between turbulent and molecular transport, a foundation was recently presented for an energy-vorticity turbulence model. The new turbulent-energytransport equation contains two closure coefficients; a viscous-dissipation coefficient and a turbulent-transport coefficient. To help evaluate the closure coefficients and provide insight into the energy-vorticity turbulence variables, fully rough pipe flow is considered. For this fully developed flow, excellent agreement with experimental data for velocity profiles and friction factors is attained over a wide range of closure coefficients, provided that a given relation between the coefficients is maintained.
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E. B. Fowler et al.Lifting-Line Predictions for Induced Drag and Lift in Ground Effect
http://digitalcommons.usu.edu/mae_facpub/87
http://digitalcommons.usu.edu/mae_facpub/87Thu, 18 Feb 2016 14:14:53 PST
Closed-form relations are presented for estimating ratios of the induced-drag and lift coefficients acting on a wing in ground effect to those acting on the same wing outside the influence of ground effect. The closed-form relations for these ground-effect influence ratios were developed by correlating results obtained from numerical solutions to Prandtl's lifting-line theory. Results show that these influence ratios are not unique functions of the ratio of wing height to wingspan, as is sometimes suggested in the literature. These ground-effect influence ratios also depend on the wing planform, aspect ratio, and lift coefficient.
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W. F. Phillips et al.Momentum Theory with Slipstream Rotation Applied to Wind Turbines
http://digitalcommons.usu.edu/mae_facpub/86
http://digitalcommons.usu.edu/mae_facpub/86Thu, 18 Feb 2016 14:14:50 PST
A momentum theory which includes the effects of slipstream rotation for wind turbines is presented. The theory accounts for the axial and radial pressure gradients within the slipstream as well as the wake expansion caused by wake rotation. Because of the limiting approximations of previous methods, the effects of slipstream rotation have not been accurately realized. The method included here, which does not suffer from the unrealistic approximations of previous methods, predicts that the effects of slipstream rotation are manifest entirely through an increase in the turbine thrust coefficient. The method predicts, as previous methods do, that the Lanchester-Betz-Joukowski limit of 16/27 is an upper limit for the maximum efficiency, or power coefficient, of a wind turbine. Unlike the results from classical methods that are traditionally reported in terms of the axial induction factor, results of this work are presented in terms of two independent variables, the tip-speed ratio and the torque coefficient. The results included here allow the dependent variables including the thrust coefficient, power coefficient, axial induction factor, and circumferential induction factor to be evaluated in terms of the tip-speed ratio and torque coefficient. Additionally, relationships for the ideal operating conditions of a wind turbine are presented.
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Doug F. Hunsaker et al.