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Numerical solution of two-dimensional incompressible flow about an airfoil
Title
Numerical solution of two-dimensional incompressible flow about an airfoil.
Creator
Barnes, Robert Stuart., Florida Atlantic University, Bober, William
Abstract/Description
A numerical scheme for determining the two dimensional, incompressible flow field about an airfoil is described. The scheme combines two methods: the Neumann (panel) method to determine the potential flow and a hybrid numerical method to determine the boundary layer flow. In the panel method, the fundamental theorems of potential theory are employed to derive the pressure and velocity fields around and along the airfoil. The velocity field obtained in the panel method is used in the hybrid...
Show moreA numerical scheme for determining the two dimensional, incompressible flow field about an airfoil is described. The scheme combines two methods: the Neumann (panel) method to determine the potential flow and a hybrid numerical method to determine the boundary layer flow. In the panel method, the fundamental theorems of potential theory are employed to derive the pressure and velocity fields around and along the airfoil. The velocity field obtained in the panel method is used in the hybrid method to determine the boundary layer thickness along the surface of the airfoil. The hybrid numerical method is an implicit finite difference numerical scheme which combines central and upwind differencing for the convective terms. The boundary layer thickness obtained is introduced back into the panel method to determine new pressure and velocity fields, thus imposing the effects of laminar, viscous flow on the solution. Lift coefficients for various angles of attack are derived and compared with experimental data presented in appropriate NACA technical reports. Reasonable agreement was obtained.
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Date Issued
1988
PURL
http://purl.flvc.org/fcla/dt/14428
Subject Headings
Aerofoils--Aerodynamics
Format
Document (PDF)
Flow Control Through Geometric Modifications to Improve Airfoil/Hydrofoil Performance
Title
Flow Control Through Geometric Modifications to Improve Airfoil/Hydrofoil Performance.
Creator
Ni, Zao, Dhanak, Manhar, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Geometric modification as the most effective passive flow control method has recently received wide attention due to its enormous potential in enhancing performance characteristics of airfoils or hydrofoils without expensive manufacturing and maintenance cost. Two primary passive flow control modifications, known as leading-edge tubercles and internal slots and their applications in airfoils/hydrofoils have been investigated in this dissertation. For the hydrofoil, since free surface effects...
Show moreGeometric modification as the most effective passive flow control method has recently received wide attention due to its enormous potential in enhancing performance characteristics of airfoils or hydrofoils without expensive manufacturing and maintenance cost. Two primary passive flow control modifications, known as leading-edge tubercles and internal slots and their applications in airfoils/hydrofoils have been investigated in this dissertation. For the hydrofoil, since free surface effects cannot be neglected, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil has been studied as well. In the theoretical approach aspect, an empirically-based model based on an iteration scheme has been proposed for predicting the lift coefficients of twisted airfoils with leading-edge tubercles by using experimental data for untwisted airfoils. With both numerical and experimental investigations, this dissertation has discussed the application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. The combined effect of an internal slot in an airfoil and transverse leading-edge tubercles on its performance has been further studied both numerically and experimentally. Moreover, performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of AoAs has been studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high AoAs close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. A similarly submerged hydrofoil with a custom-designed internal slot has further been studied. The performance characteristics of the slotted hydrofoil in the presence of the free surface are investigated both numerically and experimentally.
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Date Issued
2019
PURL
http://purl.flvc.org/fau/fd/FA00013248
Subject Headings
Hydrofoils, Aerofoils, Performance, Flow control
Format
Document (PDF)
Synchronization and phase dynamics of oscillating foils
Title
Synchronization and phase dynamics of oscillating foils.
Creator
Finkel, Cyndee L., Charles E. Schmidt College of Science, Department of Physics
Abstract/Description
In this work, a two-dimensional model representing the vortices that animals produce, when they are flying/swimming, was constructed. A D{shaped cylinder and an oscillating airfoil were used to mimic these body{shed and wing{generated vortices, respectively. The parameters chosen are based on the Reynolds numbers similar to that which is observed in nature (104). In order to imitate the motion of ying/swimming, the entire system was suspended into a water channel from frictionless air...
Show moreIn this work, a two-dimensional model representing the vortices that animals produce, when they are flying/swimming, was constructed. A D{shaped cylinder and an oscillating airfoil were used to mimic these body{shed and wing{generated vortices, respectively. The parameters chosen are based on the Reynolds numbers similar to that which is observed in nature (104). In order to imitate the motion of ying/swimming, the entire system was suspended into a water channel from frictionless air{bearings. The position of the apparatus in the channel was regulated with a linear, closed loop PI controller. Thrust/drag forces were measured with strain gauges and particle image velocimetry (PIV) was used to examine the wake structure that develops. The Strouhal number of the oscillating airfoil was compared to the values observed in nature as the system transitions between the accelerated and steady states... As suggested by previous work, this self-regulation is a result of a limit cycle process that stems from nonlinear periodic oscillations. The limit cycles were used to examine the synchronous conditions due to the coupling of the foil and wake vortices. Noise is a factor that can mask details of the synchronization. In order to control its effect, we study the locking conditions using an analytic technique that only considers the phases.. The results suggest that Strouhal number selection in steady forward natural swimming and flying is the result of a limit cycle process and not actively controlled by an organism. An implication of this is that only relatively simple sensory and control hardware may be necessary to control the steady forward motion of man-made biomimetically propelled vehicles.
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Date Issued
2013
PURL
http://purl.flvc.org/fcla/dt/3362333
Subject Headings
Mathematical physics, Fluid dynamics, Unsteady flow (Fluid dynamics), Aerofoils, Aerodynamics
Format
Document (PDF)
Experimental study of the wake-modes for propulsion of two-dimensional heaving airfoils
Title
Experimental study of the wake-modes for propulsion of two-dimensional heaving airfoils.
Creator
Buzard, Alan Joe., Florida Atlantic University, von Ellenrieder, Karl
Abstract/Description
Particle image velocimetry and flow visualization are used to characterize the wake of a heaving airfoil in a set of two experiments. In the first experiment a tandem airfoil configuration is used, with a stationary airfoil downstream of a heaving airfoil (modified Schmidt wave-propeller). Several vortex structures are identified for a forced Strouhal number (St)---based on airfoil chord-length, forcing frequency, and free-steam velocity---for 0.1
Show moreParticle image velocimetry and flow visualization are used to characterize the wake of a heaving airfoil in a set of two experiments. In the first experiment a tandem airfoil configuration is used, with a stationary airfoil downstream of a heaving airfoil (modified Schmidt wave-propeller). Several vortex structures are identified for a forced Strouhal number (St)---based on airfoil chord-length, forcing frequency, and free-steam velocity---for 0.1 < St < 0.7. An asymmetric average velocity profile is measured in the upper St range. In the second experiment, the wake behind a single heaving airfoil is further inspected, with the purpose of highlighting the asymmetric wake, for 0.1 < St < 1.0. A maximum wake excursion of 18 degrees is measured at St = 0.6, and a minimum excursion of 5.7 degrees occurs at St = 0.9. Using averaged velocity profiles, a virtual origin of the wake excursion is also calculated.
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Date Issued
2005
PURL
http://purl.flvc.org/fcla/dt/13216
Subject Headings
Particle accelerators--Research, Aerofoils, Aerodynamics, Wakes (Aerodynamics), Flow visualization
Format
Document (PDF)
Broadband blade self noise prediction for subsonic prop fans
Title
Broadband blade self noise prediction for subsonic prop fans.
Creator
Jochault, Cyrille Andre., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
Broadband self-noise generated by rotating blades in a subsonic ducted propfan is studied for a hard walled cylindrical duct in a uniform flow. An expression for the induct sound power radiated by three self-noise mechanisms is derived: the Turbulent-Boundary-Layer-Trailing-Edge noise, the Laminar-Boundary-Layer-Vortex-Shedding noise and the Trailing-Edge-Bluntness noise. The present theory uses NASA's self-noise prediction methodology for an isolated airfoil. An efficient method of...
Show moreBroadband self-noise generated by rotating blades in a subsonic ducted propfan is studied for a hard walled cylindrical duct in a uniform flow. An expression for the induct sound power radiated by three self-noise mechanisms is derived: the Turbulent-Boundary-Layer-Trailing-Edge noise, the Laminar-Boundary-Layer-Vortex-Shedding noise and the Trailing-Edge-Bluntness noise. The present theory uses NASA's self-noise prediction methodology for an isolated airfoil. An efficient method of programming is presented which reduces the time of computation for multiple radial modes. The results obtained are presented, discussed and compared with Blade-Tip-Boundary-Layer fan noise predictions obtained using the SDPF code developed at FAU. The most important parameters which affect self-noise are found to be the angle of attack, the effective Mach number and the chord length of the blade. For high angles of attack, the TBL-TE noise gives significant amount of sound power especially at the low frequencies. For low effective Mach numbers and at certain angles of attack, the LBL-VS noise can have high power levels in the mid and high frequencies. Trailing edge bluntness noise appeared to give insignificant amounts of energy over the whole spectrum compared to the other self-noise mechanisms.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/15255
Subject Headings
Blades--Noise, Rotors--Noise, Noise control, Aerofoils--Noise
Format
Document (PDF)
Karhunen-Loeve decomposition for non stationary propulsor flow noise
Title
Karhunen-Loeve decomposition for non stationary propulsor flow noise.
Creator
Kersulec, Jean-Luc., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The aim of this thesis is to develop a theory for non stationary propulsor flow noise. The model which is proposed is based on Amiet's paper "Acoustic Radiation from an Airfoil in a Turbulent Stream" [1], which describes broad band noise when a simple model of airfoil interacts with a turbulent flow, under the assumption of stationarity. The Karhunen-Loeve method provides a set of modes which describe the turbulent flow without the assumption of stationarity. A method is described to obtain...
Show moreThe aim of this thesis is to develop a theory for non stationary propulsor flow noise. The model which is proposed is based on Amiet's paper "Acoustic Radiation from an Airfoil in a Turbulent Stream" [1], which describes broad band noise when a simple model of airfoil interacts with a turbulent flow, under the assumption of stationarity. The Karhunen-Loeve method provides a set of modes which describe the turbulent flow without the assumption of stationarity. A method is described to obtain broad band noise calculations when the mean turbulent flow varies with time and produces non stationary turbulence. A comparison of the numerical results obtained with the results from the paper of reference [1] shows the characteristics of time varying sound radiation. The various mathematical formulae will give a starting point to the analysis of real time varying flows, which are not considered in this thesis.
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Date Issued
2005
PURL
http://purl.flvc.org/fcla/dt/13233
Subject Headings
Aerodynamic noise, Turbulence, Aerofoils, Unsteady flow (Aerodynamics), Nonlinear control theory, Differential equations, Nonlinear
Format
Document (PDF)
Prediction of broadband self-noise of an airfoil
Title
Prediction of broadband self-noise of an airfoil.
Creator
Gomez, Carlos L., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
With the increase of air traffic and the introduction of larger aircraft and therefore larger engines, the noise generated by aircraft engines have become of greater importance. In order to address these problems, noise prediction codes must be developed in order to better understand the noise generating process. This thesis addresses important issues related to broadband self-noise from ducted fans based on the prediction model developed by Glegg and Jochault [1]. By addressing issues...
Show moreWith the increase of air traffic and the introduction of larger aircraft and therefore larger engines, the noise generated by aircraft engines have become of greater importance. In order to address these problems, noise prediction codes must be developed in order to better understand the noise generating process. This thesis addresses important issues related to broadband self-noise from ducted fans based on the prediction model developed by Glegg and Jochault [1]. By addressing issues regarding the prediction of broadband self-noise from an isolated airfoil with the observer in the far field directly overhead (at 90° above), improvements can be made to Glegg and Jochault's approach for ducted fans. The prediction of broadband self-noise at 90° above a single airfoil is done by considering boundary layer parameters, the results obtained are compared with theoretical approaches, as well as experimental results obtained by Brooks [2] in order to verify its accuracy.
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Date Issued
2006
PURL
http://purl.flvc.org/fcla/dt/13377
Subject Headings
Aerofoils--Noise, Noise control, Blades--Noise, Rotors--Noise, Acoustical engineering--Mathematical models, Acoustic models
Format
Document (PDF)