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- Title
- Dynamic stall and three-dimensional wake effects on isolated rotor trim and stability with experimental correlation and parallel fast-Floquet analysis.
- Creator
- Subramanian, Shanmugasundaram., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Hingeless rotors are susceptible to instabilities of the lead-lag or lag modes, which are at best weakly damped. The lag mode derives its damping primarily from the complex rotor flow field that is driven by interdependent dynamics of airfoil stall and rotor downwash or wake. Therefore, lag-damping prediction requires an aerodynamic representation that adequately accounts for quasisteady stall, dynamic stall and three-dimensional dynamic wake. Accordingly, this dissertation investigates these...
Show moreHingeless rotors are susceptible to instabilities of the lead-lag or lag modes, which are at best weakly damped. The lag mode derives its damping primarily from the complex rotor flow field that is driven by interdependent dynamics of airfoil stall and rotor downwash or wake. Therefore, lag-damping prediction requires an aerodynamic representation that adequately accounts for quasisteady stall, dynamic stall and three-dimensional dynamic wake. Accordingly, this dissertation investigates these stall and wake effects on lag damping and demonstrates the strengths and weaknesses of the aerodynamic representation with a comprehensive experimental correlation. The database refers to a three-bladed rotor operated untrimmed and to a fourbladed rotor operated trimmed; for both rotors, the blade collective pitch and shaft tilt angles are set prior to each test run. The untrimmed rotor is tested with advance-ratios as high as 0.55 and shaft angles as high as 20°, and it has intentionally builtin structural simplicity: torsionally stiff blades and no swash plate. The trimmed rotor has torsionally soft blades; it is trimmed in the sense that the longitudinal and lateral cyclic pitch controls are adjusted through a swash plate to minimize l/rev root flap moment. Therefore, for the untrimmed rotor, the database refers to lagdamping levels, and for the trimmed rotor, it refers to lag-damping levels as well as to trim results of lateral and longitudinal cyclic pitch controls and steady root flap moments. The dynamic stall representation is based on the ONERA models of lift, drag and pitching moment, and the unsteady wake is described by a finite-state three-dimensional wake model. The root-flexure-blade assembly of the untrimmed rotor is represented by a root-restrained rigid flap-lag model as well as by an elastic flap-lag-torsion model. Similarly, the trimmed rotor is represented by an elastic flaplag- torsion model. The predictions are from three aerodynamic theories ranging from a quasisteady stall theory to a fairly comprehensive dynamic stall and wake theory. This dissertation also addresses the computational aspects of lag-damping predictions by parallel F!oquct analysis based on classical and fast Floquet theories. In a typical trimmed flight, the Floquet analysis comprises (i) trim or equilibrium analysis, (ii) generation of the Floquet transition matrix (FTM) about the trim position, and (iii) eigenanalysis of the FTM. The trim analysis involves the computations of the unknown control inputs that satisfy flight conditions of required thrust and force-moment equilibrium as well as the initial conditions that guarantee periodic forced response. The shooting method is increasingly used for the trim analysis since it generates the FTM as a byproduct and is not sensitive to damping levels. The QR method is used almost exclusively for the FTM eigenanalysis. Presently, the Floquet analysis with shooting and QR methods is widely used for small-order systems (number of states or order M < 100). However, it has been found to be practical neither for design nor for comprehensive-analysis models that lead to large systems (A11 > 100); the run time on a conventional sequential computer is simply prohibitive. Nevertheless, all three parts of Floquet analysis can be algorithmically structured such that they lend themselves well to parallelism or concurrent computations. Furthermore, the conventional Floquet analysis requires integrations of equations of motion through one complete period T; and the bulk of the run time is for repeated integrations over one period. However, for rotors with Q identical blades, it is computationally advantageous to use the fast Floquet analysis, which requires integration through a period T/Q. Accordingly, this dissertation develops parallel algorithms for classical Floquet analysis with classical shooting and for the fast Floquet analysis with fast shooting; in each case the FTM eigenanalysis is baseJ on a parallel QR tibrary routine. The computational reliability· of the sequential anJ parallel Floquet analyses is quantified by (i) the condition number of the converged Jacobian matrix in Newton iteration of trim analysis, (ii) the condition numbers of the FTM eigenvalues of interest, and (iii) the corresponding residual errors of the eigenpairs (eigenvalue and the corresponding eigenYector). These algorithms are applied to study (i) linear flap stability with dynamic wake, (ii) nonlinear flaplag stability with dynamic wake under propulsive- or flight-trim conditions. and (iii) noniinear fiap-iag stabiiity with dynamic staii and wake under flight trim conditions. The parallel and sequential algorithms are compared with respect to computational reliability, saving in run time and growth of run time with increasing system order. Other parallel performance metrics such as speedup, efficiency, and sequential and parallel fractions are included as well. The computational reliability figures of the four algorithms - classical and fast-Floquet analyses each in sequential and parallel modes - are comparable. The fast-Floquet analysis brings in nearly Q-fold reduction in run time in both the sequential and parallel modes; that is, its advantages apply equally to both the modes. 'While the run times for the classical- and fast-Floquet analyses in sequential mode grow in between quadratically and cubically with the system order, the corresponding run times in parallel mode are far shorter and more importantly remain nearly constant. These results offer considerable promise in making large-scale Floquet analysis practical for rotorcrafts with identical as well as with dissimilar blades.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/12462
- Subject Headings
- Rotors (Helicopters), Stalling (Aerodynamics), Drag (Aerodynamics), Wakes (Aerodynamics), Floquet theory
- Format
- Document (PDF)
- Title
- Dynamic stall effects on hingeless rotor stability with experimental correlation.
- Creator
- Barwey, Dinesh., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The effects of dynamic stall, lift, drag and pitching moment on the aeroelastic stability of hingeless rotors are predicted. The emphasis is on correlating the predictions with the measured lag-damping levels of a three-bladed model rotor operated in an untrimmed mode. The correlation covers a wide range of test conditions for several values of rotor speed, collective pitch angle, shaft-tilt angle and advance ratio. The database includes cases that vary from near zero-thrust conditions in...
Show moreThe effects of dynamic stall, lift, drag and pitching moment on the aeroelastic stability of hingeless rotors are predicted. The emphasis is on correlating the predictions with the measured lag-damping levels of a three-bladed model rotor operated in an untrimmed mode. The correlation covers a wide range of test conditions for several values of rotor speed, collective pitch angle, shaft-tilt angle and advance ratio. The database includes cases that vary from near zero-thrust conditions in hover to highly stalled forward-flight conditions with dimensionless speed or advance ratios as high as 0.55 and shaft angles as high as 20$\sp\circ$. The aerodynamic representation is based on the ONERA dynamic stall models comprising virtually independent unified lift, drag and pitching-moment models. The nonlinear equations of blade motion and stall dynamics are perturbed about a periodic forced response, and the damping is evaluated by Floquet analysis. The extensive correlation study, based on a rigid-blade flap-lag analysis, demonstrates the viability of Floquet analysis in predicting lag-mode damping under dynamically stalled forward-flight conditions. It also demonstrates the limitations of the linear and quasisteady stall aerodynamic theories. In comparison to these theories, the theory with dynamic stall lift and quasisteady stall drag qualitatively improves the correlation and is viable over the entire range of the database. Addition of dynamic stall drag provides further quantitative improvement. Also presented is a comparative study of two dynamic stall drag models: circulation-like drag variables incorporating unsteady air-velocity variations and conventional drag-coefficient variables. While the formulation with drag coefficients exhibits computational sensitivity to convergence with respect to blade discretization for some isolated cases, the formulation with circulation-like drag variables removes this sensitivity and is computationally robust. The investigation concludes with an elastic blade analysis that includes blade flexibility in lag bending, flap bending and torsion as well as root-flexure elasticity. This analysis shows increasing sensitivity to structural refinements in blade and root-flexure modeling, and this sensitivity increases with increasing pitch setting. Correlation and parametric studies show that the root-flexure elasticity introduces significant bending-torsion couplings that have considerable impact on the stability of a rotor for which the root-flexure is soft, and the blade is stiffer in comparison with the root. This research is expected to serve as a reference comparison with other correlations based on different approaches of modeling dynamic stall and the elasticity of hingeless rotor blades and root-flexure.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/12288
- Subject Headings
- Rotors--Dynamics, Stalling (Aerodynamics), Lift (Aerodynamics)
- Format
- Document (PDF)
- Title
- Effects of rotating frame turbulence and dynamic stall on gust response of helicopter blades.
- Creator
- Madhavan, R., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Rotating frame turbulence, or RFT, refers to the actual turbulence experienced by the helicopter blades and requires noneulerian description and rotational sampling of measurements. In the stationary case of axial flight, as investigated earlier, its spectra has peaks centered at integer multiples of rotational speed P, as in wind turbines. In forward flight, as investigated here, its instantaneous or frequency-time spectra has split peaks centered at P/2, P, 3P/2, 2P etc. Though...
Show moreRotating frame turbulence, or RFT, refers to the actual turbulence experienced by the helicopter blades and requires noneulerian description and rotational sampling of measurements. In the stationary case of axial flight, as investigated earlier, its spectra has peaks centered at integer multiples of rotational speed P, as in wind turbines. In forward flight, as investigated here, its instantaneous or frequency-time spectra has split peaks centered at P/2, P, 3P/2, 2P etc. Though nonstationary, it is wide sense cyclostationary in that its autocorrelation function R(t1,t2) = R(t1 + 2m pi, t2 + 2n pi) for integers m = n only. The major RFT characteristics--spectral peaks, the consequent transfer of energy essentially from the low-frequency region (<1P) to the high-frequency region (>1P) and cyclostationarity--cannot be predicted by conventional space-fixed description. However, these characteristics are simultaneously predicted by the instantaneous spectra, and for their qualitative and parametric investigation, a closed-form solution of an instantaneous spectrum is presented for a space-fixed turbulence model. The RFT effects on the blade response statistics of rms values and average threshold crossing rates are presented as well. The blade model includes flap bending degrees of freedom and dynamic stall effects. The blade response statistics demonstrate that RFT effects are appreciable for low-advance ratio and low-altitude flight conditions and that dynamic stall increases gust sensitivity.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/14613
- Subject Headings
- Helicopters--Aerodynamics
- Format
- Document (PDF)
- 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.
Show less - Date Issued
- 1988
- PURL
- http://purl.flvc.org/fcla/dt/14428
- Subject Headings
- Aerofoils--Aerodynamics
- Format
- Document (PDF)
- Title
- Base pressure resulting from sudden expansion in cross-sectional area from a conical converging nozzle.
- Creator
- Hwang, Chi-bok., Florida Atlantic University, Chow, Wen L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This research concerns with the determination of the base pressure related to the conical convergent nozzle flow when a sudden enlargement in cross-sectional area occurs. It is recognized at the outset that the problem belongs to the category of strong interaction where inviscid and viscous flows must be considered together before a solution can be established. The viscous flow analyses based on the integral formulations are guided more or less by the boundary layer concept. The inviscid flow...
Show moreThis research concerns with the determination of the base pressure related to the conical convergent nozzle flow when a sudden enlargement in cross-sectional area occurs. It is recognized at the outset that the problem belongs to the category of strong interaction where inviscid and viscous flows must be considered together before a solution can be established. The viscous flow analyses based on the integral formulations are guided more or less by the boundary layer concept. The inviscid flow field is established from the hodograph transformation, and the method of characteristics. Again the point of reattachment behaves as a saddle point singularity for the system of equations describing the viscous flow recompression process. After the point of reattachment is approached, an overall momentum balance is applied so that the base pressure and the location where recompression starts, may be determined. Experimental studies with specific conical angles and area ratios are also conducted in the laboratory. The results obtained from the theoretical analysis agreed well with the experimental data produced in the laboratory and the data available elsewhere. These evidences lead to the conclusion that the method developed in this investigation is effective in dealing with problems of this type.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/12280
- Subject Headings
- Base flow (Aerodynamics), Viscous flow, Aerodynamics, Supersonic, Pressure vessels
- Format
- Document (PDF)
- Title
- Experimental Investigation of Skin Friction Drag Reduction on a Flat Plate using Microbubbles.
- Creator
- Grabe, Zachary A., Dhanak, Manhar R., Florida Atlantic University
- Abstract/Description
-
A microbubble generation system has been designed, constructed, and tested in a circulating water tunnel. A 1.0 m long flat plate was subjected to a flow where the Reynolds number ranged from ReL = 7.23x 10^5 - 1.04 x 10^6. Bubble diameters and skin friction measurements were studied at various airflow rates and water velocities. Bubbles were produced by forcing air through porous plates that were mounted flush with the bottom of the test plate. Once emitted through the plates, the bubbles...
Show moreA microbubble generation system has been designed, constructed, and tested in a circulating water tunnel. A 1.0 m long flat plate was subjected to a flow where the Reynolds number ranged from ReL = 7.23x 10^5 - 1.04 x 10^6. Bubble diameters and skin friction measurements were studied at various airflow rates and water velocities. Bubbles were produced by forcing air through porous plates that were mounted flush with the bottom of the test plate. Once emitted through the plates, the bubbles traveled downstream in the boundary layer. The airflow rate and water velocity were found to have the most significant impact on the size of the bubbles created. Skin friction drag measurements were recorded in detail in the velocity and airflow rate ranges. The coefficient of skin friction was determined and relationships were then established between this coefficient and the void ratio.
Show less - Date Issued
- 2007
- PURL
- http://purl.flvc.org/fau/fd/FA00012523
- Subject Headings
- Frictional resistance (Hydrodynamics), Drag (Aerodynamics), Skin friction (Aerodynamics), Fluid mechanics
- Format
- Document (PDF)
- 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.
Show less - 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)
- Title
- Aerodynamic analysis of a propeller in a turbulent boundary layer flow.
- Creator
- Lachowski, Felipe Ferreira., Glegg, Stewart A. L., Graduate College
- Date Issued
- 2013-04-12
- PURL
- http://purl.flvc.org/fcla/dt/3361938
- Subject Headings
- Turbulent boundary layer, Propellers, Aerodynamics
- Format
- Document (PDF)
- Title
- Utilizing "bills" for drag reduction below transition on spherical bodies.
- Creator
- Adamson, James Edward., Florida Atlantic University, Tennant, Jeffrey S.
- Abstract/Description
-
Russian experimenters Kozlov and Leonenko have reported substantial drag reduction on a sphere using a "bill" or "spike" extending from the body upstream into the flow. A systematic series of experiments was conducted to determine the extent of the reduction and to identify the parameters of the reported drag reduction effect. The tests were performed in the Florida Atlantic University Ocean Engineering Department's Aerolab wind tunnel. A sphere was fitted with tapering bills of various...
Show moreRussian experimenters Kozlov and Leonenko have reported substantial drag reduction on a sphere using a "bill" or "spike" extending from the body upstream into the flow. A systematic series of experiments was conducted to determine the extent of the reduction and to identify the parameters of the reported drag reduction effect. The tests were performed in the Florida Atlantic University Ocean Engineering Department's Aerolab wind tunnel. A sphere was fitted with tapering bills of various lengths, base diameters, and bill/sphere fillet radii. Experiments indicated that the effect was restricted to Reynolds numbers below 4.0 x 10^5 and that the drag of the sphere/spike combination was actually increased at Reynolds numbers greater than this. A smoke generator was used to visualize the drag reduction mechanism, which appears to be a recirculating cell at the base of the sphere/spike intersection.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14514
- Subject Headings
- Drag (Aerodynamics), Wind tunnel models
- Format
- Document (PDF)
- Title
- Trailing edge noise propagation through a cascade of blades.
- Creator
- Roy, Charlie Desire., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Aircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It...
Show moreAircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It completely blocks the sound and limits the study to entirely subsonic flow. In this type of flow, a sound propagation simulator has been implemented. The linearized form of Howe's equation is solved by a high frequency method. The ray caustic problem which causes regular ray tracing failure is fixed by interpolating the field on a preset grid. Results are compared with the analytical solution in uniform flow and computations in realistic flow are presented.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/12990
- Subject Headings
- Trailing edges (Aerodynamics), Blades, Turbulent boundary layer
- Format
- Document (PDF)
- Title
- Interaction of vortex sheet with a finite vortex.
- Creator
- Viswanathan, K. S., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is...
Show moreThe rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is shown to substantially affect the development of the vortex sheet rollup. The vortex sheet undergoes significant deformation at the rolling up tip region due to its devouring the vortex patch as well as due to the formation of secondary rollup features on the sheet. These features are believed to be important in inhibiting rollup considerably. The interaction is quantified by using a criterion developed to measure the extent of the tip vortex rollup and its characteristics are studied for a range of flow parameters. The strength of the rolling up tip region of the vortex sheet is found to be highly dependent on the location and the vorticity in the finite vortex.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/15048
- Subject Headings
- Turbulence, Whirlwinds, Vortex-motion, Wakes (Aerodynamics)
- Format
- Document (PDF)
- Title
- Non-Invasive Measurement Methods for Transient Flows in Wind Tunnels.
- Creator
- Marcheggiani, Joseph P., Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
A non-invasive transient state measurement method for wind tunnels would be very valuable as an experimental tool. Traditional measurement techniques for transient flows, e.g., hot wire anemometry, require sensors that are placed in the flow. Alternatively, particle image velocimetry (PIV) may be used to measure transient flows non intrusively, but applying PIV requires sensors that are expensive, and it may take months to process the data. The non-invasive measurement techniques considered...
Show moreA non-invasive transient state measurement method for wind tunnels would be very valuable as an experimental tool. Traditional measurement techniques for transient flows, e.g., hot wire anemometry, require sensors that are placed in the flow. Alternatively, particle image velocimetry (PIV) may be used to measure transient flows non intrusively, but applying PIV requires sensors that are expensive, and it may take months to process the data. The non-invasive measurement techniques considered in this thesis utilize sensors that are imbedded into the wall of a wind tunnel, or the response of a Kevlar walled wind tunnel to obtain the pressure time histories of a transient flow. These measurements are suitable and accurate for analyzing steady state flows but the feasibility of using them on time varying flows has yet to be explored. If this method proves possible, it would be very beneficial even if it is less accurate than current invasive methods because it would give results in real time. This thesis investigates a simple transient flow of the startup vortex of an airfoil caused by a step change in angle of attack. Based on thin airfoil theory, two models of an airfoil were created. It was determined that the response of a Kevlar wall can measure the unsteady lift of an airfoil.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013837
- Subject Headings
- Wind tunnels, Transient flow (Aerodynamics), Measurement, Sensors
- Format
- Document (PDF)
- Title
- On the Low Order Model of Turbulence in the Wake of a Cylinder and Airfoil – URANS Approach.
- Creator
- Whelchel, Jeremiah Mark, Glegg, Stewart A. L., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This thesis has described a Reynolds Averaged Navier Stokes approach to modeling turbulence in the wake of a cylinder and airfoil. The mean flow, cross stresses, and two-point space time correlation structure was analyzed for an untripped cylinder with a Reynolds number based on the cylinder diameter and freestream velocity of 60,000. The same features were also analyzed using this approach for an untripped NACA 0012 airfoil with a Reynolds number based on the airfoil chord and freestream...
Show moreThis thesis has described a Reynolds Averaged Navier Stokes approach to modeling turbulence in the wake of a cylinder and airfoil. The mean flow, cross stresses, and two-point space time correlation structure was analyzed for an untripped cylinder with a Reynolds number based on the cylinder diameter and freestream velocity of 60,000. The same features were also analyzed using this approach for an untripped NACA 0012 airfoil with a Reynolds number based on the airfoil chord and freestream velocity of 328,000. These simulation results were compared to experimental and newly developed models for validation. The ultimate goal of this present study was to create the two-point space time correlation function of a cylinder and airfoil wake using RANS calculations which contributes to a larger study where the sound radiated by an open rotor due to ingestion of turbulence.
Show less - Date Issued
- 2018
- PURL
- http://purl.flvc.org/fau/fd/FA00013105
- Subject Headings
- Turbulence--Noise--Mathematical models., Aerodynamic noise., Wakes (Aerodynamics)., Reynolds number.
- Format
- Document (PDF)
- Title
- caHydrodynamic analysis of flapping foils for the propulsion of near surface under water vehicles using the panel method.
- Creator
- Bustos, Julia, Ananthakrishnan, Palaniswamy, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the...
Show moreThis thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the case of a deeply submerged hydrofoil followed by the case where it is located in shallow water depth or near the free surface. In the second case, the presence of the free surface and wave effects are taken into account, specifically at high and low frequencies and small and large amplitudes of flapping. The objective is to determine the thrust and efficiency of the flapping –foils under the influence of added effects of the free surface. Results show that the free-surface can significantly affect the foil performance by increasing the efficiency particularly at high Frequencies.
Show less - Date Issued
- 2015
- PURL
- http://purl.flvc.org/fau/fd/FA00004351, http://purl.flvc.org/fau/fd/FA00004351
- Subject Headings
- Aerodynamics -- Mathematical models, Fluid mechanics, Naval architecture, Ships -- Aerodynamics, Steering gear
- Format
- Document (PDF)
- Title
- Simulation and modeling of flow field around a horizontal axis wind turbine (HAWT) using RANS method.
- Creator
- Sargsyan, Armen., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The principal objective of the proposed CFD analysis is to investigate the flow field around a horizontal axis wind turbine rotor and calculate the turbine's power. A full three dimensional computational fluid dynamics method based on Reynolds Averaged Navier Stokes approach was used in this study. The wind turbine has three blades and a rotor diameter of six meters. One third of the wind turbine rotor was modeled by means of 120o periodicity in a moving reference frame system. The power...
Show moreThe principal objective of the proposed CFD analysis is to investigate the flow field around a horizontal axis wind turbine rotor and calculate the turbine's power. A full three dimensional computational fluid dynamics method based on Reynolds Averaged Navier Stokes approach was used in this study. The wind turbine has three blades and a rotor diameter of six meters. One third of the wind turbine rotor was modeled by means of 120o periodicity in a moving reference frame system. The power coefficient curve obtained from the CFD results is compared with experimental data obtained by NREL Phase VI rotor experiment. The numerical result for the power coefficient curve shows close agreement with the experimental data. The simulation results include the velocity distribution, pressure distribution along the flow direction, turbulent wake behind the wind turbine, and the turbine's power. The discussion will also include the effect of wind speed on turbine's power.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2979383
- Subject Headings
- Wind turbines, Aerodynamics, Computer simulation, Fluid dynamics, Computational methods, Vibration (Aerodynamics)
- Format
- Document (PDF)
- Title
- Helicopter stability during aggressive maneuvers.
- Creator
- Mohan, Ranjith., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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The dissertation investigates helicopter trim and stability during level bank-angle and diving bank-angle turns. The level turn is moderate in that sufficient power is available to maintain level maneuver, and the diving turn is severe where the power deficit is overcome by the kinetic energy of descent. The investigation basically represents design conditions where the peak loading goes well beyond the steady thrust limit and the rotor experiences appreciable stall. The major objectives are:...
Show moreThe dissertation investigates helicopter trim and stability during level bank-angle and diving bank-angle turns. The level turn is moderate in that sufficient power is available to maintain level maneuver, and the diving turn is severe where the power deficit is overcome by the kinetic energy of descent. The investigation basically represents design conditions where the peak loading goes well beyond the steady thrust limit and the rotor experiences appreciable stall. The major objectives are: 1) to assess the sensitivity of the trim and stability predictions to the approximations in modeling stall, 2) to correlate the trim predictions with the UH-60A flight test data, and 3) to demonstrate the feasibility of routinely using the exact fast-Floquet periodic eigenvector method for mode identification in the stability analysis. The UH-60A modeling and analysis are performed using the comprehensive code RCAS (Army's Rotorcraft Comprehensive Analysis System). The trim and damping predictions are based on quasisteady stall, ONERA-Edlin vi (Equations Differentielles Lineaires) and Leishman-Beddoes dynamic stall models. From the correlation with the test data, the strengths and weaknesses of the trim predictions are presented.
Show less - Date Issued
- 2012
- PURL
- http://purl.flvc.org/FAU/3342237
- Subject Headings
- Helicopters, Aerodynamics, Helicopters, Control systems, Rotors (Helicopters), Aerodynamics, Stability of helicopters, Vibration (Aeronautics), Damping
- Format
- Document (PDF)
- 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
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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.
Show less - 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)
- Title
- NOISE PREDICTION METHODS.
- Creator
- Perry, Nicole Kent, Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
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Noise prediction methods are necessary in aspects of aerodynamic and hydrodynamic engineering. Predictive models of noise from rotating machinery ingesting turbulence is of much interest and relatively recently studied. This thesis presents a numerical method processed in a series of three codes that was written and edited to receive input for geometrical features of rotating machinery, as well as, adjustments to turbulent operating conditions. One objective of this thesis was to create a...
Show moreNoise prediction methods are necessary in aspects of aerodynamic and hydrodynamic engineering. Predictive models of noise from rotating machinery ingesting turbulence is of much interest and relatively recently studied. This thesis presents a numerical method processed in a series of three codes that was written and edited to receive input for geometrical features of rotating machinery, as well as, adjustments to turbulent operating conditions. One objective of this thesis was to create a platform of analysis for any rotor design to obtain five parameters necessary for noise prediction; 1) the hydrodynamic inflow angle to each blade section, 2) chord length as a function of radius, 3) the cylindrical radius of each blade section, 4) & 5) the leading edge as a function of span in both the rotor-plane and as a function of axial distance downstream. Another objective of this thesis was to use computational fluid dynamics (CFD), specifically by using a Reynold’s-Averaged Navier-Stokes (RANS) Shear Stress Transport (SST) 𝑘 − 𝜔 model simulation in ANSYS Fluent, to obtain the turbulent kinetic energy distribution, also necessary in the noise prediction method presented. The purpose of collecting the rotor geometry data and turbulent kinetic energy data was to input the values into the first of the series of codes and run the calculation so that the output spectra could be compared to experimental noise measurements conducted at the Stability Wind Tunnel at Virginia Tech. The comparison shows that the prediction method results in data that can be reliable if careful attention is payed to the input parameters and the length scale used for analysis. The significance of this research is the noise prediction method presented and used simplifies the model of turbulence by using a correlation function that can be determined by a one-dimensional function while also simplifying the iterations completed on rotor blade to calculate the unsteady forces.
Show less - Date Issued
- 2020
- PURL
- http://purl.flvc.org/fau/fd/FA00013487
- Subject Headings
- Noise, Aerodynamic noise, Hydrodynamics, Noise control--Mathematical models
- Format
- Document (PDF)
- Title
- Synchronization and phase dynamics of oscillating foils.
- Creator
- Finkel, Cyndee L., Charles E. Schmidt College of Science, Department of Physics
- Abstract/Description
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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.
Show less - 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)
- Title
- STATISTICAL MODELING OF SHIP AIRWAKES INCLUDING THE FEASIBILITY OF APPLYING MACHINE LEARNING.
- Creator
- Krishnan, Vaishakh, Gaonkar, Gopal, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
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Airwakes are shed behind the ship’s superstructure and represent a highly turbulent and rapidly distorting flow field. This flow field severely affects pilot’s workload and such helicopter shipboard operations. It requires both the one-point statistics of autospectrum and the two-point statistics of coherence (normalized cross-spectrum) for a relatively complete description. Recent advances primarily refer to generating databases of flow velocity points through experimental and computational...
Show moreAirwakes are shed behind the ship’s superstructure and represent a highly turbulent and rapidly distorting flow field. This flow field severely affects pilot’s workload and such helicopter shipboard operations. It requires both the one-point statistics of autospectrum and the two-point statistics of coherence (normalized cross-spectrum) for a relatively complete description. Recent advances primarily refer to generating databases of flow velocity points through experimental and computational fluid dynamics (CFD) investigations, numerically computing autospectra along with a few cases of cross-spectra and coherences, and developing a framework for extracting interpretive models of autospectra in closed form from a database along with an application of this framework to study the downwash effects. By comparison, relatively little is known about coherences. In fact, even the basic expressions of cross-spectra and coherences for three components of homogeneous isotropic turbulence (HIT) vary from one study to the other, and the related literature is scattered and piecemeal. Accordingly, this dissertation begins with a unified account of all the cross-spectra and coherences of HIT from first principles. Then, it presents a framework for constructing interpretive coherence models of airwake from a database on the basis of perturbation theory. For each velocity component, the coherence is represented by a separate perturbation series in which the basis function or the first term on the right-hand side of the series is represented by the corresponding coherence for HIT. The perturbation series coefficients are evaluated by satisfying the theoretical constraints and fitting a curve in a least squares sense on a set of numerically generated coherence points from a database. Although not tested against a specific database, the framework has a mathematical basis. Moreover, for assumed values of perturbation series constants, coherence results are presented to demonstrate how coherences of airwakes and such flow fields compare to those of HIT.
Show less - Date Issued
- 2020
- PURL
- http://purl.flvc.org/fau/fd/FA00013629
- Subject Headings
- Ships--Aerodynamics, Turbulence--Statistical methods, Machine learning
- Format
- Document (PDF)