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Mina R Mankbadi - One of the best experts on this subject based on the ideXlab platform.
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experimental study of tip vortex flow from a periodically pitched Airfoil Section
AIAA Aerospace Sciences Meeting (SciTech 2016), 2016Co-Authors: Khairul Q Zaman, Amy F Fagan, Mina R MankbadiAbstract:An experimental investigation of a tip vortex from a NACA0012 Airfoil is conducted in a low-speed wind tunnel at a chord Reynolds number of 4x10(exp 4). Initially, data for a stationary Airfoil held at various angles-of-attack (alpha) are gathered. Detailed surveys are done for two cases: alpha=10 deg with attached flow and alpha=25 deg with massive flow separation on the upper surface. Distributions of various properties are obtained using hot-wire anemometry. Data include mean velocity, streamwise vorticity and turbulent stresses at various streamwise locations. For all cases, the vortex core is seen to involve a mean velocity deficit. The deficit apparently traces to the Airfoil wake, part of which gets wrapped by the tip vortex. At small alpha, the vortex is laminar within the measurement domain. The strength of the vortex increases with increasing alpha but undergoes a sudden drop around alpha (is) greater than 16 deg. The drop in peak vorticity level is accompanied by transition and a sharp rise in turbulence within the core. Data are also acquired with the Airfoil pitched sinusoidally. All oscillation cases pertain to a mean alpha=15 deg while the amplitude and frequency are varied. An example of phase-averaged data for an amplitude of +/-10 deg and a reduced frequency of k=0.2 is discussed. All results are compared with available data from the literature shedding further light on the complex dynamics of the tip vortex.
Mac Gaunaa - One of the best experts on this subject based on the ideXlab platform.
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aerodynamic response of an Airfoil Section undergoing pitch motion and trailing edge flap deflection a comparison of simulation methods
Wind Energy, 2015Co-Authors: Leonardo Bergami, Vasilis A Riziotis, Mac GaunaaAbstract:The study presents and compares aerodynamic simulations for an Airfoil Section with an adaptive trailing edge flap, which deflects following a smooth deformation shape. The simulations are carried out with three substantially different methods: a Reynolds-averaged Navier–Stokes solver, a viscous–inviscid interaction method and an engineering dynamic stall model suitable for implementation in aeroelastic codes based on blade element momentum theory. The aerodynamic integral forces and pitching moment coefficients are first determined in steady conditions, at angles of attack spanning from attached flow to separated conditions and accounting for the effects of flap deflection; the steady results from the Navier–Stokes solver and the viscous–inviscid interaction method are used as input data for the simpler dynamic stall model. The paper characterizes then the dynamics of the unsteady forces and moments generated by the Airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady-state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among the investigated methods at attached flow conditions, both for Airfoil pitching and flap deflection. At high angles of attack, where flow separation is encountered, the methods still depict similar overall dynamics, but larger discrepancies are reported, especially for the simpler engineering method. Copyright © 2014 John Wiley & Sons, Ltd.
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stability investigation of an Airfoil Section with active flap control
Wind Energy, 2010Co-Authors: Leonardo Bergami, Mac GaunaaAbstract:This work presents a method to determine flutter and divergence instability limits for a two-dimensional (2-D) Airfoil Section fitted with an actively controlled trailing edge flap. This flap consists of a deformable trailing edge, which deformation is governed by control algorithms based on measurements of either heave displacement, local angle of attack or aerodynamic pressure difference measured over the Airfoil. The purpose of the controlled deformable flap is to reduce fluctuations in the aerodynamic forces on the Airfoil, which, according to recent studies, have a significant potential for fatigue load alleviation. The structural model of the 2-D Airfoil Section contains three degrees of freedom: heave translation, pitch rotation and flap deflection. A potential flow model provides the aerodynamic forces and their distribution. The unsteady aerodynamics are described using an indicial function approximation. Stability of the full aeroservoelastic system is determined through eigenvalue analysis by state–space formulation of the indicial approximation. Validation is carried out against an implementation of the recursive method by Theodorsen and Garrick for ‘flexure–torsion–aileron’ flutter. The implemented stability tool is then applied to an Airfoil Section representative of a wind turbine blade with active flap control. It is thereby observed that the Airfoil stability limits are significantly modified by the presence of the flap, and they depend on several parameters: flap structural characteristics, type of control, control gain factors and time lag. Copyright © 2009 John Wiley & Sons, Ltd.
Khairul Q Zaman - One of the best experts on this subject based on the ideXlab platform.
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experimental study of tip vortex flow from a periodically pitched Airfoil Section
AIAA Aerospace Sciences Meeting (SciTech 2016), 2016Co-Authors: Khairul Q Zaman, Amy F Fagan, Mina R MankbadiAbstract:An experimental investigation of a tip vortex from a NACA0012 Airfoil is conducted in a low-speed wind tunnel at a chord Reynolds number of 4x10(exp 4). Initially, data for a stationary Airfoil held at various angles-of-attack (alpha) are gathered. Detailed surveys are done for two cases: alpha=10 deg with attached flow and alpha=25 deg with massive flow separation on the upper surface. Distributions of various properties are obtained using hot-wire anemometry. Data include mean velocity, streamwise vorticity and turbulent stresses at various streamwise locations. For all cases, the vortex core is seen to involve a mean velocity deficit. The deficit apparently traces to the Airfoil wake, part of which gets wrapped by the tip vortex. At small alpha, the vortex is laminar within the measurement domain. The strength of the vortex increases with increasing alpha but undergoes a sudden drop around alpha (is) greater than 16 deg. The drop in peak vorticity level is accompanied by transition and a sharp rise in turbulence within the core. Data are also acquired with the Airfoil pitched sinusoidally. All oscillation cases pertain to a mean alpha=15 deg while the amplitude and frequency are varied. An example of phase-averaged data for an amplitude of +/-10 deg and a reduced frequency of k=0.2 is discussed. All results are compared with available data from the literature shedding further light on the complex dynamics of the tip vortex.
Leonardo Bergami - One of the best experts on this subject based on the ideXlab platform.
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aerodynamic response of an Airfoil Section undergoing pitch motion and trailing edge flap deflection a comparison of simulation methods
Wind Energy, 2015Co-Authors: Leonardo Bergami, Vasilis A Riziotis, Mac GaunaaAbstract:The study presents and compares aerodynamic simulations for an Airfoil Section with an adaptive trailing edge flap, which deflects following a smooth deformation shape. The simulations are carried out with three substantially different methods: a Reynolds-averaged Navier–Stokes solver, a viscous–inviscid interaction method and an engineering dynamic stall model suitable for implementation in aeroelastic codes based on blade element momentum theory. The aerodynamic integral forces and pitching moment coefficients are first determined in steady conditions, at angles of attack spanning from attached flow to separated conditions and accounting for the effects of flap deflection; the steady results from the Navier–Stokes solver and the viscous–inviscid interaction method are used as input data for the simpler dynamic stall model. The paper characterizes then the dynamics of the unsteady forces and moments generated by the Airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady-state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among the investigated methods at attached flow conditions, both for Airfoil pitching and flap deflection. At high angles of attack, where flow separation is encountered, the methods still depict similar overall dynamics, but larger discrepancies are reported, especially for the simpler engineering method. Copyright © 2014 John Wiley & Sons, Ltd.
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stability investigation of an Airfoil Section with active flap control
Wind Energy, 2010Co-Authors: Leonardo Bergami, Mac GaunaaAbstract:This work presents a method to determine flutter and divergence instability limits for a two-dimensional (2-D) Airfoil Section fitted with an actively controlled trailing edge flap. This flap consists of a deformable trailing edge, which deformation is governed by control algorithms based on measurements of either heave displacement, local angle of attack or aerodynamic pressure difference measured over the Airfoil. The purpose of the controlled deformable flap is to reduce fluctuations in the aerodynamic forces on the Airfoil, which, according to recent studies, have a significant potential for fatigue load alleviation. The structural model of the 2-D Airfoil Section contains three degrees of freedom: heave translation, pitch rotation and flap deflection. A potential flow model provides the aerodynamic forces and their distribution. The unsteady aerodynamics are described using an indicial function approximation. Stability of the full aeroservoelastic system is determined through eigenvalue analysis by state–space formulation of the indicial approximation. Validation is carried out against an implementation of the recursive method by Theodorsen and Garrick for ‘flexure–torsion–aileron’ flutter. The implemented stability tool is then applied to an Airfoil Section representative of a wind turbine blade with active flap control. It is thereby observed that the Airfoil stability limits are significantly modified by the presence of the flap, and they depend on several parameters: flap structural characteristics, type of control, control gain factors and time lag. Copyright © 2009 John Wiley & Sons, Ltd.
Earl H. Dowell - One of the best experts on this subject based on the ideXlab platform.
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Compact Implementation Strategy for a Harmonic Balance Method Within Implicit Flow Solvers
AIAA Journal, 2013Co-Authors: Jeffrey P Thomas, Earl H. Dowell, Kenneth C. Hall, Chad H. Custer, Christophe Eric CorreAbstract:A two-step approximate factorization technique for implementing a computationally stable nonlinear unsteady frequency-domain harmonic balance solution method within existing implicit computational fluid dynamic flow solver codes is presented. The approach uses an explicit discretization of the harmonic balance source term, and no new implicit code development is required. Both of these features enable the harmonic balance method to be implemented within existing implicit flow solver codes with minimal modification necessary to the underlying flow solver code. The resulting harmonic balance solver can then be used for modeling nonlinear periodic unsteady flows. The methodology is applied to the NASA OVERFLOW flow solver code, and results are presented for transonic viscous flow past an unsteady pitching Airfoil Section.
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unsteady flow computation using a harmonic balance approach implemented about the overflow 2 flow solver
19th AIAA Computational Fluid Dynamics, 2009Co-Authors: Jeffrey P Thomas, Earl H. Dowell, Chad H Custe, Kenneth C. HallAbstract:A novel approach for implementing a nonlinear unsteady frequency domain harmonic balance solution technique about existing implicit computational fluid dynamic flow solvers is presented. This approach uses an explicit discretization of the harmonic balance source term, which enables the harmonic balance method to be applied to existing implicit flow solvers with minimal need for modification to the underlying implicit flow solver code. The resulting harmonic balance solver can then be used for modeling nonlinear periodic unsteady flows. The methodology is applied to the OVERFLOW 2 flow solver code, and results are presented for transonic viscous flow past an unsteady pitching Airfoil Section. Unsteady aerodynamic and aeroelastic results for the F-16 fighter wing are also presented.
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worst case gust response analysis for typical Airfoil Section with control surface
Journal of Aircraft, 2005Co-Authors: Atsushi Kanda, Earl H. DowellAbstract:We determine the worst-case gust response of a typical Airfoil Section with a control surface. Matched filter theory is employed in order to compute the gust that produces a maximum response. These results are compared with a tuned one-minus-cosine gust, one of the standard representations of discrete gusts
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nonlinear response of Airfoil Section with control surface freeplay to gust loads
AIAA Journal, 2000Co-Authors: Deman Tang, Denis B Kholodar, Earl H. DowellAbstract:A nonlinear response analysis of a typical Airfoil Section with control surface freeplay excited by periodic gust loads in low subsonic flow is presented along with a companion wind-tunnel test program. The analytical model uses Peters's finite state model for the two-dimensional aerodynamic flow over the Airfoil (Peters, D. A., Finite-State Airloads for Deformable Airfoils on Fixed and Rotating Wings, Symposium on Aeroelasticity and Fluid/Structure Interaction, American Society of Mechanical Engineers, Winter Annual Meeting, Nov. 1994, rev. 3, May 1996). Results for a single harmonic gust and a continuous frequency sweep gust have been computed and measured for flow velocities below the flutter speed. A theoretical and experimental chaotic response phenomenon for the nonlinear structural model was observed. These results further confirm some conclusions about limit cycle oscillations and complement our earlier theoretical and experimental studies of self-excited oscillations. The experimental investigation has been carried out in the Duke University wind tunnel using a rotating slotted cylinder gust generator. The fair to good quantitative agreement between theory and experiment verifies that the present analytical approach has reasonable accuracy and good computational efficiency for nonlinear gust response analysis in the time domain.
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nonlinear behavior of a typical Airfoil Section with control surface freeplay a numerical and experimental study
Journal of Fluids and Structures, 1997Co-Authors: Mark D Conner, Earl H. Dowell, Deman Tang, L N VirginAbstract:Abstract A three degree-of-freedom aeroelastic typical Section with control surface freeplay is modeled theoretically as a system of piecewise linear state-space models. The system response is determined by time marching of the governing equations using a standard Runge-Kutta algorithm in conjunction with Henon’s method for integrating a system of equations to a prescribed surface of phase space Section. Henon’s method is used to locate the ‘‘switching points’’ accurately and efficiently as the system moves from one linear region into another. An experimental model which closely approximates the three degree-of-freedom typical Section in two-dimensional, incompressible flow has been created to validate the theoretical model. Consideration is given to modeling realistically the structural damping present in the experimental system. The effect of the freeplay on the system response is examined numerically and experimentally. The development of the state-space model offers a low-order, computationally efficient means of modeling fully the freeplay nonlinearity and may offer advantages in future research which will investigate the effects of freeplay on the control of flutter in the typical Section.