Thrust augmentation of flapping airfoils in low Reynolds number flow using a flexible membrane
TL;DR: In this paper, the effect of membrane prestress and elasticity on aerodynamic thrust and aeroelastic response of a two-dimensional membrane airfoil under prescribed harmonic motion was investigated with a high-order Navier-Stokes solver coupled to a nonlinear membrane structural model.
About: This article is published in Journal of Fluids and Structures.The article was published on 2015-01-01 and is currently open access. It has received 16 citations till now. The article focuses on the topics: Flapping & Reynolds number.
Citations
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TL;DR: In this article, a simulation of a symmetric foil undergoing prescribed oscillations in a two-dimensional free stream is presented, and the authors compare measurements and simulations when the foil is forced with pitching oscillations, and find a close correspondence between flow visualisations using thickness variations in the soap film and numerically determined vortex structures.
Abstract: We present a combined numerical (particle vortex method) and experimental (soap film tunnel) study of a symmetric foil undergoing prescribed oscillations in a two-dimensional free stream. We explore pure pitching and pure heaving, and contrast these two generic types of kinematics. We compare measurements and simulations when the foil is forced with pitching oscillations, and we find a close correspondence between flow visualisations using thickness variations in the soap film and the numerically determined vortex structures. Numerically, we determine wake maps spanned by oscillation frequency and amplitude, and we find qualitatively similar maps for pitching and heaving. We determine the drag–thrust transition for both pitching and heaving numerically, and we discuss it in relation to changes in wake structure. For heaving with low oscillation frequency and high amplitude, we find that the drag–thrust transition occurs in a parameter region with wakes in which two vortex pairs are formed per oscillation period, in contrast to the common transition scenario in regions with inverted von Karman wakes.
112 citations
TL;DR: In this article, the authors derived the auxiliary potentials that separate the total vortex force into lift and drag (or thrust) coefficients by using an elliptic airfoil, and the added-mass components of the lift and charge coefficients were also obtained analytically for any heaving motion of the air-foil and for any value of the mean angle of attack α.
Abstract: The thrust efficiency of a two-dimensional heaving airfoil is studied computationally for a low Reynolds number using a vortex force decomposition. The auxiliary potentials that separate the total vortex force into lift and drag (or thrust) are obtained analytically by using an elliptic airfoil. With these auxiliary potentials, the added-mass components of the lift and drag (or thrust) coefficients are also obtained analytically for any heaving motion of the airfoil and for any value of the mean angle of attack α. The contributions of the leading- and trailing-edge vortices to the thrust during their down- and up-stroke evolutions are computed quantitatively with this formulation for different dimensionless frequencies and heave amplitudes (Stc and Sta) and for several values of α. Very different types of flows, periodic, quasi-periodic, and chaotic described as Stc, Sta, and α, are varied. The optimum values of these parameters for maximum thrust efficiency are obtained and explained in terms of the inte...
44 citations
TL;DR: In this article, the effects of added mass and fluid damping on a flapping membrane are quantified using a simple damped oscillator model, and an analytic model based on thin airfoil theory coupled with a membrane equation is developed to characterize the steady and unsteady aeroelastic behavior of compliant membrane wings under different conditions.
Abstract: We present a theoretical framework to characterize the steady and unsteady aeroelastic behaviour of compliant membrane wings under different conditions. We develop an analytic model based on thin airfoil theory coupled with a membrane equation. Adopting a numerical solution to the model equations, we study the effects of wing compliance, inertia and flapping kinematics on aerodynamic performance. The effects of added mass and fluid damping on a flapping membrane are quantified using a simple damped oscillator model. As the flapping frequency is increased, membranes go through a transition from thrust to drag around the resonant frequency, and this transition is earlier for more compliant membranes. The wake also undergoes a transition from a reverse von Karman wake to a traditional von Karman wake. The wake transition frequency is predicted to be higher than the thrust–drag transition frequency for highly compliant wings.
34 citations
Journal Article•
TL;DR: In this paper, the effects of added mass and fluid damping on a flapping membrane are quantified using a simple damped oscillator model, and an analytic model based on thin airfoil theory coupled with a membrane equation is developed to characterize the steady and unsteady aeroelastic behavior of compliant membrane wings under different conditions.
Abstract: We present a theoretical framework to characterize the steady and unsteady aeroelastic behaviour of compliant membrane wings under different conditions. We develop an analytic model based on thin airfoil theory coupled with a membrane equation. Adopting a numerical solution to the model equations, we study the effects of wing compliance, inertia and flapping kinematics on aerodynamic performance. The effects of added mass and fluid damping on a flapping membrane are quantified using a simple damped oscillator model. As the flapping frequency is increased, membranes go through a transition from thrust to drag around the resonant frequency, and this transition is earlier for more compliant membranes. The wake also undergoes a transition from a reverse von Karman wake to a traditional von Karman wake. The wake transition frequency is predicted to be higher than the thrust–drag transition frequency for highly compliant wings.
27 citations
TL;DR: In this article, the effect of reinforced leading or trailing edge on the aerodynamic performance of a two-dimensional perimeter-reinforced (PR) membrane wing at Re =2500 is investigated numerically, using a novel model of membrane wing and a fluid-structure interaction solution procedure based on the characteristic-based split (CBS) finite element method.
21 citations
References
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TL;DR: In this article, the authors present finite-difference schemes for the evaluation of first-order, second-order and higher-order derivatives yield improved representation of a range of scales and may be used on nonuniform meshes.
5,832 citations
01 Jun 1981
TL;DR: In this paper, a new combination of a finite volume discretization in conjunction with carefully designed dissipative terms of third order, and a Runge Kutta time stepping scheme, is shown to yield an effective method for solving the Euler equations in arbitrary geometric domains.
Abstract: A new combination of a finite volume discretization in conjunction with carefully designed dissipative terms of third order, and a Runge Kutta time stepping scheme, is shown to yield an effective method for solving the Euler equations in arbitrary geometric domains. The method has been used to determine the steady transonic flow past an airfoil using an O mesh. Convergence to a steady state is accelerated by the use of a variable time step determined by the local Courant member, and the introduction of a forcing term proportional to the difference between the local total enthalpy and its free stream value.
4,220 citations
Book•
01 Jan 1984
TL;DR: In this paper, a reference record was created on 2005-11-18, modified on 2016-08-08 and used for CFD-based transfert de chaleur.
Abstract: Keywords: CFD ; numerique ; transfert de chaleur ; ecoulement Reference Record created on 2005-11-18, modified on 2016-08-08
3,629 citations
02 May 1934
TL;DR: In this paper, the Kutta condition was used to analyze the aerodynamic forces on an oscillating airfoil or an air-foil-aileron combination of three independent degrees of freedom.
Abstract: The aerodynamic forces on an oscillating airfoil or airfoil-aileron combination of three independent degrees of freedom were determined. The problem resolves itself into the solution of certain definite integrals, which were identified as Bessel functions of the first and second kind, and of zero and first order. The theory, based on potential flow and the Kutta condition, is fundamentally equivalent to the conventional wing section theory relating to the steady case. The air forces being known, the mechanism of aerodynamic instability was analyzed. An exact solution, involving potential flow and the adoption of the Kutta condition, was derived. The solution is of a simple form and is expressed by means of an auxiliary parameter k. The flutter velocity, treated as the unknown quantity, was determined as a function of a certain ratio of the frequencies in the separate degrees of freedom for any magnitudes and combinations of the airfoil-aileron parameters.
2,153 citations
TL;DR: An implicit finite-difference scheme is developed for the numerical solution of the compressible Navier-Stokes equations in conservation- law form and, although a three-time-lev el scheme, requires only two time levels of data storage.
Abstract: An implicit finite-difference scheme is developed for the numerical solution of the compressible Navier-Stokes equations in conservation- law form. The algorithm is second-order- time accurate, noniterative, and spatially factored. In order to obtain an efficient factored algorithm, the spatial cross derivatives are evaluated explicitly. However, the algorithm is unconditional ly stable and, although a three-time-lev el scheme, requires only two time levels of data storage. The algorithm is constructed in a "delta" form (i.e., increments of the conserved variables and fluxes) that provides a direct derivation of the scheme and leads to an efficient computational algorithm. In addition, the delta form has the advantageous property of a steady state (if one exists) independent of the size of the time step. Numerical results are presented for a two-dimensiona l shock boundary-layer interaction problem.
2,096 citations