The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform

Avshalom Manela - One of the best experts on this subject based on the ideXlab platform.

  • Vibration and sound of a flapping Airfoil: The limit of small bending rigidity
    The Journal of the Acoustical Society of America, 2017
    Co-Authors: Avshalom Manela, Michael Weidenfeld
    Abstract:

    We investigate the near and far fields of a Thin elastic Airfoil set at uniform low-Mach flow and subject to leading-edge heaving actuation. The Airfoil is “hanged” in the vertical direction and is free at its downstream end, so that “hanging chain” gravity-induced tension forces apply. The structure bending rigidity is assumed small, and we focus on analyzing the differences between a highly elastic Airfoil and a membrane (where the bending rigidity vanishes). The near field is studied based on potential Thin Airfoil Theory, whereas the acoustic field is investigated using the Powell-Howe acoustic analogy. The results shed light on the specific effect of structure bending stiffness on the dynamics and acoustic disturbance of an Airfoil.

  • On the acoustic signature of tandem Airfoils: The sound of an elastic Airfoil in the wake of a vortex generator
    Physics of Fluids, 2016
    Co-Authors: Avshalom Manela
    Abstract:

    The acoustic signature of an acoustically compact tandem Airfoil setup in uniform high-Reynolds number flow is investigated. The upstream Airfoil is considered rigid and is actuated at its leading edge with small-amplitude harmonic pitching motion. The downstream Airfoil is taken passive and elastic, with its motion forced by the vortex-street excitation of the upstream Airfoil. The non-linear near-field description is obtained via potential Thin-Airfoil Theory. It is then applied as a source term into the Powell-Howe acoustic analogy to yield the far-field dipole radiation of the system. To assess the effect of downstream-Airfoil elasticity, results are compared with counterpart calculations for a non-elastic setup, where the downstream Airfoil is rigid and stationary. Depending on the separation distance between Airfoils, Airfoil-motion and Airfoil-wake dynamics shift between in-phase (synchronized) and counter-phase behaviors. Consequently, downstream Airfoil elasticity may act to amplify or suppress s...

  • The sound of an elastic Airfoil in the wake of a vortex generator
    The Journal of the Acoustical Society of America, 2016
    Co-Authors: Avshalom Manela
    Abstract:

    The acoustic signature of an acoustically compact tandem Airfoil setup in high-Reynolds number flow is investigated. The upstream Airfoil is rigid and is actuated at its leading edge with small-amplitude sinusoidal pitching motion. The downstream Airfoil is taken passive and elastic, with its motion forced by the vortex-street excitation of the upstream Airfoil. The near-field description is obtained via potential Thin-Airfoil Theory. It is then applied as a source term into the Powell-Howe acoustic analogy, to yield the far-field dipole radiation of the system. To assess the effect of downstream-Airfoil elasticity, results are compared with calculations for a non-elastic setup, where the downstream Airfoil is rigid and fixed. Depending on separation distance between Airfoils, Airfoil-motion and Airfoil-wake dynamics shift between in-phase (synchronized) and counter-phase behaviors. Downstream Airfoil elasticity acts to either amplify or suppress sound, through the direct contribution of elastic-Airfoil m...

  • On the attenuating effect of permeability on the low frequency sound of an Airfoil
    Journal of Sound and Vibration, 2016
    Co-Authors: Michael Weidenfeld, Avshalom Manela
    Abstract:

    Abstract The effect of structure permeability on the far-field radiation of a Thin Airfoil is studied. Assuming low-Mach and high-Reynolds number flow, the near- and far-field descriptions are investigated at flapping-flight and unsteady flow conditions. Analysis is carried out using Thin-Airfoil Theory and compact-body-based calculations for the hydrodynamic and acoustic fields, respectively. Airfoil porosity is modeled via Darcy׳s law, governed by prescribed distribution of surface intrinsic permeability. Discrete vortex model is applied to describe Airfoil wake evolution. To assess the impact of penetrability, results are compared to counterpart predictions for the sound of an impermeable Airfoil. Considering the finite-chord Airfoil as “acoustically transparent”, the leading-order contribution of surface porosity is obtained in terms of an acoustic dipole. It is shown that, at all flow conditions considered, porosity causes attenuation in outcome sound level. This is accompanied by a time-delay in the pressure signal, reflecting the mediating effect of permeability on the interaction of fluid flow with Airfoil edge points. To the extent that Thin-Airfoil Theory holds (requiring small normal-to-Airfoil flow velocities), the results indicate on a decrease of ~ 10 percent and more in the total energy radiated by a permeable versus an impermeable Airfoil. This amounts to a reduction in system sound pressure level of 3 dB and above at pitching flight conditions, where the sound-reducing effect of the seepage dipole pressure becomes dominant. The applicability of Darcy׳s law to model the effect of material porosity is discussed in light of existing literature.

  • On the acoustic radiation of a pitching Airfoil
    Physics of Fluids, 2013
    Co-Authors: Avshalom Manela
    Abstract:

    We examine the acoustic far field of a Thin elastic Airfoil, immersed in low-Mach non-uniform stream flow, and actuated by small-amplitude sinusoidal pitching motion. The near-field fluid-structure interaction problem is analyzed using potential Thin-Airfoil Theory, combined with a discrete vortex model to describe the evolution of Airfoil trailing edge wake. The leading order dipole-sound signature of the system is investigated using Powell-Howe acoustic analogy. Compared with a pitching rigid Airfoil, the results demonstrate a two-fold effect of structure elasticity on Airfoil acoustic field: at actuation frequencies close to the system least stable eigenfrequency, elasticity amplifies Airfoil motion amplitude and associated sound levels; however, at frequencies distant from this eigenfrequency, structure elasticity acts to absorb system kinetic energy and reduce acoustic radiation. In the latter case, and with increasing pitching frequency ωp, a rigid-Airfoil setup becomes significantly noisier than an...

Cox, Clifton A. - One of the best experts on this subject based on the ideXlab platform.

  • Two Element Linear Strength Vortex Panel Method
    DigitalCommons@CalPoly, 2011
    Co-Authors: Cox, Clifton A.
    Abstract:

    A linear strength vortex panel method was developed to predict the Cp and Cl for a lifting two element Airfoil. The linear strength vortex panel method was first validated against Thin Airfoil Theory and experimental data for a single NACA 2412 Airfoil. At 2 degrees angle of attack, the linear strength vortex panel method predicted a Cl of about 0.49. Experimental data and Thin Airfoil Theory gave Cl estimations of 0.45 and 0.22 respectively. The Matlab code was then modified to accept a two element Airfoil. The two key modifications were the separation of the two different sets of wing element panels and the subsequent addition of a second Kutta condition. The linear strength vortex panel method was then used to determine the Cl and Cp distribution of a two element wing. The two element wing of study was the rear wing Airfoil used on the 2008 Formula SAE car. Using a reference length of 1.43 and an angle of attack of 2 degrees, the panel method predicted a Cl of 3.98. Improved results can be obtained by using more panels or better geometry resolution around the leading edge and the gap between the two wing elements

Clifton Cox - One of the best experts on this subject based on the ideXlab platform.

  • Linear Strength Vortex Panel Method for a Two Element Airfoil
    2011
    Co-Authors: Clifton A. Cox, Clifton Cox
    Abstract:

    A linear strength vortex panel method was developed to predict the Cp and Cl for a lifting two element Airfoil. The linear strength vortex panel method was first validated against Thin Airfoil Theory and experimental data for a single NACA 2412 Airfoil. At 2 degrees angle of attack, the linear strength vortex panel method predicted a Cl of about 0.49. Experimental data and Thin Airfoil Theory gave Cl estimations of 0.45 and 0.22 respectively. The Matlab code was then modified to accept a two element Airfoil. The two key modifications were the separation of the two different sets of wing element panels and the subsequent addition of a second Kutta condition. The linear strength vortex panel method was then used to determine the Cl and Cp distribution of a two element wing. The two element wing of study was the rear wing Airfoil used on the 2008 Formula SAE car. Using a reference length of 1.43 and an angle of attack of 2 degrees, the panel method predicted a Cl of 3.98. Improved results can be obtained by using more panels or better geometry resolution around the leading edge and the gap between the two wing elements

Mrinal Kaushik - One of the best experts on this subject based on the ideXlab platform.

  • Thin Airfoil Theory
    Theoretical and Experimental Aerodynamics, 2018
    Co-Authors: Mrinal Kaushik
    Abstract:

    Thin Airfoil Theory is a straightforward hypothesis of Airfoils that relates angle of attack to lift for an incompressible and inviscid flow past an Airfoil. This Theory idealizes the flow past an Airfoil as two-dimensional stream around a Thin Airfoil which can be envisioned as tending to an Airfoil of zero thickness and infinite wingspan.

  • Theoretical and Experimental Aerodynamics
    2018
    Co-Authors: Mrinal Kaushik
    Abstract:

    PART I: THEORETICAL AERODYNAMICS -- Chapter 1: The Standard Atmosphere -- Chapter 2: Basic Concepts -- Chapter 3: Governing Equations of Fluid Flows -- Chapter 4: Potential Flow Theory -- Chapter 5: Thin Airfoil Theory -- Chapter 6: Finite Wing Theory -- Chapter 7: Panel Methods -- Chapter 8:Thermodynamics of Fluids in Motion -- Chapter 9: Compressible Flows -- Chapter 10: Hypersonic Flows -- Chapter 11: Boundary Layers -- Chapter 12: Wind Tunnels -- PART II: APPLIED AERODYNAMICS -- Chapter 13: Supersonic Jets -- Chapter 14: Shock Wave and Boundary Layer Interactions -- Appendix.

Raymond E. Gordnier - One of the best experts on this subject based on the ideXlab platform.

  • High-Order Simulations of Low Reynolds Number Membrane Airfoils under Prescribed Motion
    Journal of Fluids and Structures, 2012
    Co-Authors: Justin W. Jaworski, Raymond E. Gordnier
    Abstract:

    The aerodynamics and aeroelastic response of a membrane wing under prescribed motion are investigated using a high-order, two-dimensional Navier-Stokes solver coupled to a geometrically-nonlinear membrane model. The impact of increasing Reynolds number on the vortex dynamics and unsteady aerodynamic loads is examined for moderate-amplitude plunge and combined pitch-plunge motions at low frequency. Simulation results are compared with classical Thin Airfoil Theory and highlight the differences between rigid and flexible membrane Airfoils undergoing small and moderate amplitude motions. Most notably, the present study demonstrates the ability of lifting membrane surface flexibility to enhance thrust production, which may inform the design of flapping wing membrane fliers.