The Experts below are selected from a list of 9 Experts worldwide ranked by ideXlab platform

Haili Liao - One of the best experts on this subject based on the ideXlab platform.

  • direct measurement of the Sears Function in turbulent flow
    Journal of Fluid Mechanics, 2018
    Co-Authors: Yang Yang, Haili Liao
    Abstract:

    The applicability of the strip assumption in the estimation of the unsteady lift response of a two-dimensional wing in turbulent flow is investigated. The ratio between the lift spectrum calculated from the two-wavenumber analysis and the lift spectrum calculated from the strip assumption is used to evaluate the accuracy of the strip assumption. It is shown that the accuracy of the strip assumption is controlled by the ratio of the turbulence integral scale to the chord and the aspect ratio. With an increase of these two parameters, the ratio for evaluating the accuracy of the strip assumption increases, the one-wavenumber transfer Function obtained from the strip assumption approaches the Sears Function gradually. When these two parameters take suitable values, the strip assumption could be applicable to the calculation of the unsteady lift on a wing in turbulent flow. Here, the term aspect ratio refers to the ratio of the specified span (an finite spanwise length of the two-dimensional wing) to the chord, the unsteady lift is calculated over this specified spanwise length. The theoretical analysis is verified by means of force measurement experiments conducted in a wind tunnel. In the experiment, a square passive grid is installed downstream of the entrance of the test section to generate approximately homogeneous and isotropic turbulence. Three rectangular wings with different aspect ratios ( , 5 and 7) are used. These wing models have an NACA 0015 profile cross-section and a fixed chord length . The testing results show that, at a fixed ratio of turbulence integral scale to chord, the deviation between the experimental one-wavenumber transfer Function obtained from the strip assumption and the Sears Function is reduced with increasing aspect ratio, as expected by the theoretical predictions. However, due to the effect of thickness, the experimental values at high frequencies cannot be captured by the Sears Function which is derived based on the flat plate assumption. In practical applications, the effect of thickness on the transfer Function should be considered.

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

  • direct measurement of the Sears Function in turbulent flow
    Journal of Fluid Mechanics, 2018
    Co-Authors: Yang Yang, Haili Liao
    Abstract:

    The applicability of the strip assumption in the estimation of the unsteady lift response of a two-dimensional wing in turbulent flow is investigated. The ratio between the lift spectrum calculated from the two-wavenumber analysis and the lift spectrum calculated from the strip assumption is used to evaluate the accuracy of the strip assumption. It is shown that the accuracy of the strip assumption is controlled by the ratio of the turbulence integral scale to the chord and the aspect ratio. With an increase of these two parameters, the ratio for evaluating the accuracy of the strip assumption increases, the one-wavenumber transfer Function obtained from the strip assumption approaches the Sears Function gradually. When these two parameters take suitable values, the strip assumption could be applicable to the calculation of the unsteady lift on a wing in turbulent flow. Here, the term aspect ratio refers to the ratio of the specified span (an finite spanwise length of the two-dimensional wing) to the chord, the unsteady lift is calculated over this specified spanwise length. The theoretical analysis is verified by means of force measurement experiments conducted in a wind tunnel. In the experiment, a square passive grid is installed downstream of the entrance of the test section to generate approximately homogeneous and isotropic turbulence. Three rectangular wings with different aspect ratios ( , 5 and 7) are used. These wing models have an NACA 0015 profile cross-section and a fixed chord length . The testing results show that, at a fixed ratio of turbulence integral scale to chord, the deviation between the experimental one-wavenumber transfer Function obtained from the strip assumption and the Sears Function is reduced with increasing aspect ratio, as expected by the theoretical predictions. However, due to the effect of thickness, the experimental values at high frequencies cannot be captured by the Sears Function which is derived based on the flat plate assumption. In practical applications, the effect of thickness on the transfer Function should be considered.

J M R Graham - One of the best experts on this subject based on the ideXlab platform.

  • the effect of three dimensionality on the aerodynamic admittance of thin sections in free stream turbulence
    Journal of Fluids and Structures, 2015
    Co-Authors: Matteo Massaro, J M R Graham
    Abstract:

    Abstract The unsteady behaviour of a thin plate section or aerofoil strip in a turbulent wind field is described by a two-wavenumber extension of the well known single wavenumber Sears Function. The second (spanwise) wavenumber is introduced to deal with the three dimensional effects of the turbulence. The present work considers the unsteady forces induced on finite span sections and investigates the influence of the ratio of span to chord (aspect-ratio) of the section on these three dimensional effects. The analysis shows that the influence of the spanwise wavenumber becomes negligible for the aerodynamic admittance of buffeting lift forces for large enough aspect-ratios, such as those typical of modern long-span bridges, thus supporting the use of strip-theory in these cases.

Matteo Massaro - One of the best experts on this subject based on the ideXlab platform.

  • the effect of three dimensionality on the aerodynamic admittance of thin sections in free stream turbulence
    Journal of Fluids and Structures, 2015
    Co-Authors: Matteo Massaro, J M R Graham
    Abstract:

    Abstract The unsteady behaviour of a thin plate section or aerofoil strip in a turbulent wind field is described by a two-wavenumber extension of the well known single wavenumber Sears Function. The second (spanwise) wavenumber is introduced to deal with the three dimensional effects of the turbulence. The present work considers the unsteady forces induced on finite span sections and investigates the influence of the ratio of span to chord (aspect-ratio) of the section on these three dimensional effects. The analysis shows that the influence of the spanwise wavenumber becomes negligible for the aerodynamic admittance of buffeting lift forces for large enough aspect-ratios, such as those typical of modern long-span bridges, thus supporting the use of strip-theory in these cases.

James Quackenbush Rice - One of the best experts on this subject based on the ideXlab platform.

  • IN STEADY AND UNSTEADY FLOWS By
    1991
    Co-Authors: James Quackenbush Rice, Professoi Douglas A. Carmichael
    Abstract:

    Numerical investigations were done on a two-dimensional hydrofoil under steady and high reduced frequency unsteady loading in the MIT Ocean Engineering Marine Hydrodynamics Laboratory (MHL). The computational findings were supplemented by steady flow experimental aata taken with the hydrofoil in the MHL variable pressure water tunnel (VPWT). A linear, inviscid computer code was developed to estimate the influence of one or a number of vortex generators upon the induced velocities in a confined channel flow. A typical marine propeller section shape with a standard anti-singing trailing edge was chosen as the experimental test piece. The steady flow properties of this unbounded shape were determined using a strongly-coupled viscous/inviscid solver. An unsteady boundary element method (BEM) solved for the unsteady pressure distributions around the hydrofoil surface using the output from the induced velocity code, and a Sears Function approach. The power needed to drive the unsteady apparatus was then estimated by combining the solid body inertial effects with the hydrodynamic effects as determined from both the added mass and the Theodorsen approximations. Using a steady BEM code which is capable of modeling tunnel walls, th