Purpose In this paper, experimental and numerical results of a lambda wing have been compared. The purpose of this paper is to study the behaviour of lambda wings using a CFD tool and to consider different numerical models to obtain the most accurate results. As far as the consideration of numerical methods is concerned, the main focus is on the evaluation of computational methods for an accurate prediction of contingent leading edge vortices’ path and the flow separation occurring because of the burst of these vortices on the wing. Design/methodology/approach Experimental tests are performed in a closed-circuit wind tunnel at the Reynolds number of 6 × 105 and angles of attack (AOA) ranging from 0 to 10 degrees. Investigated turbulence models in this study are Reynolds Averaged Navior–Stokes (RANS) models in a steady state. To compare the accuracy of the turbulence models with respect to experimental results, sensitivity study of these models has been plotted in bar charts. Findings The results illustrate that the leading edge vortex on this lambda wing is unstable and disappears soon. The effect of this disappearance is obvious by an increase in local drag coefficient in the junction of inner and outer wings. Streamlines on the upper surface of the wing show that at AOA higher than 8 degrees, the absence of an intense leading edge vortex leads to a local flow separation on the outer wing and a reverse in the flow. Research limitations/implications Results obtained from the behaviour study of transition (TSS) turbulence model are more compatible with experimental findings. This model predicts the drag coefficient of the wing with the highest accuracy. Of all considered turbulence models, the Spalart model was not able to accurately predict the non-linearity of drag and pitching moment coefficients. Except for the TSS turbulence model, all other models are unable to predict the aerodynamic coefficients corresponding to AOA higher than 10 degrees. Practical implications The presented results in this paper include lift, drag and pitching moment coefficients in various AOA and also the distribution of aerodynamic coefficients along the span. Originality/value The presented results include lift, drag and pitching moment coefficients in various AOA and also aerodynamic coefficients distribution along the span.
In this paper, acoustic power radiation of a submerged finite length ribbed cylinder subject to a harmonic point load is minimized by a new fast scheme. For this purpose, two arrangements of non-uniformly distributed sequential point masses and mass springs attached on stiffening ribs of the cylinder are used to optimally reduce the acoustic power radiation. A fully coupled analysis is here carried out based on Finite/Boundary element (FEM/BEM) model. Instead of direct BEM formulation, two beneficial procedures have been proposed for computing BEM matrices in each frequency line. In order to fast solving of equations, the Krylov vectors (produced via Ritz or Arnoldi iterative procedures) and structural mode shapes (modal truncation approach) have been used and validated before performing optimization. As a result, the best strategy for evaluation of response and cost function is using Taylor series expansion for computing BEM matrices and applying Krylov vectors for order reduction. The results show good agreement with previous studies and experiments. The optimization results show noticeable reductions in the acoustic power radiation. In point mass optimization, the most of additional masses has been placed in regions which are near to the excitation point whereas for the absorber design, they are put in the places in opposite side of the excitation point.
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