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    Wall-modelled large-eddy simulation of turbulent flow past airfoils

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    Wall-modelled large-eddy simulation of turbulent flow past airfoils.pdf
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    Type
    Article
    Authors
    Gao, Wei cc
    Zhang, Wei
    Cheng, Wan
    Samtaney, Ravi cc
    KAUST Department
    Fluid and Plasma Simulation Group (FPS)
    Mechanical Engineering
    Mechanical Engineering Program
    Physical Science and Engineering (PSE) Division
    KAUST Grant Number
    URF/1/1394-01
    Date
    2019-06-24
    Online Publication Date
    2019-06-24
    Print Publication Date
    2019-08-25
    Embargo End Date
    2019-12-25
    Permanent link to this record
    http://hdl.handle.net/10754/656250
    
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    Abstract
    We present large-eddy simulation (LES) of flow past different airfoils with, based on the free-stream velocity and airfoil chord length, ranging from to. To avoid the challenging resolution requirements of the near-wall region, we develop a virtual wall model in generalized curvilinear coordinates and incorporate the non-equilibrium effects via proper treatment of the momentum equations. It is demonstrated that the wall model dynamically captures the instantaneous skin-friction vector field on arbitrary curved surfaces at the resolved scale. By combining the present wall model with the stretched-vortex subgrid-scale model, we apply the wall-modelled LES approach to three different airfoil cases, spanning different geometrical parameters, different attack angles and low to high. The numerical results are verified with direct numerical simulation (DNS) at low, and validated with experiment data at higher, including typical aerodynamic properties such as pressure coefficient distributions, velocity components and also more challenging measurements such as skin-friction coefficient and Reynolds stresses. All comparisons show reasonable agreement, providing a measure of validity that enables us to further probe simulation results into aspects of flow physics that are not available from experiments. Two techniques to quantify hitherto unexplored physics of flows past airfoils are employed: one is the construction of the anisotropy invariant map, and the second is skin-friction portraits with emphasis on flow transition and unsteady separation along the airfoil surface. The anisotropy maps for all three cases, show clearly that a portion of the flow field is aligned along the axisymmetric expansion line, corresponding to the turbulent boundary layer log-law behaviour and the appearance of turbulent transition. The instantaneous skin-friction portraits reveal a monotonic shrinking of the near wall structure scale. At, the interaction between the primary separation bubble and the secondary separation bubble contributes to turbulent transition, similar to the case of flow past a cylinder. At higher, the primary separation breaks into several small separation bubbles. At even higher, near the turbulent separation, the skin-friction lines show small-scale reversal flows that are similar to those observed in DNS of the flat plate turbulent separation. A notable feature of turbulent separation in flow past an airfoil is the appearance of turbulence structures and small-scale reversal flows in the spanwise direction due to the vortex shedding behaviour.
    Citation
    Gao, W., Zhang, W., Cheng, W., & Samtaney, R. (2019). Wall-modelled large-eddy simulation of turbulent flow past airfoils. Journal of Fluid Mechanics, 873, 174–210. doi:10.1017/jfm.2019.360
    Sponsors
    The Cray XC40 Shaheen II at KAUST was used for all simulations reported. This research was partially supported under KAUST OCRF URF/1/1394-01 and under baseline research funds of R.S.
    Publisher
    Cambridge University Press
    Journal
    Journal of Fluid Mechanics
    DOI
    10.1017/jfm.2019.360
    Additional Links
    https://www.cambridge.org/core/product/identifier/S0022112019003604/type/journal_article
    ae974a485f413a2113503eed53cd6c53
    10.1017/jfm.2019.360
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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