A mesh resolution study for large eddy simulation of flow interactions of a finite-span synthetic jet on an airfoil

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Larrabee, Erik
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Aeronautical engineering
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The primary objective of this study is to investigate the effect of mesh resolution on the accuracy of large eddy simulation (LES) based prediction of complex flow interactions that arise between a finite-span synthetic jet and a crossflow. The focus is on the accurate prediction of the dynamics of the resulting vortical structures, including their interactions and breakdown, as well as spatial and temporal frequencies that develop. We employ a dynamic LES approach based on a combined subgrid-scale model within the context of a stabilized finite element formulation. The problem case exhibits a spatiotemporal inhomogeneity and involves complex geometry, where a finite-span synthetic jet is placed on a NACA 4421 airfoil at 0 degrees angle of attack and a chord-based Reynolds number of 100,000. In this study, the jet operates at a momentum coefficient of 8.93e-3 corresponding to a blowing ratio of 1.2 and at a reduced or relative frequency of about 38 with respect to the characteristic frequency of the flow. This setting is selected to compare the current LES predictions with a prior joint investigation involving experimental measurements and direct numerical simulation (DNS). The LES meshes range from about 2.4 million vertices and 11 million elements (i.e., the smallest LES mesh) to 4 million vertices and 20 million elements (i.e., the largest LES mesh) and each simulation uses 120 steps per jet cycle. The increase in the number of vertices and elements in the largest LES mesh comes from the increase in the extent of the near-jet fine mesh resolution in the downstream direction. LES predictions on the largest mesh compare well with prior DNS and experimental datasets, where the computational cost of the DNS case is about an order of magnitude more, with 15 million vertices, 80 million elements, and 360 time steps per jet cycle.
December 2018
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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