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Published in Malcolm S. Gordon, Reinhard Blickhan, John O. Dabiri, John J. Videler, Animal Locomotion, 2017
John O. Dabiri, Malcolm S. Gordon
More fundamentally, we must concern ourselves with whether the spatial extent of the region in which viscous forces act is limited. If so, then we can often neglect the effects of viscous forces despite their existence in the flow. In a steady flow, large Reynolds numbers are indicative of such vorticity confinement. The basic limitation of the time-averaged Reynolds number is that it is by itself insufficient to deduce the existence of vorticity confinement.
Vorticity Confinement Technique and Blade Element Method for Accurate Propeller Modelling
Published in International Journal of Computational Fluid Dynamics, 2022
Y. Chandukrishna, T. N. Venkatesh
Inviscid and turbulent studies on hovering rotors with vorticity confinement were carried out by Pierson (2014). As far as the author is aware, there have not been any studies on aircraft propellers using the vorticity confinement technique. The present study applies the vorticity confinement technique to study the flows involving aircraft propellers. In the current study, SU2 (Palacios et al.2013), an open-source CFD tool, was modified to incorporate the vorticity confinement technique, which was then applied to several cases. Initially, the inviscid vortex transport case is solved to verify the implementation. Later, VC is applied for the isolated propeller case, and the effect of the confinement parameter is studied. A viscous analysis is carried out in the current study by solving compressible RANS equations with vorticity confinement. A new propeller modelling method is implemented into SU2, where the propeller is modelled as a disk with discrete points on its surface. The propeller blade loading is calculated recursively with Blade Element Method (BEM) using the given geometry and airfoil details at different blade sections. This technique is termed SU2-BEM. To ensure that the tangential velocities induced by the propeller are conserved over greater distances, VC is also applied to the SU2-BEM technique.
Combined Vorticity Confinement and TVD Approaches for Accurate Vortex Modelling
Published in International Journal of Computational Fluid Dynamics, 2020
Alex Povitsky, Kristopher C. Pierson
CFD solvers typically employ upwind discretisation schemes for convective terms, and while the schemes improve numerical stability, they come at the cost of elevated numerical dissipation compared to central difference schemes. Numerical dissipation causes decay of vortices at a much greater rate than physical dissipation (Snyder and Povitsky 2014). As the vortices are convected downstream, this decay is clearly observed through the rapid decrease of peak velocity and expansion of the vortex core. Vorticity confinement (VC) can be used to improve the results of the vortex modelling without the computational cost of a highly refined grid. The VC method can be used to counteract nonphysical numerical dissipation and eliminate the decay of vortices even for coarse grids, which would normally be plagued by unnatural levels of dissipation through numerical viscosity. The VC method can be implemented through the addition of a body force term to the inviscid momentum equation (Steinhoff, Lynn, and Wang 2005; Lohner, Yang, and Roger 2002; Snyder 2012; Steinhoff and Underhill 1994), as shown in Equation (1): The vector is given by Equation (2) as the product of the direction vector , defined in Equation (4), and the local pseudo-vector of vorticity, :