# R. Krasny

The equations governing periodic vortex sheet roll-up from analytic initial data are desingularized. Linear stability analysis shows that this diminishes the vortex sheet modelâ€™s short wavelength instability. yielding a numerically more tractable set of equations. Computational evidence is presented which indicates that this approximation converges, beyondâ€¦ (More)
The initial-value problem for perturbations of a flat, constant-strength vortex sheet is linearly ill posed in the sense of Hadamard, owing to Kelvin-Helmholtz instability. Previous numerical studies of this problem have experienced difficulty in converging when the mesh was refined. The present work examines Rosenheadâ€™s point-vortex approximation and seeksâ€¦ (More)
• 2001
A particle method is presented for computing vortex sheet motion in three-dimensional flow. The particles representing the sheet are advected by a regularized Biotâ€“ Savart integral in which the exact singular kernel is replaced by the Rosenheadâ€“ Moore kernel. New particles are inserted to maintain resolution as the sheet rolls up. The particle velocitiesâ€¦ (More)
• ROBERT KRASNYt
• 1987
Two vortex-sheet evolution problems arising in aerodynamics are studied numerically. The approach is based on desingularizing the Cauchy principal value integral which defines the sheetâ€™s velocity. Numerical evidence is presented which indicates that the approach converges with respect to refinement in the mesh-size and the smoothing parameter. For ellipticâ€¦ (More)
In this article we shall review some recent developments for computing vortex sheet roll-up. A vortex sheet is an asymptotic model of a free shear layer in which the transition region between the two fluid streams is approximated by a surface across which the tangential velocity component is discontinuous. A common theme in fluid dynamics is that the vortexâ€¦ (More)
Chorin's vortex blob method has been proposed as a way to extend vortex sheet motion past the singularity formation time, into the physically important roll-up regime. Basic questions are: 1. Does the vortex blob method converge to an infinite spiral as the smoothing parameter tends to zero? 2. Do vortex blob computations approximate real fluid motion? Thisâ€¦ (More)
• 2000
Regularized point-vortex simulations are presented for vortex sheet motion in planar and axisymmetric flow. The sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and aâ€¦ (More)
• IEEE Transactions on Plasma Science
• 2006
A common approach to modeling kinetic problems in plasma physics is to represent the plasma as a set of Lagrangian macro-particles which interact through long-range forces. In the well-known particle-in-cell (PIC) method, the particle charges are interpolated to a mesh and the fields are obtained using a fast Poisson solver. The advantage of this approachâ€¦ (More)
Thermal management is important for the efficient operation of organic light-emitting diodes (OLED, or PHOLED) at high brightness, with the device operating temperature influencing both lifetime and performance. We apply a transmission-matrix approach to analytically model the effects of thermal conduction, convection and radiation on OLED temperature. Theâ€¦ (More)