TY - JOUR
T1 - Nonlinear resonances in a laminar wall jet
T2 - Ejection of dipolar vortices
AU - Wernz, Stefan
AU - Fasel, Hermann F.
N1 - Funding Information:
Support for this research was provided by the Air Force Office of Scientific Research under grant F49620-00-10069 and by the Office of Naval Research under grant N000014-01-0932. The three-dimensional simulations were made possible by a grant of HPC time on the Cray X1 at the Army High Performance Research Center.
PY - 2007/10/10
Y1 - 2007/10/10
N2 - Nonlinear mechanisms leading to the ejection of dipolar vortices from a laminar wall jet are being investigated using highly accurate Navier-Stokes simulations. With a set of well-defined numerical experiments for a forced Glauert wall jet, the nonlinear resonant interaction between the large-amplitude harmonic disturbance and a small-amplitude wave packet is systematically explored using two-dimensional simulations. Generated by a small-amplitude pulse, the wave packet experiences rapid resonant growth in the subharmonic part of its spectrum resulting in vortex mergings and, ultimately, the ejection of a pair of counter-rotating vortices from the wall jet. This two-dimensional subharmonic instability, if not mitigated by competing three-dimensional instabilities, can lead to the detachment of the entire wall jet from the surface. As shown using three-dimensional direct numerical simulations, vortex ejection still occurs in a forced transitional wall jet if the two-dimensional wave packet can reach a large amplitude level upstream of the region of three-dimensional turbulent breakdown. Movies are available with the online version of the paper.
AB - Nonlinear mechanisms leading to the ejection of dipolar vortices from a laminar wall jet are being investigated using highly accurate Navier-Stokes simulations. With a set of well-defined numerical experiments for a forced Glauert wall jet, the nonlinear resonant interaction between the large-amplitude harmonic disturbance and a small-amplitude wave packet is systematically explored using two-dimensional simulations. Generated by a small-amplitude pulse, the wave packet experiences rapid resonant growth in the subharmonic part of its spectrum resulting in vortex mergings and, ultimately, the ejection of a pair of counter-rotating vortices from the wall jet. This two-dimensional subharmonic instability, if not mitigated by competing three-dimensional instabilities, can lead to the detachment of the entire wall jet from the surface. As shown using three-dimensional direct numerical simulations, vortex ejection still occurs in a forced transitional wall jet if the two-dimensional wave packet can reach a large amplitude level upstream of the region of three-dimensional turbulent breakdown. Movies are available with the online version of the paper.
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U2 - 10.1017/S0022112007007562
DO - 10.1017/S0022112007007562
M3 - Article
AN - SCOPUS:37749030917
SN - 0022-1120
VL - 588
SP - 279
EP - 308
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -