Large-eddy simulation of Kelvin-Helmholtz waves

A large-eddy simulation model is used to study the three-dimensional structure and evolution of Kelvin-Helmholtz (KH) waves in several shear flows varying the speed and direction with height. Three flows are simulated: the first is a parallel shear flow without the v velocity component, and the second and third are rotating shear flows with uniform wind speed. The differences of wind direction between upper and lower layers are 180 and 90 degrees in the second and third flows, respectively. Results show that the ratio of the wave length of KH waves to the depth of the shear layer is about 5.5 in the first and second flows, and about 7.1 in the flow. The increasing rate of the shear production before its maximum is the largest in the third flow, while its decreasing rate after its maximum is the largest in the first flow. The period for which the shear production exceeds a threshold is the longest in the second flow. These characteristics may depend on the magnitude of the shear of the v velocity component.