INTERNAL WAVES PRODUCED BY THE TURBULENT WAKE OF A SPHERE MOVING HORIZONTALLY IN A STRATIFIED FLUID

The internal gravity wave field generated by a sphere towed in a stratified fluid was studied in the Froude number range 1. 5 less-than-or-equal-to F less-than-or-equal-to 12.7, where F is defined with the radius of the sphere. The Reynolds number was sufficiently large for the wake to be turbulent (Re is-an-element-of [380,30000]). A fluorescent dye technique was used to differentiate waves generated by the sphere, called lee waves, from the internal waves, called random waves, emitted by the turbulent wake. We demonstrate that the lee waves are well predicted by linear theory and that the random waves due to the turbulence are related to the coherent structures of the wake. The Strouhal number of these structures depends on F when F less than or similar to 4.5. Locally, these waves behave like transient internal waves emitted by impulsively moving bodies.