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 strat ified fluid was studied in the Froude number range 1. 5 less-than-or-e qual-to F less-than-or-equal-to 12.7, where F is defined with the radi us of the sphere. The Reynolds number was sufficiently large for the w ake to be turbulent (Re is-an-element-of [380,30000]). A fluorescent d ye technique was used to differentiate waves generated by the sphere, called lee waves, from the internal waves, called random waves, emitte d by the turbulent wake. We demonstrate that the lee waves are well pr edicted by linear theory and that the random waves due to the turbulen ce are related to the coherent structures of the wake. The Strouhal nu mber 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.