THE GENERATION OF INTERNAL WAVES BY A TOWED SPHERE AND ITS WAKE IN A THERMOCLINE

This report describes a combined experimental and numerical study of i nternal gravity waves generated by a sphere which is towed horizontall y in a density stratified fresh water tank which exhibits a strong the rmocline at mid-depth. The Reynolds number range covered extends from 2000 < Re = UD/v < 100000, and the Froude number range was 0.44 < Fr = U/N-max D < 22. Both the kinematics as well as the dynamics of the in ternal waves are studied. The internal wave field is shown to be gener ated by two very distinct types of sources, one stationary with respec t to the body and one which is nonstationary. The stationary part of t he internal wave field is shown to be generated by an ''effective'' bo dy comprised of the sphere plus a stationary separation bubble which f ollows it. The nonstationary part of the internal wave field is shown to be generated by the nonstationary oscillations associated with the large-scale eddies of the turbulent wake. While such nonstationary int ernal waves have been observed in previous investigations, their physi cal origin has not been clearly identified. This paper presents a simp le physical model for their generation. (C) 1997 American Institute of Physics.