Experiments on evolution characteristics of momentum wakes generated by the towed sphere with a horizontal jet

Abstract

The model of the towed sphere with a L-shape nozzle jet was used to generate both drag and jet momentum wakes due to the body and cooling discharge water of the underwater vehicle, the results of experiments were presented for the evolution characteristics of such combined momentum wakes in a stratified fluid. It is shown that for J D/ J C D, the evolution characteristics for the combined momentum wakes are mainly attributed to the drag momentum wake generated by the towed sphere, and the far wake becomes quasi two-dimensional (2D) in the form of a Karman-like dipolar vortex street, where J D is the drag momentum flux due to the towed sphere, J is the jet momentum flux due to the L-shape nozzle jet and C D is the drag coefficient of the sphere. For J D/ J C D, the evolution characteristics for the combined momentum wakes are strongly dependent of the ( Rej , Frj ) combinations, and the far wake can become quasi 2D in the form of an anti-Karman-like dipolar vortex street being mainly attributed to the jet momentum wake under some ( Rej , Frj ) combinations, but there may be no occurrence of large-scale coherent structures, where Rej and Frj are Reynolds and Froude numbers duo to the L-shape nozzle jet respectively. The conditions under different Reynolds and Froude numbers ( Rej , Frj ) combinations where the anti-Karman-like dipolar vortex streets can be formed by such combined momentum wakes were determined by use of data based on the present series experiments, and the dependence of the dimensionless formation time and inverse dimensionless average wavelength of the quasi 2D dipolar vortex streets on Frj for different values of Rej was obtained, results indicate that these parameters are independent of Rej and approximately follow some power exponent laws on Frj .