Investigation of internal wave wakes generated by a towed sphere in stratified flow using planar array measurements

The stable thermohaline stratification of the ocean gives rise to complex generation, propagation and evolution characteristics of internal wave wakes produced by moving bodies. This study proposes a pycnocline injection approach to construct a stratified flow field representative of typical oceanic pycnoclines and develops a high-precision planar array conductivity measurement system to systematically capture the spatiotemporal evolution of internal wave amplitudes induced by a towed sphere. Using statistical analysis, spectral decomposition and filtering techniques, three distinct internal wave components with different generation mechanisms and propagation behaviours are identified. Their dominant Froude number ranges and spatial distribution characteristics are further clarified. Focusing on the predominant component at high Froude numbers, collapse-stage internal waves, this study examines how key parameters, including waveform, propagation speed, wavelength and wave amplitude, vary with the Froude number. Moreover, by incorporating oscillating-source theory, it is shown that the characteristic semicircular or circular concentric patterns of collapse-stage internal waves can be reasonably explained by pulsating disturbances in the turbulent wake and the resulting vertical restoring motions in the stratified fluid.