Void Waves Developing in Gas-Liquid Two-Phase Turbulent Boundary Layers Beneath a Flat Bottom Model Ship

To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-mlong transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.