Experimental investigations on the bubbly wake of a transom stern model using optical laser beam scattering characteristics

Abstract

In this paper a new procedure for detection and quantification of the main features of ship models bubbly wake is presented. The method is based on light scattering characteristics of laser beams passing through the wake of ship models. An optical light scattering model is developed and validated in a series of steady bubbly flow tests in a water tank, with time-invariant mean multiphase flow properties. Then a series of unsteady tests are conducted in a towing tank so as to study bubbly wake properties of a transom stern model. Temporal wake strength and its final detection time and length are measured using light scattering measurements. Light scattering analysis provides longitudinal, lateral, and vertical distributions of the wake without any flow intrusion. Also by combining the experimental and analytical results, a complementary assay for determination of average bubble size and bubble number density distribution is presented. Effects of model velocity on the bubbly wake features of the transom stern are also investigated using the suggested procedures. Results indicate that increasing the model velocity increases the total bubbly wake length and lifetime. Details of the wake lateral distribution reveal the prominent contribution of transom stern diverging waves on the bubbly wake air entrainment.