Computational and experimental determination of waterjet aeration exposure in waves

Abstract

Object and purpose of research. The object of research was a model of a fast seaworthy boat with discretevariable bottom deadrise and two waterjet propulsors. The purposes of research were to experimentally determine hydrodynamic characteristics of the model in calm water and head regular waves corresponding to the irregular waves of sea states 3 and 4, as well as to determine the possibility of air penetration to waterjet inlets for two variants of their arrangement on model bottom in head-wave conditions, numerical simulation of the full-scale boat movement in oblique irregular waves (sea state 4) for two variants of waterjet arrangement, with an assessment of waterjet duct aeration exposure.
 Materials and methods. Model hydrodynamics was estimated experimentally by means of towing tests in highspeed seakeeping basin in calm water and head regular waves using standard test equipment; air penetrations were recorded by a GO PRO digital video camera installed on the model above the water inlets. Numerical simulation of the full-scale boat movement was carried out in Star-CCM+ CFD package.
 Main results. The study yielded the curves of towing resistance, running trim and sinkage versus model speed in calm water and head regular waves of different length for two longitudinal CG positions, as well as the areas of air penetration to waterjet inlets on model bottom. Analysis of the experimental data enabled the estimation of attainable speed for the boat with displacement of 50 and 29 tf in waves for given delivered power. Numerical simulation of the full-scale boat movement in oblique irregular waves for two variants of waterjet arrangement has also been carried out.
 Conclusion. The results have shown that seakeeping performance of the boat is quite satisfactory and that the most obvious way to mitigate air penetrations is to reduce the speed. Other important factors were shifting the waterjet inlet towards the transom and to the CL, as well as shifting the longitudinal CG forward. The obtained results can be used to select the position of the waterjet inlets on boat bottom in order to increase waterjet efficiency. Using the methods of numerical hydrodynamics, the characteristics of the waterjets have been obtained, the probability and volumes of air penetrations to waterjet ducts (for different variants of waterjet arrangement) at several angles of oblique irregular waves have been estimated.

Influence of the Inclined Pipe Section on the Performance of a Waterjet Propulsion Device

“…Park et al [20] compared the flow line and pressure distribution obtained through numerical simulation and experiment to understand flow characteristics in the inlet passage and predict the position of stagnation point in the labial part. Dyakova et al [21] improved the propulsion efficiency of the device by changing the position of the water inlet through a numerical fluid dynamics method but did not analyse the relationship between water inlet angle and conduit length. On the basis of the basic principle of waterjet propulsion, Kortunova and Yakovleva [22] evaluated water flow at the inlet passage of a waterjet propulsion device in a self-propulsion test and described the influence of its coverage area on induction efficiency.…”