Computational and experimental determination of waterjet aeration exposure in waves

• Main Authors: Tatyana A. Dyakova, Sergey O. Rozhdestvensky, Nikolai V. Marinich, Alexey A. Rudnichenko
• Format: Article
• Language: English
• Published: Krylov State Research Centre 2020-12-01
• Series: Труды Крыловского государственного научного центра
• Subjects: high-speed boat with discrete-variable bottom deadrise; seakeeping tests; numerical simulation; head waves; oblique irregular waves; hydrodynamic characteristics; air penetration; waterjet propulsion
• Online Access: https://transactions-ksrc.ru/eng/archive/Computational-and-experimental-determination-of-waterjet-aeration-exposure-in-waves/

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.