The cylindrical flow around a cylinder is present in several engineering problems. Moreover, the flow pattern around a rotating cylinder is more complex than that around a cylinder. In this paper, a rotating cylinder at different speed ratios is investigated by means of large-eddy simulations. In particular, the lift coefficient CL, drag coefficient CD, lift-to-drag ratio k, Strouhal number St, the flow field in each section, and the three-dimensional eddy structure are compared at different speed ratios. In addition, the effects of an end disk on the aerodynamic loads and flow field of the rotating cylinder were investigated. The results showed that, in the absence of an end disk, CL increased, CD increased and then decreased, k increased and then decreased, and St increased and then decreased as the speed ratio increased. The turnaround occurs for each parameter at a speed ratio of n = 2, and vortex shedding is suppressed at this speed ratio. Notably, the tip vortex at the free end was not suppressed. The CL, CD, and k values of the cylinder when adding the end disk were greater than those of the normal cylinder. For example, when the speed ratio is 3, the lift coefficient is increased by 27%, the drag coefficient is increased by 24%, and the lift-to-drag ratio is increased by 23% after adding the end plate. In addition, the vortex structure at the free end differed substantially. This study provides a systematic method to evaluate the aerodynamic loads and flow field changes around a cylinder, laying the foundation for solving the problems of cylinder flow and rotating cylinder flow.
The acceleration characteristics of a water jet-propelled ship during startup are related to its performance under mooring conditions. Water jet propulsion cavitation during startup increases the vibration and noise of the whole ship. Therefore, accurately predicting and analyzing the performance, hydrodynamics and flow field characteristics of water jet-propelled ships under mooring conditions can help elucidate the startup characteristics of the ships and optimize their acceleration strategies. In this study, the hydrodynamic and flow field characteristics of water jet propulsion and water jet propulsion ships under mooring conditions were studied using three-dimensional numerical modeling. First, the hydrodynamic performance of the water jet propeller was analyzed, and the relevant flow field law was derived. Then, the hydrodynamic performance, internal and external flow field characteristics, pulsation pressure and flow rate at the nozzle, and pulsation pressure at the monitoring points around the impeller of the water jet propulsion ship model were analyzed under mooring conditions. We obtained the open-water law for the water jet propeller and the hydrodynamic force and flow field law for a two-pump water jet propulsion ship. The ship model developed in this study provides a good theoretical foundation for further research on water jet propulsion.
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