Toroidal propellers hold significant potential as underwater propulsion systems compared to traditional propellers, primarily due to their unique shape, which effectively reduces and minimizes hydrodynamic noise and enhances structural stability and overall strength. To investigate hydrodynamic loads, flow fields, and vortex characteristics of toroidal propellers, numerical simulations were conducted on both toroidal and conventional propellers using the detached eddy simulation (DES) method in Star CCM+ computational fluid dynamics software. Results show that at low advance coefficients, the primary thrust generated by toroidal blades comes from pressure difference in the front section, whereas at high advance coefficients, it originates in the back section. A high-velocity region exists between the front and back sections of the toroidal propeller, with the range and intensity of this region gradually increasing from front to back. The wake vortex of the toroidal propeller comprises two parts: the tip vortex, where the front section tip vortex, back section tip vortex, and transition section leakage vortex merge, and the trailing edge vortex, which forms from the fusion of the front and back section leakage vortices. The fusion of these vortices is influenced by the advance coefficient. Compared to conventional propellers, the toroidal propellers exhibit a more extensive and intense trailing edge vortex in the wake flow field. These findings provide guidance for the optimization design research of toroidal propellers.

The presence of broken ice in the flow field around a propeller causes severe blade erosion, shafting, and hull vibration. This study investigates the performance of the propeller of a ship sailing in the polar regions under the propeller–ice non-contact condition. To this end, we construct a test platform for the propeller-induced excitation force due to ice blockage in a large circulating water channel. The hydrodynamic load of the propeller, and the cavitation and propeller-induced fluctuating pressure, were measured and observed by varying the cavitation number and ice–propeller axial distance under atmospheric pressure and decompression conditions. The results show that the fluctuation range of the blade load increases with a decrease in cavitation number and ice–propeller axial distance. The decrease in the cavitation number leads to broadband characteristics in the frequency-domain curves of the propeller thrust coefficient and blade-bearing force. Under the combined effects of ice blockage and proximity, propeller suction, the circumfluence zone around the ice, and the Pirouette effect, propeller–hull vortex cavitation is generated between the ice and propeller. The decrease in cavitation number leads to a sharp increase in the amplitude of the high-order frequency of the propeller-induced fluctuating pressure.

To address the impact of layered ice and seawater on polar vessels navigating in icy waters, this study employs a coupled finite element method (FEM) and smoothed particle hydrodynamics (SPH) algorithm to simulate the collision dynamics between the bow and stern of a designated icebreaker and the ice layers. The foundational principles and deployment strategies of the coupling algorithm have been meticulously delineated, with a subsequent simulation conducted to model the trajectory of icebreakers navigating through stratified ice conditions. The ice load on the hull, the movement of broken ice bodies, and the temporal variation of ice resistance during collision were analyzed. The method’s applicability and precision were substantiated through a comparative analysis between the simulated ice resistance outcomes and the ice load estimations derived from the Lindqvist formula. Finally, the differences between the bow and stern icebreaking methods were compared. The research findings indicate that the coupling algorithm demonstrates high precision in simulating the navigation of icebreakers under layered ice conditions, aligning with actual scenarios. This provides a solid foundation for further exploration of the ice load on polar vessels. Furthermore, at equivalent speeds and ice thicknesses, stern icebreaking was observed to induce greater oscillations in ice load and yield a higher mean resistance compared to bow icebreaking.

In this paper, the commercial computational fluid dynamics software STAR-CCM+ (18.04.008-R8) is utilized to analyze the hydrodynamic performance of BB2 underwater vehicles under various navigation conditions, as well as the flow field disturbances caused by the free surface and ice surface during navigation. After dividing the computational domains based on different navigation scenarios, numerical simulations are conducted for BB2 underwater vehicles (without a propeller) at infinite depth, near the free surface, and near the ice surface under various operating conditions. The analysis focuses on changes in resistance, velocity fields, and pressure fields of the BB2 at different velocities and navigation depths, followed by a comparison of the navigation differences of BB2 vehicles under varying operating conditions. Furthermore, to simulate realistic navigation conditions for underwater vehicles, numerical simulations are performed for BB2 underwater vehicles equipped with a propeller under different operating conditions. The results indicate that both the free surface and ice surface significantly influence the resistance, velocity field, and pressure field of the BB2. When the navigation depth exceeds 2D, the impact of ice on the vehicle can be nearly disregarded, and when the navigation depth exceeds 3D, the influence of the free surface on the vehicle can also be considered negligible.

When the ice-class propeller sails in an icy sea, it is affected by external factors such as water, ice, and cavitation, and the process of mutual interference is extremely complicated. In order to study the influence of water and cavitation on propeller load during the ice-propeller milling process, a test platform for ice–water propeller milling action was constructed. The load and cavitation of the propeller and single blade were measured during ice-propeller milling in air and water (atmospheric pressure and decompression conditions). Simultaneously, the changes in the load and bearing force of the propeller and blade were studied at different working conditions. The results show that, in the process of ice–water propeller milling, the direction of the propeller thrust generated by the water is opposite to that of the axial force generated by ice; the combined action of the two causes propeller thrust loss, whereas the combined action of water and ice increases propeller torque. The presence of water increases the thrust, torque, and bearing force of the fluctuating amplitude of the blade. The occurrence of cavitation reduces the thrust and torque of the propeller and blade and increases thrust fluctuating amplitudes while decreasing the tangential force fluctuating amplitude of the blade.

To investigate the impact of different computational strategies on the self-propulsion hydrodynamic performance of a submarine model, a study was conducted using the RANS method, employing both the steady-state Moving Reference Frame (MRF) method and the unsteady Rigid Body Motion (RBM) method. Numerical simulations of the self-propulsion hydrodynamic performance of the submarine model were performed under different computational strategies, including submarine with propeller, submarine first and propeller second, and propeller rotational speed iteration. The differences between these strategies were analyzed from various perspectives, such as submarine resistance, propeller hydrodynamic performance, total solver actual runtime, propeller unsteady bearing forces, and induced fluctuating pressure. The results indicated that when conducting numerical simulations of the self-propulsion hydrodynamic performance of the submarine with a propeller, the fluctuation ranges of the submarine resistance, propeller thrust, and torque obtained by the steady MRF method were within 0.1% to 0.8%, compared with the three strategies in the unsteady state. In terms of computational efficiency, strategy 3 (RBM—submarine with a propeller) had the lowest computational efficiency, and the time to obtain a self-propulsion curve was 11.9 times, 4.4 times, and 3.1 times that of strategy 1 (MRF + RBM—submarine with a propeller), strategy 2 (RBM—submarine first, then propeller), and strategy 4 (RBM—propeller rotational speed iteration). When analyzing the propeller excitation forces under the submarine’s self-propulsion state using the steady-state MRF method combined with the unsteady RBM method, the frequency domain peak fluctuations were within 5% compared with the three strategies in the unsteady state, making this method suitable for numerical simulations of propeller excitation forces. These findings provide methodological support for evaluating the performance of the submarine’s hydrodynamic propulsion system.