<p>This study was built upon previous works conducted by the authors in a series of numerical studies on submarine hydrodynamics, developing the computational fluid dynamics (CFD) method to estimate the self-propulsive performance of underwater vehicles. The Defense Advanced Research Projects Agency (DARPA) SUBOFF submarine model was adopted as a benchmark. The computational modeling was based on the Reynolds-averaged Navier–Stokes (RANS) turbulence model for simulations. A body force propeller method was used to model the propulsion, instead of resolving the actual propeller geometry. Verification study was carried out through systematic mesh refinement, and validation study was performed by comparing the computational solutions with available experimental results. Parametric study was carried out using the verified and validated method, and Reynolds number effect varying the locations of the stern planes and free surface effect on the self-propulsive performance were investigated.<br>
In the verification and validation studies, the numerical solutions at a self-propulsive condition converged monotonically or oscillatorily, along with mesh refinement. The self-propulsive performance was validated in terms of the Taylor wake fraction, thrust deduction fraction, and hull efficiency. The computed hull efficiency agreed well with the experimental results, showing a slight comparison error of less than 3%. The influence of struts which were used to mount the hull to a carriage at the experiment was investigated, and the difference of the computed self-propulsive performance between with and without the struts was only less than 1%. As for the free surface effect, the volume of fluid (VOF) method was used to detect the interface between air and water, and an adaptive mesh refinement approach was employed to track the free surfaces. General humps and hollows characteristics of the straight-ahead resistance as a function of Froude number were captured in the range tested. However, several computations were slightly offset from the experimental values, which could have been caused by the supporting sting and post, and the transition strip used in the experiment.<br>
The computed Taylor wake fractions significantly depended on Reynolds number and monotonically decreased by approximately 30% within the range tested, while the thrust deduction fractions were invariable. The Taylor wake fractions and thrust deduction fractions for the model of aft-fitted stern planes were approximately 3–7% and 8–10% higher than those of baseline and fore-fitted stern planes, respectively. Slight differences were observed in the hull efficiency among the models. However, the differences were considered insignificant, accounting for the obtained numerical uncertainties in the verification study. Regarding the free surface effect, the Taylor wake fractions and the hull efficiencies slightly decreased as Froude number, showing several hollows and humps. The computed suction heave forces monotonically decreased, while the pitching moment varied from negative to positive as the increase in Froude number. These results can contribute to the future designs and operations of underwater vehicles to avoid unexpected broaching and possible collisions with surface ships. In the future study, the similar simulations will be performed in both model and full scale varying the submergences, to comprehensively understand the hydrodynamic performance of underwater vehicles cruising close by a free surface.</p>

Parametric Numerical Study on the Self-Propulsive Performance of The DARPA Suboff Submarine via the Body-Force Propeller Method

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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