Rans-Based CFD Prediction of the Hydrodynamic Coefficients of Darpa Suboff Geometry in Straight-Line and Rotating Arm Manoeuvres

Abstract

Computational Fluid Dynamics (CFD) simulations using Reynolds Averaged Navier-Stokes (RANS) equations are increasingly adopted as an analysis tool to predict the hydrodynamic coefficients of underwater vehicles. These simulations have shown to offer both a high degree of accuracy comparable to experimental methods and a greatly reduced computational cost compared to Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). However, one of the major challenges faced with CFD simulations is that the results can vary greatly depending on the numerical model settings. This paper uses the DARPA SUBOFF hull form undergoing straight-line and rotating arm manoeuvres at different drift angles to analyse the hydrodynamic forces and moments on the vehicle against experimental data, showing that the selection of the boundary conditions and turbulence models, and the quality of the mesh model can have a considerable and independent effect on the computational results. Comparison between the Baseline Reynolds Stress Model (BSLRSM) and Shear Stress Transport with Curvature Correction (SSTCC) were carried out for both manoeuvres, showing that with a sufficiently fine mesh, appropriate mesh treatment, and simulation conditions matching the experiments; the BSLRSM predictions offer good agreement with experimental measurements, while the SSTCC predictions are agreeable with the longitudinal force but fall outside the experimental uncertainty for both the lateral force and yawing moment.

Free Surface Effect on the Hydrodynamics of an Underwater Vehicle Hullform, the Darpa Suboff

“…The experiments were conducted for a deeply submerged SUBOFF at a Froude number, Fn of 0.512 over a drift angle range of 0° ≤ β ≤ 18°. The predictions were found to be in good agreement with the positive angle data set of experimental measurements and a previous study byLeong et al (2012) shows similar agreement. The experimental measurements were reported with an uncertainty of 10% although it does not include the contribution from the mounting structure.…”

Effects of Length-to-Diameter Ratio on a Near Free Surface Underwater Vehicle

“…The y + on the SUBOFF hull is shown in Fig. 7 and is well below the target of 0.5 as established by Leong et al (2015) required to accurately capture flow separation in the boundary layer that occurs in the stern region.…”

“…Previous work (Leong et al, 2015;Ling et al, 2022a;Ling et al, 2022b;Ling et al, 2022c) has established the mesh requirements of a near free surface underwater vehicle with respect to the turbulence model, the effect of mesh resolution, inflation layer around the hull (total thickness and y + ), and the free surface mesh resolution and as will be seen in the following sections, are accurate in predicting the hydrodynamic coefficients of a near free surface submarine with experimental comparisons. The free surface mesh was sized according to the recommendations from CD-Adapco, in Spence (2014) where 80 to 100 cells per wavelength and 20 cells per amplitude are recommended; and ITTC (2011) where 40 cells per wavelength and 10 cells per amplitude are recommended.…”

Combining CFD, ASE, and HEKF approaches to derive all of the hydrodynamic coefficients of an axisymmetric AUV

“…Beside analytical methods, experimental ones have been developed to derive the hydrodynamic derivatives. These methods include Straight-Line Test (SLT), 10 Planar Motion Mechanism (PMM), 11 Rotating Arm Test (RAT), 12 and Coning Motion Test (CMT). 13,14 These maneuvers could be accomplished in horizontal and vertical planes, and each of which would lead to extraction of some hydrodynamic derivatives.…”