Abstract
This study identifies the role of isotropic blended k-ε/k-ω (BKW) versus anisotropic Reynolds stress (RS) RANS models for steady ship flows and BKW-DES versus RS-DES for unsteady ship flows. Capability of RS model to predict anisotropy is shown for a solid/free-surface juncture and demonstrated for ship flow (DTMB 5415) at Fr=0.28. No significant anisotropy effect is observed for DTMB 5415 due to the weaker anisotropy and insufficient grid resolution. KVLCC2 at drift angle 0, 12, 30, and 60 degrees are investigated neglecting the effect of free surface. Results of using BKW and RS RANS models for 0 and 12 degrees show that RS model significantly improves the predictions of the resistance coefficients, axial velocity, and turbulent kinetic energy distributions at the propeller plane. For drift angle 30 degrees, BKW and RS RANS models show steady solutions whereas BKW-DES and RS-DES models show unsteady solutions. In the latter case, limited differences on forces, moments and instabilities are observed. The previous analysis for vortical structures and instabilities for NACA0024 and tip vortex instability for delta wings is extended to study flows at drift angle 30 degrees using RS-DES, including quantitative verification. Two shear layer instability modes, a Karman-like vortex shedding, and three helical mode instabilities are identified. Compared to previous experimental and computational results, the Strouhal number (St) for Karman-like instability is in the same range whereas St for shear layer instability is smaller. Similarities and differences between the helical mode instabilities of the current study and those of delta wing flows are also discussed. RS-DES model is also applied to study KVLCC2 at drift angle 60 degrees. Further evaluation of relative merits for using BKW-DES and RS-DES for analysis of turbulent structures will be conducted in the future.