RANS study of Strouhal number effects on the stability derivatives of an autonomous underwater vehicle

Abstract

This paper presents a numerical procedure to calculate the stability derivatives of an Autonomous Underwater Vehicle (AUV). In addition, the effects of Strouhal number on the stability derivatives are investigated. The stability derivatives are obtained by finding the body hydrodynamic responses to some specified time variant motions. Here, three distinct oscillating maneuvers: surge, pure-heave, and pure-pitch are proposed based on the linearized equations of motion. A Computational Fluid Dynamics (CFD) method based on Reynolds Averaged Navier–Stokes (RANS) equations with dynamic mesh technique is used to simulate the specified maneuvers. To verify the numerical scheme, computational results for simulation of the flow field are then validated by comparison with experimental data. In addition, a comparison between quasi-steady (Theodorsen’s theory) and RANS approaches is taken into account, which shows that the quasi-steady methods do not guarantee the solution accuracy for the purpose of stability derivative calculation. Finally, the effects of Strouhal number variations on these coefficients are investigated which shows that the dimensionless damping coefficients (except longitudinal damping coefficient) are evidently dependent on the Strouhal number, specially at high frequencies. However, the Strouhal number variation effects on the added-mass coefficients are small.