Numerical assessment of incoming atmospheric boundary layer effects generated by various approaches on ship airwake turbulence characteristics

Abstract

The unsteady and extensively separated turbulent airwake flows around a ship’s deck significantly impact helicopter pilot performance during shipboard operations. Hence, incorporating realistic, unsteady incoming mainstream conditions such as the atmospheric boundary layer (ABL), is crucial in numerical simulations of the ship airwake. This study employed delayed detached eddy simulations (DDES) to evaluate the effect of steady and unsteady ABL modeling methods on the turbulent flow characteristics of the ship airwake. A 1:12.5 scaled Simple Frigate Shape 1 (SFS1) ship model was utilized in the numerical simulations, and three distinct ABL profiles (one steady and two unsteady) were simulated at two different wind direction angles (HW and RW30). Synthetic and turbulator modeling methods were utilized to generate the unsteady ABL profiles. Time-averaged and instantaneous flow fields calculated by various ABL profiles were compared with experimental data at multiple points within the ship airwake. The numerical findings indicated that while the time-averaged data remained unaffected by the ABL profile presence, the instantaneous flow quantities experienced significant alterations, especially under the red wind condition. The introduction of an unsteady ABL profile was shown to augment the unsteadiness and fluctuation of the flow field within the ship airwake compared to the steady ABL scenario. Cross-correlation analyses between the velocity fields computed using steady and unsteady ABL profiles unveiled distinct patterns and behaviors of flow structures over the deck. Moreover, evaluation of the velocity and pressure fields of unsteady ABL across time/space domains revealed incremented turbulence and disturbances over the flight deck, intensifying with wind direction angle. The synthetic ABL modeling approach was found to deliver promising outcomes in comparison to the turbulator method, while requiring significantly lower computational resources.