Helicopter Shipboard Operation: Effect of Atmospheric Boundary Layer on Turbulent Ship Airwake and Rotor Aerodynamic Loads

Abstract

This paper studies the effect of two different boundary layer models on the airwake of the Simple Frigate Shape 1 and further on the unsteady aerodynamic loads of a scaled helicopter model operating inside the ship airwake. The unsteady airwake of the isolated SFS1 is computed in a time-accurate approach using the open-source SU2 solver, implementing two types of boundary conditions: a Uniform Flow (UF) and a steady Atmospheric Boundary Layer (ABL), where the reduction of the velocity due to the surface roughness is also considered. The simulations are performed in two wind conditions, including headwind and 30? from the port-side (R30). The airwake data are implemented into a multibody simulation of a scaled helicopter model, developed using the open-source multibody software MBDyn, based on the one-way coupling approach. Hover tests are performed at different positions with respect to the deck and the unsteady aerodynamic loads are compared in frequency domain. In addition to the increase of unsteadiness in the red wind compared to the headwind simulation, the results indicate that in both wind conditions, the unsteadiness is reduced with the presence of the steady ABL. Since the unsteady loads are expected to directly affect the pilot workload, the results highlight the importance of modelling a realistic boundary layer considering both steady and turbulent profiles.