A Study of the Airwake Aerodynamics Over the Flight Deck of an AOR Model Ship

Abstract : This study investigated the airwake of an AOR Class model ship to provide basic flow pattern and velocity information to aid in solving the elusive problem of blade strikes experienced by H-46 helicopters when they engage or disengage rotors aboard AOR ships. This investigation used the NPS flow visualization tunnel modified to simulate the atmospheric boundary layer. A detailed visualization was completed of the airflow near the flight deck area of a four-foot model in a stationary mode, utilizing helium bubbles, smoke, photographic and video equipment. The results show that the airwake is usually made up of two regions, one that is relatively smooth and one that is extremely turbulent. The dividing line is a shear layer that is created from the air flowing around the port face of the hangar. Another feature found both in the flow visualization, as well as the velocity measurements, was the presence of a significant upward component of flow over the port edge of the flight deck. It was found that this flow had nearly the same speed as the velocity measured at the ship's anemometer position but was inclined at an angle of between 15 and 25 degs. This upward flow, combined with the highly variable recirculations over the flight deck could be a significant contributing factor in the occurrence of blade strikes. In addition, some attempts were made to eliminate some of the more unruly flow patterns by using curved deflectors. These attempts had some success but will require further study.