Abstract:
This paper describes the results of a Computational Fluid Dynamics (CFD) study into the modelling of unsteady ship airwakes and their interaction with a ship's exhaust efflux. The fluctuating temperatures in the air flow above the flight deck were assessed to determine potential impacts on maritime helicopter operations. A generic ship model was created that is representative of a modern naval single-spot frigate. Included in the simulation was the hot exhaust efflux from three exhaust uptakes representing a ship operating combined gas turbine and Diesel engines, typically found in modern frigates. The unsteady airwake was computed at 40 knots for a Headwind, Green 30° and Green 45° Wind Over Deck (WOD) conditions and the unsteady temperatures were sampled at various locations around the flight deck. The temperature rise limits over the deck as specified in CAP 437 were found to be exceeded for the Headwind and Green 30° cases. The trajectory of the plumes for the Green 30° and Green 45° WOD cases showed that although the over-deck temperatures were within limits, the exhaust gases were entrained in the downwash in the lee of the ship causing the air temperatures to increase in the region where a helicopter would operate for a port-side approach. The resulting air temperatures over and around the flight deck are discussed in relation to helicopter performance and safety, drawing on the experience and practices in the offshore oil industry.