Title: Ship Engine Exhaust and its Implications for Maritime Helicopter Operations
Author(s): leuan Owen
Abstract: "This presentation is based on Chapter 5 of the NATO AVT-217 Task Group Report on “Modeling and Simulation of the Effects of Ship Design on Helicopter Launch & Recovery” Modern, single-spot naval vessels often rely on combinations of both Diesel and gas turbine engines to provide power for propulsion, and in doing so emit large volumes of hot exhaust gases which will mix with the ship’s airwake and be carried over the flight deck. The air flow over and around the ship’s landing deck will therefore have elevated temperatures that may affect the helicopter. The exhaust gases can potentially impact on a helicopter’s performance when they are drawn into and through the rotor, creating changes in lift due to the reduction in air density. In addition, the helicopter engine intakes are often situated directly beneath the main rotor, so any hot gas passing through the rotor is likely to be ingested by the engines, possibly leading to a loss of power, compressor surge or even flame-out. The effect of air temperatures over and around a naval ship’s flight deck on helicopter operations has so far received little attention. In contrast, the oil & gas industry has established strict recommendations for air temperature limits over offshore oil platform landing decks. The presentation will include the results of an unsteady CFD analysis of a ship’s airwake with entrained exhaust gases and will consider these in light of the safety practices adopted in the oil industry. The presentation will also contrast the design of a ship’s funnel from some 50 years ago when the aerodynamic profile of the funnel was seen to be important, while in modern ships the major criteria are to minimise radar cross-section and infra-red signature. Key Points This presentation will make the following key points: 1. Elevated air temperatures due to ship exhaust have potential to adversely affect a helicopter through reduced rotor lift and reduced engine power 2. Practice for offshore oil rigs is that helicopter operators should be notified if the air temperature over the landing deck is expected to increase by more than 2°C for a period of 3 sec. While this criterion may be too restrictive for naval helicopter operations, there is no widely accepted equivalent criterion. 3. Funnels were historically designed to reduce entrainment of engine exhaust into the ship airwake and working areas; funnels are currently designed to minimise radar cross-section and infra-red emissions and exhaust dispersion is a secondary issue 4. Wind tunnel testing and CFD are useful techniques to be used during the ship’s design phase to inform exhaust gas dispersion and air temperatures. 5. Research is required to establish how ship exhausts can affect helicopter performance and whether air temperature limits are required for naval helicopter operations. "