Experimental Investigation of a 16 Inch Diameter Water Piston Propulsor at Speeds up to 23 Feet Per Second and Gas Temperatures up to 3600 F

Abstract : The Water Piston Propulsor (WPP) combines prime mover, transmission, and propulsor into a single unit. High pressure heated gas is expanded directly on columns of water so as to add momentum to ingested fluid and thereby produces thrust. The WPP theoretically has a very high power per unit volume and power per unit weight if the gas can be transmitted to the rotor with minor pressure loss and if the gas can be expanded in the water passages with only a moderate transfer of heat to the ejected water. This potentially high power-to-volume ratio makes the WPP an attractive candidate to propel Marine Corps high speed amphibians. This report describes the investigation carried out using a full- scale water piston rotor and its fuel oil gas generator. The main study results are that heat lost to the expelled water during its expulsion when the input gas temperature is about 3000 F is approximately 67% of input heat and that the thrust produced by the WPP was substantially less than predicted. Consequently, the power-to-unit volume ratio of the system tested will be significantly greater than that for a conventionally propelled amphibious vehicle. Although the WPP is shown to be unattractive as applied to a Marine Corps vehicle with an air-breathing fuel-oil gas generator, it is believed that it may be attractive for high speed underwater missiles with other types of gas generators. The report also discusses a typical Marine Corps amphibious propulsion requirement and the reason that water piston propulsion is potentially attractive.