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Preliminary Investigation of an Underwater Ramjet Powered by Compressed AirPart I contains the results of a preliminary experimental investigation of a particular design of an underwater ramjet or hydroduct powered by compressed air. The hydroduct is a propulsion device in which the energy of an expanding gas imparts additional momentum to a stream of water through mixing. The hydroduct model had a fineness ratio of 5.9, a maximum diameter of 3.2 inches, and a ratio of inlet area to frontal area of 0.32. The model was towed at a depth of 1 inch at forward speeds between 20 and 60 feet per second for airflow rates from 0.1 to 0.3 pound per second. Longitudinal force and pressures at the inlet and in the mixing chamber were determined. The hydroduct produced a positive thrust-minus-drag force at every test speed. The force and pressure coefficients were functions primarily of the ratio of weight airflow to free-stream velocity. The maximum propulsive efficiency based on the net internal thrust and an isothermal expansion of the air was approximately 53 percent at a thrust coefficient of 0.10. The performance of the test model may have been influenced by choking of the exit flow. Part II is a theoretical development of an underwater ramjet using air as "fuel." The basic assumption of the theoretical analysis is that a mixture of water and air can be treated as a compressible gas. More information on the properties of air-water mixtures is required to confirm this assumption or to suggest another approach. A method is suggested from which a more complete theoretical development, with the effects of choking included, may be obtained. An exploratory computation, in which this suggested method was used, indicated that the effect of choked flow on the thrust coefficient was minor.
Document ID
19980227735
Acquisition Source
Headquarters
Document Type
Other - NASA Technical Note (TN)
Authors
Mottard, Elmo J. (NASA Langley Research Center Hampton, VA United States)
Shoemaker, Charles J. (NASA Langley Research Center Hampton, VA United States)
Date Acquired
September 6, 2013
Publication Date
December 1, 1961
Subject Category
Mechanical Engineering
Report/Patent Number
NASA-TN-D-991
L-1249
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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