MK25 Torpedo Exhaust Gas Investigation

Abstract

This report covers tests made on models of the Mk 25 Torpedo to determine the effect of gas discharged in the vicinity of a power-driven propeller. It also covers, briefly, tests made on a double exhaust pipe and a single exhaust pipe, both with the vertical rudder set at 10° port but without propeller. All of the above was authorized by Dr E. H. Colpitts, Chief of Section 6.1, NDRC, in a letter dated May 4, 1944. This report is the fourth supplement to the report, Section No. 6.1-sr207-1275. Memorandum Reports dated June 22, 1944, July 15, 1944, and September 29, 1944 have been issued giving preliminary results on the tests reported herein. Tests were made on models having a scale ratio of 11:21. However, all dimensions and data refer to the prototype unless otherwise noted. Gas discharges are expressed in per cent. These figures have been calculated with reference to the amount of gas discharged from the prototype when running at 40.5 knots. Allowances for temperature and composition of the exhaust gases have been made by calculating the exit velocity when the torpedo is running at 40.5 knots and 15 feet submergence, computing the ratio of this velocity to that of the torpedo, and then calculating the amount of air required by the model to obtain this velocity ratio when operating at the equivalent submergence. This criterion requires that a different rate of air flow be taken as the 100% amount for each torpedo velocity investigated. However, as in the prototype the mass rate of gas flow in the model is constant for any given water velocity, independent of the changes in the tunnel pressure (i.e. submergence). With this torpedo operating at the normal speed of 40.5 knots and a submergence of 15 feet, the cavitation parameter is calculated to be 0.67. The appendix to this report gives definitions of terms and other pertinent data.

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