Optimum Slenderness Ratio of a Stable Low-Drag Body

摘要

This paper presents a theoretical and experimentaludmethod of selecting the optimum slenderness ratio of audbody with cylindrical midsection. Whether such a bodyudis a large submarine or its arch enemy, the depth charge,udthe problem rem a ins to find a slenderness ratio whichudwill permit the fastest possible velocity consistentudwith the power or sinking weight available.ududConsiderable research has been done to determine theudhydrodynamic characteristics of nose shapes both aloneudand combined with various afterbodies. In one of ourudreports we have pointed out that any one of severaluddifferent nose shapes could be used on a particularudbody with little change in the total drag coefficient, andudtests for certain afterbody shapes would probablyudbring similar results.ududDue to practical considerations, most bodies have audcylindrical midsection. Therefore, a typical underwaterudbody of axial symmetry consists of arbitrarily selectedudnose and afterbody shapes separated by a cylindricaludmidsection.ududFor dynamic stability, any underwater body must haveudfins which increase the surface area and, to some degree,udthe residual drag. We must necessarily considerudthe effect of such fins on slenderness ratio. In theudfollowing discussion of a particular concrete example,udthe emphasis has been placed on a body with a noseudand afterbody with fins, of the same geometrical shapeudas the MK 13-1 torpedo (less shroud ring). The MK 13-1udtorpedo is dynamically stable, has a cylindrical midsection,udand has been tested with other nose shapes.ududAfter examination of the factors affecting the optimumudslenderness ratio, it is found that a reasonably largeudvariation from the theoretical optimum value will haveudlittle practical effect on the velocity of the body.ududBecause of practical factors involved in the designudof an undersea body, it may be desirable from theuddesigner's point of view to have a relatively largeudslenderness ratio. This investigation shows that as farudas drag per unit volume is concerned, the designer willudwill pay very little, if any, penalty if he disregards theuddrag factor and bases his selection of slenderness ratioudentirely on such items as tactical requirements ofudmaneuverability, structural design and utilization ofudinternal space.