30 



nVDRODVNAMlCS IN sniP i)tsic;.\ 



Srr. 11.13 



position ami at a lixinl nttitinie on tlie Ixxly or 

 ship, t*> (2) tlu- nnn prrssure which would lie 

 registered in tlie direction of motion at an infinite 

 distiince, a simple relationship q,./q is established 

 which greatly facilitates plotting experimental 

 data. Contours of pitot-pressure coeflicient of 

 1.00, with allowable limits on each side, indicate 

 the regions where the pitot orifice of the instru- 

 ment can be located to give accurate results 

 under the coiulitions established. 



If the flow remains steady and free of rotation, 

 and if vi.scosity effects are neglected, the pressure 

 and velocity relationships are dimcnsionlcss and 

 hold regardless of scale, velocity, liquid density, 

 and overall pressure upon the sj'stem. 



A pressure determination from known velocity 

 magnitudes and direction is much less deter- 

 minate when the flow is complicated by viscosity 

 effects. 



41.13 Tables of Velocity Ratios, Pressure 

 Coefficients, Ram Pressures and Heads. To 

 facilitate the preparation of diagrams in which the 

 distribution of dilTercntial pressure and the 



variation in velocity are plotted for the potential 

 flow of an ideal li(|uid around any body. Table 

 ■ll.c gives the variation of Euler number or 

 pre.ssure coeflicient with velocity ratio as deter- 

 mined by the following relationship derived from 

 the Bernoulli Theorem: 



Ap 



-^='-^ = '-(^)" '--' 



This relationship applies to liquids of any mass 

 density p, provided the values on both sides of 

 the equality sign are for the same liquid. 



The ram pressures corresponding to 0.5p6'i = q, 

 calculated for both standard fresh water and 

 standard salt water, are set down in Tables 4l.d 

 and 41.e, respectively. These are given in both 

 lb per ft^ and lb per in', supplemented by the 

 velocity head in ft. It is to be noted that the 

 laller value is the same for water (or other liquid 

 or fluid) of any mass density. The range of veloc- 

 ities covers those normally encountered in model 

 tests and ship design. 



