Prediction Of the Velocity Field in 

 Way of the Ship Propeller 



Igor A. Titov, Alexander F. 

 Oleg P. Orlov 

 Krylov Ship Research Institute 

 Leningrad, U.S.S.R. 



Poostoshniy, and 



ABSTRACT 



The paper covers the problems involved in determin- 

 ing the velocity field in way of the ship propeller. 

 The analysis is given for both the structure of the 

 stern viscous flow and its change due to the ship 

 propeller operation. 



The method is offered for scaling the nominal 

 field of axial velocities based on the use of both 

 the semi-empirical theory of the boundary layer and 

 theory of free turbulence, and the engineering method 

 of estimating the action of the working propeller 

 upon the velocity field. 



As an illustration, the data of studying the 

 influences of the scale effect and the working ship 

 propeller upon the velocity distribution and total 

 wake flow are presented in reference to a moderate 

 displacement tanker. 



1. INTRODUCTION 



The need for a reliable definition of nonstationary 

 loads acting on the propeller blades and shafting, 

 and also of the intensity of hull vibration and 

 cavitation phenomenon, has placed the wake flow 

 problem among the most important problems of ship 

 hydromechanics in the last few years. Though this 

 problem first originated mainly in connection with 

 the building of large full ships, it is of no less 

 importance in the design of modern high speed con- 

 tainer ships and some other classes of ships . In 

 this sphere of hydromechanics shipbuilders are facing 

 two main problems: a) prediction of the velocity 

 field in way of the propeller for a ship of given 

 lines as based on geosim model test results and 

 b) finding solutions which provide a more favorable 

 distribution of the wake flow. The rationalized 

 formation of the afterbody wake is also one of the 

 possible reserves of ship propulsion which do not 

 yet appear to be fully realized. 



At present, the problem of the afterbody wake 



and particularly its prediction attracts the atten- 

 tion of a growing number of specialists in research 

 centers of the advanced shipbuilding nations in- 

 cluding the USSR. In view of the extreme complexity 

 of the afterbody flow pattern in the presence of the 

 propeller- induced disturbances, the problem of the 

 wake flow is still far from being solved. The laws 

 regulating the development of wake flow and also 

 the dependence of the velocity distributions at the 

 propeller disk upon the shape of the afterbody lines 

 are not quite clear. The test methods of defining 

 the ship model wakes and model-to-ship correlation 

 methods are as yet imperfect. Therefore the ac- 

 curacy of the flow nonuniformity data obtained in 

 way of the propeller and used as a basis for calcula- 

 tion of the abovementioned hydrodynamic character- 

 istics does not satisfy the requirements of modern 

 practice. Hence, a detailed investigation of this 

 phenomenon is needed. 



In our opinion the most important tasks are as 

 follows: First, comprehensive physical studies of 

 the afterbody velocity field. These would allow for 

 better understanding and proper evaluation of the 

 effects of different factors on the formation of 

 wake flow in that region and help create a flow 

 model exhibiting the main features of the phenomenon 

 and capable of being investigated by analytical 

 methods. At this stage the theoretical studies are 

 essential primarily for a better understanding and 

 more proper analysis of the test results, as well 

 as for improving the general knowledge of both the 

 flow laws and the scheme of breaking the wake into 

 components. Second, the results of the experiment 

 and the qualitative theoretical conclusions should 

 be the basis for the development: 



- methods for simulation of the nominal wake or 

 methods for theoretical estimation of the scale 

 effect at early stages of designing; 



- methods for experimental definition of the 

 effective wake and approximate methods for the evalu- 

 ation of propeller effect using the nominal velocity 

 field data. Since the velocity field in way of the 



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