Influence of Propeller Action on 

 Flow Field Around a Hull 



Shunichi Ishida 



Ishikawajima-Harima. Heavy Industries Co, Ltd. 

 Yokohama , Japan 



ABSTRACT 



Flow field in the vicinity of a hull is analyzed 

 by using acceleration potential, and an approximate 

 calculation method is derived. The present method 

 can calculate the change of pressure on the hull 

 caused by a propeller action. Numerical results 

 by the present method are shown with experimental 

 results. 



Wake far from a ship is analyzed by using Oseen's 

 approximation, and an optimum condition is given 

 for wake energy recovery by a propeller. This 

 condition is examined by the results of the self- 

 propulsion tests and the wake survey measurements 

 at distant positions behind a ship. 



1. 



INTRODUCTION 



When a hull is towed in still water, a flow field 

 is induced around the hull. This flow field is 

 very complicated, and becomes more complicated by 

 propeller action. Many researchers have studied 

 experimentally and theoretically the phenomena 

 caused by the interaction of the hull and propeller, 

 [Yamazaki et al. (1972)]. Unfortunately, however, 

 the number of practical uses of the study results 

 is less than those derived in other fields of naval 

 hydrodynamics . One of the reasons is because the 

 various suggested methods are themselves complicated 

 owing to the complexity of the phenomena. 



It has been popularly known that both the equa- 

 tions and the boundary conditions which describe 

 flow field can be simplified, and analyzed easily 

 if disturbance by an object in the flow is a small 

 quantity of the first order. One of the typical 

 examples is the method of acceleration potential 

 in inviscid flow fields used for propeller theory 

 [Tsakonas et al . (1973)]. Another example is 

 Oseen's method in a viscous flow field used for 

 the separation of hull resistance components [Baba 

 (1969) ]. 



In this paper, the above-mentioned concept is 

 applied to analysis of flow fields induced by the 

 interaction of the hull and propeller, and the 

 author derives practical methods relating to the 

 propeller-induced pressure change on the hull and 

 wake energy recovery by the propeller. Section 2 

 explains coordinate systems used in this paper. 

 In Section 3, the author applies the method of 

 acceleration potential for analysis of inviscid 

 flow fields in the vicinity of the hull, and derives 

 a method which can be used to calculate the change 

 of pressure induced by a propeller on a hull surface. 

 In Section 4, the author applies Oseen's method for 

 analysis of wake far from the hull, and derives a 

 method to predict recovery of wake energy by the 

 propeller. Then, this method is examined by the 

 experimental results obtained from self-propulsion 

 tests and the wake survey. Section 5 concludes 

 this paper. 



2. COORDINATE SYSTEMS 



We assume that a ship with a single propeller is 

 moving with a constant speed on the free surface of 

 still water. At first, we define a coordinate 

 system 0-XYZ fixed in space and a coordinate system 

 o-xyz fixed on the hull as indicated in Figure 1. 

 The coordinate system O-XYZ is an orthogonal coor- 

 dinate system, in which the XZ-plane coincides with 

 the still water surface and the positive direction 

 of Y-axis coincides with an upward vertical line. 

 The coordinate system o-xyz is a moving coordinate 

 system in which the origin o is moving on the X-axis 

 in the negative direction with a constant velocity 

 U, and this sytem satisfies the following relation- 

 ship with O-XYZ: 



X = X 



Ut, Y 



z. 



(1) 



where t represents time. 



Next, we define two more coordinate systems 



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