REDUCTION OF RESISTANCE DATA 



The value of the residual drag coefficient C R = D R /l/2 p U^ S is used to determine the 

 relative merits of different models, where D R is the residual drag; p, the density of the fluid; 

 U Q , the speed of the model; S, the model surface area. In the present experiments, values of 

 C R have been determined, using a method developed in Reference 1. In contrast to traditional 

 methods, the new method takes into account the location of transition on the model in the 

 analysis. This is important when, as in the present case, the object is to evaluate competing 

 models with vastly different forebody shapes and C R values with relatively small differences. 

 The extent of laminar flow can vary greatly on such models as the forebodies vary from blunt 

 to fine. This influences the measured model resistance and if not recognized will significantly 

 alter the relative body drags. An outline of the method is given as follows. 



In the analysis it is assumed that two types of flow regimes exist on a model hull: 

 laminar g and turbulent t . When a significant length of transitional flow occurrs, the 

 longitudinal extent xg of the laminar flow regime, having a wetted area S x „, will be assumed 

 to terminate where intermittent turbulent bursting first occurs; see Type 3 of Figure 7. When 

 the wire stimulator is installed, it is assumed that xg will coincide with the wire location, 

 When laminar separation occurs, it is assumed that xg coincides with the computed separation 

 location. The latter two assumptions are in accord with available experimental data. 1 



The value of C R can be expressed as 



C R = C T - C F - A C T (6) 



where C T is the total drag coefficient D/l/2 p U Q 2 S 



C p is the frictional drag coefficient D p /l/2 p U^ S 



C T is the wire drag coefficient AD T /l/2 p U^ S 



and D T is the total drag 



D F is the frictional drag 



AD T is the stimulator drag 



S is the model surface area 



The value of C T is obtained by measurement; however, the value of C p and AC y must be 

 obtained from empirical relations. 



Following Reference 1, the drag coefficient AC D of the wire has been taken as 0.75 for 

 all experimental conditions where AC D is defined as 



12 



