434 



DEflEPallON jlltE 



FIGURE 1. Schematic diagram of high 

 speed cavitation tunnel with polymer 

 injection system. 



section. Injection of polymer solutions from the 

 nose of the models was made by a Hughes Centurion- 

 100 pump unit. The unit consists of a drive mech- 

 anism fitted with two pump heads. A pulse-damper 

 was used to minimize flow variations . Further 

 details are given by Van der Meulen (1974b) . A 

 schematic diagram of the tunnel with the polymer 

 injection system is shown in Figure 1. 



To measure the influence of polymer additives 

 on the friction factor and the surface tension of 

 the solutions, a turbulent-flow rheometer and a 

 surface-tensionmeter have been used. Details on 

 these measuring devices are given by Van der Meulen 

 (1974a, 1976b). 



Test Models 



According to Arakeri and Acosta (1973) , most 

 axisymmetric models used in cavitation inception 

 studies , such as the hemispherical nose and the 

 ITTC standard headform, exhibit laminar boundary 

 layer separation. It means that the laminar boundary 

 layer is unable to overcome the adverse pressure 

 gradient and the flow separates from the wall . 

 Schiebe (1972) introduced a standard series of 

 axisymmetric models which, theoretically, should 

 not exhibit boundary layer separation. To distin- 

 guish between these two classes of axisymmetric 

 models, a hemispherical nose and a blunt nose, 

 selected from Schiebe ' s standard series, were used 

 in the present investigations. Both models were 

 made of stainless steel (SST) . In addition, a 

 third model (hemispherical nose) was used, made of 

 Teflon. The contour of the blunt nose is derived 

 from the combination of a normal source disk and 

 a uniform flow. Schiebe (1972) calculated the 

 dimensionless coordinates and pressure coefficients 

 for a series of models in the range, Cp^^^^ = 0.33 

 (point source) - 1.0. From this series a blunt 

 nose with a minimum pressure coefficient of 0.75 

 was selected. 



The diameter, D, of the cylindrical part of the 

 hemispherical nose is 10.00 mm. Theoretically, 

 the diameter of the blunt nose increases smoothly 



to an asymptotic value, D, with increasing axial 

 distance, x. This value was set at 10.00 mm. 

 However, for the manufacture of the blunt nose a 

 minor deviation from the theoretical contour had 

 to be permitted. Thus, the actual contour coincides 



'9.88 



''OB 



'0.8 



HEMISPHERICAL NOSE 



BLUNT NOSE 



FIGURE 2. Cross sections of stainless steel models 

 (dimensions in mm) . 



