The Strouhal number St* is plotted against the wake Reynolds number Re* = Vj,d'lv in Fig. 2.16 

 and the legend for the data is given in reference 26. The results span five decades of the Reynolds 

 number, from Re* = 10^ to 10^, except for the critical regime near Re* = 10^. The data for St* 

 encompass both stationary and vibrating bluff cylinders and bodies with blunt trailing edges, both yawed 

 and normal to the incident flow. There is some Reynolds number dependence at the lowest Reynolds 

 numbers, as is the case for the classical 5? vs. Re relationship, but only a slight dependence of St* upon 

 Re* o\Qr the remainder of the subcritical range below 2(10^). 



The inverse dependence between 5/* and the drag coefficient C^ is plotted in Fig. 2.17 to demon- 

 strate the universal drag coefficient versus Reynolds number dependence. The solid line corresponds to 

 a prediction (26) of the drag coefficient, which is in excellent agreement with a representative sampling 

 of data points from experiments conducted at NRL and elsewhere. There is a universal correlation 

 between the Strouhal number St*, the Reynolds number Re*, and the flow-induced drag coefficient C^ 

 over the entire range of flow conditions where vortices are shed. 



2.5 Yaw or inclination effects. Yawed cylindrical structures and cables are those which are inclined 

 forward or backward in the plane of the incident flow. Many practical ocean engineering structures are 

 inclined rather than normal to the incident flow; these include cables, raked marine piles and braced 

 frame members of jacket structures. Two recent studies (10,28) have considered the eff"ects of yaw 

 upon the wakes of stationary and vibrating flexible cylinders. King (10) has studied the eifect of yaw 

 angle upon the criieria for the onset of vortex-excited oscillations and upon the steady drag forces act- 

 ing on the structure. His study also includes a complete survey of previous studies on the subject 

 through 1975. More recently, Ramberg (28) has completed a detailed study of the combined efl"ects of 

 inclination and finite length (end conditions) on the vortex wakes of stationary and vibrating cylinders. 

 Included in this study were the eff"ects of yaw angle on the drag and pressure forces on stationary 

 cylinders and on the boundaries of the lock-on range for vibrating cylinders. The experiments of King 

 and Ramberg covered the Reynolds number range from Re = 500 to 2(10''). 



19 



