Estimating the viscous drag of a moving floating body

Question

I am interested in the viscous drag of a floating body (let's say an cylindrical iceberg in water) moving with a constant velocity, s.t. the Reynolds number of the fluid is very large. I am taking a course in continuum dynamics and I am able to write down the equations of the fluid and the corresponding boundary conditions (I also got some prior knowlegde in Perturbation theory and PDEs). I am well aware that determining a drag coefficient for some flow with an awful geometry is nearly impossible. I know that even for fully immersed cylinders this drag coefficent cannot be determined analytically as function of the Reynolds number.

My question is now: what methods/estimates can one use to say something meaningful about the drag on such a floating body for a stationary flow of high reynolds number? Is there a possibility to do apply boundary layer theory in some way to get some crude estimate for a drag coefficient? I am not very familiar with the art of estimating.

By the way, I want to refrain myself from solving the PDEs numerically, since I am just looking for a very (very!) crude estimate.

I hope that you guys could help me to find a place to start.

I thank you in advance!

Answer 1

You are correct that it would be difficult to compute the drag of such shapes very accurately. There would be large areas of flow separation, in which boundary-layer theory would not be a realistic approximation.

Since you only want a crude estimate, a look at experimental data for cylinders with axial flow would be a good starting point. Here's a chart taken from the book Fluid-Dynamic Drag by S.F. Hoerner.

Note that these data are for fully submerged bodies, with no consideration of the drag due to wavemaking, which would depend on the Froude number rather than the Reynolds number. If your high Reynolds number is attained because of the large size of the cylinder, then the speed could be slow enough that the Froud number would be small & the wavemaking effects possibly unimportant.

Hoerner's book is available at https://www.scribd.com/doc/117103507/Hoerner-Fluid-Dynamic-Drag