Background and Objectives: The Lagrangian SVP drifter, developed by Niller, has a good non-slip flow tracking capability in a variety of atmospheric conditions due to its holey-sock drogue. An important factor in the design of drifters is the surface drag coefficient. In the design of drifters, the drag area coefficient of the drogue should be about 40 times of total drag area coefficient of the surface float and tether, and also the amount of torque applied to the tether should be low to minimize the slip of the float surface in waves and strong winds.
Methods: In this research, ANSYS-FLUENT has been used to investigate the holey-sock drogue in three-dimensional turbulent environment. Flow field around the holey-sock drogue clarified the rule of them on hydrodynamic forces. Holes on the drogue cause uniform distribution of the pressure and viscous force around the drogue.
Findings: By modeling the blade drogue, it was found that the presence of the blade on the drogue causes a significant increase in pressure force, which in turn increases the drag coefficient, but these blades cause an undesirable increase in torque on the tether.
Conclusion: It was found that if the blade width is about 10% of the drogue diameter, the drag coefficient is improved by 26%, while the torque on the tether changes by only 3%.