Drag coefficients for rotating expendable bathythermographs and the impact of launch parameters on depth predictions

Computational fluid dynamics techniques have been applied to model fluid flow in the vicinity of oceanographic temperature probes. A major goal of the modeling effort is the determination of drag coefficients for probe descent into ocean water. These drag coefficients can be used, in conjunction with a dynamic model of the probe, to predict the depth of the probe during descent. Accurate depth information is essential for the proper measurement of ocean temperatures and, consequently, ocean heating associated with climate change. Until recently, probe depths were predicted with the use of experimental calibrations which relate time-of-flight and depth. Those calibrations are limited in their accuracy, they are confined to conditions that match the experiments from which the calibrations were determined, and they are unable to account for variations in quantities such as the drop height or initial probe mass. The dynamic model and drag coefficient calculations presented here are, to the best knowledge of the authors, the first to include the impact of probe rotation. It is hoped that this new technique can be applied to the archive of oceanographic probe measurements and that improvements to ocean temperature monitoring will result.