Vapor layers reduce drag without the crisis

The drag of a solid sphere moving in fluid is known to be only a function of the Reynolds number, Re and diminishes rapidly at the drag crisis around Re $\sim $ 3 \texttimes 10$^{\mathrm{5}}$. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect, can occur over a wide range of Re, from as low as $\sim $ 600. The Navier slip model with a viscosity dependent slip length captures the observed drag reduction and wake shape.