Drag increase at the very start of drag reducing flows in a rotating cylindrical double gap device

•Cylindrical double gap rheometer device is used.•Analysis on the drag increase in the first few seconds of the test.•Drag increase is strongly related to the molecular conformation.

In this note we present some results concerning the time required for turbulent structures to achieve their steady state, called here the developing time. Notably, there is a drag increase at the very start of the test. Such a drag increase is strongly dependent on the concentration, molecular weight, temperature, Reynolds number, and molecule conformation before the test start-up. The analysis conducted here improves the understanding of the way drag reduction evolves over time, which was considered in Pereira et al. (2013).