Experimental Research on Turbulent Flow over Compliant Walls

Abstract

Since Kramer’s successful experiments in late 1950s and early 1960s, there have been a series of study on compliant coating for drag reduction in the following three decades. As a result, it is now believed that compliant coatings, if suitably fabricated mimicking dolphins’ skin, could delay the transition of the laminar boundary layer to turbulence, therefore resulting in a substantial drag reduction. As for the use of compliant coatings in the turbulent boundary layer, however, experimental investigations offered mixed results on a possibility of drag reduction. No single experimental result has been successfully repeated by others. As we went into the 1990s, there has been resurgence in compliant coating research, partly because the former Soviet Union’s research data became available to the West. Since then, there have been a number of tests in Usa, Uk and Russia, demonstrating a strong possibility that compliant coatings could reduce the skin-friction drag of turbulent boundary layers. In this paper, some of the recent experimental work on compliant coating is reviewed, with a current understanding of the mechanisms of turbulent drag reduction.