Fast-response underwater TSP investigation of subcritical instabilities of a cylinder in crossflow

Abstract

We investigate the classic cylinder in crossflow setup to test the effectiveness of a fast-response underwater Temperature Sensitive Paint coating (TSP) in providing highly resolved spatial and time observations of the action of a flow over a bluff body surface. The flow is investigated at Reynolds number < 190k, i.e. before the onset of the drag-crisis state. TSP images provide a high frequency description of the evolution of some of the main features in the fluid-cylinder interaction, like the separation line position and the pattern of the coherent structures acting on the cylinder surface. Ad-hoc data-management and features extraction techniques are proposed which allow extraction of quantitative data, such as separation line position and vortex shedding frequency, and results are compared to literature. Use of TSP to water applications introduces an interesting point of view about the fluid-body interactions by focusing directly on the effect of the flow on the model surface.