Characteristics of Recirculation Regions on Ribs of Varying Length

Abstract

Ribs represent a class of two-dimensional surface mounted obstacles generating a maximum of three distinct recirculating regions: upstream, on top, and downstream. We investigate the effect of rib length on the shape and strength of phenomena occurring within these three recirculation regions. An experiment was designed accordingly where six ribs of varying length ($0.1\le L/H \le 8$) were submerged in a fully turbulent boundary layer ($\delta /H = 1.37$) with a Reynolds number based on rib height of $Re_H = 20000$. Particle Image Velocimetry (PIV) was carried out along the centre line of the obstacles. Comparable properties show consistency with previous literature (The flow past a surface-mounted obstacle. J Fluids Eng 105:461–463 (1983), [5]). Results of dimensions of recirculation regions in the plane of measurements, as well as results based on proper orthogonal decomposition of flow field velocity as a function of rib length show two different behaviours in the wake of the obstacles which coincide with the presence or absence of a mean reattachment point on the top surface.