LOW-REYNOLDS-NUMBER FLOW OVER A SQUARE RIB

Laminar flow over a square rib placed in a fully developed channel flo w is investigated over the Reynolds number range 80 - 350. The effect of Reynolds number on the flow and the variation of the primary reatta chment length with Reynolds number are investigated using flow visuali zation and laser-Doppler velocimetry. The primary recirculation region length is found to increase in a slightly non-linear fashion with Rey nolds number up to Re-h = 250, at which point shear layer instabilitie s first appear downstream of the rib. Increasing the Reynolds number f urther, first results in continuing growth of the separation bubble, a nd then for Re-h greater than or similar to 300, in the appearance of three dimensional vortices and gradual shortening of the bubble. The m easurements are complemented by two-and three-dimensional numerical si mulations using a finite volume method with a high-order descretizatio n scheme. These simulations yield excellent agreement with the measure d reattachment lengths and velocity profiles over the steady laminar f low regime.