Particle image velocimetry investigation of the flow characteristics in two-leg internal coolant passages of gas turbine airfoils

A study of flow in a stationary model of a two-pass internal coolant passage is presented which focuses on the flow characteristics in the 180degrees bend region and downstream of the bend, where the flow is re-developing. A stereoscopic digital particle image velocimetry system measured all three velocity components simultaneously to obtain mean velocity and turbulence quantities of the flow field. The coolant passage model consisted of two square passages, each having a 20 hydraulic diameter length, separated by a web of 0.2 passage widths and connected by a sharp 180degrees bend with a rectangular outer wall. Ribs were mounted on the bottom and top walls of both legs with a staggered arrangement and at 45degrees to the flow. The rib height and spacing were 0.1 and 1.0 passage heights respectively. The measurements were obtained for a flow condition with a Reynolds number of 50000. The geometry is similar in the straight sections to a previous configuration but has ribs extending into the bend region. The paper presents new measurements of the flow in the straight legs of the passage, comparison of the flow in the bend region with a previous configuration and details of the flow recovery from the bend in the second leg.