PIV Investigation of the Flow Characteristics in an Internal Coolant Passage with Two Ducts Connected by a Sharp 180o Bend

A PIV study of the flow in a stationary model of a smooth two-pass internal coolant passage is presented, which focuses on the flow characteristics in the sharp 180o bend and downstream of the bend where the flow is redeveloping. Because PIV in its traditional conception only allows for the investigation of two-dimensional flow, a stereoscopic digital PIV system was assembled that measures all three velocity components simultaneously. The mean-velocity field and turbulence quantities of the flow are obtained from the PIV measurements. The model of the coolant passage consists of two square ducts, each having a length of 19 hydraulic diameters, which are connected by a sharp 180o bend with a rectangular outer wall. The measurements were obtained at one flow condition with a flow Reynolds number of 50,000. A strong secondary flow motion occurs in the bend of the smooth passage that consists of two counter rotating vortices, which impinge on the outer wall and influence the flow in the downstream leg. Both of the outer corners contain regions of recirculating flow. A separation bubble, about 1.5 hydraulic diameters long, occurs on the inner wall of the return pass. In the symmetry plane, the flow recovers from the bend effect within 10 hydraulic diameters.