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

Abstract

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.

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

“…Also, while investigating heat transfer and pressure drop in channels with different heat transfer enhancement techniques, smooth channel data has been used as baseline by researchers [6][7][8][9]. Studies by Schabacker et al [10], Liou et al [11], Chen et al [12], Son et al [13] and Elfert et al [14] have focused attention on the two-pass channels to study flow, pressure distribution and heat transfer characteristics. These studied the flow field in a two-pass smooth channels and provides good information about the flow characters, such as secondary flow, impingement, separation and recirculation induced by turn.…”

A 3D-PIV System for Gas Turbine Applications

“…A factor of 2 or greater in the Nusselt numbers between trailing and leading surfaces have been reported (Guidez, 1989;Han et al, 1993;Bons and Kerrebrock, 1998). The bend-induced secondary flows direct the flow from the inner-side wall to the outer side wall producing a two-roll flow pattern (Schabacker et al, 1998), and can considerably distort the Coriolis-induced secondary flow in the near-field following the bend. Heat/mass transfer measurements following the bend have shown high heat transfer along the outer walls and low heat transfer along the inner wall (possibly associated with flow separation).…”

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

“…[2], [5], [6] demonstrated the applicability of the presented stereoscopic PIV technique in details. Following are comments on small variations from those measurements (see also [7]).…”

“…The uncertainty of the normal stresses depends only on the number of samples and on the confidence level. Further details of the uncertainty method are given in [6].…”