PASSAGE FLOW STRUCTURE AND ITS INFLUENCE ON ENDWALL HEAT-TRANSFER IN A 90 DEG TURNING DUCT - MEAN FLOW AND HIGH-RESOLUTION ENDWALL HEAT-TRANSFER EXPERIMENTS

Three-dimensional measurements of the mean velocity field have been ma de in a square-cross-sectional, strongly curved, 90 deg turbulent duct flow. The mean radius to duct width ratio was 2.3. The study was perf ormed as part of an overall investigation of the physics of endwall co nvective heat transfer. All three components of the velocity vector an d the static and total pressure fields were measured using a five-hole probe at four duct cross sections: inlet, 0, 45, and 90 deg. Prelimin ary turbulence measurements using a single sensor hot wire at the inle t cross section were also obtained to provide streamwise fluctuation l evels through the boundary layer. The endwall heat transfer coefficien t distribution was determined using a steady-state measurement techniq ue and liquid crystal thermography, A high-resolution heat transfer ma p of the endwall surface from far upstream of the curve through the 90 deg cross section is presented. The three-dimensional velocity field measurements indicate that a highly symmetric, strong secondary flow d evelops in the duct with a significant transfer of streamwise momentum to the transverse directions. The cross-stream vorticity components w ithin the measurement plane were estimated using the Jive-hole probe d ata and an inviscid form of the incompressible momentum equation. The development of the total and static pressure fields, the three-dimensi onal mean velocity field, and all three components of the vorticity fi eld are discussed. The endwall hear transfer distribution is interpret ed with respect to the measured mean flow quantities.