Measurements using a triaxial hot-wire anemometer in channels containing helically ribbed pins

The research was part of on-going work to improve the thermal efficiency of the Advanced Gas cooled Reactor. A subminiature triple hot-wire probe was used to measure the three-dimensional turbulent air flow (Re = 2.4 x 105) in a large scale simulation of part of a reactor fuel channel. This consisted of six helically ribbed rods (or pins) arranged around a central rod, promoting substantial swirl flow. The results were used to validate and improve a finite difference, bench-mark, thermal-hydraulic code called SCANDAL, which models AGR fuels channels and experimental geometries. The triaxial probe used in the work was a novel design, so it was tested by taking measurements of fully developed turbulent pipe flow (Re = 1.0 x 105 - 3.5 x 105). The measurements showed that the probe over-estimated the radial and azimuthal normal Reynolds stresses by ≅ 20%. An investigation into the probe's directional response and calibration methods was undertaken and the probe performance characteristics were fully determined. The probe measured mean axial and secondary velocities accurately (within ± 2%) when aligned with the flow. The investigation of the directional response showed that the probe was accurate (± 8% of U) up to mis-alignments with the flow of 150. For angles > 150, the results worsened (up to 40% of U). However, the flow encountered in the 7-pin rig was mostly inside the 150 limit. Good, although more qualitative, turbulence measurements were obtained both in the empty pipe and 7-pin rigs. Pipe flow results agreed well with expected and other worker's results. Discrepancies were due to the probe's small size and complicated geometry, because comparison measurements with a large standard probe were as expected. Detailed flow measurements in the 7-pin rig were compared with the results form a SCANDAL run. The comparison highlighted some errors in SCANDAL and have led to its improvement. (author)