Development of a measurement technique for detailed flow characterization in fuel bundles

Highlights: • Sliding pressure sensors are developed for flow characterization in complex geometries. • 3-D pressure mappings help visualizing flow characteristics in the vicinity of grid spacers. • Dynamical analysis of the pressure signals allows identifying structures in the flow. • Technique able to study interference and correlation between complex flow structures. - Abstract: Investigating the flow behavior in fuel rod bundles has been an active research topic since many decades. Nowadays, despite the great advances in computational fluid dynamic techniques and resources, blind benchmarks have shown numerical results are still very dependent on schemes and closure models. Moreover, most experimental studies in flow mixing and flow structure identification were performed in simplified geometries and/or in a very limited test domain. In addition, reliable experimental data from mixing experiments in the vicinity of a spacer grid in rod bundles are almost non-existent, especially with high spatial and temporal resolution. Generating experimental data relevant for fuel bundle geometries is costly and generally limited to a small measurement region. In this work a novel non-intrusive technique is developed and tested in order to characterize the flow in a geometry resembling a fuel bundle by using of detailed pressure measurements. The measurement device makes use of electronic micromachined deformable membrane differential pressure sensors with fast dynamical response, allowing capturing local pressure fluctuations. Such differential pressure sensors are connected to a fix pressure tap and a movable pressure tap drilled in each of the rods. Each instrumented rod is free to move both axially and azimuthally allowing scanning the static pressure drop values at the surface of the rod. In addition, by analyzing the static pressure fluctuations it is possible to capture valuable information of turbulence phenomenon such as the turbulence kinetic intensity and the turbulence power spectrum in a wide spatial range, including regions within spacer grids.