Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

2 Publications

Reconstruction of the 3D velocity field of the two-phase bubbly flow around a half moon obstacle using wire-mesh sensor data

Al Issa, S.; Beyer, M.; Prasser, H.-M.; Frank, T.

The TOPFLOW facility at Forschungszentrum Dresden-Rossendorf (FZD) is used to investigate two-phase upward flows in 50 mm diameter and 200 mm dia meter pipes. The facility enables conducting Experiments with air-water and steam-water flows for temperature range of 35-280 °C and pressure range of 1-70 bar. The test pipes are equipped with a wire -mesh sensor, which is a conductivity-based void fraction sensor developed by FZD. It provides void fraction measurements in a matrix of 64×64 points and a measuring frequency of 2.5 kHz. CFD models have to demonstrate their validity in geometries, where phenomena like flow separation, recirculation regions, stagnation points, free jet formation and similar are present. In the experiment described in this paper the flow around an asymmetric, half-moon shaped obstacle put into the large vertical test section of TOPFLOW is studied. In order to obtain information in three dimensions, the obstacle was traversed along the pipe axis. In this way, it was possible to record 2D void fraction distributions at different distances upstream and downstream of the obstacle using a stationary wire-mesh sensor. The fact that the high resolution data supplied by the sensor contains information on all individual bubbles that cross the measuring plane gives the opportunity to extract more detailed information on the flow structure. In particular, from the transit time of bubbles through the sensor plane approximate axial profiles of the liquid velocity were obtained. The lateral movement of the 2D image of bubbles in the measuring plane during their passage was evaluated to reconstruct 2D velocity fields in the environment of the obstacle. In this way, a full three-dimensional vector field of the velocity was provided for code validation. The paper presents the methods of data evaluation, an assessment of the obtained accuracy of the velocity estimation, experimental results and a comp arison to the results of CFD calculations.

Keywords: 3D velocity field; two-phase flows; obstacle; CFD

  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany