Investigation of 3D effects of two-phase flow around an asymmetric obstacle
Scientific backround and experimental setup
Distinct three-dimensional fluid flows are investigated since the year 2005 and 2006 within the scope of BMWI-projects (TOPFLOW-I, funding code: 150-1265), to improve thermal fluid dynamic calculation programs used for two-phase flow. For this purpose a vertical test section was installed, with an inner diameter of 193.7 mm and a half-moon shaped obstacle. At this time no ultra-fast x-ray tomography was available at the used nominal size of the pipe. Therefore, wire mesh sensors were installed definitely between a pair of flanges on the test section. To realize variable distances between the measurement plane and the obstacle, the last had to be moveable. This functionality was realized by a driving mechanism that was mounted inside the pipe as upstream (see following figure) as downstream of the wire mesh sensor. Thereby it was turned by 180°. So in each case 8 distances between obstacle and measurement plane were analyzed.
On this configuration air-water and steam-water flows were investigated. For the adiabatic measurements the pressure was set to about 1.5 bar and the temperature to about 30 °C respectively. The steam-water-mixture flows around the obstacle at approximately saturation condition and pressures of 10, 20, 40 and 65 bar. The superficial velocities for gas and water were selected in a way, to allow measurements in the range from disperse bubble flow up to churn turbulent flow.
The wire mesh sensor provides information about the local void fraction at high spatial and temporal resolution. A frequency of 2.5 kHz was used for the measurements, which results in a temporal sequence of measurement frames of 0.4 ms. The distance of the wires at the measurement plane was 3 mm that defined the spatial resolution. The evaluation of the measured data resulted in void fraction-, bubble size- and gas velocity distributions. The analysis of the movement of bubbles with a defined size (so called marker bubbles) allowed the estimation of water velocities in flow direction and in the measurement cross section.
The following figures display data of an air water- and a steam water run. Both show void fraction distribution and water velocities. In its left part a plane is visualized that is defined by a central cut along the tube axis perpendicular to the straight edge of the obstacle. On the right hand distributions of both parameters at 16 measurement levels are shown.
The distinct three-dimensional flow structures are well identified for both cases. As an example can be mentioned, that the curved streamlines deviate significant from the gravitation vector, recirculation sections occur in the wake region and phase separation appears on the edges of the obstacle.
- E. Krepper, M. Beyer, T. Frank, D. Lucas, H.-M. Prasser (2009).
CFD modelling of polydispersed bubbly two phase flow around an obstacle.
Nuclear Engineering and Design 239, 2372-2381.
- H.-M. Prasser, M. Beyer, S. Al Issa, H. Carl, H. Pietruske, P. Schütz (2008).
Gas-liquid flow around an obstacle in a vertical pipe.
Nuclear Engineering and Design 238, 1802-1819.
- T. Frank, H.-M. Prasser, M. Beyer, S. Al Issa (2007).
Gas-liquid flow around an obstacle in a vertical pipe – CFD simulation and comparison to experimental data.
6. Internationale Konferenz für Mehrphasenströmungen, ICMF 2007, Artikel: S6_Thu_B_50.
- S. Al Issa, M. Beyer, H.-M. Prasser, T. Frank (2007).
Reconstruction of the 3D velocity field of the two-phase bubbly flow around a half moon obstacle using wire-mesh sensor data.
6. Internationale Konferenz für Mehrphasenströmungen, ICMF 2007, Artikel: S6_Thu_D_60.
The aforementioned work was realized in the frame of a project founded by the Federal Ministry of Economic Affairs and Energy (Reactor Safety Research-project number: 150 1265). The authors assume the full responsibility for the content.