Gas-liquid flow around an obstacle in a vertical pipe - experiments and cfd simulation

In the frame of the TOPFLOW project, vertical pipe flow is experimentally studied in order to develop and validate models for bubble forces as well as for bubble coalescence and fragmentation in a gas-liquid two-phase flow. The advantage of TOPFLOW [1] consists in the combination of (1) a large scale of the test channel with (2) a wide operational range both in terms of the superficial velocities and the system pressure and finally (3) the availability of an instrumentation that is capable in resolving structures of the gas-liquid interface, namely the wire-mesh sensors.
After a large number of experiments in plain vertical pipes, which are the basis of the development for a multi-bubble size model for ANSYS CFX 10.0, the large test section with a nominal diameter of DN200 was used to study the flow field around an asymmetric obstacle. This is an ideal test case for the CFD code validation, since the obstacle creates a pro-nounced three-dimensional two-phase flow field. Curved stream lines, which form significant angles with the gravity vector, a recirculation zone in the wake and a flow separation at the edge of the obstacle are phenomena widespread in real industrial components and installations. Recently, test series were performed with an air-water flow at ambient conditions as well as with a steam-water mixture at a saturation pressure of 6.5 MPa. Before the experiments were commissioned, an ANSYS CFX 10.0 pre-test calculation was carried out for one of the experimental tests, which resulted in a good agreement with the experiment in terms of all significant qualitative details of the void fraction and velocity distributions.