Eulerian Multiple Flow Regimes: Pressurized Water Reactor

This tutorial demonstrates how to use the Multiple Flow Regimes model in Simcenter STAR-CCM+ to simulate the counter-current air-water flow in a pressurized water reactor.

The Multiple Flow Regimes model combines the benefits of the VOF model and the Eulerian Multiphase model in a single model that can capture a number of different co-existing flow regimes:

  • Stratified flow / free surfaces
  • Dispersed sprays
  • Dispersed bubbles

The Multiple Flow Regimes model captures sharp free surfaces in a similar manner to the VOF model. However, when droplets or bubbles are smaller than the mesh can resolve, the Multiple Flow Regimes model treats them as dispersed phases. This approach is analogous to the Large Eddy Simulation (LES) model where scales larger than the grid are resolved, and subgrid scales are modeled.

This tutorial uses the Multiple Flow Regimes model to simulate the counter-current air-water flow in a pressurized water reactor (PWR). In some scenarios, the flow rate of liquid coolant into the PWR can be highly reduced by a counter-flow of gas. This flow can be very unsteady and include all of the flow regimes that are listed above.

The geometry that is used is a 2D 1/3rd scale model of the hot leg PWR of a German Konvoi Pressurized Water Reactor. The geometry is shown below.



The reactor pressure vessel (RPV) on the left and steam generator (SG) separator on the right are connected by a test section. The test section is composed of a horizontal rectangular channel, a bend that connects it to an upward inclined and expanded channel, and a quarter of a circle representing the steam generator inlet chamber. The horizontal part of the test section is 2.12 m long and 0.25 m high. The riser is 0.23 m long, has an inclination of 50 degrees to the horizontal plane, and an expansion angle of 7.5 degrees. The inner and outer bend radii of curvature are 0.25 m and 0.5 m, respectively.

In this simulation, a constant water flow rate is injected at the bottom of the steam generator simulator from where it flows through the test section to the RPV. Air is injected into the top of the RPV and flows through the test section to the SG separator in counter-current to the water flow.