Large Eddy Simulation of a Main-Steam Line in a Nuclear Plant

Figure 1: Main-steam line and branch-pipe geometry.
Figure 1: Main-steam line and branch-pipe geometry.

Objective

To calculate the pressure fluctuations due to vortex shedding at the branch-pipes in main-steam line of a nuclear power plant.

Analysis Details and Results

A detailed 3D model of the main-steam line with three branch-pipes was modeled in CFD as shown in Figure 1.

A fine inflated grid (prismatic element layers near the pipe walls) was used to resolve the boundary layer. A very fine mesh was used around the SRV branch-pipes to accurately resolve the boundary layer shear and vortices shed by the upstream round radius of the branch-pipes. (see Figure 2).

When fluid flowing through a pipe passes over a cavity, the boundary layer at the upstream edge of the branch-pipe forms a free shear layer that travels toward the downstream edge of the branch-pipe. The unstable shear layer combined with the upstream disturbances develops waves that roll into vortices. The shear layer vortices impinge on the downstream corner of the branch-pipe, causing an alternate inward and outward flow to the branch-pipe resulting in pressure oscillations. The vortices generated at the branch-pipes are shown in Figure 3.

Figure 2: Mesh details at the branch-pipe

Figure 2: Mesh details at the branch-pipe

 

Figure 3: Shedding vortex formations due to flow 
across a closed stand pipe modeled with Large Eddy Simulation.

Figure 3: Shedding vortex formations due to flow across a closed stand pipe modeled with Large Eddy Simulation.