A 1000 MW CCGT in the Middle East had reports of foam generation and pressure issues at its cooling water discharge point. R&R Consult was commissioned by Tetra Engineering to model the fluid dynamics in the outfall system. The cause of the problem appeared to be a free fall of the cooling water in a weir located upstream of the outfall to control the system pressure.
Without the need for physical tests, R&R Consult developed a CFD model capable of simulating various design alterations, one of which successfully reduced the air entrapment in the discharged water by 47%.
The CFD analysis included a two-phase model to assess the initial amount of air in the discharged water downstream of the weir, and subsequently simulated the effects of multiple design changes. The required CFD model was a transient (time dependent), two-phase Volume of Fluid model, which visualized the water/air interface under various operating conditions.
Animation shows Volume fraction of water in the weir cross section
Simulating the system numerically has several great advantages: it limits time and costs and allows an immediate and highly accurate evaluation of design alterations. The most promising design change was to install baffle blocks after the weir free fall to increase the settling time and to separate the air from the water before the outlet.
Volume fraction of water in the weir cross section with baffle blocks
A similar modelling approach of quickly analyzing design changes through CFD, can be applied in various engineering fields and processes such as product development, system scaling and optimization.
Animation shows water surface