Simulation of pressure loss and cavitation
Sector: Machinery and plant engineeringSpecialist field: Fluid mechanicsAxpo AG is responsible, among other things, for the operation and maintenance of two nuclear power plants in Switzerland. Already installed Venturi nozzles of the AFW system are to be optimized with regard to pressure loss and cavitation using Ansys CFD.
Summary
Task
As part of an inspection of a nuclear power plant, already installed components are to be optimized with simulation. In particular, the aim was to understand pressure losses and uncertainties in the evaluation of the flow limiters installed in the emergency water supply systems (AFW) of the steam generators.
Solution
Calculations of turbulence in Ansys CFD with parametric models related to manufacturing tolerances and surface roughness provided the corresponding pressure loss coefficients and removed uncertainties for two flow restrictor geometries.
Customer benefits
The costs resulting from downtime were significantly reduced, and important information was obtained that was not available through experimental measurements.
Project Details
Task
Axpo AG is responsible, among other things, for the operation and maintenance of two nuclear power plants in Switzerland. As part of an inspection of a nuclear power plant, already installed components are to be optimized with simulation. In particular, the aim was to understand pressure losses and uncertainties in the evaluation of the flow limiters (Venturi nozzle) installed in the emergency water supply systems (AFW) of the steam generators.
Customer Benefit
The costs resulting from downtime were significantly reduced, and important information was obtained that was not available through experimental measurements. After acquiring a deeper understanding of the relevant effects and parameter variations (pipe roughness, tolerances, cavitation), the properties of the flow restrictor could be re-examined. Thanks to quality controls and CADFEM’s knowledge transfer, Axpo was able to reliably calculate further geometries and flow conditions, including cavitation.
Solution
Calculations of turbulence in Ansys CFD with parametric models related to manufacturing tolerances and surface roughness provided the corresponding pressure loss coefficients and removed uncertainties for two flow restrictor geometries. The consulting project was followed by know-how transfer and best practice trainings, focusing on cavitation effects, which are responsible for a 300% increase in pressure loss under certain flow conditions. Targeted measurements for several attainable operating conditions and for each flow restrictor were performed by Axpo as a final validation step after the flow restrictor was installed (see table). These results, which include deviations of stochastic model parameters (tolerances, viscosity, roughness) and measurement errors, showed that measurement and simulation results were accurate within the error limits.
Images: © Axpo AG