This is the report of a master’s thesis performed at FS Dynamics in Solna and is a perfect example of cooperation between the Nuclear Engineering branch and the Computational Fluid Dynamics branch. The nuclear industry has got high requirements on safety since a failure could have devastating consequences.
A typical nuclear power plant has got large piping systems pumping around water at high pressure and it is of importance that the system could resist all possible loadings due to for example a pipe rupture. Numerical simulations of these systems are therefore performed where 1D-codes are used to simulate different analyses. All though these 1D-solvers are well established they have got deficiencies when it comes to model the dynamics of certain components, e.g. a swing check valve.
This master’s thesis is made to increase the understanding of the dynamic characteristics of a typical large swing check valve used in a system that transports pressurized water to a reactor tank. 3D FSI-simulations are performed for a number of transients in order to study the dynamic characteristics their dependence of the deceleration rate. The purpose is to find information about the dynamics that could be used in a future improvement of a 1D-model.
Steady state simulations are performed for angles in the whole spectrum. Seven transient FSI-simulations with different constantly decelerating flows from 630 kg/s2 (6.7 m/s2) to 40 320 kg/s2 (430 m/s2) have been performed. The pressure on the disc caused by the hydraulic torque is integrated and the corresponding torque contribution, together with the weight torque, is used in the second law of motion to calculate the movement of the disc throughout the transients. Steady state simulations yield the pressure drop over the valve, which could be compared with field measurements in order to validate the CFD-simulations.
Comparison of the pressure distribution on the disc for the steady state and transient simulations shows the importance of taking the disc angular velocity into account when modelling in 1D. Correlations between the angle, angular velocity, torque and mass flow are obtained from the transient FSI-simulations.
Torque coefficients according to (Li & Liou, Vol. 125) are also brought out from the simulated transients, but in order to create a model in line with this approach further simulations have to be performed. A prediction of the pressure rise that occurs when a swing check valve closes in backward flow according to the Joukowsky equation is brought out and gives an idea of the loadings that the system has to be able to handle.
Source: Linköping University
Author: Boqvist, Emil
