Comparison between tests and calculations for the thermo-hydraulical and thermo-mechanical behavior of valves
by D. Hersant, J. Ferrari, J.-P. Mathieu, J.-F. Rit, S. Meunier, EDF R&D / MMC
Context
A valve qualification test campaign regarding thermal shock was conducted on an instrumented specimen. The tests consist in successively pumping pressurized hot water in the valve then cold water and so on until the desired number of cycles is reached (ten cycles for the current comparison). The instrumentation consists of 38 thermocouples distributed over the entire height of the valve, twelve strain gauges into the studs of the body-cap flange and clearance measurements of this flange. Meanwhile, a numerical model of the device was built with the same conditions of stress and the measured physical quantities.
Numerical simulation
The fluid simulation was performed with Code_Saturne. This results in a map of heat exchange coefficients near the walls, used as boundary conditions for the thermal part of the thermomechanical calculation, which is carried out with Code_Aster.
The mesh for the thermal calculation includes 2.7 million tetrahedrons and the numerical solution with the PETSc solver requires two hours on eight processors of EDF cluster. The mesh for the mechanical calculation includes 0.8 million elements and 5000 contact pairs (continuous formulation). Numerical resolution (linear elasticity) with the MUMPS solver requires 21 hours on twelve processors.
Comparison
Comparison between tests and simulation is based on the curves obtained from the fifty measurement channels along with those from the simulation results following the ten alternating shocks.
Such a comparison allows:
- to improve the understanding of physical phenomena at play during thermal shocks;
- to identify the domain of validity of the simulations;
- to possibly justify simplifications;
- and finally, to answer questions inaccessible to testing such as the valid representation of low rates or the sizing effect in a range of valves.
Finally, the vast amount of data collected, including information on the residual deformation of the body, not yet exploited, will also allow further investigation of the effects of plasticity.
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| Figure 2: Results of the thermal simulation |