Future designs of combustion engines for motor-vehicles require modern high performance valves. Internally cooled valves have been used in engines for more than 90 years. Water was initially used as coolant and later mercury, but finally, after difficulties with these liquids, sodium was found to be an appropriate working fluid. The technique of using a liquid to carry the heat from the hot valve head to the valve stem, where it can pass through the valve guide, is now well established in industry. However, the design of such valves is mostly based on empirical knowledge within the industry. A simulation of the processes during the movement of the valve including detailed information about the highly transient two phase flow and the heat transfer in this system has not been realized so far. For this, an inhouse 3D DNS (direct numerical simulation) program (FS3D) was used to simulate the flow phenomena. The simulations have been performed on an equidistant rectangular computational grid in 2D. It was found that a typical fill level of sodium between 50% and 60% of the stem volume provides the best results for the averaged time evolution of the kinetic energy and also of the heat flux in the system. Furthermore, detailed descriptions of the realtime movement in the flow are shown for different fill levels. These results can be used to enhance and improve future designs.
Direct numerical simulation of reactor two-phase flows enabled by high-performance computing
