CFD analysis of the hydrogen explosion test with (a) high ignition energy in (the) open space

A CFD analysis of an overpressure buildup and a flame propagation at the hydrogen explosion test with a high ignition energy of 40 J in the open space (Sato, 2006) was performed using a commercial CFD code of ANSYS CFX-11 to establish a proper CFD analysis methodology for a simulation of the hypothetical hydrogen explosion between the VHTR and the hydrogen production facility (Chang, 2007). The hydrogen explosion test in the open space was performed by varying the hydrogen concentration and the existence of an obstacle and a barrier wall to measure the overpressure buildup and the flame front Time of Arrival (TOA) for a long distance of 41 m. And also, the high ignition energy of 40 J was used to intentionally induce a detonation phenomenon, but a deflagration was happened. In the CFD analysis, the developed spark ignition model (Kang, 2008) was used for the high ignition energy, and also the eddy dissipation model (EDM) and the standard k-e turbulent model implemented in the CFX-11 were used for the simulation of the hydrogen combustion. A preliminary result for the test results without the obstacle shows that the CFD analysis predicts well the global hydrogen flame propagation after the ignition, but the CFD results do not predict accurately the overpressure buildup and the flame front TOA. Therefore, a series of sensitivity analysis is being performed by varying a grid cell distribution, the constant values of the EDM, a turbulent model and the Courant number to find out the BPG (Best Practice Guideline) for the simulation of the overpressure buildup and the flame front TOA of the experimental results. A validated CFD analysis methodology will be used in the determination of the safety distance between the VHTR and the hydrogen production facility to increase the VHTR safety. (authors)