The present work is concerned with numerical simulations of large scale hydrogen detonations. Euler equations have been solved along with a single step reaction for the chemistry. Total variation diminishing (TVD) numerical schemes are used for shock capturing. The equations are solved in parallel in a decomposed domain. Predictions were firstly conducted with a small domain to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure and velocity. On this basis, simulations were set up for the detonation tests carried out at the RUT tunnel facilities in Russia. This is one of the standard benchmark test cases selected for HYSAFE. Comparison is made between the predictions and measurements. Reasonably good agreement has been obtained on pressure decay and the propagation speed of detonation. Further simulations were then conducted for a hypothetical hydrogen-air cloud in the open to assess the impulse as well as overpressure. The effects of cloud height, width were investigated in the safety context.

Numerical investigations have been conducted on the effect of the internal geometry of a local contraction on the spontaneous ignition of pressurized hydrogen release through a length of tube using a 5th-order WENO scheme. A mixture-averaged multi-component approach was used for accurate calculation of molecular transport. The auto-ignition and combustion chemistry were accounted for using a 21-step kinetic scheme. It is found that the internal geometry of a local contraction can significantly facilitate the occurrence of spontaneous ignition by producing elevated flammable mixture and enhancing turbulent mixing from shock formation, reflection and interaction. The first ignition kernel is observed upstream the contraction. It then quickly propagates along the contact interface and transits to a partially premixed flame due to the enhanced turbulent mixing. The partially premixed flames are highly distorted and overlapped with each other. Flame thickening is observed due to the merge of thin flames. The numerical predictions suggested that sustained flames could develop for release pressure as low as 25 bar. For the release pressure of 18 bar, spontaneous ignition was predicted but the flame was soon quenched. To some extent this finding is consistent with Dryer?s experimental observation in that the minimum release pressure for the release through a tube with internal geometries is only 20.4bar.