DYNAMIC EFFECTS UNDER GASEOUS DETONATION AND MECHANICAL RESPONSE OF PIPING STRUCTURES

A series of experiments and numerical simulations on hydrogen detonations in piping geometry was performed in order to reproduce the worst case scenario regarding the maximum internal pressure load and integrity of a piping structure to detonation pressure loads. To reproduce different scenarios of the detonation process and different pressure loads on the piping structure, nitrogen-diluted hydrogen-oxygen mixtures were studied. The mechanical response of 12.5-m long austenitic steel pipe with an outer diameter of 510 mm and wall thickness of 15 mm was investigated as well. A novel 1-D CFD code with a prescribed flame velocity model was used for the numerical simulation of the deflagration to detonation transition (DDT) and for the calculation of pressure loads at various positions along the tube. Different gas dynamic effects such as precursor shock waves and shock reflections on the maximum pressure were investigated in the calculations. Maximum pressure load of a pipe with two end flanges can be achieved near the DDT point and at the tube ends. Dilution of the hydrogen-oxygen mixture with nitrogen leads to a reduction of the mixture reactivity and to an increase of the run-up distance to the DDT point. In this case so called "late detonation initiation", a cumulative effect of precursor shock wave, detonation ignition and shock wave reflections, can occur near the tube end. It produces extremely high pressure loads which can be 10 times higher than the CJ-detonation pressure of the initial gas mixture. Such scenarios of the combustion process have been experimentally reproduced with detailed pressure and strain measurements along the test tube.