In order to reduce the damage caused by a gas explosion in a ventilation duct, a Large Eddy Simulation (LES) model was used to simulate the hydrogen/air explosion process in the ventilation duct under different side vent. The results show that in the process of flame propagation, the large size side vent near the ignition end produces a larger discharge effect, which causes more serious distortion and longer time for the flame front passing through the side vents. The influence mechanism of the side vent on the flame propagation is different at different stages of flame propagation. When the flame front is behind the side vent, the positive flow field traction on the flame front increases the contact area between the flame front and unburned gas, and thus accelerates the flame propagation. When the side vent is 1 m away from the ignition end, with the side vent diameter increasing from 40 mm to 80 mm, the peak flame propagation speed increases by 19.02% before the flame reaches the vent. When the flame front passes through the side vent, the exhaust of the side vent and the disturbance of the vertical flow field can restrain the flame propagation. However, when the flame front is in front of the vent, the synergistic effect between turbulent vortex and reverse flow field causes the flame propagation speed to fluctuate greatly. The influence of the side vent size on the explosion relief effect is restricted by the side vent position. When the side vent is located in the pressure rising section, the pressure relief effect of the side vents with different sizes is very great and is almost unaffected by the size of the side vent. When the side vent is 1 m away from the ignition end, the peak overpressure in the tube decreased by 50.75%, 52.88% and 55.43%, respectively, when the diameter of the side vent was 40 mm, 60 mm and 80 mm. On the contrary, when the side vent is outside the pressure rising section, the pressure relief effect of the side vent will be weakened, and vents with different sizes have a great alteration to pressure relief effect. For the side vent being 5 m from the ignition end, the peak overpressure in the tube decreased by 4.49%, 13.41%, and 35.51%, respectively, when the diameter of the side vent was 40 mm, 60 mm, and 80 mm.

To reduce the injury caused by hydrogen explosion accident, numerical simulation study is carried out to study the characteristics of hydrogen explosion in confined space under different venting conditions. The results show that in the process of the flame passing through the side vent, the position of the side vent can affect the leading role of the side venting on the flame front distortion. When the flame front is in front of the side vent, the flame is accelerated by the traction of co-flow. When the flame front passes through the side vent, the flame propagation speed under various working conditions is greatly reduced due to the combined action of reflected wave and vertical flow field. When the front of the flame is located behind the side vent, the flame propagation speed fluctuates greatly only when the side vent is 1 m away from the ignition end, and the flame propagation to the end of the pipe is kept at a low speed in other venting conditions. The pressure relief effect of the side vent is positively related to the size of the side vent. When the side vent is located in the middle of the pipe, the pressure relief effect is the best. When the size of the vent is small, the pressure relief effect is greatly affected by the location of the vent. The peak overpressure in h-1-40, h-3-40, h-5-40 decreases by 49.21%, 83.89%% and 78.03%, respectively. With the increase of the size of the side vent, the pressure relief effect of the side vent is almost not affected by its size. The peak overpressure in H-1-80, H-3-80, H-5-80 only decreases by 90.17%, 94.99% and 92.78%, respectively.

To investigate the evolution process of LNG (Liquefied Natural Gas) liquid pool and gas cloud diffusion, the Realizable k-ε model and Eluerian model were used to numerically simulate the liquid phase leakage and diffusion process of LNG storage tanks. The experimental results showed that some LNG flashed and vaporized rapidly to form a combustible cloud during the continuous leakage. The diffusion of the explosive cloud was divided into heavy gas accumulation, entrainment heat transfer, and light gas drift. The vapor cloud gradually separated into two parts from the whole “fan leaf shape”. One part was a heavy gas cloud; the other part was a light gas cloud that spread with the wind in the downwind direction. The change of leakage aperture had a greater impact on the whole spill and dispersion process of the storage tank. The increasing leakage aperture would lead to 10.3 times increase in liquid pool area, 78.5% increase in downwind dispersion of methane concentration at 0.5 LFL, 22.6% increase in crosswind dispersion of methane concentration at 0.5 LFL, and 249% increase in flammable vapor cloud volume. Within the variation range of the leakage aperture, the trend of the gas cloud diffusion remained consistent, but the time for the liquid pool to keep stable and the gas cloud to enter the next diffusion stage was delayed. The low-pressure cavity area within 200 m of the leeward surface of the storage tank would accumulate heavy gas for a long time, forming a local high concentration area, which should be an area of focus for alert prediction.

In order to reveal the influence of pipe section size effect on hydrogen detonation characteristics, Large Eddy Simulation (LES) model was used to numerically investigate the hydrogen/air detonation process in closed space of different size. The results show that in the process of flame propagation, the reflection frequency of the shear wave produced by the small cross-section pipeline is higher, which increases the probability of the tulip flame and flame structure distortion. For a 6-m-long square-closed pipe, the influence mechanism of the cross-section size on the flame propagation is different at different stages of flame propagation. In the early stage of flame propagation (that is, in the pipe segment 0–0.8 m away from the ignition end), the internal friction caused by the friction between the flame and the tube wall increases the turbulent intensity of the flammable cloud and accelerates the flame propagation. In a confined space with the cross-section edge length of 100 mm, the maximum flame propagation speed is 176.7 m/s, which is 48.5% faster than that in the confined space with the cross-section edge length of 250 mm. In the middle of the flame propagation (that is, in the pipe segment 0.8-5m away from the ignition end), the flame area increases sharply during combustion and releases more energy. Therefore, larger vortices are formed, and the flame propagation is accelerated by turbulence efficiency. The maximum flame propagation speed can reach 500 m/s when the cross-section edge length is 250 mm, which is 140.8% faster than that when the cross-section edge length is 100 mm. In the later stage of flame propagation (that is, in the pipe segment 0.8–5 m away from the ignition end), the pressure in the pipe increases sharply, and the reflected wave from the pipe end produces great resistance to the propagation of the flame front, and the flame propagation speed decreases sharply in the pipeline of various cross-sections.