Study On Interaction Between Premixed Flame And Obstacles

Fire accident is a big threat for safety of people's life and public property. The shape of flame front can be changed significantly due to its interactions with various obstacles placed in the fire scene, as well as speed of flame propagation and environmental pressure. Therefore, the study on interaction between the flame and obstacles is extremely important to reduce losses caused by this kind of disasters. Meanwhile, this study can provide theoretical basis for development pulse detonation engine (PDE).In this dissertation, series of experiments have been performed to investigate the premixed flame behavior during its propagation in a rectangular chamber with obstacles, such as a rectangle cylinder, a wedge cylinder, a rectangle cylinder with a square hole, a circle cylinder, a square cylinder and a triangle cylinder. A high speed shadowgraph system was used to obtain the sequential images of flame front development, and to record correctly the interaction process between the fluid flow and flame. The numerical simulations above phenomena have been carried out by Large Eddy Simulation (LES) and high accuracy five point TVD schemes. The SGS model is Smagorinsky model. The reaction rate model is Eddy-Break-Up (EBU) model. The shapes of obstacle's boundary were different in the chamber; the immersed boundary method (IBM) in 3D compressible viscous flow by momentum equation is deduced, and applied to solve boundary condition with various shapes.According to the experimental and computational results, we discussed the complicated phenomenon of interaction between flame and various obstacles in detail. The expansion of combustion can promote the unburned gas flow in front of flame. The flame will be deformed in varying degrees when it interacted with variety of obstacles. In addition, both of the instability of flame and the shear-layer near the wall of chamber also are important factor for flame deformation. If the vortex produced by shear-layer near the wall of chamber is ignored, another two types of vortexes still existed in the flow field. One kind of vortex is produced by baroclinic effect of combustion; it was distributed on the flame front mainly. Another kind of vortex was produced by fluidity field of unburned gas. With the distribution of turbulence intensity, it can be find that the turbulent kinetic energy on the flame front enhanced gradually as flame propagating forward. The turbulent kinetic energy of unburned gas in front of flame can also be enhanced by the accelerated flame. The positive feedback effect of the turbulent unburned gas and flame are generated and displayed. During the combustion, the chamber pressure continued to grow. Specially, The pressure grew significantly when flame propagates through the channels of obstacles. Although the turbulence was enhanced in the flow field when flame interacted with obstacles, the flame propagation velocity is not always increased.