The Investigation Of V-gutter’s Effects On The Mixing And Combustion In Subsonic Flow

The present thesis, focusing on the V-gutter as a flameholder in Air Turbo Rocket engine’s combustion chamber, investigated characteristics of mixing and combustion numerically and experimentally.Large Eddy Simulation method was provided to investigate the unsteady process of mixing. The velocity of air was 0.4Ma, and methane was injected into air upstream. The weak region was dominated by von Karman vortexes generated and shedding from the downstream face of V-gutter. It was also affected by normal vortices caused by velocity gradient between methane and air, generated from inlet. A series small eddy was presented from the tips of V- gutter during the generation of von Karman vortices. Pressure wave was generated in the weak flow where complex interaction between vortices, vortices and walls took place. In subsonic flow, the pressure wave moved upstream. Normal vortices were influenced by unsteady pressure, as well as the horizontal jet of methane. Compared with the process of mixing without V-gutter, it was found that recirculation zone existed, and V- gutter could improve the mixing with large total pressure loss.The present thesis investigated the effects of angle and block ratio of V- gutter on non-reacting flow field. It was found that the change of angle had a little effect on total pressure loss. With an increase in the angle of V-gutter, the length of the recirculation zone downstream decreased, meanwhile the fluctuating velocity increased. At the same distance behind the trailing edge of the V-gutter, there was no obvious effect of the angle on the mixing efficiency. At the same distance behind the inlet, however, bigger angle of the V- gutter gave better performance of mixing. Due to the increasing of block ratio of the V-gutter, the size of recirculation zone, the loss of the total pressure, turbulence intensity and fluctuation of flow field increased. With the same distance behind the inlet and intersecting surface, the larger block ratio, the better mixing performance.Reacting flow flied of the V- gutter was investigated primarily by numerical simulation. Results showed that the Karman Vortex Street(KVS) played a dominate role in the flow field with reaction, and a small high temperature region existed in the recirculation zone within a short period. The vortex shedding of high frequency enhanced the stretching and breakup of the high temperature vortices, which was the main reason of blowoff. Therefore the key of flame holding behind the V-gutter was the conversion of reacting flow from high frequency KVS to K-H shear layer.In the experiment, high speed schlieren captured the production and development of the KVS, which validated the numerical results. Numerical results of the mean velocity were matched well with the results of Particle Image Velocimetry(PIV) measurement.