Numerical And Experimental Investigation Of Partly-covered Cavities

Igniting the room temperature kerosene by spark plug directly is always a crucial thing in scramjet engine investigation.The present research studied the isothermal and exothermic flowfield, using different experimetal investigations numerical simulation.To investigate the effects of geometric parameters and free stream Ma on the partly-covered cavity flow field, the partly-covered cavity flow field were simulated. It is found that the cover-plane length doesn’t have evident influence on the free stream. The L/D of cavity is the main factor which effects the mass exchange of covered region in the cavities with different cavity-depth. The mass exchange of covered-region decreases as the L/D of cavities increases. As the Ma of free stream increases, the mass exchange of covered-region decreases. Compared with the cavities with large L/D, the covered-region mass exchange is more sensetive to L/D and free stream Ma in the cavities with small L/D.Aimed at investigating the effects of partly-covered shape on the flowfield of combustor, both the isothermal and exothermic 2-D flowfiled of a partly-covered cavity were simulated.The effects of cover-plane on fuel distribution, static temperature distribution and combustion efficiency were checked on both lean and rich fuel condition. In the lean fuel flowfield, the cover-plane is helpful in accumlating the fuel in cavity, and the flameholding stability can be improved. In the flowfield with a partly-covered cavity, the region with feasible ignition equivalence ratio is located inside the cavity with low-speed. So the ignition capability of the partly-coved cavity is also improved. In the rich fuel flowfield, the cover-plane makes the rich condition worsen inside cavity, the flameholdering stability and combsution efficiency are both reduced. A part of main combustion region moves downstream.The 3D flowfield of partly-covered cavities with different L/Ds were investigated by numerical simulation, in order to check the effect of sawtooth structure on the cavity flowfield. It was found that the sawtooth structure can lead to the velocity nonuniform in the shear layer on spanwise, producing the streamwise vortices. In the plane without a slot, the stream will be captured by the coverplane, while in the plane with a slot, the stream will be exhausted be the slot. This capture-exhaust mode can improve the mass-exchange of the covered region. The sawtooth structure seem to make the cavity flowfield more easy to be closed.Many explore experiments were conducted in order to ignite the room temerature kerosene in partly-coverd cavtiy. The result of these experiments show that partly covered cavity have a robust flameholding capacity. The partly-covered cavity can achieve the stable flame only with the room temperature kerosene injected from the front wall. The stable flame in the partly-covered cavity will affect the flameholding of the downstream cavity. The direct injection at the front wall can control the equivalent ratio in the covered region, leading to a better igniton ablity. After the kerosene is ignited by the spark, the initial kernel will be covected by the stream to the covered region or the shear layer.