The Dynamics Characteristics And Shock Structure Of Interaction Between Shock Waves And Solid Sphere Arrays

The interaction between a shock wave and solid particles has always been one of the important research topics in supersonic gas-solid two-phase flows. Many important applications are closely related to this research topic, for instance, the needle-free drug powder injection, supersonic cold spraying, pulse type powder fire extinguisher, solid fuel booster nozzle, etc. It is extremely important to master the mechanism of the interaction between a shock wave and particles for the development and perfection of the supersonic gas-solid two-phase flow theory, industrial production and technological improvement. Therefore, the research on the mechanism and evolution law of unsteady drag force induced by shock wave loadings on sphere array models has great significant academic value and engineering guiding significance.The experiments were conducted in a large horizontal shock tube with an inner diameter of 200 mm. The direct measurements of unsteady drag on solid sphere array models were achieved by using a dynamic force measuring system composed of acceleration sensors, a high-speed data acquisition system and a dedicated computer. A schlieren device combined with a high-speed photographic instrument was used to capture the schlieren photographs of dynamic shock structures.The influence of the spatial arrangement of sphere arrays(two-spheres-in-one-row, four-spheres-in-one-row and four-spheres-in- two-rows, the sphere diameters are Φ40mm), incident shock Mach number Ms(1.06- 1.41) and the dimensionless distance H(1.2- 3.0) on the drag force was experimentally investigated.The main goal of this thesis is to achieve a further understanding of the mechanism and evolution law of shock-induced unsteady drag force on sphere-array models with experimental and numerical simulation methods.The numerical simulations and analyses were based on a CFD computing platform composed of ICEM and FLUENT softwares, and data post-processing softwares such as Tecplot, Origin, etc. The numerical calculations for the shock-induced flows and drag forces around three sphere-array models were carried out under the experimental conditions. The mechanism and evolution law of unsteady drag force were revealed by analyzing its dependency on the dynamic shock structure(or pressure distribution) around a sphere-array.The main conclusions of this thesis are as follows:1. The three sphere-array models have basically the same time-histories of drag coefficient. As elapsed time increases, Cd sharply increases from zero to a peak value, and then goes down rapidly, which causes the appearance of a valley of the Cd curve with minus values, and next Cd increases again and the second peak appears, and finally Cd tends to a stable positive value. Furthermore, the smaller the shock Mach number, the greater the peak value of Cd, the more drastically the curve of Cd fluctuates, and the longer the duration for Cd tending to be stable.2. For two-spheres-in-one-row and four-spheres-in-one-row models, the peak value of Cd decreases with increasing H. For a four-spheres-in-two-rows model, the peak value of Cd in the front row does not change monotonically, while the one in the back row increases with decreasing H.3. When a shock wave propagates near to the equator of a sphere, the pressure in the shock-affacted sphere-surface region increases, resulting in the appearance of the peak of Cd. The focusingof the diffracted shock waves at the rear stagnation of the sphere leads to high pressure in the vicinity and the appearance of a valley of Cd with minus values. The secondary reflection of the shock wave from the sphere surface near the front stagnation point causes a locally high-pressure area and the appearance of a second peak of Cd, when the incident shock wave coincidentally arrives at the rear stagnation point.4. The obvious interference between the reflected shock waves from the adjacent spheres occurs. Furthermore, the smaller the dimensionless distance H, the more obvious the interference of the reflected shock waves.5. For a four-spheres-in-two-rows model, the valley and the second peak values of Cd in the front row are respectively smaller and greater than those in the back row.