The Dynamics Characteristics Of Interaction Between Shock Waves And Sotid Sphere Arrays

The interaction between shock wave and solid particle group has always been one of theimportant research topics in supersonic gas-solid two-phase flows. Many important applicationsare 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. Itis extremely important to master the mechanism of interaction between shock wave and particlegroup for the development and perfection of the supersonic gas-solid two-phase flow theory,industrial production and technological improvement. Therefore, the research on themechanism and evolution law of unsteady drag force induced by shock wave loadings onsphere array models has great significant academic value and engineering guiding significance.The main aim of this thesis is to further study the mechanism and evolution law ofunsteady drag force caused by shock wave loadings on sphere array models by combiningexperimental investigation and numerical simulation methods.The experiments were conducted in a large horizontal shock tube with the inner diameterof200mm. The direct measurements of unsteady drag on solid sphere array models wereachieved by using a dynamic force measuring system composed of acceleration sensors, forcetransducers, a high-speed data acquisition system and a dedicated computer. Band-eliminationfilter technology and high-order polynomial curve fitting method were applied to processacceleration signals. The effects of sphere-array spatial configuration (three sphere-arraymodels including four spheres in one row, abreast four spheres in two rows and staggered fourspheres in two rows, each sphere in diameter of40mm), incident shock Mach number Ms(1.086~1.283) and dimensionless interval distance H (1.0~3.0) on drag force (coefficient)upon the sphere-array models were experimentally investigated.The numerical simulations and analyses were based on a CFD computing platformcomposed of Gambit and Fluent softwares, and data post-processing softwares such as Tecplot,Origin, etc. The numerical calculations for shock-induced flows around spheres and drag forcesof sphere models were carried out under the experimental conditions of three types of spherearray models. The mechanism and evolution law of unsteady drag force were revealed byanalyzing the dependency of unsteady drag force on the pressure around a sphere and the pressure distribution on the sphere surface.The main conclusions of this thesis are as follows:1. With the increase of elapsed time, drag coefficient Cdsharply increases from zero, thenthe curve of Cdgoes down rapidly after a sharp peak, and next the amplitude of the curvedecreases continuously, and finally Cdtends to a stable positive value. As shock Mach numberdecreases, the peak value of drag coefficient Cdincreases, the curve of Cdfluctuates moredrastically, and it is more difficult for Cdto tend to a stable value.2. For the cases of four spheres in one row, the reflected shock interference of adjacentspheres is more intense than that of the opposite spheres. As dimensionless distance H increases,the interference phenomenon between two spheres becomes less distinct, and the peak value ofdrag coefficient Cddecreases.3. For the cases of abreast four spheres in two rows, the drag coefficient Cdreaches itsmaximum peak value when H=1. The peak value of Cddoes not vary much with H rangingfrom1.5to3. But there still exists a same change rule that the peak values of Cdfirst decreasesand then increases, and finally decreases again as H increases gradually. In contrast, thedifference of the peak values of Cdacting on the spheres in front and rear two rows firstincreases and then decreases, and finally increases again as H increases. The reflected shockwave from the spheres in the rear row acts on the spheres in the front row, and then causes thedrag force in the front row to diminish again.4. For the cases of staggered four spheres in two rows, the peak value of Cdin the frontrow presents the same change rule as that for the cases of abreast four spheres in two rows withthe increase of H. However, with increased H, the peak value of Cdin the rear row firstdecreases and then increases, by contrast, the difference of the peak values of Cdin front andrear two rows first increases and then decreases. The reflected shock wave from the rear rowalso acts on the front row and causes the second downward trend of Cdin the front row.Compared to the cases of abreast four spheres in two rows, the changes of Cdcurve appear later.5. By comparison of three sphere models including a single sphere, double spheres andfour spheres in one row, both the experimental and calculated results consistently show thatwith the increase of sphere number, the peak value of Cdincreases. This indicates that theinterference among the shock waves around the adjacent spheres leads to the increase of drag force acting on each single sphere.