本文選題：顆粒對(duì)流 + 準(zhǔn)二維垂直振動(dòng)楔形顆粒床　； 參考：《北京理工大學(xué)》2015年碩士論文

【摘要】：本文采用實(shí)驗(yàn)和離散元模擬方法研究不同側(cè)壁傾角下準(zhǔn)二維垂直振動(dòng)楔形顆粒床的對(duì)流模式，及其隨側(cè)壁傾角和振動(dòng)加速度的變化。發(fā)現(xiàn)側(cè)壁傾斜顆粒床在振動(dòng)作用下發(fā)生了反向?qū)α�，即顆粒沿側(cè)壁向上流動(dòng)，在表面匯聚到中心，然后沿中心下降通道運(yùn)動(dòng)到底部，最后沿底部向兩側(cè)分流，形成左右兩個(gè)對(duì)流卷。 同等振動(dòng)強(qiáng)度下65°側(cè)壁傾角顆粒床的對(duì)流速度最大，傾角偏離該角度越大，對(duì)流速度越小。將對(duì)流速度隨傾角變化曲線外推至對(duì)流速度為零，發(fā)現(xiàn)反向?qū)α鹘K止時(shí)對(duì)應(yīng)的臨界傾角為86.5°。保持側(cè)壁傾角不變，對(duì)流速度隨加速度大致呈線性增長(zhǎng)。但65°側(cè)壁傾角時(shí)，加速度從10g增加到12g時(shí)，對(duì)流速度增加了117%，遠(yuǎn)大于其它傾角平均增長(zhǎng)10%。對(duì)流卷中心也隨著振動(dòng)加速度的增加而緩慢下降。以上實(shí)驗(yàn)觀察可以和離散元模擬結(jié)果相吻合。 顆粒對(duì)流主要發(fā)生在顆粒床兩側(cè)翼在重力波作用下的橫向膨脹階段。當(dāng)膨脹后的顆粒床側(cè)翼邊緣顆粒與側(cè)壁在更高的位置碰撞并向上運(yùn)動(dòng)時(shí)，仍然保持橫向運(yùn)動(dòng)分量的側(cè)翼內(nèi)側(cè)顆粒填補(bǔ)到沿側(cè)壁向上流動(dòng)顆粒的下方，形成對(duì)流卷的底部。顆粒床側(cè)翼橫向膨脹程度與此區(qū)域內(nèi)顆粒床上拋?zhàn)畛蹼A段的橫向力鏈強(qiáng)度呈正相關(guān)。當(dāng)顆粒床底部離開(kāi)底壁時(shí)，底部力鏈迅速消失，而側(cè)壁與顆粒床在短時(shí)間內(nèi)仍保持接觸，側(cè)翼區(qū)域內(nèi)力鏈得以維持。隨著顆粒床上拋距離的增大，顆粒床側(cè)翼與側(cè)壁分離，橫向力鏈的松弛導(dǎo)致側(cè)翼開(kāi)始膨脹。但速度的變化較力鏈存在滯后性，在顆粒側(cè)翼反向下落時(shí)，，側(cè)翼的膨脹才變得明顯。 側(cè)翼膨脹程度相同時(shí)，側(cè)壁傾角更大的側(cè)翼顆粒將更早與側(cè)壁碰撞，導(dǎo)致對(duì)流速度增大。但上拋?zhàn)畛蹼A段側(cè)翼顆粒與側(cè)壁接觸時(shí)間隨傾角增大而延長(zhǎng)，導(dǎo)致側(cè)翼顆粒受到側(cè)壁向下摩擦更強(qiáng)，上拋速度減小，在空中飛行時(shí)間縮短，以至于側(cè)翼還未充分膨脹就與側(cè)壁碰撞。在這兩種競(jìng)爭(zhēng)效應(yīng)的作用下，65°傾角顆粒床對(duì)流最強(qiáng)。小于此角度，削弱了橫向膨脹程度；大于此角度，側(cè)壁摩擦效應(yīng)會(huì)明顯抑制反向?qū)α鳌?br/>[Abstract]:In this paper, experimental and discrete element simulation methods are used to study the convection model of quasi two-dimensional vertical vibrational wedge granular bed with different lateral wall inclination, and its variation with the lateral wall inclination and vibration acceleration. It is found that reverse convection occurs in the lateral inclined granular bed under the action of vibration, that is, the particles flow upward along the lateral wall, converge to the center on the surface, then move along the central descending channel to the bottom, and then shunt along the bottom to the two sides. Form two convection rolls on the left and right. At the same vibration intensity, the convection velocity of 65 擄sidewall obliquity granular bed is the largest, and the larger the inclination angle is, the smaller the convection velocity is. By extrapolating the curve of convection velocity with inclination to zero, it is found that the critical inclination angle at the end of reverse convection is 86.5 擄. The velocity of convection increases linearly with acceleration. However, when the slope angle of the lateral wall is 65 擄and the acceleration increases from 10 g to 12 g, the convection velocity increases by 117, which is much larger than the average increase of the other inclination angles by 10%. The convection coil center also decreases slowly with the increase of vibration acceleration. The above experimental observations agree well with the results of discrete element simulation. Particle convection mainly occurs in the lateral expansion stage of the wings on both sides of the granular bed under the action of gravity waves. When the expanded particle bed flanking edge particles collide with the lateral wall at a higher position and move upward, the inner flanking particles that still maintain the lateral motion component are filled under the flowing particles upward along the lateral wall, forming the bottom of the convection roll. The lateral expansion of the flank of the granular bed is positively correlated with the strength of the transverse force chain in the initial stage of the pellet throwing in this region. When the bottom of the granular bed leaves the bottom wall, the bottom force chain disappears rapidly, while the lateral wall and the granular bed remain in contact with each other for a short period of time, and the internal force chain in the flanking region can be maintained. With the increase of the throwing distance on the granular bed, the flank of the granular bed is separated from the lateral wall, and the relaxation of the transverse force chain leads to the expansion of the flank. However, the variation of velocity is more lag than that of the force chain, and the expansion of the flank becomes obvious when the particle flanks fall in reverse direction. With the same expansion degree of the flank, the flank particles with larger sidewall inclination angle will collide with the lateral wall earlier, resulting in the increase of convection velocity. However, in the initial stage of upper throwing, the contact time between the flank particles and the side wall increases with the increase of the inclination angle, which results in stronger friction between the flank particles and the downward friction on the side wall, a decrease in the throwing velocity, and a shortening of the flying time in the air. The flank collides with the side wall before it is fully inflated. Under these two competitive effects, the convection of 65 擄tilted granular bed is strongest. Smaller than this angle, the lateral expansion degree is weakened, and the lateral wall friction effect obviously inhibits the reverse convection when the angle is larger than this angle.
【學(xué)位授予單位】：北京理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ021.1

【參考文獻(xiàn)】

相關(guān)期刊論文 前2條

1 湯燕;胡林;吳宇;張忠政;曲東升;白光富;孔維姝;;振動(dòng)條件下顆粒的分離現(xiàn)象[J];大學(xué)物理;2008年06期

2 李芳芳;薛琨;白春華;;豎直振動(dòng)顆粒床對(duì)流機(jī)制的顆粒尺度實(shí)驗(yàn)研究[J];實(shí)驗(yàn)力學(xué);2013年03期

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