顆粒體在具阻礙物滑道中流動行為研究：DEM的實驗驗證及傳輸性質與內部性質探討

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题名:	顆粒體在具阻礙物滑道中流動行為研究：DEM的實驗驗證及傳輸性質與內部性質探討
作者:	吳朝旺;Wu, Chao-Wang
贡献者:	機械工程學系
关键词:	滑道顆粒流;阻礙物;離散元素法;傳輸性質;內部性質;邊界摩擦效應
日期:	2017-01-18
上传时间:	2017-05-05 17:42:02 (UTC+8)
出版者:	國立中央大學
摘要:	本研究使用驗證合理的離散元素法(DEM, discrete element method)模型，探討球型顆粒體在具阻礙物滑道中的流動行為。本研究旨在探討滑道中阻礙物對於重力驅動顆粒體的傳輸性質及內部性質之影響，藉由計算滑道系統中顆粒體流場深度，體積佔有率，速度場，旋轉角速度，粒子溫度，配位數，應力，接觸力方向分佈及組構張量等性質，並觀察顆粒體受邊壁摩擦效應影響後的性質變化。本研究結果顯示，顆粒體的流動行為受阻礙物影響，在阻礙物前產生堆積，通過阻礙物顆粒體產生飛濺，而後受重力影響掉落至滑道。因顆粒體與邊壁產生摩擦，使得邊壁處的流速較中央為小，而垂直滑道方向角速度及滑道平面方向剪應力則較中央為大，且由邊壁摩擦所產生的剪力使顆粒體產生體積膨脹，導致兩側體積佔有率，配位數，正向應力及滑道邊壁方向剪應力較中央為小，且兩側顆粒體滾動方向角速度較中央為大。粒子溫度的結果顯示，在飛濺的顆粒體掉落至滑道處有較高的粒子溫度，邊壁的顆粒體受摩擦所產生的剪力影響，使得顆粒體較為擾動，因此在滑道邊界處及自由表面有較高的粒子溫度。應力的結果顯示，由於滑道中阻礙物造成顆粒體的堆積，導致正向應力及剪應力上升。並觀察接觸力方向分佈及組構張量的變化，受滑道中阻礙物影響，使得流動方向的接觸分佈增加，且在飛濺時顆粒體會向兩側邊壁散開，而後顆粒體受重力影響掉落至滑道，使得流場深度方向的接觸增加。;The aim of the study is to investigate the flow behavior of spherical particles in an inclined chute with a cylindrical obstacle by using PIV measurement technique and discrete element modelling. The proposed DEM model is first validated against the corresponding experiment. After reasonable justification, the DEM results are further employed to explore the transport and internal properties of granular flow driven by gravity in the inclined chute. The physical properties, including flow depth, solid fraction, velocity profile, angular velocity, granular temperature, coordination number, stress state, contact force orientation and fabric tensor, are evaluated. In addition, the effect of the obstacle and friction on physical properties is also examined. The particles adjacent to the side walls exhibit smaller translational velocity in the streamwise direction, but larger angular velocity and in-plane shear stresses due to boundary friction effect. This boundary friction also leads to granular dilatancy, which makes solid fraction, coordination number, normal stress and out-of-plane shear stresses decrease. The granular flow shows higher granular temperature at the place where particles fly in the air and fall onto the inclined chute again. In addition, the granular temperature near the boundary (sidewalls and bottom wall) and at the free surface is larger than that in the central part. Due to the obstacle, the granular jamming forms and results in an increase of coordination number, normal and shear stresses. The contact force orientation become more streamwise as a result of granular deposit, but scatters when the particles fly in the air. After the particles fall onto the inclined chute again, the contact force orientation becomes steeper.
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