2018-01-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/699856摘要：固體顆粒在密度分層的背景的流體中懸浮是自然環境中常見的現象，本研究將著重於在固液二相懸浮流體中，流場的不穩定現象與所引起的對流運動，藉由最新穎的顆粒追蹤法，本研究將分析顆粒分散性及群聚顆粒所引起的密度效應的影響，這與過去的相關研究的不同點在於過去的研究使用了純量濃度模式已描述懸浮顆粒的傳輸，這只對於顆粒在大約為1 微米的情況下成立，本研究將處理兩種濃度梯度分布，分別為順向及逆向濃度分布，前者為不穩定的型態並且會引起雷利-泰勒不穩定，此類流體不穩定與背景因為溫鹽所引起的密度層化的交互作用對河口地區的混合，傳輸及懸浮物沉積都有很大的影響，逆向濃度分布在沒外力的情況下是一個穩定的型態，而它的生成，演進，以及對水動力作用的反應對於探討河口，海灣等的能量消散及近底床的泥沙傳輸有很重要的關聯，本研究對於懸浮顆粒粒徑約在10 到100 微米的案例非常重要，而這樣的粒徑尺寸是自然界流體中常見的懸浮物粒徑尺寸。基於本研究詳細的探討，我們將更進一步發展基於外在參數的理論模型，並可用於改善大尺度預測工具的準確性。<br> Abstract: Suspension of solid particles in stratified fluid is a common phenomenon in natural environment. The study will focus on flow instabilities and the resulting convective motions arising from the sharp concentration gradient in solid-liquid two phase suspension flows. By using the novel particle-tracking approach, the study will examine effects of both particle discreteness and buoyancy effect in these problems. This is very different from previous studies, in which the scalar-limit model has always been applied to model transport of suspended matters, which is only valid for particles of very small sizes (O(1 μm)). The study will focus two types of problem configurations, namely positive concentration gradient and negative concentration gradient. The former case is an unstable case which can be triggered by Rayleigh-Taylor instability. Its further interactions with the background density stratification due to the temperature and salinity plays the key role in mixing, transport and sedimentation in the river mouth. The latter case is a stable case without any external forcing and its generation, evolution and response to hydrodynamic forcing are closely related to energy dissipation and near-bed sediment transport in estuaries. The present study is of critical importance for particles of sizes ranging from O(10 μm) to O(100 μm), which is a common size range for suspended sediments in natural environments. Moreover, based on the numerical findings, theoretical derivations, and experimental evidence, the study attempts to build up theoretical models that can be used in the large-scale predictive frameworks.對流沉降懸浮顆粒流體不穩定性convection sedimentationsuspended sedimenthydrodynamic instability