Instability and Transition in Transient Vertical Buoyancy Driven Flows

过去对中等加热的瞬态驱动流的研究 条件已经阐明了流体流动和传热 保持层流的瞬态流的响应。 其他和 最近的实验表明， 导致许多不同类型的下游瞬态 运输制度，这取决于所施加的加热速率。 在 发展中的下游反应，一个和两个 维瞬态不稳定性和过渡被发现， 起来。 测量还表明， 局部产生运输效应。 的常规方法 瞬态不稳定性分析仅限于近似 这在这些制度中的一些制度中是不合适的。 研究 这里提出的包括两个并行的组件。 一是 瞬态层流对加热条件的响应。 第二种是下游处理，通过开发流程 小的强加的和随机的速度扰动。 他们将 在特定的时间，在下游位置， 在感兴趣的特定局部流态内。 他们的 进化将在时间上或下游进行， 适当 随后的诊断将导致 扰动增长率和谱分布。 的 主要结果将是扰动增长的数值模型 和行为分析来理解这种现象。 浮力驱动的瞬变流出现在许多重要的 应用. 这种流动是由瞬态加热驱动的， 静止流体中的垂直边界面。 这些 在许多环境和 技术流程。 他们可能会从改变 表面的辐射加热。 这些也是固有的， 批处理操作，在启动和关闭 设备. 它们在大范围的电气瞬变中很常见， 高密度电子阵列。 它们也非常重要 在评估内部加热元件的冷却后， 电源或泵故障。 这项研究旨在了解 瞬态加热时的传热和流动 不稳定的流动和过渡。

Past studies of transient-driven flows for moderate heating conditions have clarified the fluid flow and heat transfer responses in transient flows which remain laminar. Other and more recent experiments have shown that more vigorous heating results in many different kinds of downstream transient transport regimes, depending on the imposed heating rate. In the developing downstream response, both one and two dimensional transient instability and transition were found to arise. Measurements also show that very large transient transport effects arise locally. Conventional methods of transient instability analysis are limited to approximations which are not suitable in some of these regimes. The study proposed here includes two parallel components. The first is the transient laminar flow response to the heating condition. The second is the downstream treatment by the developing flow of small imposed and random velocity disturbances. They will be introduced, at specific times, at a downstream location inside the particular local flow regime of interest. Their evolution will be followed in time or downstream, as appropriate. The subsequent diagnostics will be of resulting disturbance growth rates and spectral distributions. The central result will be a numerical model of disturbance growth and behavior analysis to understand this phenomena. Buoyancy driven transient flows arise in many important applications. Such flows are driven by transient heating at a vertical bounding surface in a quiescent body of fluid. These kinds of transients arise in many environmental and technological processes. They may follow from changing radiative heating of a surface. The are also inherent in batch processing operations, in the start up and shutdown of equipment. They are common in electrical transients in large high density electronic arrays. They are also very important in assessing the cooling of internally heated elements after a power or pump failure. This research seeks to understand the heat transfer and flow when transient heating leads to unstable flows and to transition.