Exchange Flows

研究的主要目的是提高我们对现代建筑自然通风的理解和预测能力。具体而言，重点将放在“交换”流动上。该术语涵盖了当穿过给定通风开口同时存在从外部进入房间的气流和从房间到外部的气流时的一系列不同情况。例如，当温暖的房间中有一个单独的高层通风口时，交换流就会发生-例如，通过窗扇开口或定制通风口。虽然对这一特殊情况作了简化描述，但如果有多个高位喷口（无论是水平的还是垂直的），情况就复杂得多。例如，对于两个水平通风口，在切换到气流从一个通风口进入并从另一个通风口流出的模式之前，气流可能会在两个通风口之间交换一段时间，然后又恢复到交换气流，等等。挑战之一是要理解不同气流模式之间的这种循环，包括对低能耗通风设计的影响。许多其他方面的交换流量将被检查，包括通风口的方向上的交换率的影响，循环行为和内部温度分布。此外，一个额外的重点将是“不平衡”的交换流量，即那些发生时，除了上通风口，下通风口打开。研究这些流动所采用的方法将是小规模物理模拟和补充理论模拟。

The primary aim of the research is to enhance our understanding and predictive capability of the natural ventilation of modern buildings. Specifically, the focus will be on 'exchange' flows. This terminology encompasses a spectrum of different situations when across a given ventilation opening there is simultaneously a flow into the room from the exterior and a flow out of the room to the exterior. Exchange flow occurs when there is, for example, a single high-level vent in a warm room - for example, via a sash window opening or bespoke vent. Whilst simplified descriptions of this particular situation have been developed, the picture is considerably more complex when there are multiple high-level vents (whether horizontal or vertically oriented). For example, with two horizontal vents the flow may exchange through both vents for a period before switching to a mode in which the flow is in through one vent and out through the other -- and then reverting back to exchange flow and so on. One of the challenges will be to develop an understanding of this cycling between different modes of flow, including the implications for low-energy ventilation design. Numerous other aspects of exchange flows will be examined, including the influence of vent orientation on the rate of exchange, on the cyclic behaviour and internal temperature distribution. Moreover, an additional key focus will be on 'unbalanced' exchange flows, namely, those which occur when, in addition to the upper vent, a lower vent is opened. The approach adopted to study these flows will be small-scale physical modelling and complementary theoretical modelling.