Unsteady wind effects on natural ventilation

不稳定风对自然通风的影响

• 批准号: EP/E040845/1
• 负责人: David Etheridge
• 金额: $ 10.35万
• 依托单位: University of Nottingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FE040845%2F1
• 关键词: Unsteady; wind; effects; natural; ventilation

In recent years natural ventilation has become increasingly accepted as a desirable alternative to mechanical ventilation in non-domestic buildings. This stems not only from the potential for reduced costs (capital and maintenance), but also from environmental benefits (reduced CO2 emissions; reduced incidence of sick building syndrome). This trend has been accompanied by gradual improvements in design procedures, yet in some areas the procedures are still somewhat lacking. One such area is addressed by this proposal, namely the effects of the unsteady wind. The presence of wind leads to unsteadiness in the velocity and pressure fields around openings. Previous research has shown that this can have two major effects on the flow characteristics of ventilation openings. One effect is the reduction in the discharge coefficient of an opening. The discharge coefficient is a measure of the ability of the opening to pass flow and is a major factor in design calculations. Current design procedures make use of coefficients obtained under still-air conditions. For at least one type of opening the presence of wind has been observed to reduce the coefficient by a factor of two or more, whereas for another type the effect is negligible. The current understanding is that the effect depends primarily on the shape of the opening, the direction of flow through the opening and on the external velocity field around the opening. If this is correct it should be possible to take account of the effect in design procedures, basically by applying the basic concept of dimensional analysis. One aim of the research therefore is to carry out wind tunnel tests over a wide range of variables and to apply dimensional analysis to express the results in a concise and simple form for inclusion in design procedures. The second important wind effect is flow reversal in ventilation stacks (chimneys). Stacks are increasingly being used in non-domestic buildings, because in principle they allow the designer to fix the flow pattern of air entry and exit under all weather conditions. When flow reversal occurs the basic design is compromised, so it is desirable to design the stack/building configuration such that flow reversal is avoided. There has been very little work done in this area, but previous research by the applicant has identified a relatively simple parameter (based on wind pressures) that can be used to determine whether or not flow reversal will occur. Another aim of the research is to see whether this can be applied to more realistic configurations. The bases for the proposed research are (a) an experimental technique and (b) a theoretical model, both of which were developed by the applicant under previous EPSRC contracts. The experimental technique is particularly interesting, since it allows the instantaneous flow in a stack to be measured and this has not been possible before. The technique has attracted international interest and has been used by three overseas Universities (Japan, Sweden and Brazil). The theoretical model is important since it allows tests to be made that are not possible in a wind tunnel. The wind tunnel can however be used to assess the theoretical model and this is the third aim of the research. The present proposal will allow the collaboration with Tokyo Polytechnic University to continue. This will be of overall benefit, because although their objectives are similar, they have concentrated on large openings for summer ventilation, which requires a different theoretical approach. The work at Nottingham University is concerned with smaller openings, for which the theoretical model was specifically developed.

近年来，自然通风越来越被认为是非住宅建筑中机械通风的理想替代方案。这不仅源于降低成本（资本和维护）的潜力，还源于环境效益（减少二氧化碳排放；减少病态建筑综合症的发生率）。这一趋势伴随着设计程序的逐步改进，但在某些领域，程序仍然有些欠缺。该提案解决了其中一个领域，即不稳定风的影响。风的存在会导致开口周围的速度和压力场不稳定。先前的研究表明，这会对通风口的流动特性产生两个主要影响。一种影响是开口的流量系数降低。流量系数是开口通过流量能力的量度，是设计计算中的主要因素。当前的设计程序利用在静止空气条件下获得的系数。对于至少一种类型的开口，已观察到风的存在使系数降低两倍或更多，而对于另一种类型，这种影响可以忽略不计。目前的理解是，该效果主要取决于开口的形状、通过开口的流动方向以及开口周围的外部速度场。如果这是正确的，那么基本上可以通过应用尺寸分析的基本概念来考虑设计程序中的效果。因此，该研究的目的之一是对各种变量进行风洞测试，并应用尺寸分析以简洁明了的形式表达结果，以便纳入设计程序。第二个重要的风效应是通风烟囱（烟囱）中的流动逆转。烟囱越来越多地用于非住宅建筑，因为原则上它们允许设计者在所有天气条件下固定空气入口和出口的流动模式。当发生逆流时，基本设计就会受到影响，因此需要设计烟囱/建筑结构以避免逆流。 There has been very little work done in this area, but previous research by the applicant has identified a relatively simple parameter (based on wind pressures) that can be used to determine whether or not flow reversal will occur.该研究的另一个目的是看看这是否可以应用于更现实的配置。拟议研究的基础是（a）实验技术和（b）理论模型，这两者都是申请人根据之前的 EPSRC 合同开发的。该实验技术特别有趣，因为它可以测量烟囱中的瞬时流量，而这在以前是不可能的。该技术引起了国际关注，并已被三所海外大学（日本、瑞典和巴西）使用。理论模型很重要，因为它可以进行风洞中无法进行的测试。然而，风洞可用于评估理论模型，这是研究的第三个目标。目前的提案将使与东京工业大学的合作得以继续。这将具有整体效益，因为尽管他们的目标相似，但他们都集中在夏季通风的大开口上，这需要不同的理论方法。诺丁汉大学的工作涉及较小的开口，为此专门开发了理论模型。