The Smart Cube: a national calibration standard for urban canopy flows

城市空气质量已被认为是一个迫切需要关注的问题。影响城市空气质量的主要因素之一是建筑物之间的空气流动：这可能会影响车辆尾气和其他污染物如何从街道（以及建筑物的新鲜空气入口）被带走，以及建筑物内热的、停滞的空气如何以最小的能量输入被外部凉爽的、新鲜的空气所取代，最终对公众健康产生影响。城市的存在也会影响风、温度和当地的天气模式。研究建筑物周围的风的一个主要问题是涉及到广泛的空间尺度：为了得到准确的结果，你通常需要能够跟踪甜瓜大小的空气袋。那么，在整个城市街区，瓜太多了：我们最快、最强大的计算机仍然无法管理足够大的城市区域（比如一个社区）。因此，研究建筑物间风的最佳方法是在风洞中。这就带来了一个不同的问题：城市上空的风远非均匀的。它已经受到逆风地形的影响，对温度和速度产生了复杂而微妙的影响。我们可以在大气风洞（如萨里的EnFlo）中模拟这些上游条件，但它永远不可能是完美的。因此，每个风洞都会略有不同，而这些差异对测量结果的影响可能很大。这里的目标是制造一个通用的模型建筑，可以安装在任何风洞中，携带一套复杂的压力，空速和温度传感器。同样的仪器可以在不同的风洞中使用，以确保它们固有的缺陷不会影响研究结果。因为同样的仪器可以在不同的设施中使用，我们可以肯定地知道，任何结果的差异都是由于风洞，而不是测量方法的不同。此外，一旦已知风洞产生了合理的结果，该仪器就可以用来为科学家返回极有价值的数据。压力测量是至关重要的，不仅因为它告诉我们通风系统的工作效果如何，还因为它告诉我们风是如何在建筑物周围循环的，而不需要任何其他可能干扰气流的测量工具。相比之下，大多数常见的电流实践需要的探针可能会干扰测量。最重要的量之一——风对地球施加的阻力，用来近似计算城市对大气的影响——也可以从压力中得到。目前，我们无法在同一时间获得足够的压力测量值，以使其准确：压力传感器通常太贵了。由于温度也会对风在建筑物周围的移动产生强烈影响（即热空气上升），我们将安装加热器并使用多个传感器监测温度。一旦完成，我们将获得模型建筑周围的压力和气流的详细测量集。这将在测试期间用作基准，以确保使用该模型的每个人都得到相同的结果：如果不是，这就提供了明确的证据，表明出了问题。该仪器将成为宝贵的NCAS-AMF资源；它将提供给全国各地的研究实验室使用，要么确保他们的风洞产生接近城市的风的良好近似值，要么能够在城市流动实验中收集数据，否则这些数据是无法获得的。这些测量还可以精确到典型窗户或通风入口的大小，从而可以模拟外部风对室内空气质量的影响（这是一个对公共卫生非常重要的新兴领域）。

Air quality in cities has been recognised to be a matter of urgent concern. One of the major factors driving urban air quality is the flow of air between buildings: this can affect how vehicle exhaust and other pollutants are carried away from street level (and building fresh air intakes), how hot, stagnant air within buildings can be replaced with cool, fresh air from outside with minimal energy input, ultimately with repercussions for public health. The presence of cities also affects wind, temperatures and local weather patterns. A major problem in studying the wind around buildings is the wide range of spatial scales involved: to get accurate results, you typically need to be able to track pockets of air the size of melons. Over an entire city block, then, there are just too many melons: our fastest and most powerful computers are still not able to manage this for a large enough city area (like a neighborhood). The best way to study the wind between buildings, then, is in a wind tunnel. This poses a different problem: the wind that flows over a city is far from uniform. It has already been affected by the terrain upwind, with a complicated and nuanced impact on temperature and speed. We can simulate these upstream conditions in an atmospheric wind tunnel (such as EnFlo at Surrey), but it can never be perfect. Each wind tunnel will, therefore, be slightly different - and the effects of these differences on the measurements can be large. The aim here is to produce a generic model building which can be mounted into any wind tunnel, carrying a sophisticated set of pressure, airspeed and temperature sensors. The same instrument could then be used in different wind tunnels to make sure that their inherent imperfections are not affecting the results of the research. Because the same instrument can be used in different facilities, we will know for certain that that any differences in the results are due to the wind tunnel, and not to the way in which the measurements were done.Also, once the wind tunnel is known to be producing reasonable results, the instrument can be used to return extremely valuable data for scientists. Pressure measurements are critical, not only because these tell us how well ventilation systems will work, but also because these inform us about how wind is circulating around the buildings without the need of any other measurement tools which may interfere with the flow. By comparison, most common current practices need probes which can interfere with the measurements by their very presence. One of the most important quantities - the drag exerted by the wind on the Earth, used to approximate the effect of the city on the atmosphere - can be obtained from the pressure as well. Currently, we cannot acquire enough pressure measurements at a time for this to be accurate: the pressure sensors have usually been just too expensive. Since temperature also can have a strong effect on how wind moves around buildings (i.e warm air rises), we will install heaters and monitor temperature with multiple sensors as well. Once complete, we will obtain a detailed set of measurements of pressure and air flow around the model building. This will be used as a benchmark during tests, to make sure that everyone using the model is getting the same results: if not, this provides clear evidence that something is wrong. This instrument will become a valuable NCAS-AMF resource; it will be made available for use at research laboratories around the country, either to ensure that their wind tunnels are producing a good approximation of the wind approaching a city or to be able to collect data during city-flow experiments that would otherwise not have been available. The measurements may also be resolved down to the size of typical windows or ventilation intakes, allowing the effects of exterior wind on interior air quality to be modelled (an emerging area of great importance to public health).