Reconciling wind tunnel data with real performance: influence of freestream turbulence intensity and large-scale unsteadiness

我们目前无法使测试数据与陆地、海上和空中飞行器的实际性能相一致，特别是在它们在现实世界中经常遇到的不稳定条件下，这是改进大型平台能源效率设计的主要障碍。许多形式的交通工具都面临着不稳定或动荡的场景，如果不了解这对车辆的影响，就没有办法自信地改进车辆的设计和效率。在CFD工具开发之前，有关车辆性能及其流场的模型试验数据几乎都是在风洞(或水洞)中采集的，采用各种技术方法获取物理测量数据。通常，这些流动设施包括精心设计的流动调节装置，以确保车辆模型处于稳定的均匀流动条件下，并故意保持较低的自由流动湍流(FST)强度。然后，可以使用被动网格或主动网格或两者的组合来故意增加这些FST水平。由强度和长度尺度(例如，积分、泰勒、柯尔莫戈洛夫)定义的FST对边界层流动，特别是向湍流的转变所起的作用仍然没有完全了解。例如，即使在流经光滑平板的最简单情况下，FST强度和积分长度尺度对边界层转变的直接作用直到最近才被表征。除了这一典型情况外，FST的作用，以及一般情况下的流入不稳定，对应用的空气动力和流体动力应用还需要进一步的研究。随着添加剂制造的快速增长和发展，研究界现在有能力快速创建原型，从而快速测试各种复杂几何形状的流动调节设备，远远超过简单的屏幕和网格。这可以在风洞内以比传统制造技术更低的成本和更快的速度创造条件，无论是稳定的还是不稳定的。该项目利用了先前存在的物理基础设施，以及为所研究问题的具体情况而设计的新设备。该项目将促进风洞流动调节装置的设计、建造和测试，特别是在能够诱导一定水平的剪切流动的同时，提高湍流强度。这将导致在代表陆地、海上和空中车辆的测试模型上对各种钝体车辆进行“极端”测试。这些数据随后将作为计算流体动力学(CFD)验证案例，并将使洞察力增加，从而改进经验模型和改进平台设计。该项目的初始前提是使用简化的钝体模型，如Ahmed Body，对其进行高保真的流动和性能测量。一旦进行了测试，该项目将转向更复杂的几何形状。

Our current inability to reconcile test data with actual performance of land, sea, and air vehicles, especially under the unsteady conditions which they often encounter in the real world represents a major barrier in improving designs for the energy efficiency of large platforms. Many forms of transportation vehicles face unsteady or turbulent scenarios and without the understanding of what effects this has on the vehicle, there is no way of confidently improving the vehicles design and its efficiency. Prior to the development of CFD tools, model test data pertaining to vehicle performance and their flow fields was almost always acquired in wind-tunnels (or water-tunnels) with various technical methods used to acquire physical measurements. Typically, these flow facilities incorporated carefully designed flow conditioning devices to ensure that the vehicle model was subjected to steady uniform flow conditions with a purposely low free-stream turbulence (FST) intensity. These FST levels can then be deliberately increased using passive or active grids or a combination of the two.The role that FST, defined by both intensity and length scales (e.g. integral, Taylor, Kolmogorov), plays on boundary layer flows, particularly transition-to-turbulence, is still not fully understood. For example, even in the simplest case of flow over a smooth flat plate, the role that the FST intensity and integral length scale directly plays on boundary layer transitions has only recently been characterised. Beyond this canonical case, the role of FST and, indeed inflow unsteadiness in general on applied aero- and hydrodynamic applications requires further investigation. With the rapid growth and development of additive manufacturing, the research community now has at its disposal the ability to rapidly create prototypes and therefore rapidly test different flow conditioning devices with various intricate geometries far being simple screens and grids. This can create conditions, whether steady or unsteady, within a wind tunnel at lower cost and more rapidly than with conventional fabrication technologies.This project leverages pre-existing physical infrastructure in addition to new equipment designed for the specifics of the problems researched. The project will facilitate the design, build and test of a wind-tunnel flow conditioning device, specifically to elevate the turbulence intensity in addition to being able to induce a level of shear flow. This will lead to 'extreme' testing of various bluff-body vehicles on test models representative of land, sea and air vehicles. This data will then serve as computational fluid dynamics (CFD) validation cases and will allow insight gains leading to improved empirical models and improved platform designs. The initial premise of this project is to use a simplistic bluff body model such as the Ahmed body to conduct high-fidelity flow and performance measurements on. Once this testing has been conducted the project will move onto more complex geometries.