A new model heating capability and study of wall temperature effects in hypersonic boundary layer transitio

想象一下，从英国到澳大利亚只用不到5个小时。或者想象一下，乘坐商业太空飞机往返太空酒店的价格与现在乘坐行政舱的价格相同。在引领人类踏上月球的技术奇迹半个多世纪之后，这两个概念似乎仍然离现实有些遥远。然而，如果要发展可持续的高超音速能力，这可能成为常态。高速、高效的交通系统使高度互联文明的愿景更加大胆，符合21世纪全球化社会的内在要求。为了使这成为现实，人们必须能够自信地模拟和预测流动行为。这是非常困难的，因为在这样的速度下，空气动力学效应与热力学和化学反应结合在一起，并且依赖于大量的参数。无论是以五倍音速在大气层巡航，还是进行行星再入，在设计飞行器时，壁温和表面粗糙度等参数都变得极其重要。这项研究的第一个目标是开发一种机制来提高测试模型的表面温度，以更好地匹配高超音速飞行条件，这是牛津热流体研究所目前所缺乏的能力。在真正的高超音速飞行中，壁面温度可以达到超过1200摄氏度的值，这在风洞中很难复制。在风洞中加热进入的气体不是一种选择，因为它通常会导致高噪音水平，而且测试时间太短，模型无法稳定地达到所需的温度。在牛津大学，过去曾使用过加热技术，但只能达到600 K，这不足以在高超音速下正确封装流场。因此，需要进行一项调查，以评估在牛津热流体研究所可用的高超音速风洞内部可以使用哪些加热技术来实现有意义的壁面温度（例如，电加热、等离子加热、激光加热等）。最终，一旦做出选择，这项研究将集中于构建、测试和验证所述系统，从台式测试开始。这对未来的高超声速研究也有很大的好处，因为关于如何加热模型的基础设施和知识将留在大学里，在这些研究中，壁温效应需要进一步研究。本研究的第二个主要目标是利用上述选定的加热技术，研究壁面温度和表面吹气对边界层转变的影响。我们的想法是了解这些效应如何耦合在一起，可以触发从层流到湍流的转变，并为这一现象提供新的相关性和方法，以促进当前的文献。这是高超音速飞行器设计的基础，因为它目前是一个具有高度不确定性的研究领域。虽然已经研究了许多影响这种转变的参数，但目前还没有文献（据研究人员所知）分析壁温和表面吹气的影响；因此，这将是对上述文学的重大贡献。这将需要设计和建立一个新的测试活动，可能是在牛津热流体研究所以前的测试活动的基础上进行的。该项目属于EPSRC流体动力学和空气动力学研究领域。

Imagine traveling from the United Kingdom to Australia in less than five hours. Or imagine a round-trip flight aboard a commercial spaceplane to a space hotel for the same price as flying executive class nowadays. More than half a century after the technological marvels that led Humankind to set foot on the Moon, both concepts still seem somewhat distant from reality. However, this can become the norm if sustainable hypersonic capabilities are to be developed. High-speed, efficient transportation systems embolden the vision of a highly interconnected civilization, attending to the requirements of an inherently globalized society for the 21st century. For this to become a reality, one must be able to confidently simulate and predict flow behaviour. This is extremely difficult since aerodynamic effects become coupled with thermodynamics and chemistry at such speeds, and are dependent on a multitude of parameters. Whether cruising the atmosphere at five times the speed of sound, or performing a planetary re-entry, when designing a vehicle, parameters such as wall temperature and surface roughness become extremely important.The first objective of this research is to develop a mechanism to increase surface temperatures of test models to better match hypersonic flight conditions, a capability that is currently lacking at the Oxford Thermofluids Institute. During real hypersonic flights, wall temperatures can reach values in excess of 1200 C, which is difficult to replicate in wind tunnels. Heating up the incoming gas in a wind tunnel is not an option since it usually leads to high noise levels, and the test times are so short the model would not be able to reach steadily reach required temperatures. At Oxford, heating techniques have been used in the past but were only able to reach 600 K, which is not enough to properly encapsulate the flow field at hypersonic speeds. As such, a survey needs to be conducted to assess what heating techniques could be used inside of the available hypersonic wind tunnels at the Oxford Thermofluids Institute to achieve meaningful wall temperatures (e.g., electrical heating, plasma heating, laser heating, etc.). Ultimately, once a choice is made, this research will focus on building, testing and validating said system, starting with benchtop tests. This will also be of great benefit for any future research in hypersonics where wall temperature effects want to be studied with further detail, since the infrastructure and knowledge on how to heat up a model will remain with the university.The second main objective of this research is to study the effect of wall temperature and surface gas blowing on boundary layer transition, using the selected heating technique mentioned above. The idea is to understand how these effects, coupled together, can trigger transition from laminar to turbulent flow, and contribute to the current literature with new correlations and methods for this phenomena. This is fundamental for hypersonic vehicle design, as it is currently a field of study with high levels of uncertainty. While many parameters that influence this transition have been studied while coupled, there is currently no literature (to the best of the researcher's knowledge) that analyses the effect of wall temperature and surface gas blowing combined; therefore this would be a significant contribution to said literature. This will require designing and building a new test campaign, possibly building up on previous test campaigns done at the Oxford Thermofluids Institute.This project falls within the EPSRC Fluid dynamics and aerodynamics research area.