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Shock/turbulence interactions in dense gases

稠密气体中的冲击/湍流相互作用

基本信息

批准号：
EP/L021676/1
负责人：
Emile Touber
金额：
$ 12.77万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FL021676%2F1
关键词：
Shock turbulence interactions dense gases

项目摘要

To reduce the UK's greenhouse-gas emissions anywhere near the legally-binding 2050 targets, a major attack on both energy wastes and unsustainable forms of electricity production is essential. Owing to their appealing thermo-physical properties (e.g. large heat capacity relatively to the molecular weight, low boiling point, elevated density), molecularly-complex and dense gases (e.g. hydrocarbons, perfluorocarbons, siloxanes) are at the heart of realistic solutions for thermal power stations to operate efficiently on low-temperature heat sources (e.g. solar, biomass, geothermal), where they are used as substitute for water steam (e.g. organic Rankine cycle). Flow expanders in such power stations partially operate in the vicinity of the thermodynamic critical point, where the speed of sound is substantially reduced, turning the expander flow into a highly supersonic gas flow, inevitably leading to the formation of shock waves.Shock waves have the detrimental property of degrading the expander efficiency by dissipating kinetic energy into heat, and by promoting viscous losses through boundary-layer separation and thickening. Quite remarkably, and contrary to ideal gases, shock waves in molecularly-complex and dense gases can be made almost isothermal, therefore relieving part of the efficiency losses imparted by the shock wave. This remarkable property is a direct consequence of the exceptionally large number of active degrees of freedom of the gas molecule. While the prospect of efficient supersonic expanders is appealing, little is known on the implication near-isentropic shocks have on the amplification of turbulence fluctuations (which are always present in turbines). In particular, shock/turbulence interactions in dense gases can lead to the emission of energetic acoustic waves, which are significantly more powerful than in standard ideal gases. If present, such acoustic forcing can erode the expected turbine efficiency, generate vibrations and cause premature blade fatigue. The proposed research will establish a robust and fundamental understanding of sound emission from shock/turbulence interactions in dense gases, and provide a new understanding of the underlying physics, which will allow the development of predictive tools that can inform future design choices.

为了将英国的温室气体排放量减少到接近具有法律约束力的2050年目标，必须大力打击能源浪费和不可持续的电力生产形式。由于其具有吸引人的热物理性能（例如，相对于分子量的大热容、低沸点、高密度）、分子复杂和致密气体（例如碳氢化合物、全氟化碳、硅氧烷）是热电站在低温热源上高效运行的现实解决方案的核心（例如太阳能、生物质、地热），其中它们用作水蒸汽的替代物（例如有机朗肯循环）。在这种发电站中的流量膨胀器部分地在热力学临界点附近操作，在该临界点处声速显著降低，将膨胀器流转变成高度超音速的气流，不可避免地导致冲击波的形成。冲击波具有通过将动能耗散成热而降低膨胀器效率的有害特性，以及通过边界层分离和增厚促进粘性损失。非常值得注意的是，与理想气体相反，分子复杂和致密气体中的激波几乎可以等温，因此减轻了激波造成的部分效率损失。这种显著的性质是气体分子的活动自由度异常大的直接结果。虽然高效超音速膨胀机的前景很吸引人，但对近等熵激波对湍流波动放大（涡轮机中总是存在湍流波动）的影响知之甚少。特别是，稠密气体中的激波/湍流相互作用可以导致高能声波的发射，其比标准理想气体中的能量大得多。如果存在的话，这种声学强迫会侵蚀预期的涡轮机效率，产生振动并导致叶片过早疲劳。拟议的研究将建立对致密气体中激波/湍流相互作用的声音发射的强大和基本的理解，并提供对基础物理的新理解，这将允许开发预测工具，为未来的设计选择提供信息。