基于边界层流动特性的音速喷嘴测量机理研究

Sonic nozzles have been widely used as flowmeters and transfer standards for natural gas and hydrogen. To meet the ‘energy-saving’ and ‘emission-reduction’ requirement, sonic nozzle ought to have high measurement accuracy in wider range of Reynolds number. In this project, centering on ‘viscous boundary layer’, the physical mechanisms of the interactions between the key factors and boundary layer under different conditions (high and low Reynolds numbers, condensation) are investigated, and the evolution of boundary layer and flow-rate characteristic of sonic nozzle are discussed in detail. A general expression of discharge coefficient of sonic nozzle is proposed. Firstly, to study the effect of surface roughness on the boundary layer, both CFD transition model and the nozzle sensors with adjustable roughness are built. HWA and PIV are utilized to measurement the velocity field and analyze roughness effects on transition. Combing the pVTt-based flow-rate experiments, the flow-rate of rough sonic nozzle can be determined. Secondly, the CFD laminar model and relevant measurement sensors are built. The fluid-solid coupling ‘thermal effect’ and non-equilibrium ‘vibrational relaxation effect’ are studied in detail. The relationships among these two phenomena and boundary layer are obtained. Thirdly, a two-phase turbulent model and an experimental platform for homogeneous/heterogeneous condensing flow are established. The effects of the condensing ‘thermal chocking’ and ‘unsteady flow’ self-excited oscillation phenomena on the flow field and boundary layer are obtained. The multi-parameter correction methods for the condensing flow of sonic nozzle are proposed. Finally, taking everything together, a general flow-rate formula is determined. The results of this project provide the basis for the accuracy measurement and reliable standard transfer of sonic nozzle.

音速喷嘴是天然气和氢气等清洁能源流量的计量元件和传递标准，节能减排的大趋势要求其在更宽的雷诺数范围内保持高精度。本项目将围绕“粘性边界层”这条主线，分析不同条件下(高雷诺数、低雷诺数和凝结条件)关键因素与边界层的作用机理及演化规律，并提出多参数的流出系数通用关系式。首先建立转捩模型及粗糙度可调的喷嘴传感器，利用HWA和PIV等测速仪分析粗糙度对转捩过程的影响，结合pVTt法实验获得流量变化规律。其次，建立层流模型和相应的测量传感器，研究小口径喷嘴流固耦合“热效应”和非平衡“振动弛豫效应”及其与边界层作用机理。然后，建立凝结流动两相湍流模型和凝结研究实验平台，分析凝结“热阻塞”和“非稳态”自激振荡现象与边界层的作用规律，并提出多参数的凝结校正方法。最后，综合各因素对边界层影响，提炼通用流量公式，为音速喷嘴精确计量和可靠传递提供依据。

本项目以满足ISO 9300标准结构及加工精度的音速喷嘴为研究对象，为解决“边界层转捩机理和湍流特性”问题，研究了宏观轮廓以及微观粗糙度对边界层发展与转捩特性的影响，获得了高雷诺数下粗糙度对边界层发展和转捩的作用机制。针对热效应传热过程，建立了管壁动态温度分布采集系统，并利用克里金插值算法获得了管壁动态温度分布图。建立了SST k-w流固耦合传热模型，讨论了流体在喷嘴内的激波分离形式、准则和管壁温度分布的不对称性，并发现喷嘴壁面最低温度点位于分离点附近。推导获得了考虑壁面传热的热边界层相似解，并建立了喷嘴固体内部结构约束膨胀的热应力与热应变有限元模型，分析了“热效应”过程中的热边界层和热应力/位移特性。以上结果有助于气固两相流的标定实验与颗粒流动分析。为解决“两相凝结现象与粘性边界层作用机制”问题，针对含湿气体两相“凝结”现象，将“亚稳态凝结与边界层的相互作用”作为研究核心，获取两相凝结流动参数，尤其是边界层分布规律。建立了含湿气体凝结流动的Eulerian两相凝结模型，并讨论跨音速凝结流动的不稳定性，确定了非稳态振荡的形成条件。通过研究不同自激振荡模式喷嘴喉部边界层位移厚度的变化，从边界层的角度分析凝结现象中不同自激振荡模式的质量流量特性。采用Young经典成核率和水滴生长率方程以及Clausius-Clapeyron相平衡方程推导获得了高压条件下凝结音速喷嘴非平衡自发凝结Wilson点解析模型，为凝结实验提供了理论依据。建立了高精度可调温湿度凝结实验平台和测量传感器阵列，研究了凝结自激振荡稳态和非稳态特性，为实现高精度流量测量奠定良好基础。

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