颗粒-流体两相流拟点源模型及耗散尺度颗粒与流体相互作用机理研究

Two-phase turbulence laden with dissipation-scale particles is widely seen in various industrial applications. Thus，there are significant meanings to study the interphase interaction mechanisms between the dissipation-scale particle and fluid. In order to make up the absence of numerical models and systematic experimental results, both numerical simulation and experiment methods are employed to investigate the interaction between dissipation-scale particle and fluid in the present project. Firstly, the reaction of particle is represented by coupling the disturbance flow of particle with the continuous flow. Based on this assumption, the pseudo point source model will be developed. This model is a bridge between the point source model and the particle-resolved model. In addition, high precision speed interpolation and coupling algorithm based on the virtual grid refinement method will be developed in order to obtain accurate two phase interaction when the grid resolution is not high enough. The direct numerical simulation program will be established based on the pseudo point source model and high precision speed interpolation and coupling algorithm. Then it will be qualitatively verified by PIV experiment data. Hereafter, a series of direct numerical simulations and PIV experiments on isotropic turbulence laden with dissipation-scale particles will be carried out. In the simulation, the interphase interaction is calculated by the pseudo point source model and high precision speed interpolation and coupling algorithm. The particle dispersion law and turbulence modulation under different turbulence conditions and particle parameters will be studied. This study will be helpful to improve the direct numerical simulation method system of particle-laden turbulence. It is expected to provide part of foundation for the high precision industrial grade simulation of two phase turbulence in the future.

载有耗散尺度颗粒的颗粒-流体两相湍流是工业领域中常见的流动形式，研究该尺度颗粒与流体之间的相互作用具有重要意义。针对目前缺乏耗散尺度颗粒与流体间相互作用的数值模型和系统性实验数据的现状，本项目采用数值模拟和实验相结合的方法对耗散尺度颗粒与流体间相互作用展开研究。首先通过在流场中耦合颗粒扰流场的方式来反映颗粒对流体的反作用，开发介于点源模型和全尺度模型之间的拟点源模型；针对网格不够细密时颗粒受力和反作用计算精度低的问题，采用局部加密虚拟网格的方法开发高精度的速度插值及耦合算法；基于所开发的模型和算法构建两相湍流的直接数值模拟方案并通过PIV实验进行验证。在此基础上，对载有耗散尺度颗粒的各向同性湍流进行系列化地直接数值模拟和PIV实验研究，揭示不同湍流状态和颗粒参数下的颗粒弥散和湍流调制规律。本课题有助于完善颗粒-流体两相湍流的直接数值模拟方法体系，为后续两相湍流的较高精度工业级模拟提供基础。

载有耗散尺度颗粒的颗粒-流体两相湍流广泛存在于能源动力、化工和环保等工业领域中，研究该尺度颗粒与流体之间的相互作用并开发相应的数学模型具有重要意义。本项目采用理论分析、数值模拟和实验相结合的方法展开研究。采用耦合颗粒速度扰动的方式来反映颗粒对流体的反作用，开发了考虑颗粒尺度效应的拟点源模型，通过泊肃叶流中单颗粒绕流和自由沉降的数值模拟验证了该模型。与传统点源模型相比，该模型能模拟比网格尺度更大的颗粒与流体间的相互作用；明确了颗粒位置处流体速度计算方法对颗粒反作用模型性能的影响，发现消除颗粒自身引起的扰动能更合理地计算颗粒对流体的反作用，而拟点源模型避开了计算颗粒位置处无扰动流体速度的难点；基于拟点源模型进行了系列化直接数值模拟，研究了不同颗粒参数对湍流脉动强度和湍动能输运过程的影响；基于频率分析法提出了预估颗粒所受Basset力相对大小的先验关系式，引入特征频率的概念并用比拟法对其进行估算，预测的Basset力相对重要性与高精度数值模拟统计值吻合良好；建立了水平振荡格栅各向同性湍流实验台，采用粒子图像测试技术研究了格栅间距，行程和振荡频率对各向同性比、湍动能、湍流耗散率、湍流耗散尺度和湍动能谱的影响。本项目所开发的基于速度扰动耦合的拟点源模型是传统点源模型和颗粒解析全尺度模型之间的补充，所提出的预估颗粒所受Basset力相对重要性的先验关系式能为后续数值模拟中颗粒受力模型的选择提供指导。本项目相关成果有助于完善颗粒-流体两相湍流的直接数值模拟方法体系。