下送风空调温度分层流动稳定性与人员移动等动态扰动的影响机理研究

Floor-level air supply system generally has a higher ventilation efficiency than mixing ventilation. Indoor temperature stratification is the key to ensure its promising performance. However, our field measurements show that frequent movement of office workers can greatly weaken the vertical temperature difference to be less than 0.5℃. This project focuses on the long-neglected influence of dynamic disturbances on the thermal stratification, and investigates the negative effects of two typical disturbances indoors, i.e. the dynamic heat gain of the external envelopes and occupant movement. Firstly, the variation of the thermal plume attached to the internal wall of the perimeter envelope with the fluctuation of a whole day's cooling load will be analyzed. Then the method of high-speed camera measurement and large eddy simulation based on dynamic mesh will be adopted to illustrate the interaction between the thermal plume around a moving body and the wake vortex, to reveal its effect on the macroscopic flow field and pollutant transmission in the scale of the room. Thirdly, learning from the achievements in the field of atmosphere and oceanography, the fundamental research on the stability, destruction and recovery mechanism of stratified flow in indoor environment will be promoted, including deriving the dimensionless criterion numbers for perturbation and stability evaluation, clarifying the characteristic time scales of the stratified flow, the fluctuating wall boundary conditions, and the disturbance of occupant movement. Finally, based on theoretical analysis and data fitting, the correlation between thermal stratification gradient and dynamic disturbances will be obtained for easy-to-use engineering application. The results will provide a basis for the anti-disturbance design and reasonable assessment of the stratified air distribution systems.

下送风气流组织的通风效率优于混合通风，室内温度分层是保证其性能的关键。但实测表明办公人员的频繁走动可致人员活动区垂直温差小于0.5℃。本课题瞄准长期被忽视的动态扰动对热分层的影响，研究外围护结构得热逐时变化和人员移动两类典型的扰动对室内垂直温度梯度的削弱作用。首先分析外围护结构室内侧热羽随全天冷负荷波动的变化；再采用高速摄像机测量和动网格大涡模拟的方法，阐明热分层背景环境中移动人员周围热羽流与尾涡的相互作用机制以及该作用对房间尺度宏观流场与污染物传输的影响；再借鉴大气、海洋学科的成果，深化室内环境领域中热分层流动的稳定性、破坏机理和恢复机制的基础研究，推导扰动量和稳定性判别的无量纲准则数，理清流场得热边界条件变化和人员水平动量扰动的特征时间与稳定分层流的惯性时间；最后基于理论分析和数据拟合确定易于工程应用的热分层梯度与扰动量的准则数关联式。研究结果将为分层空调的抗扰设计和合理评估提供依据。

存在温度分层的置换通风系统相比于全混通风效率更高、空气品质和热舒适水平更好。然而室内有多种动态扰动因素会弱化基于静态设计的置换通风的温度分层效果、减小温度梯度，使得热分层带来的诸多优势不再存在。这与置换通风系统的设计和应用初衷不符。本项目针对围护结构热负荷变化、门的开关、人员的移动等动态因素对室内温度分层扰动的科学问题开展了理论、实验和模拟研究。.首先，对外围护结构传热负荷增加时变风量与定风量通风系统的表现进行数值模拟。结果表明，当围护结构热负荷变化时使用定风量系统不仅不能有效地维持温度分层，反而会大大弱化室内温度分层。其次，通过CFD微观模拟研究了门的开关过程对室内流场与温度场的影响。研究发现温度分层主要受到室内外空气温差与门的旋转速度两个因素的影响。此外，搭建了用于研究温度分层变化特性的环境舱进行正交实验，进一步使用数值模拟的方法重点分析了多因素共同作用时室内温度分层的变化规律，并建立了以Ri数为特征参数的稳定性判据。结果表明，人员移动速度是影响温度分层的首要因素，温度分层被削弱程度与Ri数呈显著线性关系。而温度分层的恢复则与其被弱化的程度相关。最后，研究借助理论分析获得人员移动时室内温度分层的预测模型。对于公式中未知的垂直卷吸空气量，利用模拟的方法建立起Ri数与垂直卷吸空气量的关系式。并根据文献调研结果进一步优化了预测模型。优化后的模型计算量有了明显降低。将两个模型与既有文献结果进行了对比验证，吻合良好。.已发表或接收标注本基金项目的SCI/EI论文7篇，其中项目负责人为第一或通讯作者的SCI论文6篇，包括《Building and Environment》(IF=7.093)、《Energy and Buildings》 (IF=7.201)等，另有3篇正准备投稿。参加ISHVAC、Roomvent、Indoor Air、COBEE、全国通风年会等共9次会议，共进行10次学术报告。