钝体分离旋涡流动的区域分解、杂交数值模拟——Ⅰ.理论方法及其应用

为克服涡旋法不能精确预计物体附近小尺度流动结构的理论缺陷,减少高Reynolds数流动N-S方程差分解的困难,本文提出一种区域分解、杂交耦合N-S方程有限差分解及涡旋法的新的数值模型和理论方法.将流场分解为内外两区,在靠近物体表面、范围为O(R)的内区进行N-S方程有限差分解,外区作Lagrange-Euler涡旋法解,建立了分区流动的联结、耦合条件,给出了杂交耦合求解的数值计算方法.用本方法作了Re=10~2,10~3的圆柱绕流计算,考察了区域交界面位置变化时解的稳定性.与全场N-S方程解及实验结果的比较表明本文方法能精确预计流动分离及近场流动的详细结构,并可有效地计算流动的总体特性,且比全场N-S方程解显著节省机时和计算量

Domain decomposition hybrid method for numerical simulation of bluff body flows:theoretical model and application

The discrete vortex method is not capable of precisely predicting the bluff body flow separation and the fine structure of flow field in the vicinity of the body surface. In order to make a theoretical improvement over the method and to reduce the difficulty in finite-difference solution of N-S equations at high Reynolds number, in the present paper, we suggest a new numerical simulation model and a theoretical method for domain decomposition hybrid combination of finite-difference method and vortex method. Specifically, the full flow. field is decomposed into two domains. In the region of O(R) near the body surface (R is the characteristic dimension of body), we use the finite-difference method to solve the N-S equations and in the exterior domain, we take the Lagrange-Euler vortex method. The connection and coupling conditions for flow in the two domains are established. The specific numerical scheme of this theoretical model is given. As a preliminary application, some numerical simulations for flows at Re=100 and Re-1000 about a circular cylinder are made, and compared with the finite-difference solution of N-S equations for full flow field and experimental results, and the stability of the solution against the change of the interface between the two domains is examined. The results show that the method of the present paper has the advantage of finite-difference solution for N-S equations in precisely predicting the fine structure of flow field, as well as the advantage of vortex method in efficiently computing the global characteristics of the separated flow. It saves computer time and reduces the amount of computation, as compared with pure N-S equation solution. The present method can be used for numerical simulation of bluff body flow at high Reynolds number and would exhibit even greater merit in that case

中国北方森林和草地生态系统碳氮耦合循环与碳源汇效应研究

全球变化自20世纪80年代以来作为一个科学问题开始出现,现今已超越科学领域,成为影响当今世界发展的重大政治、经济和外交问题。在科技部的"十三五"期间"全球变化及应对"重点研发计划专项支持下,来自中国科学院沈阳应用生态研究所、西北农林科技大学、中国科学院植物研究所等6个单位31位科学家于2016年7月开始承担"中国北方森林和草地生态系统碳氮耦合循环与碳源汇效应研究"项目。该项目旨在:1)凸显中国北方植物群落演替在温室气体吸收和排放平衡,特别是在我国未来碳汇中的作用;2)绘制森林和草地碳源汇转变的敏感区、脆弱区;3)建立和发展稳定同位素技术研究碳氮循环的多时间序列历史变化及其对全球氮沉降、大气CO_2浓度上升和气候变化的响应;4)揭示氮沉降、升温、火干扰和植被演替驱动的碳氮耦合循环生物学机制及其碳源汇响应。通过该项目5年的实施,预期能增加我国北方森林和草地生态系统碳氮耦合循环生物学机制的认识,增强对北方森林和草地生态系统对全球变化响应的预测能力和减少预测的不确定性