水动力作用对污染物在河流水沙两相中分配的影响研究进展

通过总结近年来有关水动力作用对河流中泥沙吸附/释放重金属、磷等污染物影响研究成果,分析了水流紊动强度和流速对污染物在河流水沙两相中分配的影响规律。当水流紊动强度较低时,泥沙主要以床沙形式存在,泥沙对污染物的吸附/释放速率和强度较低;随着紊动强度增大,水沙界面切应力随之增大并促使泥沙悬浮,污染物与悬浮泥沙颗粒接触面积增大,使得泥沙对污染物的吸附/释放速率和强度显著增加。流速对污染物在水沙两相间分配的影响较为复杂。泥沙静止时,流速的增大会减小边界层厚度,增大水体溶解氧含量、氧化还原电位等参数,并使污染物在水体里的扩散由分子扩散转变为以紊动扩散为主,增强污染物在水-沙界面的交换通量,对污染物在水沙两相间的分配产生影响;随着流速进一步增大,床沙逐渐起动、悬浮,此时除上述因素外,泥沙运动状态、悬浮颗粒间碰撞强度、悬浮物的絮凝等均会对泥沙吸附/释放污染物产生影响,由于影响因素较多,作用机制复杂,目前关于泥沙运动对污染物在水沙两相间分配的影响所得结论仍存在分歧。相应的机理研究及数学模型的建立均做了较大简化。综观当前的研究成果,水沙运动及其化学生物过程等对污染物在河流水沙两相中的分配作用机理和耗氧有机物、有毒有机物等污染物与泥沙的作用机理是这一领域的未来研究重点。     

GPU‐accelerated direct numerical simulations of decaying compressible turbulence employing a GKM‐based solver

Gas Kinetic Method‐based flow solvers have become popular in recent years owing to their robustness in simulating high Mach number compressible flows. We evaluate the performance of the newly developed analytical gas kinetic method (AGKM) by Xuan et al. in performing direct numerical simulation of canonical compressible turbulent flow on graphical processing unit (GPU)s. We find that for a range of turbulent Mach numbers, AGKM results shows excellent agreement with high order accurate results obtained with traditional Navier–Stokes solvers in terms of key turbulence statistics. Further, AGKM is found to be more efficient as compared with the traditional gas kinetic method for GPU implementation. We present a brief overview of the optimizations performed on NVIDIA K20 GPU and show that GPU optimizations boost the speedup up‐to 40x as compared with single core CPU computations. Hence, AGKM can be used as an efficient method for performing fast and accurate direct numerical simulations of compressible turbulent flows on simple GPU‐based workstations. Copyright © 2016 John Wiley & Sons, Ltd.     

某冰水堆积体层流-紊流过渡状态渗流特性试验研究

澜沧江上游两岸河谷地带广泛分布一套规模巨大、形成于第四纪更新世中晚期的冰水堆积体,这类冰水堆积体往往具有较特别的渗流特性。通过对澜沧江某冰水堆积体的结构特征调查和颗粒组成试验分析,从沉积相的角度,认为该冰水堆积体可分为两层:表层厚约40 m的混合巨粒土,和底部厚约17 m的粗颗粒土。通过对这两层冰水堆积体的渗流特点试验研究,结果表明地下水在表层混合巨粒土中的渗流方式主要表现为层流-紊流过渡阶段的特点,渗流速度与水力梯度成幂函数关系;而在底部粗颗粒土中的运移方式主要表现为层流特点。根据混合巨粒土的渗流特点,文中提出了两种计算其渗透系数的方法,即根据渗透速度和水力梯度关系曲线估算渗透系数,或采用文中提出的公式计算渗透系数。     

An efficient low‐dissipative WENO filter scheme

This paper presents a simple and efficient procedure developed for tracing discontinuities in flow fields. Numerical experiments are carried out to test the new sensor coupled with the associated nonlinear WENO dissipation filter developed to suppress the numerical dissipation. The tests show that, for a problem containing shocks and vortices, the implementation of the new sensor and an optimized WENO scheme can obtain a stable and highly resolved solution. The numerical experiments demonstrated that the new filter scheme performs efficiently both in parallel and serial running for one‐dimensional inviscid flow problems. Direct numerical simulation of a Mach 5 turbulent boundary layer over a flat plate was carried out to demonstrate the applicability of the scheme to the DNS practices. Copyright © 2011 John Wiley & Sons, Ltd.     

Calculation of Turbulent Flow with Pseudo-spectral Method

This paper deals with the numerical simulation of incompressible turbulent boundary flow of a flat plate with the pseudo-spectral matrix method. In order to appear more than 10 nodes in the turbulent base-stratum and transition of 43×43 computational grids,a coordinate transformation is put up from physical panel to computational panel. Several zero turbulent models are computed comparatively. The results are credible when comparing with the previous methods.     

A Novel Scheme for Calculating Pressure Fluctuations Used in Lagrangian-Eulerian Particulate Dispersion Codes

A novel scheme for pressure fluctuations in turbulent flows is developed. The pressure fluctuations are sensitive parameter in some of the fluid phenomena. In the computational methods and modeling turbulence flow, the pressure fluctuations are eliminated after averaging of the Navier-Stokes equations, and only average pressure could be calculated. In this research, the Reynolds-averaged Navier-Stokes equations are computed using SIMPLE method. The Reynolds stress transport model (RSTM) is used to determine the Reynolds stresses and the flow details. The velocity fluctuations are simulated using the Kraichnan model. The Poisson equation for the pressure fluctuations is obtained by taking the divergence of the incompressible momentum equation and algebraic operations, and this equation is numerically solved by finite difference method. The effects of Reynolds number on the pressure fluctuations are studied.     

燃烧管内悬浮铝粉燃烧爆炸过程的研究

 铝粉的燃烧与加速机理一直是相关部门研究的热点。为了深入研究其在受限空间内的燃烧与传播特性,基于双流体模型、湍流k-ε模型以及铝粉燃烧等模型,选用SIMPLE格式,对大型卧式燃烧管内铝粉颗粒与空气的两相悬浮流湍流燃烧加速转爆炸现象进行了数值研究,得到了铝粉火焰在管内的燃烧传播过程中管内各相关参数的详细变化情况,并与相关的实验结果吻合。     

轴流式水轮机三维非定常湍流计算及压力脉动预测

水轮机的稳定性研究是目前工程上大型水轮机组流动分析的重要课题,本文以某水电站的大型轴流转桨式水轮机原型为基础建立计算模型,完成了从蜗壳进口到尾水管出口整个流道的非定常湍流计算,预测了固定导叶进口、转轮后、尾水管进口等多个位置的压力脉动,并利用FFT变换进行分析得到了压力脉动的频率和幅值,探讨了水轮机全流道内压力脉动产生和传播的原理．     

Effect of pressure gradients on the different stages of roughness induced boundary layer transition

The physical mechanisms of roughness-induced transition (RIT) in pressure gradient boundary layers are studied using direct numerical simulations. Recent investigations have examined RIT processes in zero-pressure-gradient boundary layers (Suryanarayanan et al., 2019). The present study uses a vorticity dynamics point of view to examine how these processes are altered by a locally accelerating or decelerating flow that strains the vorticity field and creates a net vorticity flux at the wall. Flow acceleration is imposed on specific streamwise extents of the flow. This provides an understanding about how the fundamental mechanisms in different stages of RIT are affected by pressure gradients. The present results suggest that both lift-up and subsequent amplification of the unsteady perturbations are mitigated by flow acceleration. The effect on lift-up is explained by the compression (i.e. large negative value of the stretching term) of the wall-normal vorticity by negative dv/dy. Consistent with earlier experimental observations on spots and wedges, favorable pressure gradients reduce turbulent wedge spreading and nearly arrest the spreading when sufficiently strong. This result is also explained in terms of vorticity dynamics.