水生植物对水沙运动影响的三维湍流模型

水生植物的存在改变了明渠内水流的流动结构,也影响着泥沙的输运。建立三维湍流模型,在水流控制方程中加入植被阻力项和植被密度项来考虑刚性植物对水动力特性和泥沙输运特性的影响。应用该三维数值模型计算了矩形水槽内淹没植被对水流水平时均流速垂向分布的影响、复式明渠边滩栽种挺水植被对水流深度、平均流速分布以及植被岛周围泥沙床面的冲淤变形的影响。数值计算结果与实测结果吻合良好,表明本模型可以有效地描述刚性水生植物对水流泥沙运动的影响。

水生植物对河道形态影响的三维湍流模型

植被是河床和河岸稳定性指标中的一个重要参数,它主要通过影响水流结构进而影响河道的形态。本文建立曲线坐标系下的三维湍流模型研究水生植物对河道形态的影响,在水流控制方程中加入植物阻力项和植物密度项来描述水生植物对水动力特性的贡献,通过泥沙质量守恒方程求解河道变形,在适体网格中求解模型的控制方程。应用该三维模型数值模拟了矩形水槽内两侧交替布置的非淹没刚性植物对水流结构的影响以及梯形河道内两侧交替布置的非淹没刚性植物对河道形态的影响,数值计算结果与实测结果吻合良好。

流动环境中高浓度射流的三维数值模拟

应用流动环境中高浓度圆孔射流的三维RNG湍流模型,模拟计算不同水深和环境来流下的流态和浓度场分布,结果表明在已有射流区、冲击区以及异重流区的基础上,还存在1个上游入侵区。该上游入侵区的长度随环境流速的增大而减小,水深对其的影响相对较小。射流触底点位置随环境流速以及水深的增大而下移,触底点浓度则随环境流速以及水深的增大而减小。流态分析显示,壁面反射流形成动量较强的附壁射流时,会在较短距离内收缩和膨胀,紊动掺混剧烈,水深较浅时容易形成全水深掺混。比较而言,附壁射流较弱时无上游入侵,在射流孔口下游附近横断面上会形成较为特别的水滴状浓度等值线分布,在水体底部形成更为稳定的异重流。最后探讨了水体底面横向最大浓度沿流向的分布特征。

曲线坐标系下考虑植被影响的三维水沙数学模型

建立曲线坐标系下的三维水流泥沙湍流运动模型模拟弯曲渠道内布置水生植被后的水流结构和河床变形分布,计算了试验室60o弯道内流经植被的水流流速平面结构和断面分布以及不同植被布置情况对水流泥沙运动和床面变形的影响。数值结果较好地再现了试验规律。计算结果表明在弯道内布置植被会改变水流流速分布情况:植被覆盖区域的水流流速降低、弯道内二次流减弱和泥沙运动减弱,而非植被覆盖区域的水流流速增大、断面二次流依然存在且泥沙运动加剧。通过比较两种水生植被布置条件下的床面变形情况,发现合理布置植被可以减缓凹岸的泥沙侵蚀,但也会加剧凸岸的泥沙淤积。

开孔型缓冲结构减缓高速磁浮列车隧道初始压缩波的特征研究

以国内时速600 km磁浮列车进入隧道为研究对象,基于重叠网格法和有限体积法,采用三维可压缩非定常流动N-S方程和SST k-ω湍流模型,研究开孔型缓冲结构对初始压缩波的缓减作用。研究发现:在列车驶入隧道的过程中,刚进入隧道时压缩波呈现三维特征,在距离隧道洞口约33 m处压缩波由三维波变为一维平面波。通过对比分析距离隧道入口132 m处的压力与压力梯度,得到设置缓冲结构后初始压缩波最大峰值增加5%,压力梯度降低59%。随着列车速度提高,初始压缩波的压力峰值增大,其最大压力近似与列车速度的2次方成正比,最大压力梯度近似与列车速度的3.9次方成正比。本文结果为今后进一步认识时速600 km等级的高速磁浮隧道缓冲结构效应和设计提供了可靠依据。

Numerical simulation and analysis of solid-liquid two-phase threedimensional unsteady flow in centrifugal slurry pump

Based on RNG k-ε turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional(3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of unsteady flow characteristics on solid-liquid two-phase flow and pump performance were researched under design condition. The results show that clocking effect has a significant influence on the flow in pump, and the fluctuation of flow velocity and pressure is obvious, particularly near the volute tongue, at the position of small sections of volute and within diffuser. Clocking effect has a more influence on liquid-phase than on solid-phase, and the wake-jet structure of relative velocity of solid-phase is less obvious than liquid-phase near the volute tongue and the impeller passage outlet. The fluctuation of relative velocity of solid-phase flow is 7.6% smaller than liquid-phase flow at the impeller outlet on circular path. Head and radial forces of the impeller are 8.1% and 85.7% of fluctuation, respectively. The results provide a theoretical basis for further research for turbulence, improving efficient, reducing the hydraulic losses and wear. Finally, field tests were carried out to verify the operation and wear of slurry pump.

400km/h高速铁路隧道洞口等截面无开孔扩大型缓冲结构气动效应分析

高速列车驶入隧道产生初始压缩波,压缩波以音速传播至隧道出口处向外辐射形成压力脉冲波,影响居民的心理健康,带来了严重的环境问题。隧道微气压波与隧道出口端内压缩波梯度成正比,而列车头部驶入隧道的初始压缩波最大梯度与列车速度的3次方近似成正比,因此,在隧道洞口设置缓冲结构可大幅度降低初始压缩波的最大梯度值,是控制和消除微气压波危害的主要措施之一。本文采用三维可压缩非定常流动的N-S方程和SST-kω湍流模型,基于有限体积法和重叠网格法,在研究未设缓冲结构初始压缩波基本特征的基础上,研究400 km/h条件下等截面无开孔扩大型缓冲结构对初始压缩波波形和压力梯度的影响规律,并比较不同缓冲结构断面面积与隧道断面面积比值对压缩波波形和降低压力梯度的影响规律,以期为400 km/h隧道缓冲结构的设计提供基础。

Numerical simulation of the hydrodynamics within octagonal tanks in recirculating aquaculture systems

A three-dimensional numerical model was established to simulate the hydrodynamics within an octagonal tank of a recirculating aquaculture system. The realizable k-e turbulence model was applied to describe the flow, the discrete phase model （DPM） was applied to generate particle trajectories, and the governing equations are solved using the finite volume method. To validate this model, the numerical results were compared with data obtained from a full-scale physical model. The results show that： （1） the realizable k-e model applied for turbulence modeling describes well the flow pattern in octagonal tanks, giving an average relative error of velocities between simulated and measured values of 18% from contour maps of velocity magnitudes; （2） the DPM was applied to obtain particle trajectories and to simulate the rate of particle removal from the tank. The average relative error of the removal rates between simulated and measured values was 11%. The DPM can be used to assess the self-cleaning capability of an octagonal tank; （3） a comprehensive account of the hydrodynamics within an octagonal tank can be assessed from simulations. The velocity distribution was uniform with an average velocity of 15 cm/s; the velocity reached 0.8 m/s near the inlet pipe, which can result in energy losses and cause wall abrasion; the velocity in tank corners was more than 15 cm/s, which suggests good water mixing, and there was no particle sedimentation. The percentage of particle removal for octagonal tanks was 90% with the exception of a little accumulation of 〈5 mm particle in the area between the inlet pipe and the wall. This study demonstrated a consistent numerical model of the hydrodynamics within octagonal tanks that can be further used in their design and optimization as well as promote the wide use of computational fluid dynamics in aquaculture engineering.

Experimental Study on Jet Blast at Laboratory Scale

The flow field of 3D （three-dimensional） wall-jet is investigated. Jet-blast from airplane is simulated by wall-jet setup using a sonic nozzle at a laboratory scale. Farfield velocity and fluctuation distributions are measured by using X-type hot wire anemometer at four measurement planes. As a result, the flow properties of streamwise component are consistent with data which are obtained in previous researches. The secondary flow is also measured on each measurement plane. Reynolds stresses, v＇v＇ and w＇ w＇, are analyzed from the fluctuation of the secondary flow. The law of similarity is observed in the dimensionless distributions of mean velocity and fluctuation. However, the distributions in nearer field （i.e., in the measurement plane at X/D = 100） tend to disobey the similarity law, especially in the cases of fluctuation. It seems that jet-blast is not fully developed by reaching X/D = 100. The experimental results are compared with computational results which are obtained by CFD （computational fluid dynamics） with SST （shear-stress transport） turbulence model. And it is shown that the results by the simulation with SST turbulence model do not follow the similarity law. The present database of the Reynolds stresses is critically important for development of a new turbulence model of RANS （reynolds-averaged navier-atokes） simulations on wall-jet.

Numerical simulation of icing effect and ice accretion on three-dimensional configurations

It is common for an aircraft to encounter icing weather conditions, which would be dangerous to the flight. Thus, there is a need to study the detail of icing effect and the process of ice accretion on the aircraft. In this paper, considering three different icing models according to weather conditions, i.e., sharp-angled ice, blunt-nosed ice and double horn ice, the Reynolds-averaged N-S equations and the S-A turbulence model are used to analyze the flow field for an iced wing/body configuration with a multi-block strategy and structured grid technique. The numerical result is compared with the experimental data. A flow solver is developed based on the Euler equations to investigate the ice accretion process. The droplets are tracked by using the Lagrangian method. In addition, a revised Messinger model is proposed to simulate the ice accretion. This numerical simulation is conducted for the ice accretion on an M6 wing and a wing/body/tail configuration. The presented results preliminarily show that the numerical methods are feasible and effective.

基于流固耦合理论的山洪泥石流浆体作用下双柱墩的动力响应分析

山洪泥石流冲击双柱墩是一个复杂的过程,本文选用Bingham流体模型作为山洪泥石流浆体的本构模型,首先在三维湍流k-ε模型的基础上,考虑山洪泥石流特点,应用CFX对某地发生的山洪泥石流浆体进行数值模拟;然后通过ANSYS建立了山洪泥石流浆体与双柱墩的流固耦合模型,实现了山洪泥石流浆体冲击双柱墩的全程模拟,从而对双柱墩在不同参数的山洪泥石流浆体冲击作用下的响应情况进行了分析。结果表明:山洪泥石流浆体的密度、流速、冲刷水头高度对双柱墩的冲击力影响极大,又揭示了流固耦合效应导致了墩底的冲压坑洞,还证明了基于动量守恒的流体动压力法可近似计算山洪泥石流浆体冲击双柱墩时的冲击力,可为类似防灾工程提供参考。