进径比对方形圆弧角养殖池内流场特性的影响研究

为研究进径比(参数C/B,射流孔位置到养殖池壁的水平距离C与养殖池短边边长B之比)对单管入流模式下双通道方形圆弧角养殖池系统流场特性的影响,基于计算流体动力学仿真技术,应用Fluent前处理软件Gambit构建三维数值计算模型,采用RNG k-ε湍流模型模拟循环水养殖池内流场。物理模型试验证明,该数值模型能够准确模拟方形圆弧角养殖池系统内的流场,同时提出能量有效利用系数评价养殖池系统的能量有效利用率。结果表明:优化进径比可有效改善养殖池系统内平均流速(a=0.05,P0.000 1)、提高能量有效利用率。研究表明,进径比参数C/B在0.02～0.04区间有利于双通道方形圆弧角养殖池系统获得最佳水动力条件。本研究为工厂化循环水养殖进水管的布设位置提供理论参考。     

进径比对矩形圆弧角养殖池水动力特性影响

为研究单管入流模式下,进径比(参数C/B,C为射流孔位置到养殖池壁的水平距离,B为养殖池短边边长)对单通道矩形圆弧角养殖池系统水动力特性的影响,实验运用计算流体动力学仿真技术构建单通道矩形圆弧角养殖池三维数值计算模型,应用平均流速、阻力系数和速度分布均匀系数等流体动力学特征量分析养殖池内(尤其是池底)的流场形态,并修正...     

方形圆弧角养殖池射流间距对流场特性的影响

为研究养殖池入射流间距对双管射流模式下(射流位置位于圆弧角,射流角度为30°)方形圆弧角养殖系统内流场特性的影响.采用流体动力学仿真技术,通过有限体积法和有限差分法构建三维数值计算模型,选取RNG k-ε湍流模型模拟工厂化循环水养殖池池内流场流动状态.结果显示:通过优化入射流间距可以有效提高养殖池整体流速、流场分布均匀...     

直壁双管结构射流角度对方形圆弧角养殖池流场的影响研究

为改善水产养殖池内的水动力条件,同时兼顾降低工厂化循环水养殖的能源消耗,采用计算流体力学(Computational Fluid Dynamics,CFD)技术,建立对直双管(两个进水管布设于不相邻的两个直壁中间位置)入流的养殖池三维数值计算模型,对不同射流角度的方形圆弧角养殖池内流场特性开展数值模拟.结果显示:射流角...     

循环水养殖系统管式射流集污特性试验研究

工厂化养殖池内的污物聚集效果是养殖池设计建造和运行管理的重要指标,对提升养殖技术和管理水平具有重要意义。针对一种典型的工厂化鱼类养殖池,对边侧管式射流系统驱动下的流场特性和污物聚集效果进行研究,探讨了射流角度、射流流速和循环抽吸方式等因素对养殖池内水体流场特性及污物聚集分布规律的影响。利用手持式ADV流速仪在养殖池内进行布点测量,获得各点流速数值,然后利用MATLAB软件进行流场插值构图,研究养殖池的流场分布特性;污物聚集特性采用图像法进行处理分析。研究表明:管式射流驱动作用下,流速从池心向外呈"V"型变化。在射流角度固定为40°条件下,射流速度越大,池心低流速区域范围越小,污物聚集效果越好。当射流速度达到0.3 m/s时,污物基本聚集于池心;在流速固定的情况下,对污物聚集效果存在一个最佳的射流角度,约为40°。池内循环抽吸模式对流场和污物聚集效果同样有着显著的影响。研究表明,采用底部抽吸时,排污孔附近的径向流速与切向流速均高于边侧抽吸模式,且污物聚集效果明显优于边侧抽吸模式。该研究成果可用于工厂化鱼类养殖池管式射流水力驱动系统的优化设计,在不影响养殖对象生长的前提下,可尽量提高射流流速,最佳射流角度一般为40°左右,并尽量采用底部抽吸模式。     

工厂化对虾养殖池管式射流集污水力特性

工厂化养殖池内水体的流场分布特性直接决定了其对残饵、粪便等的排污性能。本实验研究了管式射流驱动模式下,射流角度与射流流速对养殖池内水体流场与污物聚集特性的影响。养殖池流场特性采用点式流速仪进行布点测量,利用MATLAB软件对流场特性进行分析。采用相机采集的养殖池集污效果图像,并利用Photoshop软件与自行开发的不规则图形面积分析软件对图像进行分析。研究表明,流速从池心向外呈"V"型变化,在射流角度固定的情况下,射流速度越大,池心低流速区域越小,污物向池心的聚集效果越好;在流速固定的情况下,存在一个最佳的射流角度,本实验在24 cm/s流速条件下,射流角度为40°时,池内污物聚集效果最优。结论认为在保证养殖对象生长的前提下,可尽量提高射流流速;在24 cm/s流速条件下,最佳射流角度在40°左右。本研究成果可为工厂化养鱼池、养虾池等管式射流水力驱动系统的优化设计提供参考依据。     

折角比对养殖工船舱内流场特性的影响

为改善带有顶、底边舱且低径深比的养殖工船养殖舱内流场特性,以提高水产养殖动物福利与经济效益,提出一种结构优化参数折角比(a/B,a为角壁边长,B为养殖舱壁边长),以评估养殖舱内流场的改善效果。基于计算流体动力学(CFD)仿真技术,研究折角比参数a/B(0～0.4)和进水速度(0.8～1.2 m/s)对养殖舱内流场特性的影响。结果显示：不同进水速度下,养殖舱内流体特性的变化趋势一致;养殖舱水力停留时间一致的条件下,当折角比参数0.25≤a/B≤0.40时,养殖舱内流场均匀性较好,平均流速较原方形养殖舱提高35%,能量有效利用率提高70%;角壁附近低流速区域减少,养殖舱中间排水口区域有明显涡柱形成,有助于提高养殖舱系统的自清洁性能。研究表明,折角比参数a/B控制在0.25～0.40时,有助于提高养殖舱系统的能量有效利用率和养殖空间利用率。研究结果可为养殖工船养殖舱的结构设计和优化提供参考依据。     

两种双通道圆形养殖池水动力特性的数值模拟与研究

为给养殖池的池型选择与设计提供理论依据,在相同的池体尺寸、进水速度和池底出水比例条件下,针对Cornell和Waterline两种经典双通道圆形养殖池,对其速度流场进行了计算流体动力学(CFD)仿真分析。仿真应用Ansys 15.0软件中的Fluent模块,采用RNG k-ε湍流模型对两种池型的内部速度流场进行了数值模拟,分析其流场特性并进行对比。结果显示:两种池型的水流速度向池中心方向在很短距离内随着径向距离的减少而急速增大,当达到某一径向距离时,速度达到最大值,然后速度随着径向距离的减小而减小,在池子中心轴线或附近处速度降到最小;在纵向上,与池心相同水平距离处的水体流转速度则随着高度增加而减小;在池底出水分流比小于10%时,Cornell池池底自清洁能力、池子整体流场均匀性均比Waterline池差。仿真结果从理论上验证了两种池型底流比例的经验设计值在10%以上。     

进水流速对圆形循环水养殖池流场特性影响的数值模拟

通过对工厂化循环水养殖进水流速的智能调控,可降低饵料残留,避免水质恶化。为此,本研究采用数值模拟方法探究了进水流速对工厂化循环水养殖池流场特性的影响,并基于该研究设计出一套确定进水流速调控的实验方法。首先,通过对比Standard k-ε、RNG k-ε和Realizable k-ε 3种湍流模型及多种壁面函数的仿真效果,确定RNG k-ε模型和标准壁面函数作为仿真配置。同时,针对多相流模型,对欧拉多相流模型和DPM离散相模型进行对比,为提高计算准确性选用DPM离散相模型,并基于上述模型进行网格无关性验证、制定网格划分方案。其次,以大菱鲆(Scophthalmus maximus)养殖为例,模拟不同进水流速下养殖池流场、排污和水温调节的效果。最后,针对仿真结果提出进水流速调控方案。结果显示,日常采用1.0 m/s的进水流速,可有效提高适宜流速区面积并控制水处理成本;投饵前,采用0.2 m/s的进水流速可以解决循环水养殖中存在的饵料浪费问题;进食结束后,采用1.2 m/s的进水流速可快速排出残饵避免水质恶化;水温异常时,采用15 ℃的水、以1.2 m/s的进水流速注水230 s,可使20 ℃的水下降到正常水平,精准化控制水温。采用本研究提出的方法,可针对不同养殖生物和养殖环境设计进水流速智能调控策略,可用于解决循环水养殖过程中饵料浪费、水质变差和水温异常等问题。     

立式双曲面网板水动力性能及流场可视化研究

网板是拖网作业系统中重要的属具之一,其水动力性能的优劣直接关系到拖网网口的扩张,并影响其生产效果和经济效益。采用单因素试验法,利用水槽模型试验和数值模拟(computational fluid dynamics, CFD)研究立式双曲面模型网板在不同展弦比λ(2.5、3.0、3.5、4.0)、弯曲度f/C(10%、15%、20%)、后退角Λ(0°、10°、15°)下的水动力性能,分析不同结构参数的网板水动力性能,对比两种方法的结果,并实现网板周围流场可视化。结果显示:①2号网板(λ=3.0、f/C=15%、Λ=10°)升力系数最大,冲角25°时,模型试验值为1.70,数值模拟值为1.88,阻力系数随冲角增大一直增大,且后部流速的模拟值和测定值平均偏差为4.40%,两种方法获得的结果吻合度高。②2号网板在流场分布中边界层分离点随冲角增大逐渐向翼端前沿移动,中心面后部涡旋随冲角增大一直增大,左翼板侧低压区随冲角增大呈先增大后减小趋势,网板尾部随冲角增大形成明显的翼端涡,产生涡升力对网板提供附加升力,使得立式双曲面网板比其他类型网板有较高升力。     

Comparative analysis of flow patterns in aquaculture rectangular tanks with different water inlet characteristics

The objective of the work is to improve the design rules of rectangular aquaculture tanks in order to achieve better culture conditions and improve water use efficiency. Particle tracking velocimetry techniques (PTV) are used to evaluate the flow pattern in the tanks. PTV is a non-intrusive experimental method for investigating fluid flows using tracer particles and measuring a full velocity field in a slice of flow. It is useful for analysing the effect of tank geometries and water inlet and outlet emplacements. Different water entry configurations were compared, including single and multiple waterfalls and centred and tangential submerged entries.

The appearance of dead volumes is especially important in configurations with a single entry. Configuration with a single waterfall entry shows a zone of intense mixing around the inlet occupying a semicircular area with a radius around 2.5 times the water depth. A centred submerged entry generates a poor mixing of entering and remaining water, promoting the existence of short-circuiting streams. When multiple waterfalls are used, the distance between them is shown to have a strong influence on the uniformity of the velocity field, increasing noticeably when the distance between inlets is reduced from 3.8 to 2.5 times the water depth. The average velocities in configurations with multiple waterfalls are very low outside the entrance area, facilitating the sedimentation of biosolids (faeces and non-ingested feed) on the tank bottom. The horizontal tangential inlet allows the achievement of higher and more uniform velocities in the tank, making it easy to prevent the sedimentation of biosolids.     

Controlled hatchery production of Clarias gariepinus (Burchell 1822): an investigation of tank design and water flow rate appropriate for Clarias gariepinus in hatcheries

Circular tanks are appropriate for Clarias gariepinus (Burchell) culture. Wide/shallow tanks (with a diameter to depth ration of about 10) are preferable to narrow/deeper tanks. The optimal flow rate for larvae will be one which provides sufficient oxygen yet does not generate a current velocity fast enough to cause them to swim against it. However, current velocity, for a given type and orientation of inflow, will depend particularly upon tank diameter to depth ratio and flow rate and will be related to position within the tank. Therefore for a given circular tank design a theoretical maximum flow rate and concomitant biomass can be estimated for a given mean fish size. Once airbreathing begins the optimal flow rate for fry is simply that which does not elicit swimming.     

以CFD-DEM为基础的养殖槽排污性能及底坡优化

由于能提高资源利用率,减少环境污染,低碳高效池塘循环流水养殖(IPA)作为一项新型养殖技术被大力推广。为了提高养殖过程中的集污排污效率,本研究拟采用构造负坡底面的方法对养殖槽结构进行优化。通过建立二维养殖槽简化模型,结合计算流体力学—离散单元法(CFD-DEM)模拟计算与核偏最小二乘(KPLS)建模方法,建立槽内垂向流速分布与底面坡度和粗糙度的关系模型。在此基础上结合泥沙运动理论,获得了槽内颗粒起动流速与单宽输沙率模型,在构建颗粒起动和输运两方面的性能指标后,利用基于偏好的多目标粒子群算法(DP-MOPSO)寻求最优底面坡度。寻优结果显示,随着底面粗糙度的增加,最优坡度略有减小,范围为0.013~0.015;仿真实验结果显示,构造最优底坡可有效提高颗粒的起动概率和槽体的颗粒运输能力,且对于表面较为粗糙槽体,坡型底面在颗粒起动方面的优越性更为显著,说明通过构建底坡来改变水流结构,从而实现养殖槽排污性能的优化是合理的。     

Insight into bacterial population in aquaculture systems and its implication

The current onshore aquaculture trend is to develop large scale production of diversified fingerlings and very large units for fish ongrowing. This requires an industrial type of approach including quality assurance and minimization of failures in addition to management of bio-technical and economic aspects. Therefore, all the key biological mechanisms involved in Recirculating Aquaculture Systems (RAS) need to be better understood, especially those determining the development of bacterial populations and their interactions with fish. This review presents new knowledge on bacterial community compositions in various parts of RAS and on bacterial-fish interactions in RAS, which constitute essential tools for system management.     

Prediction of water velocities in circular aquaculture tanks using an axisymmetric CFD model

Computational fluid dynamics (CFD) software was used to construct two-dimensional axisymmetric simulations of the turbulent flow inside 1.5, 5, 9.15 and 10 m tanks containing rotating water. The water rotation was induced mathematically by either placing a rotating cover on the surface of the water or locating a tangential water inlet near the top of the side wall. Central and side drains evacuated the water from the tank when using an inlet. The rotating cover produced a forced vortex in the tanks similar to the one observed in actual rearing tanks when the majority of the flow is leaving via the side drain. The predicted flow structure in tanks with an inlet can be divided into three regions: a narrow region along the side wall where the rotating water is moving down toward the floor, a thin boundary layer along the floor where the rotating water is moving radially inward, and a large region in the bulk of the tank where radial and axial velocities are small and the tangential velocity is independent of elevation but varies with radial position. Calculations were performed with the k-ε (RNG) and Reynolds stress turbulence models. Converged solutions were easier to obtain with the k-ε (RNG) model but only the Reynolds stress model could predict the strong vortex which is experimentally observed to form in the central portion of the tank as the flow leaving via the center drains is increased. The simulations predict that the thickness of the floor boundary layer is proportional to the tank diameter and that the radial velocity within the floor boundary layer is maximum at an elevation equal to about 10% of the boundary layer thickness. At any given radial position, the maximum value of the radial velocity next to the floor is between 15 and 45% of the tangential velocity in the bulk of the tank. Predicted shear stresses along bounding surfaces were used to obtain correlations for the side-wall and floor friction coefficients in terms of the Reynolds number. These correlations were in turn substituted in an overall moment balance to obtain an analytical model for predicting the maximum tangential velocity V_θw near the side wall of multi-drain rearing tanks. The predictions of the analytical model are in excellent agreement with V_θw values reported in the literature for tanks with diameters ranging from 1.5–15 m and indicate that the drag from inlet structures is non-negligible. The results demonstrate that the axisymmetric CFD model can simulate the main features of the rotating flow inside circular tanks and provide valuable boundary-layer information that is difficult to obtain experimentally.     

微孔曝气增氧机的增氧能力试验

为探究微孔曝气增氧机对氧气的传递效果,从研究增氧能力出发,依据SC/T6009-1999增氧机增氧能力试验方法的标准检测程序,以直径为10m的标准室内水池作为试验平台,试验水温为20℃、气压为101.325kPa、初始溶氧浓度为0mg/L;试验用水为清水,将微孔曝气增氧机与射流式增氧机进行对比试验研究。研究结果表明,微孔曝气增氧机能有效增加水体底部溶解氧,与1.5kW射流式增氧机相比,射流式增氧机的增氧能力平均值为2.4kg/h,微孔曝气增氧机布管长度为20m时,增氧能力平均值为0.25kg/h,布管长度为42m时,增氧能力平均值为0.40kg/h,布管长度为98m时,增氧能力平均值为1.12kg/h,布管长度为200m时,增氧能力平均值为1.55kg/h,所以在目前试验布管密度条件下,增氧能力可以超过射流式增氧机。在进气口压力相同的情况下,微孔曝气增氧机增氧速度随着布管长度增加而增加。     

Measurement and simulation of the three-dimensional flow pattern and particle removal efficiencies in a large floating closed sea cage with multiple inlets and drains

This study investigated the three-dimensional flow structures in an ellipsoid, closed sea fish cage. The results are presented using computational fluid dynamics (CFD) simulations and experimental measurements. Experimental residence time distribution (RTD) measurement and CFD simulation are the best methods to study the hydrodynamics of inflow systems. Three-dimensional numerical simulations of the flow and transport characteristics of the system were conducted using a Reynolds-averaged Navier-Stokes equation approach and the results were compared to the measurements performed using acoustic Doppler velocimetry techniques. The objective of the investigation was to characterize the flow field generated in an ellipsoid, closed tank. The flow in the enclosed volume is driven by four inlets pipes integrated into the wall of the cage. The focus is on the turbulent structures and undesirable flow patterns that lead to reduced self-cleaning efficiency and a lower quality habitat for the fish through phenomena, such as recirculation zones or low velocity areas. Correlations between CFD and the experimental data confirm the adequate reproduction of hydrodynamic conditions and reinforce the predictive capabilities of numerical models as tools to simulate field scale closed containment systems or to optimize existing and future aquaculture designs. The simulation of aquaculture-like particles demonstrates that almost 100% of particles with a diameter ranging between 1 μm and 3000 μm are removed during a maximum of two hydraulic retention time (HRT) cycles. Smaller particles are removed via the upper-side outlets and larger particles are removed via the bottom outlet.