进水流速对圆形循环水养殖池流场特性影响的数值模拟

Numerical simulation of the effect of inflow velocity on the flow field characteristics of circular circulating aquaculture ponds

中文关键词: 离散相模型  颗粒分布  流场特性  水温调控  圆形养殖池

英文关键词: Discrete phase model  Particle distribution  Flow field characteristics  Water temperature regulation  Round aquaculture pond

中文摘要:

      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。

英文摘要:

      To meet the growing demand for animal food among the population, China has proposed the strategy of building a “Blue Granary,” relying on marine space, marine biological resources, and the application of modern marine high-tech. Industrialized recirculating aquaculture (also known as land-based factory aquaculture, factory aquaculture, or industrial fish farming) has the advantages of high production efficiency and small land occupation. It is a high-density, high-yield, high investment, and cost-effective aquaculture method. The recirculating aquaculture system is in line with the “Blue Granary” strategy, effectively reducing water pollution while ensuring food security. Therefore, in recent years, recirculating aquaculture in China has developed rapidly. In this context to achieve intelligent regulation of the inflow velocity of industrial recirculating aquaculture, this article firstly summarizes the three main factors that affect the inflow velocity from previous research: The flow field velocity of the aquaculture pool, the discharge velocity of the bait (residual bait), and the velocity of temperature regulation. With the improvement of computer software and hardware, computational fluid dynamics (CFD) is gradually being applied in various fields. CFD provides cheap tools for simulation, design, and optimization, as well as tools for analyzing three-dimensional complex flows. In complex cases, measurements are often difficult, even impossible, and CFD can easily provide detailed information on all flow fields. Compared with conventional experiments, CFD has the advantages of no restrictions on parameters, lower cost, and no interference in the flow field. This method can be used in aquaculture to solve the problems of temperature control effects, solid particle emission efficiency, and flow zone division that cannot be directly measured in actual production under different flow rates. At present, there are few studies reporting CFD numerical simulation of multiphase flow in aquaculture. Existing research focuses on the impact of the inlet and outlet structure and the shape of aquaculture ponds on the flow field, and the effect of sewage collection. There are few reports on the use of numerical simulation methods to design the regulation scheme of inlet flow velocity. Because of the advantages of CFD, we chose it for simulation. Secondly, the specific model used in the numerical simulation was determined through experimental verification, research discussion, and other methods. Based on this, grid independence verification was conducted, indicating that the simulation results under the number of grids in the text are not affected by the number of grids, and the simulation results are reliable. Thereafter, based on the above research, and taking Scophthalmus maximus as an example, the effects of different inlet flow rates on the flow field, sewage discharge, and water temperature regulation in aquaculture ponds were simulated. The results showed that the inlet flow rate significantly affects these three factors. Therefore, the inlet flow rate can be adjusted according to production needs. Based on the simulation results, a set of inlet flow velocity control schemes were proposed: For the feeding stage, low flow velocity can be used to reduce feed costs (inlet flow velocity = 0.2 m/s); after eating, the feed can be quickly discharged at a high flow rate for a short period of time (inlet flow velocity = 1.2 m/s for 20 s); at abnormal water temperature, different flow rates and times can be used to adjust the water temperature in the breeding pool (water inlet temperature = 15 ℃; an inlet flow velocity of 1.2 m/s can be used to inject water for 230 s, reducing the water temperature in the breeding pool from 22 ℃ to 18 ℃). Numerical simulation experiments can be designed based on this method for different aquaculture environments and organisms to determine the inflow velocity control scheme. Unlike traditional methods, the numerical simulation method proposed in this study for regulating the inflow velocity of recirculating aquaculture systems can be used to determine the inflow velocity control scheme at a lower cost. The method can directly measure the discharge of particulate matter, the overall water temperature, and the flow field in aquaculture ponds. This method is safer than the method of indirectly measuring water quality to determine the inflow velocity control scheme. In terms of regulation time, traditional methods are only accurate to the hour in regulating the inlet flow rate, whereas this method is accurate to the second, which makes it more reliable to determine the regulation of the inlet flow rate. Therefore, from the perspectives of cost, safety, and accuracy, it is better to use numerical simulation methods to regulate the inflow velocity of recirculating aquaculture systems. In actual production, the method described in this study can be used to determine the inflow velocity control scheme, which can be combined with the control system to achieve automatic control, reduce breeding costs, and increase breeding success.