| Jet aeration is an aeration mode with high efficiency of mass transfer and mixing, and jet aerator is the key equipment of jet aeration wastewater treatment system, the performance of which has direct influence on wastewater treatment effect. The investigation on jet aerator has been widely carried out since last century, including modification of jet aerator, parameters study, and recent application of numerical simulation. Self-suction single-stage jet aerator is widely applied to engineering because of its simple structure and reliable operation; the investigation on jet aerator always focuses on how to improve its entrainment ratio and efficiency. So far, there is no essential difference between jet aerator performance research methods; all these methods are essentially semi-empirical and semi-theoretical. Numerical simulation can theoretically predict flow field of jet aerator, beyond the restriction that internal flow parameters of jet aerator cannot be directly measured, furthermore, numerical simulation combined with experimental investigation, can provide theoretical prediction, verification and basis for jet aerator design.Recently, there are many investigations on two dimensional numerical simulation of single-nozzle jet aerator, but few investigations on flow pattern of multi-phase flow inside multi-nozzle jet aerator and especially three dimensional numerical simulation of quad-nozzle jet aerator performance. Accordingly, in this paper, a three dimensional numerical investigation was conducted to simulate the air entrainment performance of quad-nozzle jet aerator by using FLUENT; the characteristics of flow field distribution and the flow pattern of gas-liquid two-phase flow inside the aerator in various working conditions were analyzed; phase content and variations of pressure were predicted; theoretical basis of improving jet aerator performance was provided. In the meantime, an experimental investigation on the performance of quad-nozzle jet aerator was carried out.The concrete content of investigation on two-phase flow mixing inside jet aerator by theoretical analysis and numerical simulation is as followed:(1) On the basis of theoretical analysis of two-phase flow mixing inside the working jet aerator, combined with previous research, physical and mathematical model of gas-liquid flow of jet aerator were established.(2) With numerical calculation by FLUENT and post-processing results, contours and charts of important parameters of two-phase flow, including pressure, velocity, fraction of gas, etc., were plotted to analyze and investigate flow field distribution and flow pattern of two-phase flow inside jet aerator in various working conditions.The concrete content of experiment investigation on the performance of jet aerator is as followed:(1) With comparison of single-nozzle jet aerator experiment result with previous research, experimental table of jet aerator performance investigation was error-analyzed to verify reliability of it.(2) Experimental results of quad-nozzle jet aerator performance were analyzed and compared with relevant numerical simulation results.The results show that, the quad-nozzle short throat jet aerator is modified with structure and size parameters to make sure that more air is well mixed into wastewater and high backpressure requirement is met; quad-nozzle jet aerator has higher air entrainment performance, lower energy loss and stable gas-liquid two-phase flow pattern. The results also show that, the interaction between fluid mainly happens in entrance segment of throat, where the variation of the mixing status of jet fluid and entrained fluid and the state parameters of two-phase flow, such as pressure, velocity, fraction of gas, is great; in the middle and posterior segment, two-phase flow pattern becomes stable. Variation of working conditions has great influence on jet aerator performance. Good agreement between the numerical simulation results and the experimental data is found. Accordingly, the numerical simulation method in this paper provides a reference for jet aerator design. For the quad-nozzle jet aerator working in No.4 working condition, working water flow rate equals 1.25m3/h, working water static pressure equals 0.400MPa, backpressure equals 0.040MPa; performance parameters of quad-nozzle jet aerator, such as entrainment ratio equals 3.20 and entrainment efficiency equals 36%. By contrast, the entrainment ratio of single-nozzle jet aerator approximately equals 1 and the entrainment efficiencyηis lower than 20%.
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