基于环形旋转射流的预掺混扩散器水力特性试验研究

预掺混扩散器在污水出流前掺入其周围的水进行预先稀释,可增强初始稀释度,减小混合区范围。为进一步提高扩散器的稀释水平,本文提出了一种基于环形旋转射流的新型预掺混扩散器,在进流方式以及排放形式方面另辟蹊径,并系统地研究了该扩散器射流的温度场、流场和内部压力分布。研究结果表明:该预掺混扩散器稀释性能稳定,流量放大倍比约为2.5,排口处温升极值可降低约50%,1.2倍排口直径处可降低约80%;排口后环形旋转射流无速度核心区,存在内掺混机制,极值温升及流速沿喷距呈幂函数衰减规律,具有更短的射程和更强的掺混稀释能力,对迅速缩减污染带十分有利;水头损失系数较小,约为2.4。采用该预掺混扩散器,可在离岸较近的浅水区域获得较常规扩散器深排的稀释效果,进而缩短排污输水管道、降低工程投资。

Experimental study on flow characteristics of a pre-dilution diffuser based on the annular swirling jet

Pre-dilution diffuser mixes the ambient water into the wastewater before it is discharged from the outfall,which can enhance the initial dilution and narrow the range of the mixing zone. In order to further improve the dilution level of diffusers,a novel pre-dilution diffuser was proposed based on the principle of annular swirling jets in this paper,which changed the conventional inlet and discharge modes. Variation rules of the velocity field,temperature field and the pressure distribution inside the diffuser were studied. The tests results show that the dilution performance of the pre-dilution diffuser is stable,and the flow magnification ratio is about 2.5. The extreme values of temperature rise decrease exponentially with the increase of jet distance,and it could be reduced by about 50% at the outlet,and by approximately 80% at a distance of 1.2 times diameter of the outlet. Moreover, annular swirling jets present no velocity core but an internal mixing area after the exit,and have shorter jet distance and greater mixing ability than straight jets. The extreme axial and tangential velocities exponentially decreased from the outlet to the downstream. In addition,the head loss coefficient is small at about 2.4. By using this pre-dilution diffuser,the dilution effect of the deep discharge of conventional diffusers can be obtained in the shallow water area near the shore,so as to shorten the sewage pipelines and reduce the project investment.