竖缝式鱼道90°转弯段水力特性的数值模拟

Numerical Simulation of Flow in the 90° Turn of a Vertical Slot Fishway

受枢纽布置与地形地质条件影响,竖缝式鱼道穿越公路、桥梁等建筑物或实现大转弯时通常需要布置90°转弯段。根据导板的布置位置,90°转弯段分为内内型、内外型、外内型与外外型4种类型。采用数值模拟技术计算4种类型90°转弯段的水流流场,主流区水流均紧贴边墙流动,主流区两侧出现尺度过大的回流区。针对出现的不利流态,提出了以增设整流导板的方式调整水流结构,并对水流结构改进后的水力特性进行了对比研究。增设整流导板后,主流区大致居中,主流衰减效果显著;回流区尺度合理,回流流速甚小。内外型90°转弯段增设一整流导板后,yi/B值介于0.30-0.71,说明主流区主要位于转弯段中间40%区域内;主流区两侧主要分布着3个回流区,位于弯段与弯段下游回流区的尺度最大,影响域为常规水池面积的0.9倍,长宽比为3.25,说明大尺度回流区的影响域为椭圆形区域,可便于鱼类游入与游出;弯段与弯段下游回流区内,靠近边墙的最大流速不超过竖缝断面平均流速的0.23倍,中心流速甚小,有利于鱼类良好休憩。内外型90°转弯段水流结构改进效果较其他3种类型更为明显,在实际工程中可考虑优先采用。

Fishways are constructed to restore river connectivity and allow migratory fish to overcome obstructions. Vertical slot fishways, composed of pools connected in sequence, are widely applied at home and aboard for flow stability, adaptability to water level fluctuation and efficient fish passage. A 90° turning pool is usually required in a vertical slot fishway when the fishway passes roads or bridges and when required by topographic or geological con- ditions. However, the turning pool can delay or inhibit passage when the flow direction changes and a large reeircu- lation zone occur. This paper presents a study on the hydraulic characteristics of a 90° turning pool in a vertical slot fishway. A two-dimensional numerical simulation method was used to simulate the flow structure of 90° turning pools of four designs, i. e. , in-in, in-out, out-in, out-out turning pools, according to the central baffle position. The numerical results of the flow structure show that the mainstream all flew near the sidewalls of the slot and a large vortex formed on both sides of the mainstream in all four 90° turning pool designs. The four turning pools were then modified by the addition of a rectifier plate to improve the poor flow pattern and the hydraulic characteristics were simulated using the same method. Results show that the rectifier plate significantly reduced the velocity in the mid-section of the 90° turning pools. The size of the reflux areas was reasonable, and the reflux velocity was low. The ratio of yi/B for the in - out 90° turning pool ranged from 0.30 to 0.71, indicating that the mainstream occu- pied 40% of the central area of the in-out 90° turning pool. Three refluxes were observed in both sides of the main- stream, with the largest one in the turning area and below. The ratio of the length to width for the largest reflux was 3.25, indicating a oval shaped reflux and fish can more easily move in and out. The velocity in the middle of the reflux was low and the maximum velocity near the sidewall was less than 23% of the average velocity of the cross section of the turning pool, beneficial for fish resting. The flow structure in the in-out 90° turning pool was im- proved significantly and the fish passage was more efficient than the other three designs and is the design recommen- ded.