水流掺气对明流泄洪洞及挑坎水力特性的影响

水流充分掺气可以避免高流速泄洪设施发生空蚀,但也会改变相关水力特性。通过对某大坝泄洪洞掺气设施水力模型试验及关于水流表面自掺气发生条件的相关分析,提出了在全程流速超过38 m/s,长度达550 m的明流洞内仅布置一级掺气设施的建议,较通常情况减少了两级;并针对泄洪洞出流方向与河道流向交角达60°的特点,研究提出了一种大差动异型鼻坎消能工。水工模型试验成果表明,其挑流水舌沿河道纵向扩散良好,水舌外缘与河道对岸保持了30 m以上的安全距离。该泄洪洞建成后经历了高水头、较长时间的泄洪运行,明流洞和鼻坎消能工均无空蚀发生,但挑坎水舌却冲刷到对岸边坡。

Analysis on flow aeration on hydraulic characteristics of free-flow spillway tunnels and flip buckets

Sufficient flow aeration could relieve cavitation erosion of high-velocity flood releasing facilities, and also change their relative hydraulic characteristics. We carried out hydraulic model tests to the tunnel spillway aeration facilities of a dam and relative analysis on the occurrence conditions of free flow self-aeration, and based on the results we proposed to set only one level aeration facilities in the free flow tunnels with a length of 550m and velocity over 38m/s in the whole length, which could reduce two level aeration facilities compared to conventional projects. Aiming at the feature that the angle between the out-flow direction and river direction reaches up to 60°, a heterogenic energy dissipation bucket lip with large differential was put forward. The model tests showed that this energy dissipater makes the nappe spread well along the longitude direction, and nappe outer edge keeps a safe distance of more than 30 m from the opposite bank. After longtime operation of the tunnel spillway under high water head since its completion, there was no cavitation erosion appeared on its free flow tunnel and energy dissipation bucket lip, but the nappe washed against the opposite bank.