进/出水口出流扩散脉动流速规律试验研究

Experimental study of velocity fluctuations in inlet/outlet under outflow diffusion

侧式进出水口出流工况水流呈现扩散态,拦污栅断面脉动流速很大,可能危及拦污栅安全,其脉动流速变化规律及产生原因有待进一步探讨。本文建立了典型进出水口试验装置,利用激光多普勒流速仪与声学多普勒流速仪开展试验研究。结果表明:在靠近扩散水流末端的拦污栅断面脉动流速很大,流速脉动值可达时均值的1.8倍,平均紊动强度为0.724,该断面流速脉动呈现出明显的正态性,其概率密度分布基本服从正态分布;水流自输水隧洞段经扩散段、调整段、防涡段、向库区流动的过程中,紊动强度沿程呈现先增大后减小的变化规律,水流在输水隧洞段脉动流速小,在扩散段及调整段内脉动流速沿程均较大,脉动流速值接近时均值,甚至大于时均值,进一步解释了拦污栅断面脉动流速很大的原因。拦污栅断面及进出水口沿程的脉动流速规律有别于对脉动流速的一般认知规律。研究成果将为进出水口体型参数优化及分析引起拦污栅振动破坏提供理论依据。

Under outflow conditions,flows in a side inlet/outlet are in the diffusion mode and produce large velocity fluctuations in the trash rack section.In this work,a test facility for typical inlet/outlet flows is used for an experimental study with flow velocity measured using a laser doppler velocimetry and an acoustic doppler velocimetry.The results show large velocity fluctuations occur at the cross section of the trash rack installed near the exit of the diffuser,with the fluctuating components reaching up to 1.8 times of the mean velocity and an average turbulence intensity of 0.724.The probability density of the fluctuations basically follows a normal distribution.Turbulent intensity shows a streamwise trend of first increasing and then decreasing along the flow starting from the diffuser inlet,through the diffusion section,adjustment section,and anti-vortex section,and to the reservoir.Velocity fluctuations are small in the upstream tunnel section and become relatively large in the diffusion and adjustment sections.Large velocity fluctuations at the trash rack cross section are explained.The results provide a theoretical basis for optimization of the inlet/outlet parameters and analysis of the vibration damage to trash racks.