曲率缓变型反弧段水流的紊动特性

Turbulence characteristics of the flow over gradually varied curvature bucket

本文在曲率缓变型反弧段水流时均特性研究的基础上，进一步使用二维激光测速系统对其紊动特性进行探讨，通过试验测得反弧段时均流速分布，流向和法向脉动流速的各种特征值；应用离心不稳定性理论分析了反弧水流特性，阐明沿程断面流速分布在反弧前半部趋于瘦弱，后半部趋于丰满的原因，并说明离心不稳定性作用导致反弧水流的混掺加剧；论证了壁面切应力和紊流强度在反弧后半段逐渐增加的原因；通过试验发现离心不稳定性效应的滞后现象．本文还就时均能量平衡、紊动能量平衡进行了较详细的分析．

Based on the researchs on the time average characteristics of the flow over gradually varied curvature bucket,the turbulence characteristics have been investigated by useing a 2-dimensional Laser Doppler Anemometer (LDA) system. The velocity. distribution of the bucket flow, the turbulent quantities along the streamlines and normal to the surface of the bucket are all measured in the experiments. The turbulent characteristics of the bucket flow are studied with the centrifugal instability theory, this explains why the velocity distribution tends to thin in the first half of the bucket while full and round in the second half and how the mixing of the bucket flow is increased due to this instability.The cause of the enhancement of the wall shear stress and turbulent intensity in the downstream of the bucket is also demonstrated. In addittion, a lag of tile instability effect has been found in experiments and analysis.The balaning of the time average and turbulent energy is studied in detail.