旋流阻塞泄洪洞内气水两相流流动特性分段数值模拟研究

Research on Characteristics of Gas-water Two-phase Flow in Swirling Spillway Tunnel with Blockage by Segmentation Simulation

在水平旋流洞内设置阻塞会形成阻塞空腔旋转水流,可以大大提高其抗空化性能及消能率。但设置阻塞后,旋流洞段为空腔旋流,阻塞扩散段为由空腔旋流转变为高紊动强混掺气水两相流,流动变得十分复杂。该文在模型试验成果的基础上,采用VOF与Mixture多相流模型分段数值模拟的方法,对旋流阻塞复合内消能泄洪洞气水两相流的流动特性进行了研究。结果表明:分段模拟结果与试验值吻合良好,可以实现精确模拟;起旋器与旋流洞段会形成空腔沿程略有减小且气水界面清晰的三维空腔旋流,空化可能性小;阻塞扩散段与退水洞前段由空腔旋流向高紊动强混掺气水两相流转变,呈现出空腔旋流区、气水混掺区和混掺发展区三个流动特征区。气水混掺始于阻塞均匀段,至扩散段末端已较充分;扩散段中上部存在大尺度漩涡,加剧了气水混掺;湍动能沿程在阻塞扩散段与退水洞前段较大,为主要消能区,横断面上则位于气水交界面混掺区域,气水相互作用加剧了水流紊动;在距起旋器起始端头9.2~15.0倍洞径长度范围的阻塞扩散段的中后部,以及退水洞前部洞顶与两侧壁靠上位置,出现了较小负压,水流空化数小,但水流充分掺气可有效减免空化。旋流洞内设置阻塞有助于增压及掺气减蚀以改善空化条件,同时可以加剧水流能量耗散以提升消能效果,使其在高坝泄洪消能中应用前景广阔。

The anti-cavitation performance and energy dissipation rate are greatly improved due to the blockage in the swirlingblocking composite internal energy dissipation spillway tunnel.However,there is cavity swirling flow in the swirling section,and which is transformed into a highly turbulent and strongly mixed gas-water two-phase flow in the blocking diffusion section,then the flow becomes very complex.In this paper,the characteristics of gas-water two-phase flow in the tunnel are studied by the method of segmental numerical simulation with VOF and Mixture model based on the model test results.The results show that the simulation results are in good agreement with the model test and that accurate simulation is possible.In the generator and swirling section,there is three-dimensional cavity swirling flow with a slightly reduced cavity along the way and a clear gas-water interface,and low possibility of cavitation.In the blocking-diffusion section and the front of the drainage tunnel,the cavity swirling flow transforms into a highly turbulent and strongly mixed gas-water two-phase flow,and there are three flow characteristic regions:cavity swirling region,gas-water mixing region and mixing continuation region.The mixing of gas and water starts from the blocking uniform section,and it is sufficient in the end of the diffusion section.There are large-scale eddies in the upper middle position of the diffusion section,which intensifies the mixing of gas and water.The turbulent kinetic energy is larger in the blocking diffusion section and the front of the drainage tunnel which is the main energy dissipation section,and larger in the gas-water mixing area on the cross section,which the intensifies turbulence region spreading to the side wall along the way.The turbulence of flow is aggravated by gas-water interaction.Small negative pressure appears on the top of the middle and rear of the blocking diffusion section and the front of the drainage tunnel which is 9.2 to 15.0 times the diameter from the generator starting section.The cavitation numbers of the flow are small in the negative pressure section,but the cavitation can be effectively prevented by sufficient aeration.The blockage is helpful for pressurization and aeration mitigation corrosion to improve the cavitation conditions in the swirling-blocking composite internal energy dissipation spillway tunnel,and intensifies the energy dissipation,so that there is a broad application prospect in high dam.