几何参数对紧凑涡轮过渡段内部流动机理影响研究

Flow and Control Mechanisms in Aggressivelnter-Turbine Ducts

本文深入探讨了定常来流条件下过渡段内部流动机理和损失机制。通过保持过渡段长高比、雷诺数和进口旋流不变,借助实验和数值模拟方法,系统地研究了过渡段中位角和出口面积对其内部流动及气动性能影响。研究发现,过渡段内部流场结构主要以对涡及轮毂和机匣区域附面层分离为主。过渡段来流尾迹、中位角及进出口面积比是影响过渡段内部流动损失的三个主要因素。其中,中位角决定了机匣第一弯逆压梯度强度,面积比主要控制第二弯静压升,上游尾迹是诱发机匣侧流动分离的主要诱因。在大中位角情况下,机匣第一弯的流动分离更严重,分离明显提前。在大面积比情况下,机匣侧不仅出现由上游尾迹堆积产生的流动分离,还会出现机匣附面层自身二维分离。随着过渡段的中位角和面积比增大,损失急剧增加。

The present workis aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries.A systematic experimental and computational study was carried out for varying duct mean rise angles and outlet-to-inlet area ratio while keeping the duct length-to-inlet height ratio,Reynolds number and inlet swirl constant in all four geometries.The flow structures within the ITDs were found to be dominated by the counter-rotating vortices and boundary layer separation in both the casing and hub regions.The duct mean rise angle determined the severity of adverse pressure gradient in the casing＇s first bend whereas the duct area ratio mainly governed the second bend＇s static pressure rise.The combination of upstream wake flow and the first bend＇s adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices.At high mean rise angle,the separation became stronger at the casing＇s first bend and moved farther upstream.At high area ratios,a 2-D separation appeared on the casing.Pressure loss penalties increased significantly with increasing duct mean rise angle and area ratio.