Abstract: To study centerline distribution and expansion ratio, which is the ratio of the maximum section area of the runner to the inlet’s area, changing impact on Circular-to-Rectangular transition duct flow field, based on the actual condition of a certain engine, numerical simulations were performed to investigate the transition duct of three different centerline distribution(rapid turning at the exit, modest turning and rapid turning at the entrance) and five expansion ratio(1.00,1.03,1.05,1.07,1.09). The internal flow field of transition duct, the total pressure recovery coefficient of the duct and the non-dimensional average streamwise vorticities were obtained. Results indicate that the static pressure distribution and streamline distribution of the cross section are different in the different structure. There is corner vortex in the cross section of the structure of the rapid turning at the entrance. And the total pressure recovery coefficient decreases along the flow direction of three different structures， while the streamwise vorticities increase and then decrease along the flow direction. In order of the maximum value of the streamwise vorticities of three different structures, it goes: the structure of the rapid turning at the entrance, the structure of the rapid turning at the exit and the structure of modest turning. Compared with the maximum value, the minimum value decreased by 19%. Due to the increase of the expansion ratio, corner vortices will occur in the cross section, and the total pressure recovery coefficient of the duct decreases gradually, and the structure of ε=1.03 has the highest total pressure recovery coefficient at the exit. The streamwise vorticities increase and then decrease along the flow direction. The local non-dimensional average streamwise vorticity at the exit section in the structure of expansion ratio 1.03 is 40.9% smaller than that of 1.07.The modest turning centerline distribution and the expansion ratio of 1.03 are optimal structure parameters.

Key words: Circular-to-Rectangular transition duct;Centerline distribution;Expansion ratio;Total pressure recovery coefficient;Corner vortex

摘要： 为了获得流道中心线变化规律和截面膨胀比ε对圆转方过渡段流场形态的影响规律，在某型发动机的真实工况下，分别对3种中心线变化规律（前缓后急、缓急相当、前急后缓）和5种膨胀比（1.00,1.01,1.03,1.05,1.07）的圆转方过渡段结构进行建模计算，得到了圆转方过渡段内部流场形态、总压恢复系数和流向涡涡量的变化规律。结果表明：不同结构的横截面静压和速度分布差异较大。前急后缓结构在圆转方横截面出现明显的角涡；在三种中心线变化规律结构中总压恢复系数沿流向均呈下降趋势，流向涡涡量沿流向均呈先增大后减小的趋势，三种结构的流向涡涡量最大值从大到小依次为前急后缓结构、前缓后急结构和缓急相当结构，最大最小值相差19%。随着膨胀比的增大，在圆转方横截面会出现角涡；在不同膨胀比结构中总压恢复系数沿流向均呈下降趋势，流向涡涡量沿流向均呈先增大后减小的趋势，膨胀比1.03结构的局部流向涡无量纲涡量比1.07结构小40.9%。缓急相当中心线变化规律和膨胀比ε=1.03为最佳结构参数。

关键词: 圆转方过渡段;中心线变化规律;膨胀比;总压恢复系数;角涡