Vortex structures downstream a lobed nozzle/mixer

An experimental study was conducted to investigate the evolutions of unsteady vortex structures downstream a lobed mixer/nozzle.A novel dual-plane stereoscopic PIV system was used to measure all 3-components of vorticity distributions to revealed both the large-scale streamwise vortices produced by the lobed mixer/nozzle and the Kelvin-Helmholtz vortex structures generated due to the Kelvin-Helmholtz instabilities simultaneously and quantitatively for the first time.The instantaneous and the ensemble-averaged vorticity distributions displayed quite different aspects about the evolutions of the unsteady vortex structures.While the ensemble-averaged vorticity distributions indicated the overall effect of the special geometry of the lobed nozzle/mixer on the enhanced mixing process,the instantaneous vorticity distributions elucidated many details about how the enhanced mixing process was conducted.In addition to quantitatively confirming conjectures of previous studies,further insight about the formation,evolution and interaction characteristics of the unsteady vortex structures downstream of the lobed mixer/nozzle were also uncovered quantitatively in the present study.

小突片强化混合结构三维流场数值模拟

采用Roe通量差分分裂格式对带有小突片的轴对称收 扩喷管内外流场进行了数值模拟。小突片形状有三角形和梯形 ,数目为 2个或 4个 ,堵塞比为 0 0 2 ,0 0 4和 0 0 6 ,相对高度为 0 0 8和 0 16 ,安装角分别为 12 0° ,135°和 15 0°。计算结果表明 :在喷管出口安装 2个或 4个小突片能使得喷管下游内外流掺混时间及掺混距离大为缩短 ,而对喷管的推力系数影响不大。

小突片强化混合研究

测试了亚声速 （Ｍａ＝ ０．３５） 下小突片 （Ｔａｂｓ） 对轴对称收缩喷管射流的强化混合效果， 并探讨了小突片安装个数、后倾角度、堵塞比等因素对强化混合作用的影响。结果表明， 小突片对喷管射流的混合具有显著的强化作用， 不仅使下游流场发生显著变形， 使核心流的衰减显著加快（核心流长度从５Ｄ 降至大约１．５Ｄ）， 还使引射系数显著增加（本文中最大增加到２．７ 倍）。

两相圆湍射流喷口小突片对强化射流混合作用影响的流动显示

通过流动显示研究了Re=2350,粒子平均直径分别为150μm和350μm的两相圆湍射流中喷口加装小突片对射流混合的作用。探讨了不同粒径颗粒的存在对喷口小突片的射流混合作用的影响。通过PDA测量验证了流动显示结果。表明在150μm和350μm颗粒存在的情况下,小突片使射流核心区缩短的作用更加明显,而对射流的扩散作用却有所抑制。

小突片红外抑制效应的实验研究

利用地面模拟试验件实验研究了主喷管流速为亚声速,温度610℃左右,下洗气流速度11m/s,位于主喷管出口的小突片的安装方式和尺寸对某型号直升机发动机出口红外隐身效果的影响,实验用的混合管主喷管面积比为1.5。结果表明,和不装小突片时的基准状态相比,安装四片小突片时出口最高气流温度和平均气流温度分别降低2.3%和1%,主喷管总压升高0.44%。而增加小突片的尺寸,对红外抑制效果有所改进,不过总压损失会增大。