论文标题
使用直接数值模拟研究高压湍流喷气机
Investigation of high-pressure turbulent jets using direct numerical simulation
论文作者
论文摘要
基于喷气直径（$ d $）和喷射式散装速度（$ u_ {e} $）以$ 5000 $的雷诺数（$ re_ {d} $）的免费圆形喷气机的直接数值模拟，以研究超级策略压力的喷气湍流特征。喷气机由$ \ mathrm {n_ {2}} $组成，该$在同一温度下注入$ \ mathrm {n_ {2}} $。为了理解湍流混合，以统一施密特数字的流量运输了一个被动标量。考虑了两组从光滑的收缩喷嘴（层流流入）或长管喷嘴（湍流流入）发出的喷气机的两组流入条件。通过一次更改一个参数，模拟检查了对热力学条件的喷气流敏感性（以可压缩因子（$ z $）和归一化的等温可压缩性为特征），流入条件和环境压力（$ p _ {\ infty} $）跨度完美至真实的环境。流入会影响大气和超临界$ p _ {\ iffty} $的近场（包含潜在核心封闭和过渡区域）的流量统计（包含具有自相似统计的完全发达的流动）。在过渡区域中，对流入的敏感性更大，在该区域中，层流式流射机表现出显着的相干结构，产生的平均应变速率和湍流动能高于湍流Inflow Jets。在固定的超临界$ p _ {\ infty} $下减少$ z $会增强压力和密度波动（分别通过局部平均压力和密度归一化），但对速度波动的影响也取决于局部流动动力学。当$ z $减少时，层流射流过渡区域中的平均应变率很大，可以显着提高速度波动（通过局部平均速度归一化）和标量混合，而湍流流入中的效果则很小。
Direct numerical simulations of free round jets at a Reynolds number ($Re_{D}$) of $5000$, based on jet diameter ($D$) and jet-exit bulk velocity ($U_{e}$), are performed to study jet turbulence characteristics at supercritical pressures. The jet consists of $\mathrm{N_{2}}$ that is injected into $\mathrm{N_{2}}$ at same temperature. To understand turbulent mixing, a passive scalar is transported with the flow at unity Schmidt number. Two sets of inflow conditions that model jets issuing from either a smooth contraction nozzle (laminar inflow) or a long pipe nozzle (turbulent inflow) are considered. By changing one parameter at a time, the simulations examine the jet-flow sensitivity to the thermodynamic condition (characterized in terms of the compressibility factor ($Z$) and the normalized isothermal compressibility), inflow condition, and ambient pressure ($p_{\infty}$) spanning perfect- to real-gas conditions. The inflow affects flow statistics in the near-field (containing the potential core closure and the transition region) as well as further downstream (containing fully-developed flow with self-similar statistics) at both atmospheric and supercritical $p_{\infty}$. The sensitivity to inflow is larger in the transition region, where the laminar-inflow jets exhibit dominant coherent structures that produce higher mean strain rates and higher turbulent kinetic energy than in turbulent-inflow jets. Decreasing $Z$ at a fixed supercritical $p_{\infty}$ enhances pressure and density fluctuations (normalized by local mean pressure and density, respectively), but the effect on velocity fluctuations depends also on local flow dynamics. When $Z$ is reduced, large mean strain rates in the transition region of laminar-inflow jets significantly enhance velocity fluctuations (normalized by local mean velocity) and scalar mixing, whereas the effects are minimal in jets from turbulent inflow.
