Abstract Cryogenic nitrogen jetting is a promising drilling rate improvement method, in which heat transfer plays an important role in inducing thermal stresses and facilitating rock breakage. In the present study, we aim to study flow field and heat transfer of a cryogenic nitrogen jet in two potential phase states (i.e. liquid and supercritical) under downhole conditions and determine the effect of some critical engineering parameters, including inlet pressure, ambient pressure and standoff distance, which are of concern for field applications of this method. Three different detached eddy simulation (DES) approaches were compared and validated to assess their performances in jet flow issues. These comparisons indicate IDDES showed better performance in predicting the flow field and heat transfer of jet flow, and thus was adopted for the present simulations. According to the simulation results, vorticity, dominant frequency fd of vortex instability and pressure oscillations grow with increasing inlet pressure for both free and impinging jets. Compared to the liquid nitrogen (LN2) jet, the supercritical nitrogen (SC N2) jet has higher vorticity magnitude and fd of temperature fluctuations, causing its vortex rings to breakdown in advance. The dominant frequency of temperature oscillations at the stagnation point falls at the same level as that of vortex instability in the shear layer, revealing the prevailing role of large-scale vortices in heat transfer. Under the same jet pressure condition, the heat transfer rate for SC N2 jet is constantly higher than that of LN2 jet. Increasing inlet pressure helps increase fd of temperature fluctuations and heat transfer rate for both LN2 and SC N2 jets. Under the same pressure difference (between inlet and outlet), lower ambient pressure is more conducive for SC N2 jets to enhance the vortex scale and heat transfer rate. In contrast, the ambient pressure has no significant influence on the LN2 jet. In the range of h/d ≤ 6, higher standoff distance delays the transition of vortex structures in the wall jet zone and contributes to the enhancement of heat transfer efficiency.

中文翻译：

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低温氮气射流流场与传热分离涡模拟

摘要 低温氮气喷射是一种很有前景的提高钻井速度的方法，其中传热在诱导热应力和促进岩石破碎方面起着重要作用。在本研究中，我们旨在研究在井下条件下处于两种潜在相态（即液体和超临界）的低温氮气射流的流场和传热，并确定一些关键工程参数的影响，包括入口压力、环境压力和间隔距离，这是该方法的现场应用所关注的。对三种不同的分离涡流模拟 (DES) 方法进行了比较和验证，以评估它们在射流问题中的性能。这些比较表明 IDDES 在预测射流的流场和传热方面表现出更好的性能，因此被用于目前的模拟。根据模拟结果，自由射流和撞击射流的涡量、涡不稳定性和压力振荡的主频率 fd 都随着入口压力的增加而增加。与液氮（LN2）射流相比，超临界氮（SC N2）射流具有更高的涡量和温度波动fd，使其涡环提前破裂。驻点温度振荡的主导频率与剪切层中的涡不稳定性处于同一水平，揭示了大尺度涡在传热中的主导作用。在相同的射流压力条件下，SC N2射流的传热率始终高于LN2射流。增加入口压力有助于增加 LN2 和 SC N2 射流的温度波动和传热速率的 fd。在相同的压差（入口和出口之间）下，较低的环境压力更有利于 SC N2 射流增强涡标和传热速率。相比之下，环境压力对 LN2 射流没有显着影响。在 h/d​​ ≤ 6 范围内，较高的间隔距离延迟了壁面射流区涡结构的转变，有助于提高传热效率。