Abstract Results reported in the literature have shown that the turbulence models currently implemented in computational fluid dynamics (CFD) commercial codes (e.g., ANSYS-CFX, STAR-CCM+, and FLUENT) have a tendency to overestimate thermal stratification and underestimate turbulent mixing when buoyancy effects become dominant with respect to momentum effects. Also, standard large eddy simulation models cannot fully capture the behavior of jets interacting with stratified environments because the assumption of turbulence isotropy of the smaller scales breaks down. Because of light diffraction and image distortion, it is challenging to apply nonintrusive optical flow measurements, like particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF), to get experimental data for CFD validations when there are density variances involved in the flow. However, a refractive index matching (RIM) technique that has been recently developed in our Experimental and Computational Multiphase Flow Laboratory allows us to perform high-resolution measurements of velocity fields and scalar fields for turbulent buoyant jet flow in the presence of density differences as high as 8.6%. To form a fully turbulent round free jet, an experimental facility was designed with a jet nozzle diameter of 2 mm, located at the bottom of a cubic tank with 30-cm side length. The jet flow is established by a servo-engine-driven piston to eliminate possible fluctuations introduced by the motor. A high-fidelity synchronized PIV/PLIF system was utilized in conjunction with RIM to measure the velocity and concentration fields in the self-similar regions of a jet flow with a density difference of 3.16% for aqueous solutions. With Reynolds numbers of 4000 and 10 000, the jet impinging with a two-layer stably stratified environment is compared to the positively buoyant jet with lighter fluid injected into denser surroundings. Detailed quantifications of the measurement uncertainties are also carried out. The experimental results are presented in terms of turbulent statistics and the analysis of jet penetration depths.

中文翻译：

---

两层分层环境中湍流浮力圆形射流的速度场和标量场测量

摘要 文献报道的结果表明，当前在计算流体动力学 (CFD) 商业代码（例如，ANSYS-CFX、STAR-CCM+ 和 FLUENT）中实施的湍流模型在浮力时有高估热分层和低估湍流混合的趋势。动量效应占主导地位。此外，标准的大涡模拟模型不能完全捕捉与分层环境相互作用的射流的行为，因为较小尺度的湍流各向同性假设不成立。由于光衍射和图像失真，应用非侵入式光流测量具有挑战性，如粒子图像测速 (PIV) 和平面激光诱导荧光 (PLIF)，当流动中涉及密度变化时，获取用于 CFD 验证的实验数据。然而，最近在我们的实验和计算多相流实验室开发的折射率匹配 (RIM) 技术使我们能够在密度差异高达为 8.6%。为了形成完全湍流的圆形自由射流，设计了一个实验装置，喷嘴直径为 2 毫米，位于边长 30 厘米的立方罐底部。喷射流由伺服发动机驱动的活塞建立，以消除电机可能引入的波动。高保真同步 PIV/PLIF 系统与 RIM 结合使用来测量射流的自相似区域中的速度和浓度场，水溶液的密度差异为 3.16%。在雷诺数为 4000 和 10000 的情况下，将撞击两层稳定分层环境的射流与注入较稠密环境的较轻流体的正浮力射流进行比较。还进行了测量不确定度的详细量化。实验结果以湍流统计和射流穿透深度分析的形式呈现。将撞击两层稳定分层环境的射流与注入较稠密环境的较轻流体的正浮力射流进行比较。还进行了测量不确定度的详细量化。实验结果以湍流统计和射流穿透深度分析的形式呈现。将撞击两层稳定分层环境的射流与注入较稠密环境的较轻流体的正浮力射流进行比较。还进行了测量不确定度的详细量化。实验结果以湍流统计和射流穿透深度分析的形式呈现。