In many equilibrium-based models for droplet size prediction, the fundamental parameters of turbulence are removed in favour of bulk quantities like velocity, and diameter. In this work we show that the upstream conditions of the jet are of critical importance and cannot be neglected, as they influence the turbulence field in jets in ways that are not accounted for in models based entirely on bulk parameters. This work presents the results of a single-phase investigation into the effect of upstream disturbances on a turbulent free jet.

Reynolds Averaged Navier-Stokes Simulations of turbulent free jets with disturbances (in the form of orifice plates with a β ratio of 0.5) located at varying locations upstream of the pipe exit have been undertaken. Validation against experimental data for an orifice plate in a pipe found the Standard k-ε model to be the most accurate of the RANS models tested for this geometry.

The additional turbulence generated from the upstream disturbances was found to be advected downstream and did not dissipate prior to the jet exit. The increased turbulence levels and altered form of the turbulence profile at exit was found to affect the evolution and observed turbulence levels of the free jet.

Two distinct ‘modes’ were observed for the influence of the disturbances on the free jet. When the orifice plate is near the exit the free jet is dominated by the behaviour of semi-confined jet forming from the blockage. For the deeper set disturbances, the predicted form of the free jet was similar to that of the free jet from a straight pipe, though the turbulence levels are still elevated at the exit, affecting spreading rates and turbulence levels in the jet.

Measures based on averages of TKE and TDR over hemispheres of varying radii are proposed for the development of models that do take into account the turbulent state of the exiting jet.

在许多基于平衡的液滴尺寸预测模型中，湍流的基本参数被移除，以支持速度和直径等体积量。在这项工作中，我们表明射流的上游条件至关重要且不容忽视，因为它们以完全基于体参数的模型中未考虑的方式影响射流中的湍流场。这项工作展示了上游扰动对湍流自由射流的影响的单相研究结果。

雷诺平均 Navier-Stokes 模拟湍流自由射流与扰动（以 β 比为 0.5 的孔板的形式）位于管道出口上游的不同位置。针对管道中孔板的实验数据进行验证后发现，标准 k-ε 模型是针对该几何形状测试的 RANS 模型中最准确的。

上游扰动产生的额外湍流被发现在下游平流并且在射流出口之前没有消散。发现增加的湍流水平和出口处湍流剖面的改变形式会影响自由射流的演变和观察到的湍流水平。

对于扰动对自由射流的影响，观察到两种不同的“模式”。当孔板靠近出口时，自由射流由堵塞物形成的半封闭射流行为支配。对于更深的扰动，自由射流的预测形式与来自直管的自由射流的预测形式相似，尽管出口处的湍流水平仍然升高，影响了射流中的扩散率和湍流水平。

提出了基于不同半径半球的 TKE 和 TDR 平均值的测量，用于开发确实考虑了退出射流湍流状态的模型。