In an attempt to redefine and improve the ISO9300 norm, it is possible to see the emergence of a universal ($C_d$) curve. For this, all the influential factors must be correctly understood within their range of variation. In recent discussions, the experimental calibration point could be limited, and a low-pressure measurement could be sufficient to extrapolate the higher part of the curve with a relatively good level of confidence. For that purpose, the cylindrical shape gives more variations and needs a higher level of measurement to understand the behavior of the curve. Roughness level is a key parameter to this understanding. Experiments have been carried out to determine the impact of cylindrical nozzle throat roughness on $C_d$ and to demonstrate the need for precise dimensional parameters, such as diameter and roughness characterization. The results show that an increase in roughness may lead to a significant decrease in $C_d$, particularly at high Reynolds numbers ($R{e}_d$). A theorization is introduced based on Colebrook & White’s formulation which allows the thickness boundary layer to be quantified. This study highlights the need for further investigation into both cylindrical nozzles and roughness effects on the discharge coefficient in order to improve the norm.

在试图重新定义和改进 ISO9300 规范的过程中，有可能看到一个通用的（$C_d$） 曲线。为此，必须在其变化范围内正确理解所有影响因素。在最近的讨论中，实验校准点可能是有限的，低压测量可能足以以相对较好的置信度推断曲线的较高部分。为此，圆柱形状提供了更多的变化，需要更高级别的测量来了解曲线的行为。粗糙度水平是这种理解的关键参数。已经进行了实验以确定圆柱形喷嘴喉部粗糙度的影响$C_d$并证明需要精确的尺寸参数，例如直径和粗糙度特征。结果表明，粗糙度的增加可能导致显着降低$C_d$, 特别是在高雷诺数 ($\mathrm{电阻}{\mathrm{电子}}_d$）。基于 Colebrook & White 的公式引入了一个理论，它允许对厚度边界层进行量化。这项研究强调需要进一步研究圆柱形喷嘴和粗糙度对流量系数的影响，以提高规范。