The new term belongs in the “basic,” free-shear-flow part of the Spalart–Allmaras (SA) model, and extends an idea of the Secundov team, incorporated in the ν_t-92 model. It detects transverse curvature in the distribution of the eddy viscosity \( \tilde{\nu } \), so that it is passive in two-dimensional thin shear flows but potent especially in round jets. It eliminates the large over-prediction of the growth rate of such jets by the SA model, first detected by Birch in 1993. The originality is that the term is proportional to the middle eigenvalue λ₂ of the Hessian operator of \( \tilde{\nu } \). This is of course an empirical concept, but it is discriminating and rises when the distance r from the cylindrical axis becomes comparable with the length scale δ of the variations in the r direction. The inverted parabola is a prime example of such a distribution, and not unlike the \( \tilde{\nu } \) distribution in the round jet. The quantity λ₂ is not infinitely differentiable, but it is free of singularities, and unlike the ν_t-92 version, is not dependent on two large quantities cancelling. The core term added to the Lagrangian derivative \( D\tilde{\nu }/Dt \) is simply c_b3 λ₂ \( \tilde{\nu } \), where c_b3 is a new constant. The computing cost of calculating and ordering the eigenvalues is moderate. We have no proof of well-posedness for the new equation set, but the evidence so far is favorable, both in structured and unstructured grids. The λ₂ term is calibrated on a fully-developed round jet, and tested in nine other cases, either 2D flows or flows in which r » δ, finding that in the latter it is negligible as expected. This is although the c_b3 constant is rather large, namely 6. The λ₂ term is not strong enough to make a mature vortex fully relaminarize as would be desirable, but the eddy viscosity drops by 74%. The raw λ₂ term reduces the eddy viscosity in pipe flow, where that is detrimental; therefore, in the final model, it is multiplied by a function of the r_SA parameter of the SA model, which is a measure of wall proximity. The λ₂ term appears to be a safe addition to the SA model, and its application in different codes and to a variety of flows to be desirable.

新的术语属于在“基本”，自由剪切流的Spalart-Allmaras湍流（SA）模型的一部分，并延伸所述Secundov队的想法，在ν并入_吨-92模型。它在涡流粘度\（\ tilde {\ nu} \）的分布中检测横向曲率，因此它在二维薄剪切流中是被动的，但在圆形射流中尤其有效。它消除了由SA模型，使得射流的速度增长，在1993年首先由桦木检测的大的过预测的独创性的是，该术语是正比于中间特征值λ ₂的Hessian矩阵的操作者\（\ {波浪号\ nu} \）。当然这是一个经验性的概念，但是随着距离r从圆柱轴开始的距离δ变得与r方向上的变化的长度尺度δ相当。倒抛物​​线是这种分布的主要示例，与圆形射流中的\（\ tilde {\ nu} \）分布没有什么不同。λ数量₂并非无限可微，但它是免费的奇点，不像ν_牛逼-92版本，不依赖于两个大批量取消。核心术语添加到拉格朗日衍生物\（d \代字号{\ NU} / DT \）是简单地Ç _B3 λ ₂ \（\代字号{\ NU} \） ，其中c _B3是一个新的常数。计算和排序特征值的计算成本适中。我们没有新方程组的适定性证据，但是到目前为止，无论在结构化网格还是非结构化网格中，证据都是有利的。所述λ ₂术语被校准上的充分发展的圆射流，并且在其它9箱子测试，无论是二维流动或流，其中[R  »δ，发现在后者它是可忽略的预期。这是虽然C _B3常数是相当大的，即6.λ ₂术语不强足以使成熟的涡流充分relaminarize作为将是可取的，但涡流粘度由74％下降。原始λ ₂该术语降低了管道流动中的涡流粘度，这是有害的；因此，在最终模型中，将其乘以SA模型的r _SA参数的函数，该参数用于衡量墙的接近程度。所述λ ₂术语似乎是安全的除SA模式，其在不同的码和各种流的应用是可取的。