标题： 螺旋流动由盐指自发生成 显示英文标题

标题： Helical flows spontaneously generated by salt fingers

摘要： 我们研究在盐度扩散缓慢（逆莱利数小）和强分层（密度比大）的条件下盐指的动态，重点关注与地球海洋相关的条件。 使用周期性区域中的三维直接数值模拟，我们表明在该条件下盐指表现出丰富的多尺度动态，具有垂直伸长的指状结构，这些结构在大尺度上由平均流扭曲成螺旋形状，并在小尺度上被各向同性涡旋破坏。 我们使用多尺度渐近分析来提出一组简化的偏微分方程，该方程过滤内部重力波并去除动量方程中所有部分的惯性，除了驱动螺旋平均流的雷诺应力。 当数值模拟时，简化方程在适当条件下能够捕捉到与完整方程相同的动态和通量。 简化方程在平均流的所有波动中强制零螺旋度，这意味着对称性破缺的螺旋流动是由严格非螺旋波动自发产生的。 显示英文摘要

摘要： We study the dynamics of salt fingers in the regime of slow salinity diffusion (small inverse Lewis number) and strong stratification (large density ratio), focusing on regimes relevant to Earth's oceans. Using three-dimensional direct numerical simulations in periodic domains, we show that salt fingers exhibit rich, multiscale dynamics in this regime, with vertically elongated fingers that are twisted into helical shapes at large scales by mean flows and disrupted at small scales by isotropic eddies. We use a multiscale asymptotic analysis to motivate a reduced set of partial differential equations that filters internal gravity waves and removes inertia from all parts of the momentum equation except for the Reynolds stress that drives the helical mean flow. When simulated numerically, the reduced equations capture the same dynamics and fluxes as the full equations in the appropriate regime. The reduced equations enforce zero helicity in all fluctuations about the mean flow, implying that the symmetry-breaking helical flow is spontaneously generated by strictly non-helical fluctuations.