AI 中文总结
本研究通过直接数值模拟探究倾斜重力流的间歇性湍流，构建延迟微分模型揭示其为延迟诱导振荡，发现增大初始雷诺数可抑制该间歇性。
AI 中文摘要
浅坡上的倾斜重力流可呈现出显著的湍流间歇性。采用直接数值模拟方法，我们针对时间发展型重力流在一系列初始雷诺数$Re_0$范围内研究该行为。当$Re_0=2500$且坡度角为$0.5^\text{o}$时，重力流的外层表现出湍流强度的大幅波动，以及湍流与弱湍流状态间的反复转变。对流动能量学的分析表明，这种间歇性与湍动能的剪切产生和耗散之间存在有限延迟相关。在过渡阶段，该延迟允许湍流发生瞬态放大，它通过从平均流中提取动能并促进夹带驱动的层增长，显著削弱平均剪切，最终导致层流化。增大$Re_0$会减小该延迟，逐步抑制间歇性，引导流场向更持续的湍流状态发展。受这些观测结果的启发，我们基于平均动能与湍动能的耦合演化，开发了一个自主延迟微分模型。该模型重现了随延迟减小从间歇性湍流向持续湍流转变的观测结果，并预测在通量理查森数更大时，间歇性倾向会增加。这些结果支持将倾斜重力流中的间歇性湍流解释为延迟诱导振荡，该振荡源于湍流对平均流变化的有限调整时间。
英文摘要
Inclined gravity currents on shallow slopes can exhibit pronounced turbulence intermittency. Using direct numerical simulations, we investigate this behaviour for a temporal gravity current over a range of initial Reynolds numbers $Re_0$. For $Re_0=2500$ and a slope angle of $0.5^\circ$, the outer layer of the current exhibits large excursions in turbulence intensity and repeated transitions between turbulent and weakly turbulent states. Analysis of the flow energetics reveals that the intermittency is associated with a finite delay between shear production and dissipation of turbulent kinetic energy. During transitional phases, this delay permits a transient amplification of turbulence, which significantly weakens the mean shear by extracting kinetic energy from the mean flow and promoting entrainment-driven layer growth, ultimately leading to relaminarisation. Increasing $Re_0$ reduces the delay and progressively suppresses intermittency, steering the flow towards a more sustained turbulent state. Motivated by these observations, we develop an autonomous delay-differential model based on the coupled evolution of the mean and turbulent kinetic energies. The model reproduces the observed transition from intermittent to sustained turbulence as the delay is reduced and predicts an increased tendency towards intermittency at larger flux Richardson numbers. The results support an interpretation of intermittent turbulence in inclined gravity currents as a delay-induced oscillation arising from the finite adjustment time of turbulence to changes in the mean flow.
