双层环境中圆桩柱对斜坡异重流动力特性影响的试验研究

Experimental study on the impacts of a circular pile on hydrodynamics of downslope gravity current in two-layer stratified ambience

利用开闸式异重流水槽试验,结合高速相机和粒子图像测速技术,量化不同强度双层环境中圆桩柱对斜坡异重流传播模式、速度与涡度场、波流作用等宏微观特性的影响。试验结果表明:在低理查森数Ri_(ρ)环境中,圆桩柱的存在抑制了异重流混合层厚度的增加,但延展了其在流向的长度;在高理查森数Ri_(ρ)环境中,圆桩柱打破了侵入流在密度跃层处对称的传播模式,并促进了异重流与环境流体的剪切过程。当内波弗劳德数Fr> 1时,产生锁定波,异重流头部出现强漩涡,在密度跃层产生有利压力梯度使内波尺寸增大;当内波弗劳德数Fr <1时,振荡产生发射波,波谷与异重流头部相互作用而使波形变平整;当内波弗劳德数Fr≈1时,锁定波和发射波并存。在低理查森数Ri_(ρ)环境中,圆桩柱的存在导致波流耦合作用减弱,而在高理查森数Ri_(ρ)环境,波流耦合作用反而增强。

Using a series of lock-exchange gravity current experiments combined with high speed cameras and Particle Image Velocimetry,the effects of a circular pile in two-layer stratified ambience with different intensities on the propagation mode,velocity and vorticity field,wave-current interaction of gravity current were quantified.Experimental results show that for the low Richardson number Ri_(ρ),the circular pile restrains the increase mixed layer thickness of gravity current but extends its length in flow direction;for the high Richardson number Ri_(ρ),the circular pile breaks the symmetrical propagation pattern of the interflow at the pycnocline and promotes the shear process between gravity current and ambience fluid.When the wave Froude number Fr>1,a locked wave is generated,a strong vortex appears at the head of the gravity current,and a favorable pressure gradient in the pycnocline increases the size of internal wave;when the wave Froude number Fr<1,the gravity current oscillations produce launched wave,the wave trough is flattened by interaction with the head;and when the wave Froude number Fr≈1,the locked wave coexists with the launched wave.For the low Richardson number Ri_(ρ),the existence of circular piles weakens the wave-current coupling effect,but for the high Richardson number Ri_(ρ),the wave-current coupling effect is reinforced.