潮间带泥沙起动切应力现场测量装置

An in situ measurement device for sediment critical shear stress in intertidal zone

为了准确获得泥沙起动参数,减小对原状土的扰动,研制了一种潮间带泥沙起动切应力现场测量装置,利用Fluent软件模拟了装置内部流场与底部切应力,确定了在底部产生均匀切应力时的内外筒最佳转速比,建立了转速与底部切应力之间的关系,探讨了装置的最佳转速比受装置尺寸的影响。结果表明,该装置的内圆筒、外圆筒、剪力环三者同向转动时可以产生较大的底部切应力。以内圆筒半径310 mm、外圆筒半径410 mm、工作水深260 mm为例,如不设置剪力环且内外圆筒同向转动,装置最佳转速比为3∶1,此时底部切应力在距离轴心0.33～0.38 m范围内最为均匀;如设置剪力环且内圆筒、外圆筒、剪力环同向转动,装置最佳转速比为3∶1∶3,此时底部切应力在距离轴心0.33～0.40 m范围内最为均匀。底部切应力与外圆筒转速之间符合二次函数关系。

An in situ measurement device for sediment critical shear stress in the intertidal zone was developed to accurately obtain the parameters of sediment incipient motion and to reduce perturbation to the undisturbed soil. The inner flow field and the bed shear stress of the device were simulated using the software Fluent. The optimal speed ratio of the inner cylinder and outer cylinder for the most uniform bed shear stress was put forward. The correlations between the rotating speed and the bed shear stress was established and the influence of the device size on the optimal speed ratio was explored. It is found that higher bed shear stress can be obtained when the inner cylinder, outer cylinder and the shear ring rotate in the same direction. A device with an inner cylinder’s radius of 310 mm and an outer cylinder’s radius of 410 mm operating in a water depth of 260 mm was taken as an example. When the inner cylinder and outer cylinder rotate in the same direction without a shear ring, the most uniform bed shear stress distributes in the annular area with a distance of 0.33~0.38 m from the axis, and the optimal speed ratio is 3∶1. When the inner cylinder, outer cylinder and the shear ring rotate in the same direction, the most uniform bed shear stress distributes in the annular area with a distance of 0.33~0.40 m from the axis and the optimal speed ratio is 3∶1∶3. There is a quadratic function relation between the bed shear stress and the rotating speed of the outer cylinder.