Experimental Investigation of Lift Forces on Horizontal Cylinder near Bottom in Oscillating Flow

The lift forces on horizontal cylinder near bottom is experimentally investigated at Reynolds numbers (Re) in the range of 2 500~10 000 and Keulegan^Carpenter numbers (Kc) in the interval of 5~20, and gap ratio (e/D) is from 0.2 to 1.0. Lift force coefficient (CL) and the deviation value of lift force (a0) are analyzed by using the Fourier analysis method. It is found that both CL & a0 are the functions of the Kc number.

Viscous Effects on Wave Forces on A Submerged Horizontal Circular Cylinder

Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.

Viscous numerical examination of hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation

As a classical topic,the hydrodynamic forces on a submerged horizontal cylinder undergoing forced oscillation have been widely studied based on potential flow theory.However,the fluid viscosity and the flow rotation may play an important role when the oscillation amplitude of the circular cylinder is large,and large discrepancy will occur between the potential flow simulation and the experimental results.This study focuses on the study of hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation by means of a viscous fluid numerical wave tank(NWT)model.The accuracy of the numerical model is validated against available experimental data.The comparisons between the hydrodynamic forces on the circular cylinder predicted by the viscous fluid model and the potential flow model are conducted to show the viscous effects on the hydrodynamic forces.By the study on the flow fields,the mechanism of the viscous effects is explained by the vortex effect.The basic reason for the difference between the results based on the viscous fluid theory and the potential flow theory is revealed by analyzing the force components.

振荡流场中近底水平圆柱升力研究

在利用傅氏级数法模拟波、流场中水平圆柱上的升力时，其傅氏系数及初相位的选取是问题的关键。本文进行了近底水平圆柱在振荡流场中的物理模型实验，采用傅氏级数法推求各参数，得到不同Ｋｃ数及间隙比（ｅ／Ｄ）情况下的各种参数值．实验要素范围 Ｋｃ数为５～２０， Ｒｅ数为２ ５００～１００００，间隙比为０．１～１．０．

水平圆柱强迫振荡水动力特性的数值模拟

为了研究处于自由面以下完全淹没状态的水平圆柱在强迫振荡运动时的水动力特性,采用基于黏性流理论建立的二维两相流数值波浪水槽模型,对不同液相黏性条件下强迫振荡水平圆柱的受力进行计算,并对压力、黏性切力和圆柱运动之间的相位关系特征进行对比和分析,进而结合流场分析解释黏性影响机理。结果表明:黏性切力和涡旋压力对流体作用力的贡献差别是导致不同流体黏性下流体作用力结果差异的主要原因;涡旋运动相对圆柱振荡运动的滞后性受流体黏性影响显著,导致不同流体黏性下压力之间有相位差;流体水质点相对于圆柱的滞后运动在大黏性流体中更为显著,这导致了其黏性切力的相位超前现象。

基于转捩的SST模型求解三维圆柱受迫振动

为了研究受迫振动时立管结构的升力系数特性和尾迹脱落模式的关系,本文采用基于两方程转捩的SST模型进行了典型亚临界雷诺数(Re=105)下的刚性三维圆柱受迫振动计算。模型采用重叠网格技术和单自由度运动方程来模拟圆柱运动,采用两方程转捩模型提高数值计算的精确度。研究了横向受迫振动振幅比与无量纲振动频率2个参数对圆柱流体载荷特性的影响,并分析了升力系数与尾流脱落模式的关联性。通过与二维结果对比分析发现:三维情况下的脉动升力系数跳跃下降现象相较于二维时发生了延迟。三维效应影响下与二维情况存在一定差异,同等“2P”模式下,由于三维轴向旋涡分布的影响,升力未出现通常“2P”模式下的衰减现象。

定常流中横向振动圆柱的升力突变现象研究

基于Realizablek-ε模型,采用有限体积法对亚临界雷诺数下(Re=105)受迫振动圆柱的涡激振动问题进行了二维数值研究,着重研究了振动频率与振动幅度两个参数对圆柱振动响应的影响,计算了三类振动频率:①共振强迫;②振动频率小于静止圆柱脱落频率;③振动频率高于静止圆柱脱落频率,并分析了尾流涡度模式与横向受迫振动圆柱升力系数的关系。数值模拟结果表明,三类振动频率模式下的动力响应差异明显,振动频率与振动幅度对圆柱的脉动升力系数影响较大。随着受迫振动振幅的增加,圆柱脉动升力系数出现了突变衰减,圆柱静止情况下的脱落频率与受迫振动频率控制的波动出现了相位逆变,使得圆柱与流体的能量传递出现了逆向改变。尾迹涡度模式反映了脉动升力系数的突变,其中的"2P"模式反映出共振条件下,升力系数在圆柱振幅处于中等范围时保持较小值且变化较小。