Effect Of Asymmetric Flow Field On Flow Induced Vibration Characteristics Of PTC Cylinder

Flow induced vibration(FIV)is common in natural phenomena and engineering.Although the intensity of FIV can cause fatigue damage to engineering structures and cause serious safety problems,FIV phenomena contain a large amount of energy.In order to improve the energy collection efficiency of the flow-induced vibration energy collection system,the passive turbulence control(PTC)method with selective additional rough bands on the surface of the cylinder was used to study the free surface flow and the shear flow.In this paper,the numerical calculation method is used to compare the parametric characteristics of the PTC cylinder in the symmetrical flow,and the static flow around the PTC cylinder and the FIV phenomenon under the free surface and the shear flow are respectively carried out.Research has realized the combination of VOF(Volume of Fluid)method and flow-induced vibration technology.The buoyancy correction of the lift coefficient calculation formula is carried out for the overall migration phenomenon of the FIV lift coefficient curve in the free surface flow,and the lift coefficient equation under the free surface flow field is obtained.In the Reynolds number range(3.5×10~4≤Re≤7.0×10~4)studied in this paper,the dynamic parameters(lift and drag coefficients),vortex structures,FIV response(amplitude ratio,frequency ratio and lift-displacement phase angle characteristics),and energy collection characteristics of PTC cylinder under different flow conditions were obtained.The study found that:Firstly,compared with symmetrical flow field,the asymmetry of asymmetrical flow field causes the instability of shear layer;the asymmetry makes the starting time of the cylindrical oscillator shorter and can dynamically control the motion of the cylindrical oscillator.When the PTC cylinder is stationary,the lift and drag coefficients change linearly with the free surface height(Z)and shear rate(k),respectively,and the reciprocating motion of the cylinder and the pressure difference resistance make the change range of the lift and drag coefficients of the PTC cylinder FIV larger than that of the stationary flow.The free surface only produces irregular changes in the positive amplitude ratio,the positive and negative amplitude ratios in the shear flow field vary linearly with the shear rates;the frequency ratio in the free surface flow field is closer to the experimental data,while the frequency ratio in the shear flow varies linearly with the shear rates;the lift-displacement phase angle in the asymmetric flow field is 0-60°,and the phase angle is larger than the symmetrical flow field,indicating that the lift in the asymmetric flow field maximizes the amplitude increase of the cylinder.Secondly,the free surface does not affect the shear pattern of vortices;with the increase of shear rate,the deviation of vortices toward high-speed direction becomes larger and the distance between vortices increases;with the increase of Reynolds number,the velocity of wake vortices in asymmetric flow changes faster and multi-vortex modes are more likely to occur;the greater the asymmetry of flow field,the greater the promotion effect on the cylinder amplitude.Finally,in the Reynolds number range studied in this paper,through the calculation of energy output power and efficiency of Vortex-induced Vibration Aquatic Clean Energy System(VIVACE),it is found that the asymmetric flow field is more conducive to flow-induced vibration to generate electricity,and can improve the energy output power and efficiency of PTC cylindrical VIVACE system.