Research On Flow-induced Vibration Of Passive Turbulence Control Cylinder With Nonlinear Springs

In the face of the issues of severe global climate increasingly,many countries in the world are developing clean and low-carbon new energy greatly to reduce reliance on fossil energy.China has put forward the strategic goal of "two-carbon" to achieve carbon emission peak before 2030 and carbon neutrality before 2060.A safe,efficient and economical hydrokinetic power conversion,which is Vortex Induced Vibration for Aquatic Clean Energy(VIVACE)converter,can convert the energy in ocean currents into electricity with the use of flow-induced vibration(FIV)of cylinder.In order to the enhance the energy harvesting efficiency of VIVACE converter,the response of amplitude and frequency of the cylinder are enhanced and performance of the converter are improved with the utilization of passive turbulence control techniques(PTC)and nonlinear springs.Meanwhile,in order to realize the visualization of vortices and reduce the cost of experiments and constraints of experimental conditions,the method of numerical simulation is used to accurately predict the flow-induced vibration response of the cylinder.Numerical simulations of flow-induced vibrations of a single PTC cylinder supported respectively by piecewise spring and cubic spring are realized for Reynolds number 24000<Re<120000.The results of simulations are compared with the experimental results.The main contents and conclusions of this thesis are as follows:Firstly,the flow-induced vibrations of PTC-cylinder supported respectively by piecewise spring and cubic spring are compared with linear spring.It is found that the oscillation of the PTC-cylinder supported by linear spring cease in the transition between the VIV and galloping branch.That shortcoming are eliminated by the use of the piecewise spring or the cubic spring.Meanwhile,amplitude and oscillation velocity of the cylinder are enhanced.At Re=1.16×105,the cylinder with the piecewise spring has a 29.4%increase in amplitude and 33.02%increase in maximum oscillation velocity.Meanwhile,the cylinder with the cubic spring has a 21.13%increase in amplitude and 25%increase in maximum oscillation velocity.Compared with the PTC-cylinder with linear springs,both the number of vortices and vortex intensity are increased by the use of the piecewise spring or the cubic spring.Compared with the power generation of the linear-stiffness converter at Re=1.16×105,the power generation has a 48.61%increase for the piecewise-stiffness converter and 47.61%increase for the cubicstiffness converter.It is show that the converter with nonlinear springs has more power generation.Secondly,the effects of piecewise springs with different piecewise points on the flowinduced vibrations of PTC-cylinder are discussed.It is found that the amplitude of the PTCcylinder increases with the decrease of the piecewise point.In the result of numerical simulations,the maximum amplitude for y0=0.5D function is 2.576D and 56.88%higher then the linear stiffness counterpart.The oscillation frequency of the cylinder increases with the increase of the piecewise point.With the increase of the Reynolds numbers,vortex shedding patterns for the smallest piecewise point y0=0.5D is 2S、2QP、2S+P、2T+4S in turn.the power generation of converter increase with the increase of piecewise point in VIV upper branch,and decrease with the increase of piecewise point in galloping branch.Compared with y0=1.5D function,the power generation has a 21.93%increase for the piecewise-stiffness converter with y0=0.5D function at Re=1.16×105.Furthermore,the flow-induced vibration of the PTC-cylinder supported by cubic springs with different nonlinearity strengths is analyzed.It is found that the nonlinearity strengths has less impact on the oscillatory response of the PTC-cylinder and the power generation of converter in the VIV initial branch and the upper branch.and has more effect in the transition between the VIV and galloping branch and the upper branch.In the transition between the VIV and galloping branch,the amplitude and the power generation increase with the increase of nonlinearity strength.The cylinder with Kcubic=10000N/m3 has a 17.26%increase in amplitude and 10.68%increase in maximum oscillation velocity at Re=1.16×105.the cylinder with Kcubic=30000N/m3 has more vortex shedding patterns of P+T、T+P and 2P.In the galloping region,the amplitude and the power generation decrease with the increase of nonlinearity strength,the oscillation frequency increase with the increase of nonlinearity strength,and shed more vorticities with small scale are shed,the vortex shedding pattern is 2T+2S pattern.Finally,the effects of piecewise springs and cubic springs on the flow-induced vibration of the PTC-cylinder with different system damping are further analyzed.It is found that for 3.0×104<Re<1.2×105,the amplitude,oscillation velocity of cylinder with the piecewise spring or the cubic spring and the range of VIV upper branch decreases with the increase of damping.The oscillating frequency of the cylinder with the piecewise spring shows a trend of increasing with the increase of damping in the range of 7.15 × 104<Re<1.2 ×105,while the oscillating frequency of the cylinder with the cubic spring increases with the increase of damping in the range of 3.0×104<Re≤6.0×104 and 8.5×104<Re<1.2×105.The power generation of converter with piecewise spring or cubic spring increases with the increase of damping.Compared with the power generation with Charness=10Ns/m at Re=1.16×105,the power generation has a 74.82%increase for the piecewise-stiffness converter with Charness=30Ns/m,and the power generation has a 74.82%increase for the cubic-stiffness converter with Charness=30Ns/m.It is shown that the system damping plays an important role in the energy harvesting power of the converter.The numerical calculation method in this thesis accurately predicts the flow-induced vibration of the PTC-cylinder supported by the piecewise spring or the cubic spring.The vortex shedding patterns are found clearly and the mechanism of flow-induced vibration of the PTC cylinder is revealed to provide a theoretical basis and technical support for the development and optimization of the VIVACE converter.