Experimental Study On Flow Induced Motion Characteristics And Energy Conversion Optimal Layout For Two Triangular Prisms

The efficient and rational utilization of marine energy resources has become one of the hot topics all over the word.The proposal of Vortex Induced Vibration Aquatic Clean Energy(VIVACE)organically combines the ocean current energy utilization with the flow induced motion(FIM).Fluid induced motion,as a common fluid-solid coupled interaction phenomenon in the engineering field,has been widely concerned on the application in the energy field.With the continuous development of FIM,the study of multi-vibrator of FIM has been gradually carried out.The research on multi triangular prisms is still rarely.In order to explore the FIM characteristics and energy conversion characteristics for two triangular prisms,based on the Flow Induced Motion Energy Conversion System(FIMECS),this paper conducted a series of experiments on FIM characteristics and energy conversion optimal layout for two triangular prisms.The main research work and achievements are as follows:(1)The experiments of FIM characteristics and energy conversion for single triangular prism have been carried out.The rules of typical hard galloping(HG)and typical soft galloping(SG)were analyzed and the energy conversion of different FIM branches were described.Subsequently,Particle Image Velocimetry(PIV)was been used to study the wake structure of single triangular prism.It can be concluded that the oscillation in galloping branch is stable and the energy is concentrated with high quality,which is beneficial to the efficient ocean current energy utilization.Wake structure of different branches are different,the 2S mode can be observed in VIV initial branch(Re?56100);the 2P mode can be observed in the VIV upper branch(Re?67800);the2P+S mode can be observed in the transition branch(Re?91,200)and galloping branch(Re?102900).(2)The experiments of FIM characteristics and energy conversion for two triangular prisms coupled has been carried out.The wake structure of two triangular prisms coupled oscillation also been analyzed.The results of FIM oscillation responses illustrated that the“Jump”phenomenon occurred on coupled tandem prisms and also can be observed for coupled parallel prisms.In the tests,the maximum active power of coupled tandem prisms is P_harn=21.04W(L/D=4).The maximum active power of coupled parallel prisms is P_harn=12.64W(T/D=1).The wake structure of the coupled two triangular prisms is very complex,which is different from that of the single triangular prism.(3)The experiments of FIM characteristics and energy conversion for two triangular prisms in tandem arrangement has been carried out.The effects of stiffness load resistances and spacing ratio on FIM and energy conversion were analyzed.The mutual interference of upstream and downstream prism was expounded.The results show that the amplitude and frequency of the upstream prism are very close to those of single prism.For U?1 m/s,the wake of upstream prism has obvious inhibition effect on the downstream prism.But with the increase of flow velocity,the wake of upstream prism has certain promoting effect on the downstream prism.The oscillation frequencies of the upstream and downstream prisms are very similar and the phase is maintained at a stable value for 6?L/D?8,because of the wake of upstream prism has a significant influence on the downstream prism.In the tests,the highest active power(P_harn=32.24W)of two prisms in tandem arrangement is 2.08 times that of single triangular prism(P_harn=15.47W).(4)The experiments of FIM characteristics and energy conversion for two triangular prisms in staggered arrangement has been carried out.The FIM characteristics of the staggered prisms in the typical VIV,typical SG and the wake interference of staggered upstream and downstream prism with different spacing ratios were analyzed.For 1?S/D?5,the amplitude of staggered upstream prism is obviously lower than that of the single upstream prism,with the frequency is close to that of the single prism.The amplitude of staggered downstream prism is higher than that of single downstream prism.It can be concluded that the wake of staggered upstream prism plays a significant role in promoting the staggered downstream prism.For 6?S/D?9,the situation is opposite.In the phase difference analysis,the phase difference between the two staggered prisms in different spacing ratios and different flow velocity are mostly maintained at a stable value.The synergistic oscillation performance of the two staggered triangular prisms is better.The optimal active power of staggered two triangular prisms is 26.43W(S/D=6),which is significantly 1.7 times that of the single triangular prism(P_harn=15W)and is 1.3 times that of two triangular prisms(P_harn=20.44W)in tandem.Based on the test results,it can be concluded that FIM responses and energy conversion of the staggered prisms with spacing ratio of 4?S/D?6are better.Which is conducive to ocean current energy utilization and the power density of the FIMECS system is in the range of 0.034?0.050k W/m³(U=1.24 m/s).