| The peripheral flow of gas-liquid two-phase fluid exists in a variety of industrial applications,e.g.the power engineering,petroleum chemical industry,nuclear power use.The alternating vortex will shed from the cylinder in a certain flow conditions,which will lead the cylinder vibrating caused by the alternating force induced by fluid,and then the damages not only threaten the safety of equipment operation,but also reduce the service life of industrial equipment greatly.In order to understand the interaction mechanism of the gas-liquid two-phase flow and the cylinder,reveal the formation and evolution propertiesof the gas-liquid two-phase vortex,and provide the scientific basis for industrial equipment's optimization design and the safe operation,both the experimental study and numerical simulation were conducted to the vortex characteristics of the gas-liquid two-phase which shed from a single-cylinder or from rotating-staggered-cylinders in a vertical rectangular pipe,which is subsidized by the National Natural Science Fund(No.50676017)and Science and Technology Key Project of the Ministry of Education(No.206037).The content is:(1)A gas-liquid two-phase flow test bed were built,which the two-phase medium is the normal temperature water and the compressed air respectively.The research on the dynamic characteristics of the thin bubbly flow around a cylinder or cylinder bundles may be carried out in the vertical ascent test bed with a rectangular cross-section.A measuring device was designed which can be used to measure continuously the cylindrical surface pressure in a multi-angle , and then the multi-point pressure measurement by a single sensor in the same condition was achieved.A set of dynamic data acquisition and analysis system was established to measure the fluctuating pressure and vortex shedding frequency around the cylinder surface.In order to reveal the formation and evolution properties of the gas-liquid two-phase vortex around staggered cylinder bundles,a set of high-speed dynamic image acquisition and analysis system was established by using the resolution of 768×512 pixels,shooting speed of 1000fps.(2)The distributions of the fluctuation pressure and time-averaged pressure were measured around a cylinder,with the diameter of 35mm,under the conditions of different air void and Reynolds number,when the gas-liquid two-phase fluid flowing cross it.The results show that:both the time-averaged pressure coefficient and fluctuating pressure coefficient on the cylinder surface are affected greatly by the void fraction,increasing with the value of void fraction,the minimum value of time-averaged pressure coefficient reduces gradually,while the peak value of fluctuating pressure coefficient reduces gradually,the back pressure increases gradually,and the vortex shedding location constantly moves backward; In the experimental range,Reynolds number affects slightly on the fluctuation pressure and time-averaged pressure.Meanwhile, according to the principle that the vortex shedding should cause the pressure different on either side of the cylinder,the dynamic pressure differential fluctuation signals were measured.The vortex shedding frequency was obtained by using the method of power spectrum analysis,and it is analyzed how the power spectrum is affected by the air void and Reynolds number.The results show that:increasing with the air void,the vortex shedding frequency increases and the power spectral energy decreases,when the air void is higher than 0.1,the phenomenon of vortex shedding alternately disappears.(3)The high-speed dynamic image processing method was used to study the evolution characteristics of the two-phase vortex around the staggered cylinder bundles.The evolution process of vortex generation,entrainment and polymerization among the cylinders was reconstructed by the dynamic image,the mechanism of vortex evolution was analyzed qualitatively,and the periodical characteristics of vortex shedding were compared by the image correlation and were analyzed by the statistical method.The analysis showed that:Strouhal number increases with the pitch ratio increasing,while it decreases with the air void increasing,when the value of air void is higher than 0.14,the periodical vortex shedding phenomenon vanishes;in addition,vortex shedding frequency increases with the Reynolds number increasing.(4)Adopted the two-fluid model for gas-liquid two-phase, the unsteady flowing processes were numerically simulated for the two-phase flowing cross the staggered cylinder bundles with different pitch-diameter ratio,Obtained spectra of transient flow field and vortex flow and void fraction distribution,the results showed that:The vortex separation does not appear around the upstream cylinder,while the downstream cylinder is surrounded by the free shear layer,and the bubble was entrained by the vortex so that the void fraction and the vorticity have the same distribution characteristics.It was primarily analyzed on how the pitch ratio,void fraction and Reynolds number affect the vortex shedding characteristics,fluctuating lift and time-averaged drag around the bundle,the results showed that:In the case of different pitch ratio,the fluctuating lift coefficient around the downstream cylinder is the largest,while the maximum value of the time-averaged drag coefficient is in the middle of bundle;In the event of critical pitch ratio, ( S /d)cr,there is the minimum coefficient value of both fluctuating lift and time-averaged drag;When the flow is of a small void fraction,α=0.03,0.12, the lift coefficient decreases with Reynolds number increasing,While at a large void fraction,α=0.2,0.3,the lift coefficient increases with Reynolds number increasing;The time-averaged drag coefficient around each row of cylinders decreases with void fraction increasing.
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