In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration (VIV) of top tensioned riser (Till), the differential equation is derive...In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration (VIV) of top tensioned riser (Till), the differential equation is derived based on work-energy principles and the riser near wake dynamics is modeled by Facchinetti' s wake oscillator model. Then Galerkin' s finite element approximation is implemented to derive the nonlinear matrix equation of the coupled equations and file corresponding numerical programs are compiled which solve the coupled equations directly in the time domain. The comparison of the predicted results with the recent experimental results and the prediction of SHEAR7 is performed. The results show the validity of the proposed method on the prediction of VIV of deep water risers. The effect of internal flow on the dynamic characteristics and dynmnic response of the riser is analyzed and several valuable conelusions are drawn.展开更多
At present, most researches on the vortex-induced vibration of submarine free spanning pipelines ignore the effect of internal flowing fluid; furthermore, there are no research reports considering the coupling effect ...At present, most researches on the vortex-induced vibration of submarine free spanning pipelines ignore the effect of internal flowing fluid; furthermore, there are no research reports considering the coupling effect of internal and external fluid with the free span. In this paper, combining Iwan's wake oscillator model with the differential equation derived for the dynamic response of submarine free spanning pipelines with inclusion of internal flow, the pipe-fluid coupling equations are developed to investigate the effect of internal flow on the vortex-induced vibration of the free spans. The finite element approximation is implemented to derive the matrix equations of equilibrium. The Newmark method combined with simple iteration is used to solve the system of equations. The results indicate that the internal fluid flow may cause the shift of resonance band to the lower frequency and a slight decrease in the peak value; the effect will be more pronounced with the increase of the span length and can be weakened in the presence of the axial tension.展开更多
Numerical study about vortex-induced vibration (V/V) related to a flexible riser model in consideration of internal flow progressing inside has been performed. The main objective of this work is to investigate the c...Numerical study about vortex-induced vibration (V/V) related to a flexible riser model in consideration of internal flow progressing inside has been performed. The main objective of this work is to investigate the coupled fluid-structure interaction (FSI) taking place between tensioned riser model, external shear current and upward-progressing internal flow (from ocean bottom to surface). A CAE technology behind the current research which combines structural software with the CFD technology has been proposed. According to the result from dynamic analysis, it has been found that the existence of upward-progressing internal flow does play an important role in determining the vibration mode (/dominant frequency), vibration intensity and the magnitude of instantaneous vibration amplitude, when the velocity ratio of internal flow against external current is relatively high. As a rule, the larger the velocity of intemal flow is, the more it contributes to the dynamic vibration response of the flexible riser model. In addition, multi-modal vibration phenomenon has been widely observed, for asymmetric curvature along the riser span emerges in the case of external shear current being imposed.展开更多
This study investigates the effects of multiphase internal flows that consider hydrate phase transitions on the parametric stability of marine risers.A numerical model of the multiphase internal flow that considers a ...This study investigates the effects of multiphase internal flows that consider hydrate phase transitions on the parametric stability of marine risers.A numerical model of the multiphase internal flow that considers a hydrate phase transition is established.The model first solves the flow parameters and subsequently obtains the natural frequencies of risers with different gas intake ratios.The stability charts of marine risers with different gas intake ratios are plotted by applying Floquet theory,and the effects of the gas intake ratio on the instability and vibration response of the risers are identified.The natural frequency increases with an increase in the gas intake ratio;thus,instability zones move to higher frequency ranges in the stability charts.As the increasing gas intake ratio reduces the damping effect of the Coriolis force,the critical amplitude of the heave in the unstable region decreases,especially when hydrodynamic damping is not considered.As a result,higher-order unstable regions are excited.When in an unstable region,the vibration response curve of a riser with a high gas intake ratio excited by parametric resonance diverges quickly due to parametric resonance.展开更多
In this paper, the nonreflecting boundary conditions based upon fundamental ideas of the linear analysis are developed for gas dynamic equations, and the modified boundary conditions for Navier-Stokes equations are pr...In this paper, the nonreflecting boundary conditions based upon fundamental ideas of the linear analysis are developed for gas dynamic equations, and the modified boundary conditions for Navier-Stokes equations are proposed as a substitute of the nonreflecting boundary conditions inside boundary layers near rigid walls. These derived boundary conditions are then applied to calculations both for the Euler equations and the Navier-Stokes equations to determine if they can produce acceptable results for the subsonic flows in channels. The numerical results obtained by an implicit second-order upwind difference scheme show the effective- ness and generality of the boundary conditions. Furthermore, the formulae and the analysis performed here may be extended to three dimensional problems.展开更多
The ejector-powered engine simulator(EPES)system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels.In this work,through the analysis of the structu...The ejector-powered engine simulator(EPES)system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels.In this work,through the analysis of the structure and principle of EPES,three parts of the internal flow force were obtained,namely,the additional resistance before the inlet,the internal flow force in the inlet and the thrust produced by the ejector.On the assumption of one-dimensional isentropic adiabatic flow,the theoretical formulae for calculating the forces were derived according to the measured total pressure,static pressure and total temperature of the internal flow section.Subsequently,a calibration tank was used to calibrate the EPES system.On the basis of the characteristics of the EPES system,the process and method of its calibration were designed in detail,and the model installation interface of the calibration tank was reformed.By applying this method,the repeatability accuracy of the inlet flow rate calibration coefficient was less than0.05%,whereas that of the exhaust flow rate and velocity was less than 0.1%.Upon the application of the calibration coefficients to the correction of the wind tunnel experiment data,the results showed good agreement with the numerical simulation results in terms of regularity and magnitude before stall,which validates the reasonableness and feasibility of the calibration method.Analysis of the calibration data also demonstrated the consistency in the variation law and trend between the theoretical calculation and actual measurement of internal flow force,further reflecting the rationality and feasibility of the theoretical calculation.Nevertheless,the numerical difference was large and further widened with a higher ejection flow rate mainly because of the accuracy of flow measurement and the inhomogeneity of internal flow.The thrust deflection angle of EPES is an important factor in correcting this issue.In particular,the thrust deflection angle becomes larger with small ejection flow and becomes smaller with an increase in flow rate,essentially exhibiting a general change of less than 10°.展开更多
A partition model of interference efficiency was constructed to study the coupling interference effect under combined internal and external flow.The concept of“internal flow efficiency”,“velocity ratio”and“interf...A partition model of interference efficiency was constructed to study the coupling interference effect under combined internal and external flow.The concept of“internal flow efficiency”,“velocity ratio”and“interference efficiency”were introduced to quantify the effect of internal flow and interference,and reveal the coupling mechanism among internal flow,external flow and interference effect.The results showed that the dynamic response of risers under variable angles was significantly different after considering the effect of internal flow.When the external flow velocity was smaller than 0.25 m/s,the vibration of risers was promoted by the internal flow.With the increase of external flow velocity,the effect of internal flow was weakened and the dynamic response of riser mainly depended on the external flow and interference effect.Under the effect of different internal flow,the interference efficiency had similar change trend.The interference effect amplified the complex secondary flow effect inside the riser,making the dynamic response of riser complex and random.In this paper,the overlap area and subdivision criterion of interference effect were constructed within the range of experimental velocity ratio,and the change curve of interference efficiency was obtained with an average meaning,which may have important practical meaning.展开更多
This study deals with base pressure management in a duct for various values of the Mach number(M),namely,Mach number corresponding to sonic and four supersonic conditions.In addition to the Mach number,the nozzle pres...This study deals with base pressure management in a duct for various values of the Mach number(M),namely,Mach number corresponding to sonic and four supersonic conditions.In addition to the Mach number,the nozzle pressure ratio(NPR),the area ratio,the rib dimension,and the duct length are influential parameters.The following specific values are examined at M=1,1.36,1.64,and 2,and NPRs between 1.5 and 10.The base pressure is determined by positioning ribs of varying heights at predetermined intervals throughout the length of the square duct.When the level of expansion is varied,it is seen that the base pressure initially drops for overexpanded flows and increases for under-expanded flows.When ribs are present,the flow field in the duct and pressure inside the duct fluctuate as the base pressure rises.Under-expanded flows can achieve a base pressure value that is suitably high without experiencing excessive changes in the duct flow in terms of static pressure if a rib height around 10%of the duct height close to the nozzle exit is considered.Rectangular rib passive control does not negatively affect the duct’s flow field.展开更多
Pipe-in-pipe(PIP)structures are widely used in offshore oil and gas pipelines to settle thermal insulation issues.A PIP structure system usually consists of two concentric pipes and one softer layer for thermal insula...Pipe-in-pipe(PIP)structures are widely used in offshore oil and gas pipelines to settle thermal insulation issues.A PIP structure system usually consists of two concentric pipes and one softer layer for thermal insulation consideration.The total response of the system is related to the dynamics of both pipes and the interactions between these two concentric pipes.In the current work,a theoretical model for flow-induced vibrations of a PIP structure system is proposed and analyzed in the presence of an internal axial flow and an external cross flow.The interactions between the two pipes are modeled by a linear distributed damper,a linear distributed spring and a nonlinear distributed spring along the pipe length.The unsteady hydrodynamic forces due to cross flow are modeled by two distributed van der Pol wake oscillators.The nonlinear partial differential equations for the two pipes and the wake are further discretized by the aid of Galerkin’s technique,resulting in a set of ordinary differential equations.These ordinary differential equations are further numeri cally solved by using a fourth-order Runge-Kutta integration algorithm.Phase portraits,bifurcation diagrams,an Argand diagram and oscillation shape diagrams are plotted,showing the existence of a lock-in phenomenon and figure-of-eight trajectory.The PIP system subjected to cross flow displays some interesting dynamical behaviors different from that of a single-pipe structure.展开更多
The complex curvature of turbomachinery rotor blade channels combined with strong rotational effect and clearance leakage brings on intricate internal flow phenomenon.It is necessary to study the internal flow and ene...The complex curvature of turbomachinery rotor blade channels combined with strong rotational effect and clearance leakage brings on intricate internal flow phenomenon.It is necessary to study the internal flow and energy loss mechanism to reveal the influence law of the key parameters and to achieve its optimal design.Considering features of flow and temperature fields in rotor passage,the concept of synergy analysis derived from equation of energy conservation was put forward.Typical NASA low-speed centrifugal compressor(LSCC)rotor was chosen for analysis using CFD.Numerical results showed remarkable agreement with experiment datum in both the tendency of the performance characteristics and quantitative pressure values.Under different flow rates and inlet total temperatures conditions,thermal-fluid interaction effect and losses were studied by synergy analysis.Results showed that peak synergy positive value zones located around blade leading edge,across the shroud wall and hub wall,and at the position where tip-leakage flow was mixing with the bulk flow and high entropy zones existed.Increasing flow rate from design condition,positive and negative synergy areas both changed tiny around leading edge and trailing edge.Reducing flow rate,positive synergy areas tended to increase and negative areas decreased at same positions.The relationship between flow separation,heat transfer and losses in turbomachinery rotor can be revealed based on synergy analyses.展开更多
This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on...This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on the cooperative shear model theory,serration-flow statistics during nanoindentation loading and creep tests during the holding stage were used to analyze the influence of hydrogen on the behavior of flow units in BMGs.Experimental observations showed that the hydrogen in the Zr_(55)Cu_(30)Ni_(5)Al_(10)BMGs caused mechanical softening,plasticity improvement,and structural relaxation.Analysis also showed that the average volume,size,and activation energy of internal flow units in the BMGs all increased as a result of the increase in the hydrogen content.The hydrogenation in the BMGs was found to lead to a prolifera-tion of shear bands,which promoted plasticity.The aggregation of these internal flow units reduced the stress required for plastic deformation through shear bands,ultimately causing softening and structural relaxation.展开更多
A numerical analytic process is suggested combining direct boundary element methodwith discrete vortex method and internal flow in cross-flow fan calculated. The process considersnot only function of impeller, but als...A numerical analytic process is suggested combining direct boundary element methodwith discrete vortex method and internal flow in cross-flow fan calculated. The process considersnot only function of impeller, but also effect of volute casing. Internal flow field of cross-flow fan ispractically measured, and results compared with that from calculation. It shows that the process isexpected to be used in predicting performances of fluid machinery.展开更多
The operational function of the trunk limbs (thoracic appendages), of Daphnia, P3 and P4, is a long-term disputed definition between “solid walls”, sieving filters. Sieving is unlikely process for routine particle c...The operational function of the trunk limbs (thoracic appendages), of Daphnia, P3 and P4, is a long-term disputed definition between “solid walls”, sieving filters. Sieving is unlikely process for routine particle collection, particle capture is not a simple mechanical process and not by sieving alone. Analysis promotion supported by direct observational examination of the in-vivo cinematographic slow-motion film and magnified solid photos of tethered Daphnia by high-speed camera (250 frames per second) resulted in a definite interpretation presented in this paper. The Daphnia’s feeding mechanism achieves particles abstraction not by sieving. The existence of two internal alternate water flow routs was indicated: Lateral and Median. These micro flow structures are suggested as vulnerability reduction.展开更多
In the present paper an unsteady thermal flow of non-Newtonian fluid is investigated which is of the flow into axisymmetric mould cavity. In the second part an unsteady thermal flow of upper-convected Maxwell fluid is...In the present paper an unsteady thermal flow of non-Newtonian fluid is investigated which is of the flow into axisymmetric mould cavity. In the second part an unsteady thermal flow of upper-convected Maxwell fluid is studied. For the flow into mould cavity the constitutive equation of power-law fluid is used as a Theological model of polymer fluid. The apparent viscosity is considered as a function of shear rate and temperature. A characteristic viscosity is introduced in order to avoid the nonlinearity due to the temperature dependence of the apparent viscosity. As the viscosity of the fluid is relatively high the flow of the thermal fluid can be considered as a flow of fully developed velocity field. However, the temperature field of the fluid flow is considered as an unsteady one. The governing equations are constitutive equation, momentum equation of steady flow and energy conservation equation of non-steady form. The present system of equations has been solved numerically by the splitting difference method. The numerical results show that the splitting difference method is suitable for the 2D problem of non-Newtonian fluid. The present application of the splitting diffference method is at first developed by us for non-Newtonian case. For the unsteady flow in the tube the finite difference scheme is given which leads to a tridiagonal system of equations.展开更多
In this paper,three-dimensional flows in laminar subsonic cascades at relatively low Reynolds numbers(Re<2500)are presented,based on numerical calculations.The stator and rotor blade designs are those for a MEMS-ba...In this paper,three-dimensional flows in laminar subsonic cascades at relatively low Reynolds numbers(Re<2500)are presented,based on numerical calculations.The stator and rotor blade designs are those for a MEMS-based Rankine microturbine power-plant-on-a-chip with 109-micron chord blades.Blade passage calculations in 3D were done for different Reynolds numbers,tip clearances(from 0 to 20%)and incidences(0◦to 15◦)to determine the impact of aerodynamic conditions on the flow patterns.These conditions are applied to a blade passage for a stationary outer casing.The 3D blade passage without tip clearance indicates the presence of two large symmetric vortices due to the interaction between hub/casing boundary layers and the blade.Opening the tip clearance introduces the tip vortex,which tends to become dominant above a tip clearance of 10%.In addition to providing a description and understanding of the 3D flow in a MEMS microturbine,these results suggest the importance of considering 3D flows in the design of microturbomachinery,even though the geometry is dominantly 2D.展开更多
Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can ...Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60-) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 rn/s. The free stream shell side velocity ranges from 0.8 rn/s to 1.3 m/s, the reduced gap velocity varies from 1,80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.展开更多
By means of the analysis of the internal flow within inlet passage of large pumping sta-tion, an analysis of 3-D direct boundary element for the flow has been presented on the potentialflow assumption, and a calculati...By means of the analysis of the internal flow within inlet passage of large pumping sta-tion, an analysis of 3-D direct boundary element for the flow has been presented on the potentialflow assumption, and a calculation and an experimental proof for the inlet passage of 30 angle-type axial pumping station have been made. Based on the analysis of the calculations and theexperiments, the calculation method is feasible and believable.展开更多
A linear theory on the internal waves generated in the stratified fluid with a pycnocline is presented in this paper. The internal wave fields such as the velocity fields in the stratified fluid and velocity gradient ...A linear theory on the internal waves generated in the stratified fluid with a pycnocline is presented in this paper. The internal wave fields such as the velocity fields in the stratified fluid and velocity gradient fields at the free surface are also investigated by means of the theoretical and numerical method. From the numerical results, it is shown that the internal wave generated by horizontally moving Rankine ovoid is a sort of trapped wave which propagates in a wave guide, and its waveform is a kind of Mach front-type internal wave in the pycnocline. Influence of the internal wave on the flow fields at the free surface is represented by the velocity gradient fields resulted from the internal waves generated by motion of the Rankine ovoid. At the same time, it is also shown that under the hypothesis of inviscid fluid, the synchronism between the surface velocity gradient fields at the free surface and the internal wave fields in the fluid is retained. This theory opens a possibility to study further the modulated spectrum of the Bragg waves at the free surface.展开更多
Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governin...Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governing partial differential equation is transformed into a nonlinear system of fourth-order ordinary differential equations by using the generalized integral transform technique(GITT).The effects of the combined excitation of base motion and pulsating internal flow on the nonlinear dynamic behavior of the pipe are investigated using a bifurcation diagram,phase trajectory diagram,power spectrum diagram,time-domain diagram,and Poincare map.The results show that the base excitation amplitude and frequency significantly affect the dynamic behavior of the pipe system.Some new resonance phenomena can be observed,such as the period-1 motion under the base excitation or the pulsating internal flow alone becomes the multi-periodic motion,quasi-periodic motion or even chaotic motion due to the combined excitation action.展开更多
基金supported by the National High Technology Research and Development Program of China(863 Program,Grant No.2006AA09Z356 and No.2007AA09Z313)
文摘In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration (VIV) of top tensioned riser (Till), the differential equation is derived based on work-energy principles and the riser near wake dynamics is modeled by Facchinetti' s wake oscillator model. Then Galerkin' s finite element approximation is implemented to derive the nonlinear matrix equation of the coupled equations and file corresponding numerical programs are compiled which solve the coupled equations directly in the time domain. The comparison of the predicted results with the recent experimental results and the prediction of SHEAR7 is performed. The results show the validity of the proposed method on the prediction of VIV of deep water risers. The effect of internal flow on the dynamic characteristics and dynmnic response of the riser is analyzed and several valuable conelusions are drawn.
基金This Project was fincianlly supported by the National Natural Science Foundation of China (Grant No. 50379050)
文摘At present, most researches on the vortex-induced vibration of submarine free spanning pipelines ignore the effect of internal flowing fluid; furthermore, there are no research reports considering the coupling effect of internal and external fluid with the free span. In this paper, combining Iwan's wake oscillator model with the differential equation derived for the dynamic response of submarine free spanning pipelines with inclusion of internal flow, the pipe-fluid coupling equations are developed to investigate the effect of internal flow on the vortex-induced vibration of the free spans. The finite element approximation is implemented to derive the matrix equations of equilibrium. The Newmark method combined with simple iteration is used to solve the system of equations. The results indicate that the internal fluid flow may cause the shift of resonance band to the lower frequency and a slight decrease in the peak value; the effect will be more pronounced with the increase of the span length and can be weakened in the presence of the axial tension.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41106077, 51109185 and 51109186)Zhejiang Provincial Natural Science Foundation of China (Grant Nos. R5110036 and Y5110071)+2 种基金Science Research Program of Science Technology Department of Zhejiang Province (Grant No. 2011C24005)Korea Research Foundation (Grant No. KRF-2008-D00556)Scientific Research Foundation of Zhejiang Ocean University
文摘Numerical study about vortex-induced vibration (V/V) related to a flexible riser model in consideration of internal flow progressing inside has been performed. The main objective of this work is to investigate the coupled fluid-structure interaction (FSI) taking place between tensioned riser model, external shear current and upward-progressing internal flow (from ocean bottom to surface). A CAE technology behind the current research which combines structural software with the CFD technology has been proposed. According to the result from dynamic analysis, it has been found that the existence of upward-progressing internal flow does play an important role in determining the vibration mode (/dominant frequency), vibration intensity and the magnitude of instantaneous vibration amplitude, when the velocity ratio of internal flow against external current is relatively high. As a rule, the larger the velocity of intemal flow is, the more it contributes to the dynamic vibration response of the flexible riser model. In addition, multi-modal vibration phenomenon has been widely observed, for asymmetric curvature along the riser span emerges in the case of external shear current being imposed.
基金funded by the National Natural Sci-ence Foundation of China(No.U2006226)the National Key Research and Development Program of China(No.2016YFC0303800)the National Natural Science Foundation of China(No.51579245)。
文摘This study investigates the effects of multiphase internal flows that consider hydrate phase transitions on the parametric stability of marine risers.A numerical model of the multiphase internal flow that considers a hydrate phase transition is established.The model first solves the flow parameters and subsequently obtains the natural frequencies of risers with different gas intake ratios.The stability charts of marine risers with different gas intake ratios are plotted by applying Floquet theory,and the effects of the gas intake ratio on the instability and vibration response of the risers are identified.The natural frequency increases with an increase in the gas intake ratio;thus,instability zones move to higher frequency ranges in the stability charts.As the increasing gas intake ratio reduces the damping effect of the Coriolis force,the critical amplitude of the heave in the unstable region decreases,especially when hydrodynamic damping is not considered.As a result,higher-order unstable regions are excited.When in an unstable region,the vibration response curve of a riser with a high gas intake ratio excited by parametric resonance diverges quickly due to parametric resonance.
文摘In this paper, the nonreflecting boundary conditions based upon fundamental ideas of the linear analysis are developed for gas dynamic equations, and the modified boundary conditions for Navier-Stokes equations are proposed as a substitute of the nonreflecting boundary conditions inside boundary layers near rigid walls. These derived boundary conditions are then applied to calculations both for the Euler equations and the Navier-Stokes equations to determine if they can produce acceptable results for the subsonic flows in channels. The numerical results obtained by an implicit second-order upwind difference scheme show the effective- ness and generality of the boundary conditions. Furthermore, the formulae and the analysis performed here may be extended to three dimensional problems.
基金supported by the funda-mental research the Funds of China Aerodynamics Research and Development Center
文摘The ejector-powered engine simulator(EPES)system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels.In this work,through the analysis of the structure and principle of EPES,three parts of the internal flow force were obtained,namely,the additional resistance before the inlet,the internal flow force in the inlet and the thrust produced by the ejector.On the assumption of one-dimensional isentropic adiabatic flow,the theoretical formulae for calculating the forces were derived according to the measured total pressure,static pressure and total temperature of the internal flow section.Subsequently,a calibration tank was used to calibrate the EPES system.On the basis of the characteristics of the EPES system,the process and method of its calibration were designed in detail,and the model installation interface of the calibration tank was reformed.By applying this method,the repeatability accuracy of the inlet flow rate calibration coefficient was less than0.05%,whereas that of the exhaust flow rate and velocity was less than 0.1%.Upon the application of the calibration coefficients to the correction of the wind tunnel experiment data,the results showed good agreement with the numerical simulation results in terms of regularity and magnitude before stall,which validates the reasonableness and feasibility of the calibration method.Analysis of the calibration data also demonstrated the consistency in the variation law and trend between the theoretical calculation and actual measurement of internal flow force,further reflecting the rationality and feasibility of the theoretical calculation.Nevertheless,the numerical difference was large and further widened with a higher ejection flow rate mainly because of the accuracy of flow measurement and the inhomogeneity of internal flow.The thrust deflection angle of EPES is an important factor in correcting this issue.In particular,the thrust deflection angle becomes larger with small ejection flow and becomes smaller with an increase in flow rate,essentially exhibiting a general change of less than 10°.
基金supported by the National Natural Science Foundation of China(Grant Nos.51709161 and U2006226)the Key Technology Research and Development Program of Shandong Province(Grant No.2019GHY112061)+1 种基金the Natural Science Foundation of Shandong Province(Grant No.ZR2022QE118)the Youth Talent Introduction and Cultivation Program of College in Shandong Province。
文摘A partition model of interference efficiency was constructed to study the coupling interference effect under combined internal and external flow.The concept of“internal flow efficiency”,“velocity ratio”and“interference efficiency”were introduced to quantify the effect of internal flow and interference,and reveal the coupling mechanism among internal flow,external flow and interference effect.The results showed that the dynamic response of risers under variable angles was significantly different after considering the effect of internal flow.When the external flow velocity was smaller than 0.25 m/s,the vibration of risers was promoted by the internal flow.With the increase of external flow velocity,the effect of internal flow was weakened and the dynamic response of riser mainly depended on the external flow and interference effect.Under the effect of different internal flow,the interference efficiency had similar change trend.The interference effect amplified the complex secondary flow effect inside the riser,making the dynamic response of riser complex and random.In this paper,the overlap area and subdivision criterion of interference effect were constructed within the range of experimental velocity ratio,and the change curve of interference efficiency was obtained with an average meaning,which may have important practical meaning.
文摘This study deals with base pressure management in a duct for various values of the Mach number(M),namely,Mach number corresponding to sonic and four supersonic conditions.In addition to the Mach number,the nozzle pressure ratio(NPR),the area ratio,the rib dimension,and the duct length are influential parameters.The following specific values are examined at M=1,1.36,1.64,and 2,and NPRs between 1.5 and 10.The base pressure is determined by positioning ribs of varying heights at predetermined intervals throughout the length of the square duct.When the level of expansion is varied,it is seen that the base pressure initially drops for overexpanded flows and increases for under-expanded flows.When ribs are present,the flow field in the duct and pressure inside the duct fluctuate as the base pressure rises.Under-expanded flows can achieve a base pressure value that is suitably high without experiencing excessive changes in the duct flow in terms of static pressure if a rib height around 10%of the duct height close to the nozzle exit is considered.Rectangular rib passive control does not negatively affect the duct’s flow field.
基金The work was supported by the National Natural Science Foundation of China(Grant 11622216).
文摘Pipe-in-pipe(PIP)structures are widely used in offshore oil and gas pipelines to settle thermal insulation issues.A PIP structure system usually consists of two concentric pipes and one softer layer for thermal insulation consideration.The total response of the system is related to the dynamics of both pipes and the interactions between these two concentric pipes.In the current work,a theoretical model for flow-induced vibrations of a PIP structure system is proposed and analyzed in the presence of an internal axial flow and an external cross flow.The interactions between the two pipes are modeled by a linear distributed damper,a linear distributed spring and a nonlinear distributed spring along the pipe length.The unsteady hydrodynamic forces due to cross flow are modeled by two distributed van der Pol wake oscillators.The nonlinear partial differential equations for the two pipes and the wake are further discretized by the aid of Galerkin’s technique,resulting in a set of ordinary differential equations.These ordinary differential equations are further numeri cally solved by using a fourth-order Runge-Kutta integration algorithm.Phase portraits,bifurcation diagrams,an Argand diagram and oscillation shape diagrams are plotted,showing the existence of a lock-in phenomenon and figure-of-eight trajectory.The PIP system subjected to cross flow displays some interesting dynamical behaviors different from that of a single-pipe structure.
基金support from the National Key R&D Plan(Grant No.2017YFB0903602)the Transformational Technologies for Clean Energy and Demonstration,Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA21070200)+1 种基金the Frontier Science Research Project of CAS(Grant No.QYZDB-SSW-JSC023)International Partnership Program,Bureau of International Cooperation of Chinese Academy of Sciences(Grant No.182211KYSB20170029)。
文摘The complex curvature of turbomachinery rotor blade channels combined with strong rotational effect and clearance leakage brings on intricate internal flow phenomenon.It is necessary to study the internal flow and energy loss mechanism to reveal the influence law of the key parameters and to achieve its optimal design.Considering features of flow and temperature fields in rotor passage,the concept of synergy analysis derived from equation of energy conservation was put forward.Typical NASA low-speed centrifugal compressor(LSCC)rotor was chosen for analysis using CFD.Numerical results showed remarkable agreement with experiment datum in both the tendency of the performance characteristics and quantitative pressure values.Under different flow rates and inlet total temperatures conditions,thermal-fluid interaction effect and losses were studied by synergy analysis.Results showed that peak synergy positive value zones located around blade leading edge,across the shroud wall and hub wall,and at the position where tip-leakage flow was mixing with the bulk flow and high entropy zones existed.Increasing flow rate from design condition,positive and negative synergy areas both changed tiny around leading edge and trailing edge.Reducing flow rate,positive synergy areas tended to increase and negative areas decreased at same positions.The relationship between flow separation,heat transfer and losses in turbomachinery rotor can be revealed based on synergy analyses.
基金supported the National Natural Science Foundation of China(51401129)Natural Science Foundation of Liaoning Province(2019-ZD-0216,20180510056)+2 种基金Foundation of Liaoning Province Education Administration(LQGD2019001)support from the National Science Foundation(DMR1611180 and 1809640)with the program directorssupported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division under Contract No.DEAC02–05-CH11231。
文摘This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on the cooperative shear model theory,serration-flow statistics during nanoindentation loading and creep tests during the holding stage were used to analyze the influence of hydrogen on the behavior of flow units in BMGs.Experimental observations showed that the hydrogen in the Zr_(55)Cu_(30)Ni_(5)Al_(10)BMGs caused mechanical softening,plasticity improvement,and structural relaxation.Analysis also showed that the average volume,size,and activation energy of internal flow units in the BMGs all increased as a result of the increase in the hydrogen content.The hydrogenation in the BMGs was found to lead to a prolifera-tion of shear bands,which promoted plasticity.The aggregation of these internal flow units reduced the stress required for plastic deformation through shear bands,ultimately causing softening and structural relaxation.
文摘A numerical analytic process is suggested combining direct boundary element methodwith discrete vortex method and internal flow in cross-flow fan calculated. The process considersnot only function of impeller, but also effect of volute casing. Internal flow field of cross-flow fan ispractically measured, and results compared with that from calculation. It shows that the process isexpected to be used in predicting performances of fluid machinery.
文摘The operational function of the trunk limbs (thoracic appendages), of Daphnia, P3 and P4, is a long-term disputed definition between “solid walls”, sieving filters. Sieving is unlikely process for routine particle collection, particle capture is not a simple mechanical process and not by sieving alone. Analysis promotion supported by direct observational examination of the in-vivo cinematographic slow-motion film and magnified solid photos of tethered Daphnia by high-speed camera (250 frames per second) resulted in a definite interpretation presented in this paper. The Daphnia’s feeding mechanism achieves particles abstraction not by sieving. The existence of two internal alternate water flow routs was indicated: Lateral and Median. These micro flow structures are suggested as vulnerability reduction.
基金The project supported by the National Natural Science foundation of China
文摘In the present paper an unsteady thermal flow of non-Newtonian fluid is investigated which is of the flow into axisymmetric mould cavity. In the second part an unsteady thermal flow of upper-convected Maxwell fluid is studied. For the flow into mould cavity the constitutive equation of power-law fluid is used as a Theological model of polymer fluid. The apparent viscosity is considered as a function of shear rate and temperature. A characteristic viscosity is introduced in order to avoid the nonlinearity due to the temperature dependence of the apparent viscosity. As the viscosity of the fluid is relatively high the flow of the thermal fluid can be considered as a flow of fully developed velocity field. However, the temperature field of the fluid flow is considered as an unsteady one. The governing equations are constitutive equation, momentum equation of steady flow and energy conservation equation of non-steady form. The present system of equations has been solved numerically by the splitting difference method. The numerical results show that the splitting difference method is suitable for the 2D problem of non-Newtonian fluid. The present application of the splitting diffference method is at first developed by us for non-Newtonian case. For the unsteady flow in the tube the finite difference scheme is given which leads to a tridiagonal system of equations.
基金This project was funded by the National Plan for Science,Technology and Innovation(MAARIFAH)-King Abdulaziz City for Science and Technology-the Kingdom of Saudi Arabia-award number 14-ENE2142-03.
文摘In this paper,three-dimensional flows in laminar subsonic cascades at relatively low Reynolds numbers(Re<2500)are presented,based on numerical calculations.The stator and rotor blade designs are those for a MEMS-based Rankine microturbine power-plant-on-a-chip with 109-micron chord blades.Blade passage calculations in 3D were done for different Reynolds numbers,tip clearances(from 0 to 20%)and incidences(0◦to 15◦)to determine the impact of aerodynamic conditions on the flow patterns.These conditions are applied to a blade passage for a stationary outer casing.The 3D blade passage without tip clearance indicates the presence of two large symmetric vortices due to the interaction between hub/casing boundary layers and the blade.Opening the tip clearance introduces the tip vortex,which tends to become dominant above a tip clearance of 10%.In addition to providing a description and understanding of the 3D flow in a MEMS microturbine,these results suggest the importance of considering 3D flows in the design of microturbomachinery,even though the geometry is dominantly 2D.
基金the financial and technical support of University of Engineering and Technology, Taxila for carrying out the research
文摘Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60-) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 rn/s. The free stream shell side velocity ranges from 0.8 rn/s to 1.3 m/s, the reduced gap velocity varies from 1,80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.
文摘By means of the analysis of the internal flow within inlet passage of large pumping sta-tion, an analysis of 3-D direct boundary element for the flow has been presented on the potentialflow assumption, and a calculation and an experimental proof for the inlet passage of 30 angle-type axial pumping station have been made. Based on the analysis of the calculations and theexperiments, the calculation method is feasible and believable.
基金The project supported by the National Natural Science Foundation of China (40576010). The English text was polished by Keren Wang
文摘A linear theory on the internal waves generated in the stratified fluid with a pycnocline is presented in this paper. The internal wave fields such as the velocity fields in the stratified fluid and velocity gradient fields at the free surface are also investigated by means of the theoretical and numerical method. From the numerical results, it is shown that the internal wave generated by horizontally moving Rankine ovoid is a sort of trapped wave which propagates in a wave guide, and its waveform is a kind of Mach front-type internal wave in the pycnocline. Influence of the internal wave on the flow fields at the free surface is represented by the velocity gradient fields resulted from the internal waves generated by motion of the Rankine ovoid. At the same time, it is also shown that under the hypothesis of inviscid fluid, the synchronism between the surface velocity gradient fields at the free surface and the internal wave fields in the fluid is retained. This theory opens a possibility to study further the modulated spectrum of the Bragg waves at the free surface.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52171288,51890914)the Key Research and Development Program of Shandong Province(Major Innovation Project)(Grant No.2022CXGC020405)+1 种基金the National Ministry of Industry and Information Technology Innovation Special Project-Engineering Demonstration Application of Subsea Oil and Gas Production SystemSubject 4:Research on Subsea Christmas Tree and Wellhead Offshore Testing Technology(Grant No.MC-201901-S01-04)CNPq,CAPES and FAPERJ of Brazil。
文摘Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governing partial differential equation is transformed into a nonlinear system of fourth-order ordinary differential equations by using the generalized integral transform technique(GITT).The effects of the combined excitation of base motion and pulsating internal flow on the nonlinear dynamic behavior of the pipe are investigated using a bifurcation diagram,phase trajectory diagram,power spectrum diagram,time-domain diagram,and Poincare map.The results show that the base excitation amplitude and frequency significantly affect the dynamic behavior of the pipe system.Some new resonance phenomena can be observed,such as the period-1 motion under the base excitation or the pulsating internal flow alone becomes the multi-periodic motion,quasi-periodic motion or even chaotic motion due to the combined excitation action.