This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,tog...This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.展开更多
A prototype cleanroom for hazardous testing and handling of satellites prior to launcher encapsulation,satisfying the ISO8 standard has been designed and analyzed in terms of performances.Unsteady Reynolds Averaged Na...A prototype cleanroom for hazardous testing and handling of satellites prior to launcher encapsulation,satisfying the ISO8 standard has been designed and analyzed in terms of performances.Unsteady Reynolds Averaged Navier-Stokes(URANS)models have been used to study the related flow field and particulate matter(PM)dispersion.The outcomes of the URANS models have been validated through comparison with equivalent large-eddy simulations.Special attention has been paid to the location and shape of the air intakes and their orientation in space,in order to balance the PM convection and diffusion inside the cleanroom.Forming a cyclone-type flow pattern inside the cleanroom is a key to maintaining a high ventilation efficiency.展开更多
In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the pred...In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the prediction of the cavitation inception of marine propulsors is investigated from the point of view of the unsteady functioning and induced pressure pulses.The VP1304(also known as PPTC)test case,for which dedicated data were collected during several workshops,is considered first.After preliminary analyses using RANS,also Detached Eddy Simulations(DES)are included to better account for the vortex dynamics and its influence on pressure pulses.Similarly to what observed in uniform inflow,results show a better agreement with the available measurements of propeller performances and confirm the reliability of the proposed approaches for unsteady,non-cavitating,model scale propeller predictions.The overall cavitation pattern is improved too by the application of the transition sensitive correction to the mass transfer model,but the complex dynamics of bubble cavitation observed in experiments prevents quantitatively better predictions in terms of thrust/torque breakdown and induced pressure pulses levels regardless the use of RANS or DES methods.展开更多
The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Men...The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Menter’s shear stress transport (SST) k-ω turbulence model. The simulation is performed at the nozzle pressure ratio of 5.0 to produce a strong shock and it is validated by a comparison with a rainbow schlieren picture of the microjet. The three-dimensional structure of the shock-containing rectangular microjet is demonstrated using the isopycnic surface and bright-field schlieren representations.展开更多
基金Foundation item： Supported by the National Natural Science Foundation of China under Grant No. 551009038 and the specialized research fund for the doctoral program of higher education under Grant No. 200802170010
文摘This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.
基金funded by Space Research and Innovation Network (www.sprint.ac.uk)for Technology Grants (OW131743P4V4M,OW131797P4V2B,ZX and CY)grateful to NERC (www.nerc.ac.uk)for the Grant (NE/W002841/1,ZX)to complete the writing of the paper。
文摘A prototype cleanroom for hazardous testing and handling of satellites prior to launcher encapsulation,satisfying the ISO8 standard has been designed and analyzed in terms of performances.Unsteady Reynolds Averaged Navier-Stokes(URANS)models have been used to study the related flow field and particulate matter(PM)dispersion.The outcomes of the URANS models have been validated through comparison with equivalent large-eddy simulations.Special attention has been paid to the location and shape of the air intakes and their orientation in space,in order to balance the PM convection and diffusion inside the cleanroom.Forming a cyclone-type flow pattern inside the cleanroom is a key to maintaining a high ventilation efficiency.
文摘In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the prediction of the cavitation inception of marine propulsors is investigated from the point of view of the unsteady functioning and induced pressure pulses.The VP1304(also known as PPTC)test case,for which dedicated data were collected during several workshops,is considered first.After preliminary analyses using RANS,also Detached Eddy Simulations(DES)are included to better account for the vortex dynamics and its influence on pressure pulses.Similarly to what observed in uniform inflow,results show a better agreement with the available measurements of propeller performances and confirm the reliability of the proposed approaches for unsteady,non-cavitating,model scale propeller predictions.The overall cavitation pattern is improved too by the application of the transition sensitive correction to the mass transfer model,but the complex dynamics of bubble cavitation observed in experiments prevents quantitatively better predictions in terms of thrust/torque breakdown and induced pressure pulses levels regardless the use of RANS or DES methods.
文摘The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Menter’s shear stress transport (SST) k-ω turbulence model. The simulation is performed at the nozzle pressure ratio of 5.0 to produce a strong shock and it is validated by a comparison with a rainbow schlieren picture of the microjet. The three-dimensional structure of the shock-containing rectangular microjet is demonstrated using the isopycnic surface and bright-field schlieren representations.
