The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles...The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles. With the commercial computational fluid dynamics (CFD) software NUMECA, the turbulent flow in the tandem axial-flow pump is simulated in various flow conditions. The detail flow structure in the leading edge region of the rear impeller is described, and the influence of the deflection angle of the rear blade on the head performance is studied. According to the simulation, the performance comparison is made between the tandem axial-flow pump and the conventional two-stage axial-flow pump with a uniform impeller size. Results of the study indicate that the tandem axial-flow pump can work in a wider range with high efficiency.展开更多
A tandem blade configuration is a significant flow control method that delays the onset of flow separation.This study numerically investigates the effects of diffusion factor and percentage pitch on the flow structure...A tandem blade configuration is a significant flow control method that delays the onset of flow separation.This study numerically investigates the effects of diffusion factor and percentage pitch on the flow structure of tandem blades.Diffusion factors vary from 0.328 to 0.484.Percentage pitches change from 0.80 to 0.92.Results show that the loss coefficient increases with diffusion factor and decreases with percentage pitch.There is a hub-corner stall of the forward blade in all cases.Gap flow determines the rear blade corner separation.Varying the percentage pitch and diffusion factor changes the momentum distribution of the gap flow.Corner separation of the rear blade is inhibited as low-momentum gap fluids are involved in the passage vortex along with the hub-corner stall of the forward blade.Increasing diffusion factor causes a change in incidence at the leading edge of the rear blade,resulting in a variation at the corner separation of the rear blade.A tandem blade is compared with the reference outlet vane.The performance of the tandem blade is superior to that of the reference outlet vane in all incidences,with a 26.35%reduction in the loss coefficient and a 7.89%enhancement in the pressurization at the designed incidence.Tandem blades stall at positive incidence because of the hub-corner stall of the forward blade.The intensity of the gap flow increases with incidence,preventing corner separation of the rear blade at positive incidences.展开更多
It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial com...It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.展开更多
Jet engine manufacturers and designers are seeking for lighter and smaller type of axial compressors.Improving the aerodynamic characteristics of blades is carried out by controlling the boundary layer.One way to cont...Jet engine manufacturers and designers are seeking for lighter and smaller type of axial compressors.Improving the aerodynamic characteristics of blades is carried out by controlling the boundary layer.One way to control the boundary layer is using tandem blades.Tandem-blade cascades are capable of using highly loaded stages for axial compressors because they provide more works than single-blade cascades.In other words,tandem blades help to achieve a specified total pressure ratio with less number of stages.Therefore,one of the most important problems for researchers is to optimize the aerodynamic parameters of tandem blades.Changing the geometrical parameters of blades is a method to achieve this purpose.In this work,the stagger and camber angle of each blade are first changed while the other geometrical parameters such as overall camber,total stagger angle,the axial overlap,percent pitch and chord ratio are fixed.Secondly,the overall camber angle of tandem blade is changed by increasing the difference between the stagger angle of the first and second blade while the type of two airfoils,axial overlap and percent pitch,overall chord length and overall stagger angle are fixed.The aerodynamic performances of the generated tandem-blade cascades are obtained using two-dimensional numerical solution of flow.For this,a viscous turbulent flow solver is used for solving the Navier-Stokes equations.In these simulations,inlet Mach number is fixed to 0.6.展开更多
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explore...Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.展开更多
基金Sponsored bythe National Natural Science Foundation of China(50679001) the Basic Research Foundation of Beijing Institute of Technology(20060342001)
文摘The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles. With the commercial computational fluid dynamics (CFD) software NUMECA, the turbulent flow in the tandem axial-flow pump is simulated in various flow conditions. The detail flow structure in the leading edge region of the rear impeller is described, and the influence of the deflection angle of the rear blade on the head performance is studied. According to the simulation, the performance comparison is made between the tandem axial-flow pump and the conventional two-stage axial-flow pump with a uniform impeller size. Results of the study indicate that the tandem axial-flow pump can work in a wider range with high efficiency.
基金supported by the National Science and Technology Major Project (Nos.2017-Ⅱ-0007-0021 and P2021-AB-I-003-001)the Heilongjiang Province Postdoctoral Special Funding (LBH-TZ2109)
文摘A tandem blade configuration is a significant flow control method that delays the onset of flow separation.This study numerically investigates the effects of diffusion factor and percentage pitch on the flow structure of tandem blades.Diffusion factors vary from 0.328 to 0.484.Percentage pitches change from 0.80 to 0.92.Results show that the loss coefficient increases with diffusion factor and decreases with percentage pitch.There is a hub-corner stall of the forward blade in all cases.Gap flow determines the rear blade corner separation.Varying the percentage pitch and diffusion factor changes the momentum distribution of the gap flow.Corner separation of the rear blade is inhibited as low-momentum gap fluids are involved in the passage vortex along with the hub-corner stall of the forward blade.Increasing diffusion factor causes a change in incidence at the leading edge of the rear blade,resulting in a variation at the corner separation of the rear blade.A tandem blade is compared with the reference outlet vane.The performance of the tandem blade is superior to that of the reference outlet vane in all incidences,with a 26.35%reduction in the loss coefficient and a 7.89%enhancement in the pressurization at the designed incidence.Tandem blades stall at positive incidence because of the hub-corner stall of the forward blade.The intensity of the gap flow increases with incidence,preventing corner separation of the rear blade at positive incidences.
基金the support of National Natural Science Foundation of China(Nos.51806004 and 51790511)National Science and Technology Major Project,China(No.2017-Ⅱ-0001-0013)。
文摘It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.
文摘Jet engine manufacturers and designers are seeking for lighter and smaller type of axial compressors.Improving the aerodynamic characteristics of blades is carried out by controlling the boundary layer.One way to control the boundary layer is using tandem blades.Tandem-blade cascades are capable of using highly loaded stages for axial compressors because they provide more works than single-blade cascades.In other words,tandem blades help to achieve a specified total pressure ratio with less number of stages.Therefore,one of the most important problems for researchers is to optimize the aerodynamic parameters of tandem blades.Changing the geometrical parameters of blades is a method to achieve this purpose.In this work,the stagger and camber angle of each blade are first changed while the other geometrical parameters such as overall camber,total stagger angle,the axial overlap,percent pitch and chord ratio are fixed.Secondly,the overall camber angle of tandem blade is changed by increasing the difference between the stagger angle of the first and second blade while the type of two airfoils,axial overlap and percent pitch,overall chord length and overall stagger angle are fixed.The aerodynamic performances of the generated tandem-blade cascades are obtained using two-dimensional numerical solution of flow.For this,a viscous turbulent flow solver is used for solving the Navier-Stokes equations.In these simulations,inlet Mach number is fixed to 0.6.
基金the Deanship of Scientific Research,Research Center of College of Engineering, King Saud University for the financial support
文摘Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.
