This article was submitted to Process and Energy Systems Engineering, a section of the journal Frontiers in Energy Research
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With the aim of improving the aerodynamic performance of axial turbomachinery, a new type of blade is designed using the equal–variable circulation method. Taking an axial flow fan as the research object, this article describes the development of a new type of turbomachinery by changing the design method and producing a blade with forward sweep. The aerodynamic performance of the fan is simulated and compared with the experimental data. The numerical results show that the equal circulation design method improves the aerodynamic performance of the blade roots, while the variable circulation design method enhances the aerodynamic performance of the blade tips. By adopting the equal–variable circulation design method, the total pressure of the experimental fan is increased by about 4%, while the efficiency remains unchanged. Forwardswept blades with an equal–variable circulation design also improve performance over the conventional blades by changing the centerofgravity stacking line. At low flow rates, the efficiency of the experimental fan can be increased by 7.5%, and the working range of the flow is expanded. Under high flow rates, the restriction of the blade tip on the airflow is decreased and the fluidity is slightly reduced.
In industrial production, lowpressure axial fans are widely used because of their uncomplicated structure, large flow rates, and stable operation. In turbomachinery research, improved efficiency and reduced noise are longstanding topics of research. The modification of turbomachinery is mainly divided into three directions: airfoil modification, blade shape modification, and tip clearance modification (
In terms of airfoil modification,
In terms of blade shape modification,
Previous research has shown that studying the flow characteristics of forwardswept structures applied to lowspeed axial fans is of certain engineering significance. However, there has been little research on the optimization of forwardswept blades for lowpressure axial fans. This article proposes a new design method of lowpressure axial flow fan, which can effectively improve the operating range and parameters of lowpressure axial flow fan for engineering practice. Moreover, studying the deep reasons for the efficiency improvement and the optimization of internal flow has practical significance for further optimization of the blade.
For lowpressure axial fans, the design methods can be divided into equal circulation design and variable circulation design according to the law of airflow parameters along the blade height direction. The inlet and outlet flow of the axial flow turbomachinery blades is usually designed according to the free vortex mode:
Here,
Taking the derivative along the radial direction, we obtain
According to the radial balance equation,
Substituting Eqs 6, 1 into
The equal circulation design method ignores the secondary radial flow and simplifies the flow of the airflow around the blade to an unmixed flow around many sections. In the variable circulation design method, the distribution of airflow parameters along the blade height does not satisfy the assumption that
During the blade design process, if the root load factor satisfies the necessary conditions, the equal circulation design and the variable circulation design can be combined to further optimize the aerodynamic shape of the blade. A blade root with a larger load factor can be designed using the equal circulation design method, while a tip with a smaller load factor can be designed with the variable circulation design method. Therefore, the equal–variable circulation design method effectively increases the chord length of each section of the blade, optimizes the aerodynamic shape of the blade, and increases the working force of the blade.
The calculation model is constructed after the aerodynamic design calculation according to the equal–variable circulation design method. As a forwardswept blade is used in the experiments, this blade type is described in detail here. The reference airfoil for the blade design is the LS airfoil. According to the reference (
Centerofgravity stacking line and airfoil:
Parameters of forwardswept blades.
Parameters of forwardswept blades  


45°–58° 

17°–30° 

12°–35° 

236.12 mm 

135.50 mm 

122.53 mm 

0.6–1 
The experimental fan is a singlestage lowspeed axialflow fan, as is widely used for indoor ventilation in the textile industry. The experimental parameters are given in
Parameters of experimental device.
Experimental method  Ctype experiment (pressure inlet and opening outlet) 

Flow measurement  Conical imported nozzle 
Power measurement  Electrometric method 
Rotor diameter  1,600 mm 
Speed  980–990 rpm 
Measuring length  4,815 mm 
Intake duct  4,000 mm 
Experimental device.
In this study, ANSYS CFX was used for numerical simulations. The calculations use a singleflowchannel model. The physical model is divided into three regions: the inlet cylinder, fan rotor, and outlet cylinder. For the inlet and outlet, ICEM was used to divide the structural grid; for the rotor part, Autogrid was used to divide the grid to ensure sufficient grid quality. The single runner grid of the rotor is shown in
Grid of the blade runner.
Boundary conditions and calculation convergence criteria.
Boundary  Value 

Inlet boundary  Mass flow rate 
Outlet boundary  Open boundary condition 
Rotational speed  980–990 rpm 
References pressure  101.325 kPa 
Blade surface  Noslip wall 
Turbulence models  SST 
Solver  Double precision 
Convergence criteria 

To eliminate the influence of the grid resolution on the numerical results, four sets of rotor partial grids were selected for calculation. In the gridindependence verification, the SST
Verification of grid independence.
Different results can be obtained with different turbulence models, so the accuracy of the turbulence model was verified. As shown in
Comparison of numerical calculation and experimental results.
The calculation results of the SST
Traditional blade characteristic curves:
It can be seen from
Under rated flow conditions, the axial velocity of the fluid in the fan is an important parameter in determining the performance of the fan blade.
Axial velocity comparison at the exit.
Axial velocity and crosssection streamlines of the three blades at 20 and 80% of the span.
The blade’s centerofgravity stacking line was modified on the basis of the equal–variable circulation design to obtain a forwardswept blade. In
Performance curve of forwardswept blades at different starting heights.
Performance curves of forwardswept blades with different forwardsweep angles.
Forwardswept blade characteristic curves:
To further study the internal flow conditions of forwardswept and traditional blades under low flow conditions, the section flow pattern method (
Streamline at the root:
Streamline at the blade tips:
Axial velocity comparison of forwardswept blades and conventional blades at the exit.
1) The equal–variable circulation design method can be applied for the design of forwardswept blades and conventional blades. The efficiency of equal–variable circulation design blades is basically the same as the blades from the equal and variable design methods, but the total pressure can be increased by 4%. The equal–variable circulation designed blades have a more stable axial velocity from the root to the tip of the blade, a greater axial velocity, and a stronger circulation capacity. The axial velocity of the equal–variable circulation designed blades is higher than that of the other two blade types. The equal–variable circulation design effectively increases the chord length of each section of the blade. Thus, combining the advantages of the equal circulation design and the variable circulation design effectively enhances the blade’s performance.
2) Different forwardsweep heights will have different impacts on the aerodynamic performance of the blade. There is an optimal forwardsweep height that gives the best aerodynamic performance. In this study, a forward sweep starting at 60% of the blade height with an angle of 20° gives the optimum efficiency.
3) The conventional blades designed by the equal–variable circulation design method achieve higher total pressures when the flow rate is larger. The forwardswept blades designed by the equal–variable circulation design method have higher efficiency and a wider stable operating area. As the flow rate decreases, the traditional blade will produce large shedding vortices at the blade tip. The forwardswept blade can effectively inhibit the formation of these vortices and improve the efficiency of turbomachinery. The change in the blade’s centerofgravity stacking line may optimize the flow at the tip of the blade while increasing the efficiency and optimizing the operating area.
The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.
SL, SW, YL, and ZZ provided experimental ideas and theoretical guidance. CS provided language guidance and writing guidance. All authors contributed to the article and approved the submitted version.
This work was supported by the National Natural Science Foundation of China (Grant No. 51776217).
Author SL was employed by the company Shandong Jirong Thermal Technology Co., Ltd.; author SW was employed by the company China National Nuclear Power Operations Management Co., Ltd.
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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