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New technologies

Efficiency Improvement of Motor Fan for Cooling Radiator

Masakazu Ishikawa* Yusuke Otsuki**

Abstract Regarding the development of the blade of the radiator-cooling motor fan, a new design approach was taken to improve the unit efficiency. A process of meridional flow analysis has been added to visualize air flow separation on the blade surface and localize the separation by combining three-dimension flow analysis. This can lead to a reduction in the separation area, thus improving the fan efficiency significantly as well as shortening the development period. This paper will describe the development of the new design approach.

Key Words: Meridional flow analysis, Air flow separation, Loading distribution

1. Introduction Recent requirement for the motor fan of radiator-cooling (hereafter referred to as motor fan) are ① the large air flow performance and ② electrical power consumption reduction. Large air flow is required for the radiator-cooling performance increasing because downsized engines and diesel engines with large heat generation is increasing. On the other hand, reduction of electric power consumption for each component is a significant factor for enhancement of fuel and electric power consumption efficiency in HEVs and EVs driven by electricity. In order to fulfill both requirements, it is essential to improve the efficiency of the fan or motor. At this time, we describes the current status of high efficiency fan development.

2. Motor Fan Structure As shown in Fig. 1, the motor fan is composed of a motor, fan, and shroud. The motor converts the input electric energy into rotating energy. The fan makes air flow by converting the rotating energy into blowing energy. The shroud assist the smooth air flow to pass through the radiator by fan.

Fig. 1 Structure of the motor fan

3. Design process In conventional designs, the fan blade shape was specified with blade angle (θ) and the blade chord (L) as shown in Fig. 2 in three cross-sections on the radial direction (innermost, center, and outermost), And we have studied those dimension of θ and L by estima-tion of fan performances from past evaluation results. After creating the 3D design models, we continue to study the shape and analyze with 3D air flow until the performance targets are met. In case of a new shape, we should have studied the design process of analysis many more times because the analysis results had big gap against the past evaluation results.

* Heat Exchange Systems Development Group in Heat Exchange Systems Business Unit ** Heat Exchange Systems Test Engineering Team in CK Engineering Corporation

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Efficiency Improvement of Motor Fan for Cooling Radiator

Fig. 2 Blade chord and angle

Fig. 3 Current fan blade design flow chart

We needed a few months to design a new blade on average, because one loop of those work had few weeks. Fig. 3 shows the current design process. Fig. 4 shows the newly developed design process flow. We added Meridional Viscosity Flow Analysis (MVFA) to the current design process and visualize the separa-tion on the near surface of blade by detail simulation in 3D air flow analysis. The MVFA is the method that 3D air flow is con-verted to 2D flow analysis on meridional surface (cut at twelve and six o’clock directions as shown in Fig. 5) with the direction of spanwise and axial by averaging the uniformed circuit flow. We can reduce the number of the re-study loops because fan performances can be estimated by the MVFA. The MVFA calculates the distribution of inlet velocity by simulating of meridional flow on considering the design factor of blade load distribution. Based on this result, the blade shape is designed and modeled. We got the final blade shape

converged by repeating the process of feedback to the MVFA iteratively. The judgment of converging is applied the inlet velocity distribution calculated by the MVFA process.

Fig. 4 New fan blade design flow chart

12

6

Meridional line

Fig. 5 Meridional section

3.1. Axially Symmetric MVFA Process

The MVFA considered the blade forces is calculated the inlet velocity variance with the impact by curva-ture of the meridional flow lines and the boundary layer on edge. As a fundamental equation in the MVFA is applied the compressible Reynolds-Averaged Navier-Stokes (RANS) equation with the k-omega turbulent model of the Wilcox(1) for Primitive equation and the Unfactored Implicit Upwind Relaxation Scheme with Inner Interac-tion(2) for numerical calculation e method. On the basis of the blade force theory(3), the blade force is modeled as a volumetric force operated perpendicu-larly to the camber line of the blade section as Fig. 6. The following equations are applied to calculate blade

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CALSONIC KANSEI TECHNICAL REVIEW vol.11 2014

forces on chord (Fθ), spanwise (Fr), and axial (FZ) direc-tions.

Fig 6. Direction of blade force

( )

=

= ・・・・（３）

=

・・・・（２）

・・（１）

Blade force on axial direction:

Blade force on chord direction:

Blade force on radial direction:

F : blade force,ρ : density, r : radius, c : absolute velocity,nr n θ nz : normal unit vectors on blade surface, andm : length of meridional flow lines

The MVFA with 2D flow analysis has the character that is much lighter calculation times than 3D analysis. Fig. 7 shows analysis meshes for the MVFA. The analysis meshes are composed of four areas: the blade area, inlet area, outlet area 1, and outlet area 2. The outlet area 2 opened to the external area is meshed in hemispherical shape as shown in Fig. 7 (b). A total number of cells for calculation are about 3,800 in the MVFA. At this time, the blade shape was applied TURBO-design-1 (Advanced Design Technology Ltd.).

(a) Meridional view (b) Whole view

Fig. 7 Computational grid system

4. Result The following is described the actually designed blade and its analysis results. Table 1 shows the design specifications.

Table 1 Design specifications

Firstly, we confirmed the effect of the designed blade loading distribution on the spanwise and chord direc-tions. Here, this load refers to the pressure differences caused by the blade operation, and the loading distribu-tion refers to the distribution of the pressure difference allocated to each part of the blade. The graph in Fig. 8 shows blade loading distribution on the spanwise direction under three conditions: the best efficient distribution in the analysis results (BEST), Heavy load on the blade tip (Tip_Loading), and Heavy load on the blade hub (Hub_Loading). In this graph, the vertical axis indicates loading posi-tions on the spanwise direction that 0 is the blade hub and 1 is the blade tip. On the other hand, the horizontal axis indicates the ratio of the loads at each chord against the overall load on blade

Fig. 8 Spanwise blade loading distribution

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Efficiency Improvement of Motor Fan for Cooling Radiator

Table 2 shows the analysis result of the loads in each condition, and Fig. 9 to 11 show air flow lines result on the blade surfaces by analysis. The heavy load shifting on the blade hub (Hub) is significantly decreased the fan efficiency against the other conditions. Furthermore, as showing in Fig. 10, the separated air flow area on the blade surface is larger in the total area of blade. The separation area is increased by the enlarging curvature in the blade section for increasing the load on the blade hub.

Table 2 Analysis result (Spanwise blade loading)

Separation area

Tip

Hub

Fig. 9 Analysis result (Flow line of blade surface)

Separation area

Tip

Hub

Fig. 10 Analysis result (Flow line of blade surface)

Separation area

Tip

Hub

Fig. 11 Analysis result (Flow line of blade surface)

Secondly the influences position of peak load was changed 10%, 30%, and 50% from leading edge of blade, because of confirming the effect by the blade loading distribution on the chord direction. The graphs in Fig. 12 to 14 show the result of blade loading distribution in each position. In the graphs, the vertical axes indicate ratio of the blade load at each position. The horizontal axes indicate positions on the chord direction: 0 is Lead-ing Edge (LE) of the blade and 1 is Trailing Edge (TE).

Fig. 12 Chord direction blade loading (Peak position 10%)

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CALSONIC KANSEI TECHNICAL REVIEW vol.11 2014

Fig. 13 Chord direction blade loading (Peak position 30%)

Fig. 14 Chord direction blade loading (Peak position 50%)

Table 3 shows the result by each loading position, and Fig. 15 to 17 show air flow lines result on the blade surfaces by analysis. The specification of peak load at Center (50%) position from the leading edge was enhanced as Table 3. It was came by that the air flow separation boundary is shifted toward the Trailing Edge due to the mild gradient in the pressure distribu-tion with the blade loading light distribution.

Table 3 Analysis Result (Chord direction blade loading)

Separation area

Tip

Hub

Fig. 15 Analysis result (Flow line of blade surface)

Separation area

Tip

Hub

Fig. 16 Analysis result (Flow line of blade surface)

Separation area

Tip

Hub

Fig. 17 Analysis result (Flow line of blade surface)

Finally, we confirm the effect of the sweep angle a shown in Fig. 18. On Fig. 19 shown a meridional flow analysis result (analysis result of air flow velocity based on averaged air flow on the chord direction under the

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Efficiency Improvement of Motor Fan for Cooling Radiator

previously-described “BEST” loading condition on the spanwise direction), the air flow lines on behind the fan was deviated the outside from the fan axial center, and the velocity gradient was steep because of the air flow lines was thick t (red painted circle area). In addition the previous analysis results, the air flow separation area inside (Hub) is increased. Thus, the blade force is directed toward the inside (blade hub) by increasing a sweep angle on the blade and the air flow lime is controlled to direct the outside It restricts air flow separation area increasing by the velocity gradi-ent being mild reduction.

Fig. 18 Sweep angle

Fig. 19 Meridional flow analysis result

On the standard of “BEST” previous explained, we compared with the loading condition: 0°(S00), 10°(S10), 20°(S20), 30°(S30), and 40°(S40). As the analysis result in Fig. 20, the fan efficiency is maximized on the sweep angle was 30°.

Fig. 20 Analysis result

Fig. 21 on sweep angle 0°, Fig 22, on sweep angle 30° was shown the analysis result of air flow lines on the blade surface According to the air flow separation area on the blade surface is decreased on the sweep angle is 30°, the fan efficiency is improved by it

Separation area

Fig. 21 Analysis result (Flow line of blade surface)

Separation area

Fig. 22 Analysis result (Flow line of blade surface)

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Table 4 is shown the evaluation results of prototype fans which were produced and designed by the previ-ous study. We got the good correlation with analysis result between the test results. The deviation in those results were the variations of the prototypes dimension and the measurement on the test.

Table 4 Analysis result

5. Conclusion By the new design process with visualization of air flow separation, we could developed and designed the high efficiency fans that have efficiency of more than 50%. Furthermore, the work-load of design can be reduced over half from the current design process. We will continue to improve the process and the design .in addition the high efficiency cooling fans will be developed.

Lastly, we would like to thank Professor M. Furukawa and his laboratory members in Kyushu University for their cooperation in the design methodology develop-ment.

References(1) Wilcox, D. C., “Reassessment of the Scale-Deter-

mining Equation for Advanced Turbulence Models,” AIAA Journal, Vol. 26, No. 11, pp. 1299-1310, 1988.

(2) Furukawa, M., Nakano, T., and Inoue, M., “Unsteady Navier-Stokes Simulation of Transonic Cascade Flow Using an Unfactored Implicit Upwind Relaxation Scheme With Inner Iterations,” Trans. ASME, Jour-nal of Turbomachinery, Vol. 114, No. 3, pp. 599-606, 1992.

(3) Tabata, S., Hiratani, F., Furukawa, M., “Axisym-metric Viscous Flow Modeling for Meridional Flow Calculation in Aerodynamic Design”, Memories of the Faculty of Engineering Kyushu University, Vol.67, No.4, December 2007

Masakazu Ishikawa Yusuke Otsuki