Study on Aerodynamic Drag Reduction at Tail of 400 km/h EMU with Air Suction-Blowing Combination
Abstract
:1. Introduction
2. Calculation Model and Method
2.1. Calculation Model and Parameters
2.2. Calculation Domain and Boundary Conditions
2.3. Meshing
2.4. Calculation Method and Turbulence Model
2.5. Reliability Analysis
3. Airflow Disturbance Characteristics and Setting of Suction and Blowing Ports
3.1. Surface Boundary Layer and Pressure Distribution of EMU
- (1)
- High-speed air strikes at the nose tip of the head car and forms a block. The speed drops sharply, and the pressure rises rapidly. Near the tip of the nose, Cv is close to 0, and Cp is about 1 at the maximum, where a strong positive pressure zone appears;
- (2)
- Due to the effect of pressure difference, on the one hand, the compressed air moves backward along the car body, forming a negative pressure zone in the transition area between the streamlined curve of the head car and the body of the equal section, and forming a boundary layer with a large velocity gradient. On the other hand, the compressed air moves to the bottom of the train, accelerating the movement between the bottom of the body and the ground to form a strong negative pressure zone, and the minimum Cp is about −1.2;
- (3)
- The airflow moves backward along the uniform section of the car body, and the pressure rises slowly and is slightly lower than the atmospheric pressure. At this time, the boundary layer gradually develops and thickens along the car body;
- (4)
- In the sudden change area where the airflow just flows through the tail section, the local vacuum above the streamlined tail causes the airflow to accelerate and form a negative pressure zone again;
- (5)
- After the airflow passes through the sudden change of the tail transverse section, the speed becomes smaller, and the pressure returns to normal, causing the boundary layer to separate from the wall surface of the EMU and forming a positive pressure near the nose end of the tail.
3.2. Setting of Suction and Blowing Ports
3.3. Expression of Related Physical Quantities
4. Results Analysis
4.1. The Influence of Different Mass Flow Rate on the EMU Aerodynamic Drag
4.2. The Influence of the Distance between the Ports on the Aerodynamic Drag
4.3. The Influence of the Number of Ports on the Aerodynamic Drag
4.4. Analysis of Drag Reduction Mechanism
5. Conclusions and Prospects
- (1)
- Suction at the upper edge of the rear windscreen and blowing at the lower edge of the rear windscreen can significantly reduce the pressure drag of the tail car. The suction can remove the low-momentum fluid and transfer it to the blowing area, and the blowing can improve the vortex structure in the near wake region of the EMU. When the mass flow rate is relatively low, the aerodynamic drag reduction effect of the tail car is better. When the mass flow rate increases too much, it will reduce the drag reduction efficiency of the tail car and consume more energy;
- (2)
- Under a certain blowing and suction flow rate, the more the number of blowing and suction ports concentrated on the upper and lower edges of the windscreen, and the smaller the spacing, the better the drag reduction effect. If five ports are set, respectively, for the suction and blowing area at the EMU tail, when the suction-blow mass flow rate is 40.826 kg m−2 s−1, the pressure drag reduction rate of the tail car can reach 7.97%;
- (3)
- Due to the simplification of the model and the omission of the bogie structure, the total aerodynamic drag of the EMU is smaller, and the corresponding drag reduction rate is larger. However, it is determined that the drag reduction method combining suction and blowing is arranged at the tail of the EMU, which can effectively reduce the differential pressure drag of the tail car. In the subsequent research, the same drag reduction method can be applied to the head car, bogie cavity, and other areas of the EMU to further reduce the differential pressure of the entire car;
- (4)
- In view of different types of train heads, the setting of air-blowing and suction ports shall be analyzed according to specific conditions.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
Symbol | Description | Symbol | Description |
Cd | Drag coefficient | p | Pressure at any point in flow field |
Fd | Aerodynamic drag | p∞ | Atmospheric pressure |
ρ | Air density | qj | Mass flow rate |
U | Speed of EMU | Vj | Speed of air blowing and suction |
S | Cross-sectional area of EMU | A | Total cross-sectional area of all air-blowing holes or suction holes |
Cv | Dimensionless velocity | Gj | Mass flux |
V | Velocity of any point in flow field | α | Drag reduction rate |
V∞ | Inlet flow velocity | Fd(n−S−B) | Aerodynamic drag of EMU without blowing and suction |
Cp | Pressure coefficient | Fd(S−B) | Aerodynamic drag of EMU under a certain suction-blowing condition. |
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Mesh Density | Mesh Number (106) | Aerodynamic Drag Coefficient | ||
---|---|---|---|---|
Head Car | Middle Car | Tail Car | ||
coarse | 5.41 | 0.120 | 0.051 | 0.092 |
medium | 10.55 | 0.115 | 0.050 | 0.090 |
fine | 16.00 | 0.114 | 0.050 | 0.090 |
Position | Drag Coefficient Under Different Mass Flow Rate | |||||
---|---|---|---|---|---|---|
0 | 0.923 kg/s | 1.846 kg/s | 2.769 kg/s | 3.692 kg/s | 4.615 kg/s | |
Entire car | 0.2571 | 0.2565 | 0.2551 | 0.2539 | 0.2531 | 0.2527 |
Head car | 0.1151 | 0.1151 | 0.1151 | 0.1151 | 0.1151 | 0.1151 |
Middle car | 0.0502 | 0.0503 | 0.0502 | 0.0503 | 0.0502 | 0.0502 |
Tail car | 0.0897 | 0.0891 | 0.0876 | 0.0864 | 0.0857 | 0.0853 |
Windshield | 0.0021 | 0.0020 | 0.0022 | 0.0021 | 0.0021 | 0.0021 |
Model | Spacing of Suction Ports along the Surface of Car Body (mm) | Spacing of Blowing Ports in Vertical Direction (mm) |
---|---|---|
A | 1060 | 150 |
B | 1060 | 300 |
C | 265 | 150 |
Model | Total Mass Flow Rate (kg s−1) | Mass Flux (kg m−2 s−1) | Ports × Holes (for Semi-Body Model) |
---|---|---|---|
B | 2.769 | 40.826 | 3 × 8 |
D1 | 2.769 | 24.496 | 5 × 8 |
D2 | 4.615 | 40.826 |
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Cui, H.; Chen, G.; Guan, Y.; Deng, W. Study on Aerodynamic Drag Reduction at Tail of 400 km/h EMU with Air Suction-Blowing Combination. Machines 2023, 11, 222. https://doi.org/10.3390/machines11020222
Cui H, Chen G, Guan Y, Deng W. Study on Aerodynamic Drag Reduction at Tail of 400 km/h EMU with Air Suction-Blowing Combination. Machines. 2023; 11(2):222. https://doi.org/10.3390/machines11020222
Chicago/Turabian StyleCui, Hongjiang, Guanxin Chen, Ying Guan, and Wu Deng. 2023. "Study on Aerodynamic Drag Reduction at Tail of 400 km/h EMU with Air Suction-Blowing Combination" Machines 11, no. 2: 222. https://doi.org/10.3390/machines11020222