In recent years, the global energy crisis and environmental pollution have intensified, driving the development and adoption of new energy vehicles, particularly pure electric vehicles, as a core direction for the automotive industry’s transformation. However, compared to traditional internal combustion engine vehicles, electric vehicles face significant challenges in terms of driving range. Industry statistics indicate that at high speeds, aerodynamic drag accounts for 30% to 40% of the total energy consumption, making it a key factor limiting the range of electric vehicles. Therefore, optimizing the aerodynamic design of the vehicle body to reduce drag is a crucial technical pathway for improving the energy efficiency of pure electric vehicles. Among the aerodynamic components, the rear spoiler is a critical structure for regulating the flow field at the vehicle’s rear, directly influencing the drag coefficient (CD) and lift coefficient (CL). Traditional rear spoiler designs often prioritize aesthetic appeal over systematic aerodynamic studies. Existing research shows that rear spoilers can control airflow separation at the rear, suppress vortex generation, and effectively reduce pressure drag while enhancing driving stability. For instance, some studies have demonstrated that adjusting the inclination angle of the rear spoiler on an electric SUV can reduce the drag coefficient by 3.9%. Other research has explored the effects of openings in the rear spoiler, suggesting that合理的开孔 can optimize turbulent structures. However, most existing studies focus on conventional fuel-powered vehicles, with limited attention to pure electric SUVs. Due to differences in powertrain layout and mass distribution, the flow characteristics of electric SUVs vary significantly, necessitating targeted optimization for specific models.
This study investigates the aerodynamic performance of an electric SUV with various rear spoiler configurations, employing computational fluid dynamics (CFD) simulations. I established a full-scale 3D model of the vehicle, with dimensions of 4,860 mm in length, 1,950 mm in width, and 1,600 mm in height. To streamline the simulation, minor components such as side mirrors, front grilles, wipers, and door handles were omitted. The computational domain was set to 4 times the vehicle height, 5 times the width, and 6 times the length, with the inlet positioned one vehicle length from the front and the outlet three vehicle lengths from the rear, ensuring accurate capture of the flow field around the electric SUV.
Mesh generation was performed using CFD software, combining trimmed cells and prism layers near the vehicle surface. Five prism layers were applied to the body surface as boundary layers, with a total thickness of 8 mm. To enhance simulation accuracy, refinement blocks with sizes of 16 mm and 32 mm were utilized, resulting in a total of 9.069 million volume cells. The boundary conditions included an inlet velocity of 33.33 m/s, simulating a driving speed of 120 km/h, and an outlet set to pressure outlet with zero pressure difference relative to standard atmospheric pressure. All vehicle surfaces were treated as no-slip walls, and the standard k-ω turbulence model was selected for its precision in handling low-Reynolds number flows near walls, effectively capturing turbulent characteristics in the wake and underbody separation regions of the electric SUV.
To evaluate the impact of rear spoiler slotting on the aerodynamic performance of the electric SUV, I analyzed four configurations: Type I (no rear spoiler), Type II (solid rear spoiler without slots), Type III (rear spoiler with a single 280 mm square slot in the middle), and Type IV (rear spoiler with three evenly distributed 140 mm square slots). The drag and lift coefficients were computed for each case, and the results are summarized in the table below.
| Spoiler Type | Description | Drag Coefficient (CD) | Lift Coefficient (CL) |
|---|---|---|---|
| I | No spoiler | 0.306 | 0.237 |
| II | Solid spoiler | 0.274 | 0.046 |
| III | Single 280 mm slot | 0.288 | 0.216 |
| IV | Three 140 mm slots | 0.313 | 0.127 |
The simulation results indicate that installing a solid rear spoiler on the electric SUV significantly improves aerodynamic performance, reducing the drag coefficient by 10.5% and the lift coefficient by 80.6% compared to the no-spoiler configuration. This reduction in lift enhances downforce, improving high-speed stability for the electric SUV. However, introducing square slots into the rear spoiler adversely affects both drag and lift. For Type III, with a single 280 mm slot, the drag coefficient increases by 5.1% and the lift coefficient by 369.6% relative to Type II. For Type IV, with three 140 mm slots, the drag coefficient rises by 14.2% and the lift coefficient by 176.1%. These increases are primarily due to the sharp geometric edges of the square slots, which induce flow separation and enhance turbulent kinetic energy dissipation. The relationship between drag force and the drag coefficient can be expressed as:
$$ F_D = \frac{1}{2} \rho v^2 C_D A $$
where \( F_D \) is the drag force, \( \rho \) is the air density, \( v \) is the velocity, and \( A \) is the reference area. Similarly, the lift force is given by:
$$ F_L = \frac{1}{2} \rho v^2 C_L A $$
For the electric SUV, the increase in \( C_D \) and \( C_L \) with slotted spoilers translates to higher energy consumption and reduced range, underscoring the importance of optimal spoiler design.
To further analyze the flow dynamics, I examined the velocity vector fields around the rear of the electric SUV for each configuration. In Type I, without a spoiler, high-speed airflow accelerates over the roof and separates at the rear windshield due to sudden curvature changes, forming a clockwise rotating vortex core in the low-pressure region behind the vehicle. This unsteady vortex motion increases kinetic energy dissipation, contributing to higher drag. In Type II, the solid spoiler creates an adverse pressure gradient that delays boundary layer separation, pushing the vortex core downstream and reducing energy loss. For Type III and Type IV, the square slots disrupt the flow, leading to localized separation and the formation of large-scale turbulent structures. In Type IV, multiple slots result in a stronger counter-rotating vortex near the rear, intensifying the low-pressure zone and increasing drag. The turbulent kinetic energy (k) and specific dissipation rate (ω) in the standard k-ω model are governed by:
$$ \frac{\partial k}{\partial t} + U_j \frac{\partial k}{\partial x_j} = \tau_{ij} \frac{\partial U_i}{\partial x_j} – \beta^* k \omega + \frac{\partial}{\partial x_j} \left[ (\nu + \sigma_k \nu_T) \frac{\partial k}{\partial x_j} \right] $$
$$ \frac{\partial \omega}{\partial t} + U_j \frac{\partial \omega}{\partial x_j} = \alpha \frac{\omega}{k} \tau_{ij} \frac{\partial U_i}{\partial x_j} – \beta \omega^2 + \frac{\partial}{\partial x_j} \left[ (\nu + \sigma_\omega \nu_T) \frac{\partial \omega}{\partial x_j} \right] $$
where \( \nu_T \) is the turbulent viscosity, and the constants are standard values. The increased dissipation in slotted configurations aligns with higher k and ω values in the wake region, explaining the performance degradation for the electric SUV.
The pressure distribution on the rear surface of the electric SUV also varies with spoiler design. For Type II, the spoiler helps maintain a more uniform pressure field, minimizing pressure drag. In contrast, slotted spoilers (Types III and IV) cause pressure fluctuations due to vortex shedding, as described by the pressure coefficient \( C_p \):
$$ C_p = \frac{p – p_\infty}{\frac{1}{2} \rho v^2} $$
where \( p \) is the local pressure and \( p_\infty \) is the freestream pressure. The root mean square of \( C_p \) fluctuations is higher for slotted cases, indicating greater unsteadiness. This is critical for electric SUVs, as stability issues can arise from lift variations. The lift coefficient sensitivity to spoiler geometry can be modeled empirically for the electric SUV as:
$$ C_L = C_{L0} + k_1 \theta + k_2 A_s $$
where \( C_{L0} \) is the base lift coefficient, \( \theta \) is the spoiler angle, \( A_s \) is the slot area, and \( k_1 \), \( k_2 \) are constants. For square slots, \( k_2 \) is positive, leading to increased lift. Similarly, the drag coefficient can be expressed as:
$$ C_D = C_{D0} + c_1 \frac{A_s}{A_{ref}} + c_2 \left( \frac{A_s}{A_{ref}} \right)^2 $$
with \( c_1 \) and \( c_2 \) positive for sharp-edged slots, consistent with the observed increases.
In terms of energy efficiency, the impact on the electric SUV’s range can be estimated using the drag power equation:
$$ P_d = \frac{1}{2} \rho v^3 C_D A $$
Assuming constant velocity, the percentage increase in power required due to spoiler slotting is proportional to the change in \( C_D \). For example, Type IV requires approximately 14.2% more power than Type II, which could reduce the range of the electric SUV by a similar margin under high-speed conditions. This highlights the trade-off between aesthetic modifications and functional performance in electric SUV design.
In conclusion, this study demonstrates that while adding a solid rear spoiler to an electric SUV significantly enhances aerodynamic performance by reducing drag and lift, incorporating square slots into the spoiler has detrimental effects. The sharp edges of the slots promote flow separation and increase turbulent dissipation, leading to higher drag and lift coefficients. For electric SUVs, this translates to increased energy consumption and compromised stability, emphasizing the need for careful aerodynamic optimization in the design process. Future work could explore alternative slot geometries or active spoiler systems to mitigate these issues while maintaining the benefits of rear spoilers for electric SUVs.