A Computational Fluid Dynamics Analysis

of a Range Extending Spoiler for Tesla Model S

Abstract 

 A Computational Fluid Dynamics (CFD) study has been carried out on the Tesla Model S using three separate configurations. The first configuration (no spoiler) is the Tesla Model S without any rear spoiler, compared to two configurations with different spoiler designs to study the effect on airflow and, ultimately, the resulting resistance. Configuration two features the standard spoiler (spoiler 1) sold as a spare part by Tesla Motors and included at delivery with performance models sold from 2012 to 2020. The third configuration uses the newly designed spoiler (spoiler 2). For comparative analysis, CFD simulations have been employed to evaluate the drag coefficient at different velocities. 

Introduction

SUNBEAMsystem is known for its optimized products. Now, the goal was set to achieve what might seem impossible: optimize the Tesla Model S. This vehicle, known for its revolutionary electric vehicle technology, now boasts increased efficiency and an extended range, courtesy of SUNBEAMsystem. 

First on the list: SUNBEAMsystem integrated our top-of-the-line lightweight, ultra-thin Tough++Race solar panels, which, in preliminary tests, demonstrated a 20-30% increase in range while idling or driving slowly in heavy traffic. This is particularly relevant for locations such as Stockholm, which is notorious for its traffic congestion. 

Secondly: the upgrade to a modern lithium utility battery to reduce weight and energy waste. We at SUNBEAMsystem developed a new branch of Smart Lithium batteries called the RACE series. The Smart Lithium Model S Race is a lightweight battery that outperforms the standard 12V lead-acid battery in terms of weight, efficiency, and lifespan. 

It’s worth noting that Tesla Model S vehicles from 2012-2021 utilized an outdated lead-acid battery to power auxiliary systems such as the computer, wipers, and lights, excluding propulsion. This century-old technology is not only environmentally unfriendly due to its lead content but also contributes to increased weight and energy waste (through added weight and energy losses). SUNBEAMsystem’s optimized design addresses these issues and paves the way for a more sustainable and efficient electric vehicle experience.  

Having addressed low-speed and parked conditions, we moved on to highway speeds. Now we arrive at the third improvement: 

SUNBEAMsystem developed a Range Extending Spoiler. This “ducktail” style spoiler generates less downforce than traditional spoilers, focusing instead on minimizing aerodynamic resistance. 

To validate the design and initial real-life tests, we employed virtual wind tunnel testing. Utilizing advanced computational fluid dynamics (CFD) calculations, we found a 6% reduction in drag on a Tesla Model S equipped with the Range Extending Spoiler at highway speeds. 

Methodology

SUNBEAMsystem hired a private engineering firm to verify the primarily real-life tests conducted in the Stockholm area. Modern “wind tunnel” testing is done by computers and is called advanced computational fluid dynamics (CFD) calculations. A CFD study consists of preprocessing, solving, and post-processing. Preprocessing includes geometry cleanup and meshing. Both of these processes were carried out in ICEM CFD. Geometry cleanup involved closing all holes and gaps in the geometry and removing unnecessary surfaces not in contact with the fluid domain. After the geometry cleanup, meshing was performed using triangular elements for surface mesh and tetrahedral elements for volume mesh. 

Analysis was conducted on a symmetric model since cars are symmetric from the center plane. 

Figure 2: Front view of the car and fluid domain   
Figure 2: Front view of the car and fluid domain

The domain size was almost 2 times in the upstream direction and about 5 times 

Figure 3 Side view of the car and fluid domain  
Figure 4: Surface meshing on the car surface  

After meshing, the mesh was imported into Fluent Solver to obtain the numerical solution. A pressure-based solver was used to obtain the solution using a standard k-epsilon turbulence model. Since the flow is incompressible, the energy equation was kept off. The following boundary conditions were used for the analysis:  

  1. Inlet as velocity inlet 
  2. Outlet as pressure outlet 
  3. Car as wall 
  4. Upper and lower boundaries as walls 
  5. Symmetry wall as symmetry 
  6. Side boundary as wall 
Contours for SUNBEAMsystem spoiler at 90 km/h
Results

The solution was obtained with a convergence criterion of 10^-3 for all flow variables. Once the solution was achieved, and the drag and lift values stabilized, data files were imported into CFD-post for post-processing. Pressure and velocity contours were obtained using CFD-post. The coefficient of drag values were compared at three different velocities. Results indicate that maximum drag is experienced when no spoiler is installed on the rear bonnet. As the velocity increases, drag tends to increase, which ultimately decreases the coefficient of drag since it is inversely proportional to the square of velocity. 

Minimum drag is experienced at all speeds (90, 120, and 140 km/h) in the case of the third configuration utilizing the new range extending spoiler, and the trend remains consistent at all velocities. The standard spoiler (provided by the car manufacturer for sportier models) displays a clear trend of closing the gap at high speeds and offering very low gains in terms of drag. As the standard spoiler was optimized to prioritize downforce and not low drag, this result is expected. 

SUNBEAMsystem Range Extending Spoiler demonstrates consistent results in lowering the drag, with results between 5.65% and 6.03%, with the best value found at 120 km/h.  

Graph 1: Showing Range extending spoiler compared to no spoiler
Conclusion

A well-designed spoiler can enhance the range of electric vehicles like the Tesla Model S by reducing air drag, particularly at higher speeds where drag forces are predominant. Utilizing the SUNBEAMsystem Range Extending Spoiler, users can gain range, especially for those who frequently travel at highway speeds, by lowering air drag by up to 6%. 

Carbon Fiber Composite | Ultra lightweight | Compatible with 2012-2020 Tesla Model S