Aerodynamic drag and lift of different car body shapes

Summary

Julian Edgar discusses a highly detailed technical paper on car aerodynamics, focusing on the drag and lift characteristics of three key car body shapes: square back, fastback, and notchback. Using precise wind tunnel testing with pressure taps and particle image velocimetry (PIV), the study provides experimental validation for CFD models. Key findings include variations in drag coefficients and lift, with the square back showing the most downforce and the fastback exhibiting the lowest drag. The video emphasizes the importance of understanding airflow and pressure distributions in optimizing vehicle stability and performance.

Takeaways

• 😀 The paper discusses experimental data validating numerical methods for car aerodynamics, specifically focusing on drag and lift across different car body shapes.
• 😀 The study uses high-quality wind tunnel models and methods, including pressure taps and Particle Image Velocimetry (PIV), which provides accurate real-world data on airflow and pressures.
• 😀 The three fundamental car shapes studied are square back, fastback, and notchback, which represent modern vehicle shapes.
• 😀 The drag coefficient (Cd) for the square back is 0.334, the fastback is lower at 0.311, and the notchback is very close to the fastback at 0.312.
• 😀 Coefficients of lift were also measured, with the square back developing downforce, the fastback producing significant lift (0.106), and the notchback having slightly less lift than the fastback.
• 😀 The pressure distribution on the square back model shows minimal change across the roof with a significant low-pressure wake at the rear.
• 😀 The fastback has a more complex pressure distribution with lower pressure over the roof and a recovery in pressure at the tail.
• 😀 The notchback shape shows a pressure recovery similar to the fastback but with a less pronounced lift due to the larger area of higher pressure.
• 😀 The airflow speeds over the car bodies show that the flow is three-dimensional, particularly at the rear of the vehicle, rather than two-dimensional as often assumed.
• 😀 The study finds that rear lift has a more significant impact on car stability than front lift, and the rear lift varies between the body shapes, with the fastback showing the highest rear lift.
• 😀 The study concludes that centerline pressure measurements provide valuable insight into aerodynamics but may not capture the full three-dimensional flow behavior around the car.

Q & A

What is the main focus of the technical paper discussed in the video?

The paper focuses on experimental data for validating numerical methods related to car aerodynamics, specifically analyzing the drag and lift of different car body shapes (square back, fastback, and notchback).

Why does Julian Edgar emphasize the credibility of the paper?

He emphasizes its credibility because the data is based on wind tunnel testing conducted with high-quality models and measurement tools, including pressure tappings and Particle Image Velocimetry (PIV), and it was published in a reputable journal.

What is the significance of the three different car shapes studied in the paper?

The three shapes—square back, fastback, and notchback—are used to understand how different rear geometries affect the drag and lift characteristics of a car, which in turn influences its aerodynamic performance and stability.

How are drag values measured in this study?

Drag values are measured using a coefficient called the drag coefficient (Cd), which quantifies the resistance a car experiences as it moves through the air. The paper compares the drag of the square back (0.334), fastback (0.311), and notchback (0.312).

What did the study find regarding the lift coefficients of the car shapes?

The study found that the square back generates downforce (negative lift), the fastback produces lift (0.106), and the notchback also has lift, but slightly less than the fastback.

What is the importance of the front and rear lift coefficients?

Front and rear lift coefficients are important because they determine how much lift (or downforce) is generated at the front and rear of the car, influencing its stability. Rear lift is particularly important for car stability at high speeds.

What do the pressure distributions tell us about the different car shapes?

Pressure distributions reveal how airflow behaves over the car surfaces. The square back has a consistent lower pressure across the roof and a low-pressure wake at the rear. The fastback has a more complex pressure pattern with lower pressure over the roof and a recovery at the tail. The notchback has a different recovery pattern with a slightly higher pressure.

How does airflow speed change across the car shapes?

The airflow speed varies depending on the car shape, with differences most noticeable at the rear of the vehicle. The square back has a large wake with slow-moving air, the fastback has a smaller wake, and the notchback shows a similar wake but with slightly different flow patterns.

What does the study suggest about using centerline pressure tappings for aerodynamic measurements?

The study suggests that while centerline pressure tappings are useful, they don't provide the full picture of aerodynamic behavior. Off-centerline measurements are important to capture the three-dimensional nature of the airflow, which is especially relevant for the rear of the car.

What practical advice does Julian Edgar give for car enthusiasts or engineers interested in aerodynamics?

Julian advises that enthusiasts or engineers can perform their own aerodynamic testing using relatively low-cost equipment, such as pressure tappings, to gather valuable insights about airflow. He also recommends referring to his books for more detailed instructions on car aerodynamics.