Ground Effect Aerodynamics of Race Cars


We review the progress made during the last 30 years on ground effect aerodynamics associated with race cars, in particular open wheel race cars. Ground effect aerodynamics of race cars is concerned with generating downforce, principally via low pressure on the surfaces nearest to the ground. The “ground effect” parts of an open wheeled car’s aerodynamics are the most aerodynamically efficient and contribute less drag than that associated with, for example, an upper rear wing. While drag reduction is an important part of the research, downforce generation plays a greater role in lap time reduction.

Aerodynamics plays a vital role in determining speed and acceleration (including longitudinal acceleration but principally cornering acceleration), and thus performance. Attention is paid to wings and diffusers in ground effect and wheel aerodynamics. For the wings and diffusers in ground effect, major physical features are identified and force regimes classified, including the phenomena of downforce enhancement, maximum downforce, and downforce reduction. In particular the role played by force enhancement edge vortices is demonstrated. Apart from model tests, advances and problems in numerical modeling of ground effect aerodynamics are also reviewed and discussed.

 

Introduction

Over the past 30 years, the race car industry has become a leader of technology innovation, a training ground for highly qualified engineers, and, for countries such as Britain and Italy, an integral part of the high tech engineering industry. The nature of the industry is such that there is a constant need for performance improvement. Among the various factors which influence the performance of a car, such as power, driver, weight, tires and aerodynamics, aerodynamics represents a major area that a constructor can invest in, investigate, and improve upon on its own _1–4_, and hence has received increasing attention in recent years, resulting in greater advances in methods and understanding. The advance in aerodynamics is partly reflected in the increase in speed. In Fig. 1, the average speed of a Formula 1 car over a race circuit is given, together with annotations on major aerodynamics development and banned technologies. The constant struggle between the regulators

and the constructors’ desire for speed pushes the frontier of science and reveals new physics, which deserves the rigor of an academic examination.

Aerodynamics, particularly ground effect aerodynamics, as applied to open wheeled race cars is still mainly an experimental science and will remain so for some time to come _4_. This is primarily due to the complex fluid flow physics involved. These include

• separation as a normal feature

• surface character changes during an event lead to early transition

• suspension motion leading to unsteady flow

• highly complex physics: wall jet, shear layer instability, vortex

meandering and breakdown, etc.

• force enhancing vortices

• turbulent wake and ground boundary layer interaction

• compressibility

However, computational fluid dynamics _CFD_ is becoming much more important and its use complements model scale experiments. This is particularly true in the case of flows around geometries such as a front wing assembly, where the flow could stay attached over the majority of the aerodynamic surface, less so for flows such as that associated with a diffuser, where the incoming flow could be highly turbulent and distorted, and large vortex flows are often coupled with flow separation.

The primary aim of race car aerodynamics is to generate a desired level of downforce _negative lift_ for the least possible drag. However, the balance of the downforce under all conditions of speed and acceleration is equally important. As such, the complex flow features associated with individual components are often interwoven and difficult to separate. Nevertheless, a clear understanding of flow physics connected to individual aerodynamic components is a prerequisite towards gaining an insight into the overall flow field and eventually a better vehicle design.

The importance of ground effect aerodynamics is easy to explain. Given a fixed distance, the average speed of a car determines the time it takes for a car to complete a circuit. However, over a closed circuit, it is the change of velocity, i.e., acceleration, which is the deciding factor in determining the speed performance of the car.

Authors:

Xin Zhang

Aerospace Engineering, School of Engineering

Sciences,

University of Southampton,

Southampton SO17 1BJ, UK

Willem Toet

Jonathan Zerihan

BAR Honda F1,

Brackley NN13 7BD, UK
 
 
Source and Full Article:

0 yorum: