# CFD for roof fairing Essay

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Zhong Hao

Roof Fairing for Truck Aerodynamics

MECH9620

Roof Fairing for Truck Aerodynamics
Zhong Hao z3431179
School of Mechanical Engineering,
The University of New South Wales,
Kensington, NSW 2052, Australia

Abstract
This assignment is the research about the external flow field of truck and the comparison of the truck with and without roof fairing. The SST turbulence model has been used to simulate this problem, k- model has also running to determine the most appropriate turbulence model. The finer mesh of tetrahedral cells can simulate this problem more accurately and effectively than the medium and coarse. In addition, the convergence target of can reach the acceptable solution and keep the running efficiency. For the result analyse, the major physical factors need be observed and compared are the drag force and drag coefficient.
The final the result is obvious that the truck with roof fairing have lower drag coefficient, therefore the roof fairing can improve the fuel economy of a truck.

NOMENCLATURE

1

Cd

Drag coefficient

CL

Lift coefficient

ρ

Density (kg/m3)

Freightliners play the most important role of land transportation. For the automotive companies（such as
FAW ） the high efficient product can help them satisfy the customer and get more market share.
Therefore, how to raise the top speed of a freightliner and cut down the fuel consumption become the most important subjects of the research and development department. A way is to raise the engine power , beside, another approach is to change the shape of freightliner and making CFD analyse to decrease the CD (dray coefficient). εi+1i k Difference between solution variable of mesh k+1 and

GCI

The Grid Convergence Index

Fs

Factor of safety for error estimators,
Lift Force
Drag Force.
Cross-sectional Area perpendicular to the flow

direction
Turbulent Dissipation Rate (epsilon) k Kinetic Energy turbulent

V

Velocity of the body relative to the medium

INTRODUCTION

1.1 PURPOSE
Aerodynamic dray and rolling resistance are the two major external force that effect Freightliner in motion.
Change the design of vehicle can be used to reduce the dray and rolling resistance influence. However, change the whole design of cabin or front end of a freightliner involves huge investment . Therefore, one of the most popular and easy methods is installing a roof fairing on existing cabin itself. The roof fairing can deflect the airflow over the truck smoothly and continuously.

Turbulence Viscosity

r

Grid Refinement Ratio

R

A Constant of Ideal gas

T

Temperature

This assignment will analysis the aerodynamic performance of the roof fairing of the freightliners, aim how a roof fairing can help a freightliner keeping speed and cut down the fuel consumption. This topic is based on the commercial vehicle industries .the analyse result can be used to determine what type of fairing is more reasonable and more efficient.

g

The Acceleration due to Gravity

1.2 REFERENCES REVIEW

Specific Dissipation Rate

1

Zhong Hao

Roof Fairing for Truck Aerodynamics

Even though, the closely-related work paper with my topic( the truck roof fairing )are very few, there are some useful and helpful research documents can be found. The most helpful one paper is Adjustable Roof
Fairing for Truck Aerodynamics by Marella vamsi
Krishna and C vijay ram. It is a very complex subject for the adjustable fairing for container truck. In his subject, the fairing can be adjust with the situation of truck speed and whether or not link container. This work are not quite same with my topic but the footing is similar. There is some other CFD work for the car and aircraft help me a lot. They are the CFD analysis of concept car in order to improve aerodynamics by
Josip Juraj Strossmayer and F6 Fairing Drag Prediction
Workshop by Edward N. Tinoco & Venkat