Thesis-1991-Farhan.pdf (6.44 MB)
Theoretical and experimental aerodynamic analysis for high-speed ground vehicles
thesis
posted on 2016-08-08, 13:24 authored by Ismail H. FarhanAn improved understanding of the aerodynamics of high-speed ground
vehicles can lead to significant reductions in the energy consumption required for
propulsion, an increase of vehicle cruising speed, and an increase in the safety and
comfort of passengers. To contribute to these goals, this thesis employs theoretical and
experimental techniques to investigate the air flow around a proposed geometry for a
high-speed electromagnetic suspension (EMS) train. Train motion at normal cruising
speed in still air and in crosswind conditions are studied, considering aerodynamic
forces and moments, the wake in the lee side of the train and the turbulent boundary
layer development.
The theoretical prediction work may be conveniently divided into two parts, for
inviscid flow, and with viscous effects included. In the first, a numerical technique
called the panel method has been applied to the representation of the body shape and the
prediction of the potential flow and pressure distribution. Two computer programmes
have been written, one for a single vehicle in the presence of the ground at different
yaw angles, and the second for application to two body problems, e.g. a train passing a
railway station or a train passing the central part of another train. Both programmes
have been developed in fully three-dimensional form, but are currently based purely on
the source distribution method. This limits the applicability of the method, in particular
to small angles of yaw, but useful results are still obtainable. In the second part of the
theoretical prediction work, two methods based on the momentum integral equations
for three-dimensional boundary layer flow have been developed for use with the
aforementioned potential flow analysis; these predict the development of the
three-dimensional turbulent boundary layer (i) on the central section (for the analysis of
crosswind conditions) and (ii) on the nose of the train.
The primary interest of the experimental programme was to provide qualitative
and quantitative results for comparison with the theoretical predictions as well as to give
insight into the flow behaviour around the train. The experimental tests also provided
the first results for the influence of both stationary and moving ground planes on the
EMS train. Extensive wind tunnel tests were performed on four purpose-made models
of the high-speed train to measure aerodynamic forces, moments and pressures to
establish ground effect characteristics. The experimental results demonstrated the
importance of ground clearance. Flow visualisation showed that the wake vortices
were both stronger and larger in the presence of a ground. At small yaw angles ground
clearance had little effect, but as yaw increased, larger ground clearance led for
example to substantial increase in lift and side force coefficients. The wind tunnel tests
also identified the differences between a moving and a fixed ground plane. The
measured data showed that the type of ground simulation was significant only in the
separated region.
A comparison of the results predicted using potential flow theory for an EMS
train model and the corresponding results from wind tunnel tests indicated good
agreement in regions where the flow is attached. For small yaw angles, not more than
15° , predicted pressure distributions reproduced measured behaviour. For greater
angles, the shed vorticity (associated with flow separation) has a strong effect on the
surface pressure field and this would have to be introduced into the panel method to
improve prediction.
The turbulent boundary layer calculations for the train in a crosswind condition
showed that the momentum thickness along the crosswind surface distance co-ordinate
increased slowly at the beginning of the development of the boundary layer but then
increased sharply at the side top roof on the lee side. The sharp increase is believed to
indicate a tendency for flow separation as the solution procedure exhibits signs of
failure in this region. Suggestions are made in the thesis for ways of improving both
this and other aspects of the theoretical approach.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Aeronautical and Automotive Engineering
Publisher
© Ismail Haider FarhanPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
1991Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en