UWE Bristol Engineering showcase 2015

Dennis Mahlstedt
Aerospace Engineering
Project Supervisor
Dr. Chris Toomer
Design Characteristics of Ram- and Scramjets
Aims of Investiganiton
At part A of the individual engineering project the aim of the investigation was to develop a design method for a simple wedged type
ramjet/scramjet intake by using isentropic flow relations and to test it with the help of computational fluid dynamics (CFD). Thereby the
intake should be capable to operate in a started condition at the design Mach number of MM = 4, without generating spilled flow.
In this part of the project the goal is to improve the CFD setup from part A, so that the operational limits of the intake design can be
investigated. Thereby the influence of an applied backpressure at the outlet of the intake will be analysed, to find out, if the intake can
run as a ramjet or scramjet depending on the pressure setting. Furthermore the design method should be evaluated on its applicability
by comparing with CFD results and improved if appropriate.
Mach number over x position for different cases of back pressure.
4 Column Grid
Type Spec: Calibri 24pt,
Align Left,
(Bold for headings medium for
paragraphs of text). Space for your
research, theory, experiments,
analysis, simulations, pictures,
tables, diagrams, flowcharts, text
4 Column Grid
Type Spec: Calibri 24pt,
Align Left,
(Bold for headings medium for
paragraphs of text). Space for your
research, theory, experiments,
analysis, simulations, pictures,
tables, diagrams, flowcharts, text
Conclusion
From the findings made so far it can be concluded, that the used method to design the
intake geometry is too simple and more in the meaning of a trial and error approach.
Moreover the current method does not produce a guaranteed ramjet of a pre-known
efficiency.
The method of characteristics (MoC) is a numerical approach that is applicable to
supersonic cases but problematic when used for subsonic problems, since it is not possible
to apply a back pressure. So it is not practical to calculate an entire ramjet flow field with
the MoC. Thus, a more accurate method needs to be worked out, that uses a modified
method of characteristics and is able to calculate subsonic and supersonic flow.
Average pressure at the out duct over set pressure value and the pressure
difference
Project summary:
This part, of the individual engineering project called
part B deals with the design characteristics of ramand
scramjet engines. At the first part of the report
important design parameter and findings made in the
first part, part A, were summed up. These concern
information on the chosen inlet- and compression
type, the calculation of flow properties, using
isentropic flow relations, as well as a recap of the
results from computational fluid dynamics simulation.
Subsequent to this, three simulations, with a new
setup that should ensure more stable solver
characteristics, were conducted. One is the
application of different back pressures to the outlet
of the intake, the second simulation contains an
extended, straight throat region and the last one an
additional bleed air exit. Thereby the influence of
these changes on the flow field has been
investigated.
For the purpose of evaluation, the findings from the
simulation were compared to the Area Mach-Number
rule to see if similarities exist. Furthermore, due to
the high spillage that is generated in front of the
intake, the contraction ratio between the lip captureand
throat area was investigated by applying the
specific Kantrowitz criteria.
Finally it was found, that the Mach number at the
intake-duct could be controlled by the backpressure
set at the outlet boundary condition. So that it is
possible to adjust the flow to an entirely subsonic or
supersonic velocity. Thus it can be switched between
ram- and scramjet mode. As a possible reason for the
choked flow the contraction ratio between the lipand
throat area should be considered, since it is
located below the range, where an inlet start should
be possible.
The influence of the bleed exit and the extended
throat region were not investigated in depth, because
of the unstable solver characteristics leading to early
abortion of the simulation.