UWE Bristol Engineering showcase 2015

Ramjet Model
Robert Sawford
Aerospace Engineering
Using the isentropic shock equations to determine the exact shock solutions
for various deflection geometries for the inlet deflection angle, the optimum
inlet geometry could be produced with the idealised ‘shock on lip’ design
scenario. This produces maximum flow capture, therefore resulting in the
highest potential mass flow rate into the intake.
The ramjet model was laser cut from 6mm thick sheets of acrylic and bonded
together using acrylic cement to form an acrylic weld between the faces of
the acrylic components. Further reinforcement was provided by integrating
four steel rods through the ramjet model to provide further structural
integrity to the model.
Ramjet CFD Testing
A Design Study into Using Air Breathing Propulsion to Produce a Single-
Stage-to-Orbit Design Capable of Achieving Mach 25
Using ANSYS CFX the same ramjet model was created for CFD testing to
compare and validate the CFD model. The model was created in a simple 2D
cross section so as to minimise computational effort, while still producing
interesting results.
However the contraction ratio to capture area for the inlet was too high,
resulting in the inlet becoming unstarted. A condition characterised by the
presence of a normal shock upstream of the inlet.
Hypersonic Waverider Testing
The waverider testing was conducted at Mach 3.0 and Mach 5.0. the goal of
the tests was to determine the effect of different leading edge wedge angles
had on the engine operation, as well as assessing the performance under
shock spillage conditions and shock ingestion.
The waveriders utilised variable inlet geometry in the form of an extending
lower engine cowl that would be able to catch the leading edge shock
generated from the waverider body, thus producing maximum flow capture
for the engine intake. Additionally the performance was assessed and
compared for the condition whereby the flow is allowed to spill over the
edge of the engine cowl, reducing shock capture but preventing the shocks
from becoming ingested.
Project Supervisor
Dr Chris Toomer
Project summary
A ramjet model was designed and
manufactured for testing in the supersonic
wind tunnel. The model was used for
comparison and validation of the same
simulated test using ANSYS CFX. Furthermore
the project transitioned into testing various
waverider designs with variable inlet
geometry under a variety of inlet conditions
at different Mach numbers.
Project Objectives
To design and asses the engine performance
of a ramjet scramjet propelled hypersonic
waverider through various Mach regimes up
to Mach 25.
Project Conclusion
The use of acrylic as the primary material for the ramjet
model proved to be too fragile. The laser cutter distorted
the geometry around the leading edges, partially melting
the acrylic and thus making it brittle. Future models will
utilise CNC milled inlet geometry sandwiched between
acrylic panels, increasing robustness while still allowing
the internal shock structure to be visualised.
From the hypersonic and high supersonic testing of
the waverider designs, the numerical accuracy of the
solutions around areas of high changes in state and
energy is lower than is required for a CFD solution
that industry can use to supplement physical testing.
However the structure of the oblique shocks,
compression and nozzle behaviour from the vehicle
forebody as well as the expansion and shocks
generated by the waveriders wake is displayed by the
simulation, providing insight into the behaviour of the
waverider at these Mach regimes. As outlined by
Segal, running the inlet under spillage conditions
produces a more stable combustion environment
than when the shocks are ingested into the engine.
However this more stable environment is created
with the sacrifice of reduced compression, and as a
consequence may not be sufficient to produce the
thrust requirements for accelerating into higher
hypersonic Mach regimes.