Thesis-2006-Trumper.pdf (18.01 MB)
A study of nozzle exit boundary layers in high-speed jet flows
thesis
posted on 2018-02-13, 09:41 authored by Miles T. TrumperThe requirement for reduced jet noise in order to meet stringent noise legislation (civil
aviation), and low infra-red observability and the use of unconventional exhaust nozzle
configurations to improve aircraft survivability and performance (military aviation) is driving
research to develop a better understanding of jet development and mixing mechanisms. One
option open to the engineer is the use of small-scale model testing to investigate jets flows
and provide valuable data for the validation of numerical models. Although more economical
than large/full scale testing, additional factors that influence jet development may be present
which would not be present at full scale and whose influence needs to be fully understood
in order to allow small scale–large scale read-across. One such factor is the nozzle exit
boundary layer. Although considerable data exist on the influence of nozzle exit boundary
layers on low speed jet flows, current information on high speed jet flows is limited. It
was, therefore, the aim of this thesis to extend the current understanding of nozzle exit
boundary layers and their influence on the jet development for high speed jet flows through
a combination of experimental and computational techniques.
A combination of pneumatic probe measurements and Laser Doppler Anemometry (LDA)
was used to investigate nozzle inlet and exit boundary layers of simple conical nozzles and
the influence of adding a parallel extension piece. The measurements showed that the rapid
acceleration of the boundary layer within the nozzle significantly reduced its momentum
thickness Reynolds number and changed the state of the boundary layer from turbulent to
laminar-like. The addition of a parallel extension to the nozzle exit returned the boundary
layer to a fully turbulent state.
A low Reynolds number RANS CFD approach was used to investigate the flow within the
nozzle. Simulations using the Launder-Sharma low Reynolds number k–ε model revealed
that the magnitude of the acceleration within the conical nozzles resulted in the boundary
layer beginning to relaminarise. Full relaminarisation was not achieved due to the short axial
distance over which the acceleration was sustained. The addition of a parallel extension
provided a relaxation region in which the boundary layer could recover from the acceleration
to become fully turbulent.
Measurements of the jet plume originating from nozzles with laminar-like and turbulent
boundary layers showed little influence of the boundary layer shape and thickness on shear
layer spreading and jet centreline development.
Funding
BAE Systems PLC. EPSRC (grant no. GR/02300852).
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Aeronautical and Automotive Engineering
Publisher
© M.T. TrumperPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 2.5 Generic (CC BY-NC-ND 2.5) licence. Full details of this licence are available at: http://creativecommons.org/licenses/by-nc-nd/2.5/Publication date
2006Notes
A doctoral thesis submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.Language
- en