Kinetic heating and transition studies at hypersonic speeds
File(s)
Author(s)
Zanchetta, Marcantony
Type
Thesis
Abstract
The thesis reports on an experimental and computational study of kinetic heating at
hypersonic speeds. Of particular interest is the transition of the laminar boundary
layer to a state of turbulent motion.
The experiments are performed in a Mach 9 Gun tunnel with a 5 ° semi-angle cone geometry.
Twelve hemispherically blunted nose radii are tested at three unit Reynolds
numbers. Testing has indicated that as the nose is progressively blunted, the transition
region moves downstream. Further amounts of bluntness enhance other instability
mechanisms and transition events are witnessed in the near nose regions. There
are clearly two transitional regimes, denoted the "small bluntness" and "transition
reversal" regime, respectively.
This study investigates the structure of the transitional boundary layer in both
regimes using thin film heat transfer rate gauges and liquid crystal surface thermography.
The heat transfer measurements indicate that the small bluntness transition
regime is governed by the rapid formation, growth and merging of turbulent events.
Transition occurs over hundreds of boundary layer lengths. The reversal regime transition
process is characterised by the birth of turbulent events in the nose and near
nose regions. The temporal formation rate of the events is governed by roughness. In
a low roughness environment, transition occurs over many model lengths. Increasing
the roughness level, increases the spot formation rate, and transition is witnessed
immediately downstream of the spherical nose region.
The role of roughness is further explored using boundary layer trips. The trip causes
a laminar wake which rapidly undergoes transition and forms a turbulent wedge.
Event circumferential spreading angles are found for a variety of trip geometries and
locations. The heat transfer distribution in the wedge is mapped using the thin film
gauges.
Computational work is used to perform laminar flow field predictions. Of interest
is the entropy layer caused by the presence of the bow shock, and its interaction
with the boundary layer. Heat transfer predictions in the transitional region are also
performed aided with the experimentally obtained intermittency information.
hypersonic speeds. Of particular interest is the transition of the laminar boundary
layer to a state of turbulent motion.
The experiments are performed in a Mach 9 Gun tunnel with a 5 ° semi-angle cone geometry.
Twelve hemispherically blunted nose radii are tested at three unit Reynolds
numbers. Testing has indicated that as the nose is progressively blunted, the transition
region moves downstream. Further amounts of bluntness enhance other instability
mechanisms and transition events are witnessed in the near nose regions. There
are clearly two transitional regimes, denoted the "small bluntness" and "transition
reversal" regime, respectively.
This study investigates the structure of the transitional boundary layer in both
regimes using thin film heat transfer rate gauges and liquid crystal surface thermography.
The heat transfer measurements indicate that the small bluntness transition
regime is governed by the rapid formation, growth and merging of turbulent events.
Transition occurs over hundreds of boundary layer lengths. The reversal regime transition
process is characterised by the birth of turbulent events in the nose and near
nose regions. The temporal formation rate of the events is governed by roughness. In
a low roughness environment, transition occurs over many model lengths. Increasing
the roughness level, increases the spot formation rate, and transition is witnessed
immediately downstream of the spherical nose region.
The role of roughness is further explored using boundary layer trips. The trip causes
a laminar wake which rapidly undergoes transition and forms a turbulent wedge.
Event circumferential spreading angles are found for a variety of trip geometries and
locations. The heat transfer distribution in the wedge is mapped using the thin film
gauges.
Computational work is used to perform laminar flow field predictions. Of interest
is the entropy layer caused by the presence of the bow shock, and its interaction
with the boundary layer. Heat transfer predictions in the transitional region are also
performed aided with the experimentally obtained intermittency information.
Version
Open Access
Date Issued
1996-04
Date Awarded
1996
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Cain, T.
Sponsor
Great Britain. Defence Evaluation and Research Agency
Publisher Department
Aeronautics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)
Author Permission
Permission granted