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|Title: ||Investigation and validation of a cubic turbulence model in isothermal and combusting flows|
|Authors: ||Carroni, Richard|
|Issue Date: ||1999|
|Publisher: ||© Richard Carroni|
|Abstract: ||Computational Fluid Dynamics relies upon turbulence models for predicting most
engineering flows. Relatively accurate models exist but are computationally intensive;
simpler, more practical models, however, often return poor predictions. The new cubic,
eddy-viscosity turbulence model is a compromise of these extremes, employing a
nonlinear (cubic) stress-strainr elationship. The primary objective of the current research
is to compare the cubic model against a range of other two-equation turbulence models,
for a variety of isothermal and combusting flows.
The TEACH research code is the main platform for the investigations of the new
turbulence model. Other, industry-standard models (standard k-c, ReNormalisation
Group k-c and Launder & Sharma low Reynolds-number models) are also implemented
for comparative purposes. The nonlinear model is found to be numerically unstable and
several remedies are required before any converged solutions can be obtained for the
complex flows investigated. The turbulent, isothermal test cases are: fully-developed
pipe flow, axisymmetric pipe expansion (three different flows) and strongly-swirling pipe
flow (for which a Reynolds Stress Model, 'available in a commercial CFD code, is also
utilised). In most cases, the nonlinear model provides the best results relative to the other
two-equation models. A detailed anälysis is carried out to account for the different ways
in which the physics of the flows are represented by the various turbulence models.
A challenging, reacting flow is the bluff-body stabilised, nonpremixed flame.
Initial simulations, utilising the flame sheet combustion model, reveal that the accuracy of
the computed temperature and mixture fraction distributions depends largely upon the
predictions of the flow field. The nonlinear turbulence model gives slightly improved
results relative to the other, standard models. However, detailed velocity distributions are
required for further analysis of the cubic model. Since no flow-field data for confined,
bluff-body burners exists in the public domain, an experimental combustor is designed
and built on-site. An optical technique, Particle Image Velocimetry (PIV), is utilised to
obtain detailed profiles of the flow, temperatures are measured using a standard
thermcouple probe. After extensive processing, the experimental results are compared
with the simulation predictions. The nonlinear turbulence model captures all the flow
features and is seen to significantly improve results compared to the other models.
Reasons for its relative success are presented.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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