Summaries of Papers
- Study on Multiple-Time-Scale Reynolds Stress Model
(Second Report, Verification for Grid Turbulence)
Conventional turbulence models have a single time-scale
of turbulence. Therefore, they can not predict the
flows that are influenced by a lot of time-scales of turbulence.
In simulating such flows it is necessary to introduce some
information about the scales of turbulence.
In order to
overcome this problem, I proposed a multiple-time-scale Reynolds
model and the model coefficients were determined
for a grid turbulent flow. In this study, the model was applied
to a variety of grid turbulent flows to verify the model performance.
The numerical results for turbulent energy, Reynolds stresses,
second and third invariants were compared with the experimental data.
The temporal change of large and small scale components
for Reynolds stresses and energy transport rates were
also checked (Fig.1).
It was found that the model can satisfactorily predict a wide range of
grid turbulent flows. In addition, it was verified that the method
used in setting initial conditions is reasonable.
Key Words : Computational Fluid Dynamics, Turbulent Flow, Turbulence,Reynolds Stress Model, Multiple-Time-Scale Model
- Computation of Turbulent Flow in a Cyclone Chamber
with a Reynolds Stress Model
(Second Report, Numerical Prediction of Cyclone Performance)
The Reynolds stress model and the standard k-e eddy viscosity model were applied to highly swirling confined
flows in six types of cyclones, which are widely used as
the centrifugal separators in industrial applications (Fig.2),
in order to predict numerically the collection efficiency of dust
particles and the pressure loss across the cyclone.
The Reynolds stress model can capture the feature of the highly
swirling turbulence field correctly, while the standard
k-e model misrepresents the flow characteristics
due to the defect in its eddy viscosity hypothesis.
Prediction of the collection efficiency is, therefore, improved
by the Reynolds stress model against the standard
k-e model. In addition, the pressure losses obtained
by the Reynolds stress model calculation are in good agreement
with experimental data (Fig.3).
Key Words : Numerical Analysis, Turbulent Flow, Swirling Flow,
Reynolds Stress Model,Cyclone Separator, 2-Dimensional Axisymmetric Flow,
Collection Efficiency, Pressure Loss
- Acceleration of Computations with Fuzzy Reasoning
(Fuzzy Reasoning for General Coordinate System)
Numerical simulations for every flow require enormous computing
time during iterations. In order to solve this problem
several techniques have been proposed, as for example
a multigrid technique. A method using fuzzy reasoning is
one such technique. We studied the possibility of accelerating
computation with fuzzy reasoning in two dimensional incompressible
laminar flow calculations. In order to obtain qualitatively
correct velocity distributions some rules were constructed
on the basis of human reasoning. Viscous and obstacle effects were
introduced. In addition, the recognition of walls was programmed
to find the separation point and the recirculation region.
It was found that (i)our procedure can reproduce the channel
flows which have some convexities and the backward-facing step flow
(Fig.4) and (ii)it can realize a considerable acceleration
in all calculations (Table 1).