Abstract: This work is to study a roll of the fluctuating density
gradient in the compressible flows for the computational fluid dynamics
(CFD). A new anisotropy tensor with the fluctuating density
gradient is introduced, and is used for an invariant modeling technique
to model the turbulent density gradient correlation equation derived
from the continuity equation. The modeling equation is decomposed
into three groups: group proportional to the mean velocity, and that
proportional to the mean strain rate, and that proportional to the mean
density. The characteristics of the correlation in a wake are extracted
from the results by the two dimensional direct simulation, and shows
the strong correlation with the vorticity in the wake near the body.
Thus, it can be concluded that the correlation of the density gradient
is a significant parameter to describe the quick generation of the
turbulent property in the compressible flows.
Abstract: In the upstream we place a piece of ring and rotate
it with 83Hz, 166Hz, 333Hz,and 666H to find the effect of the
periodic distortion.In the experiment this type of the perturbation
will not allow since the mechanical failure of any parts of the
equipment in the upstream will destroy the blade system. This type of
study will be only possible by CFD. We use two pumps NS32
(ENSAM) and three blades pump (Tamagawa Univ). The benchmark
computations were performed without perturbation parts, and confirm
the computational results well agreement in head-flow rate. We
obtained the pressure fluctuation growth rate that is representing the
global instability of the turbo-system. The fluctuating torque
components were 0.01Nm(5000rpm), 0.1Nm(10000rmp),
0.04Nm(20000rmp), 0.15Nm( 40000rmp) respectively. Only for
10000rpm(166Hz) the output toque was random, and it implies that it
creates unsteady flow by separations on the blades, and will reduce the
pressure loss significantly
Abstract: The frequency dependence of the phase field
model(PFM) is studied. A simple PFM is proposed, and is tested in a
laminar boundary layer. The Blasius-s laminar boundary layer
solution on a flat plate is used for the flow pattern, and several
frequencies are imposed on the PFM, and the decay times of the
interfaces are obtained. The computations were conducted for three
cases: 1) no-flow, and 2) a half ball on the laminar boundary layer, 3) a
line of mass sources in the laminar boundary layer. The computations
show the decay time becomes shorter as the frequency goes larger, and
also show that it is sensitive to both background disturbances and
surface tension parameters. It is concluded that the proposed simple
PFM can describe the properties of decay process, and could give the
fundamentals for the decay of the interface in turbulent flows.