UCRL-ID-124311
On the
Wall
Jet From the Ring Crevice
of
an
Internal Combustion Engine
L.D.
Cloutman
R.M.
Green
May
1996
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U.S.
Department
of
Energy by the
Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.
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ON THE
WALL
JET
FROM
THE'RING CREVICE
OF
AN
INTERNAL COMBUSTION ENGINE
Lawrence
D.
Cloutman
Lawrence Livermore National Laboratory
and
Robert
M.
Green
..
..
Sandia National Laboratories, California
-_
..
Numerical simulations and experiments
of
the jetting
of
gases
from
the ring crevices of
a.
laboratory engine shortly after-exhaust valve opening showed an unanticipated radial flow
of
the
crevice'gases into the
main
combustion chamber. We report well-resolved numerical simulations
of
a
wall jet that show that this radial motion is driven by vorticity generation in the wall boundary
layer and at the corner
of
the piston crown.
.
.
..
_.
1
..
I.
INTRODUCTION
.h
recent PLIF imaging experiments
on
flows from the ring crevice of an internal combustion
engine, Bob Green found what appears to be
a
wall jet emerging from the crevice during the
blowdown following exhaust valve opening near bottom dead center
[l].
However, the jet does
not stay attached to the cylinder wall, but the vortex ring
at
the jet tip detaches from.the wall
and moves inward radially. Shaheen Tonse has performed some preliminary simulations of this jet
using the KIVA-3 fluid dynamics program and finds the same qualitative behavior
[2].
This result
raised the question of the mechanism .that causes the jet to separate from the wall. The purpose
of
this
report
is
to describe the mechanism for this separation.
The wall jet
is
one of the classic flow systems
in
fluid
mechanics, and
this
separation is in fact
.
well
known
in
other contexts. Figure
162.
of Van Dyke
[3]
show
a
.well-developed, late-time version
'
of
awall jet, namely
a
boundary layer
on
a
flatplate, that shows bursting with vortex pairs similar
to wliat
was
observed
'in
the engine. Other relevant figures are found
in
the same section and
around Fig. 110.
A
similar
example is discussed by Bajura and Catalan0 [4]. Another example
is the boundary layer
on
the wall
of
a
shock tube used to study
a
Richtmyer:Meshkov instability
[5].
We note that the interface between the two fluids
in
that problem
is
analogous to the contact
surface between the inflo'wing and ambient media in the
ring
crevice problem. To clearly illustrate
this separation phenomenon, we performed two numerical simulations
of
a
wall jet under conditions
similar to those found near the ring crevice of an internal combustion engine during blowdown after
.
exhaust valve opening. One case uses
a
free-slip boundary condition,on the cylinder wall, and the
.
other uses
a
no-slip condition. These calculations are sufficient to demonstrate the fundamental
physical processes
at
work.
.
.
.
Ouk
approach to demonstrating the mechanism
of
the wall jet separation is
to
simplify the
problem
so
there are
no
irrelevant factors clouding the analysis. These factors include piston
.
motion, chemistry, wall heat transfer, and residual turbulence or other
gas
motions in the bulk
gas.
Our calculations show that the separation is
a
purely fluid dynamical phenomenon associated
2