U.S. patent application number 12/847190 was filed with the patent office on 2012-02-02 for systems and apparatus relating to diffusers in combustion turbine engines.
This patent application is currently assigned to General Electric Company. Invention is credited to Deepesh Dinesh Nanda.
Application Number | 20120027578 12/847190 |
Document ID | / |
Family ID | 45510478 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120027578 |
Kind Code |
A1 |
Nanda; Deepesh Dinesh |
February 2, 2012 |
SYSTEMS AND APPARATUS RELATING TO DIFFUSERS IN COMBUSTION TURBINE
ENGINES
Abstract
A discharge diffuser that includes: a forward section and a dump
cavity, the forward section being configured to direct discharge
from the compressor to the dump cavity; an inner diffuser wall that
defines an inner radial flowpath of the upstream section; and an
outer diffuser wall that defines an outer radial flowpath of the
upstream section; wherein at an aft lip of the inner diffuser wall,
the discharge diffuser comprises an overhanging step.
Inventors: |
Nanda; Deepesh Dinesh;
(Bangalore, IN) |
Assignee: |
General Electric Company
|
Family ID: |
45510478 |
Appl. No.: |
12/847190 |
Filed: |
July 30, 2010 |
Current U.S.
Class: |
415/211.2 |
Current CPC
Class: |
F04D 29/541
20130101 |
Class at
Publication: |
415/211.2 |
International
Class: |
F01D 9/00 20060101
F01D009/00 |
Claims
1. A discharge diffuser in a combustion turbine engine that
includes a compressor, a combustor and a turbine, the discharge
diffuser comprising: a forward section and a dump cavity, the
forward section being configured to direct discharge from the
compressor to the dump cavity; an inner diffuser wall that defines
an inner radial flowpath of the upstream section; and an outer
diffuser wall that defines an outer radial flowpath of the upstream
section; wherein at an aft lip of the inner diffuser wall, the
discharge diffuser comprises an overhanging step.
2. The discharge diffuser according to claim 1, wherein the outer
diffuser wall flares outwardly such that the inner diffuser wall
and the outer diffuser wall define a widening flowpath, and the aft
lip comprises the downstream termination point of the inner
diffuser wall.
3. The discharge diffuser according to claim 2, wherein the dump
cavity comprises a region of increased volume positioned downstream
of the flared inner and outer diffuser walls of the upstream
section, and wherein the dump cavity is configured to surround at
least a portion of the combustor.
4. The discharge diffuser according to claim 1, wherein the
overhanging step comprises a step wall that extends from the aft
lip of the forward section to an inner cavity wall of the dump
cavity, the inner cavity wall comprising an inner radial boundary
of the dump cavity.
5. The discharge diffuser according to claim 4, wherein the step
wall comprises a radial step that, from a beginning point at the
aft lip of the inner diffuser wall, slants in a direction that
includes both an inboard directional component and an
axial-upstream directional component.
6. The discharge diffuser according to claim 4, wherein the
overhanging step comprises a radial step that, from the aft lip,
slants radially inward and in an upstream direction so that the
radial step undercuts a portion of the inner diffuser wall.
7. The discharge diffuser according to claim 1, wherein: the dump
cavity comprises an inner cavity wall that defines an inner radial
boundary of the dump cavity; and the overhanging step includes a
step wall that connects the inner diffuser wall to the inner cavity
wall.
8. The discharge diffuser according to claim 7, wherein the inner
cavity wall comprises a position that is inboard in relation to the
inner diffuser wall; and wherein the radial height of the
overhanging step comprises the distance by which the inner cavity
wall is inboard of the inner diffuser wall.
9. The discharge diffuser according to claim 8, wherein the step
wall, at one end, connects to the inner diffuser wall at the aft
lip and, at the other end, connects to the inner cavity wall at a
dump cavity forward edge.
10. The discharge diffuser according to claim 9, wherein the
overhanging step is configured such that the aft lip comprises an
axial position that is aft relative to the axial position of the
dump cavity forward edge.
11. The discharge diffuser according to claim 10, wherein: the step
wall comprises a substantially planar shape; a step wall angle
comprises the angle formed between the plane of the step wall and a
radially oriented reference line; and the overhanging step is
configured such that the step wall angle comprises a range of
between 20 and 60 degrees.
12. The discharge diffuser according to claim 10, wherein: the step
wall comprises a substantially planar shape; a step wall angle
comprises the angle formed between the plane of the step wall and a
radially oriented reference line; and the overhanging step is
configured such that the step wall angle comprises a range of
between 30 and 50 degrees.
13. The discharge diffuser according to claim 10, wherein: the step
wall comprises a substantially planar shape; a step wall angle
comprises the angle formed between the plane of the step wall and a
radially oriented reference line; and the overhanging step is
configured such that the step wall angle comprises approximately 40
degrees.
14. The discharge diffuser according to claim 10, wherein the aft
lip comprises one of a rounded edge, a sharp edge, and a radially
aligned flat edge; and wherein the dump cavity forward edge
comprises a filleted edge.
15. The discharge diffuser according to claim 10, wherein the
radial height of the overhanging step comprises 4 to 6 inches.
16. The discharge diffuser according to claim 10, further
comprising a transition step located on the inner diffuser wall;
wherein the distance between a transition step located on the inner
diffuser wall and the aft lip comprises 3.5 to 4.5 inches; and
wherein the radial height of the transition step comprises
approximately 0.5 inches.
17. A discharge diffuser for a combustion turbine engine that
includes a compressor, a combustor and a turbine, the discharge
diffuser comprising: a forward section configured to direct
compressor discharge from the compressor to a dump cavity; wherein:
the forward section includes an inner diffuser wall and an outer
diffuser wall, the outer diffuser wall flaring outwardly to define
a widening flowpath therethrough; the dump cavity comprises a
region of increased volume positioned downstream of the upstream
section, the dump cavity being configured to surround at least a
portion of a combustor; and at an aft lip of the inner diffuser
wall, the discharge diffuser comprises an overhanging step, the
overhanging step including a step wall that, from the aft lip,
slants radially inward and in an upstream direction so that the
step wall undercuts a portion of the inner diffuser wall.
18. The discharge diffuser according to claim 17, wherein: the dump
cavity comprises an inner dump cavity wall that defines an inner
radial boundary of the dump cavity; and the step wall connects the
inner diffuser wall to the inner cavity wall, the inner dump cavity
wall comprising a position that is inboard in relation to the inner
diffuser wall.
19. The discharge diffuser according to claim 18, wherein: the step
wall, at one end, connects to the inner diffuser wall at the aft
lip and, at the other end, connects to the inner cavity wall at a
dump cavity forward edge; and the overhanging step is configured
such that the aft lip comprises an axial position that is aft
relative to the axial position of the dump cavity forward edge.
20. The discharge diffuser according to claim 18, wherein: the step
wall comprises a substantially planar shape; a step wall angle
comprises the angle formed between the plane of the step wall and a
radially oriented reference line; and the overhanging step is
configured such that the step wall angle comprises a range of
between 30 and 50 degrees.
Description
BACKGROUND OF THE INVENTION
[0001] This present application relates generally to turbine
diffuser design, which, as used herein and unless specifically
stated otherwise, is meant to include all types of combustion
turbine or rotary engines, including gas turbine engines, aircraft
engines, and others. More specifically, but not by way of
limitation, the present application relates to turbine diffuser
design providing robust diffuser and CDC performance.
[0002] In general, a turbine engine includes a compressor that
delivers a supply of highly compressed air to a combustor for
combustion with a fuel. The resulting flow of hot gases from the
combustor drives the turbines from which work may be extracted.
Turbine engines may be configured with an axial compressor that is
mechanically coupled by a common shaft or rotor to a downstream
turbine, with a combustor positioned between the compressor and the
turbine. Air leaves the compressor with a relatively high velocity
and, conventionally, a diffuser is utilized for initially
decreasing the velocity of the compressed airflow and minimizing
subsequent pressure losses. The diffuser may include splitter vanes
that divide the airflow into separate diffuser passages. A diffuser
dump region or cavity receives airflow from the diffuser, and
further deceleration occurs there before the air is directed to
annular channels surrounding the combustor. As is conventional, the
compressor is provided with an inner compressor discharge inner
barrel and a compressor discharge casing (CDC). The CDC
interconnects the inner barrel and a first-stage nozzle.
[0003] A primary source of loss and turbulence in diffusers is
vortex generation as flow enters the diffuser dump cavity. The
diffuser dump cavity has the highest diffusion gradient, leading to
vortex formation. As the fluid flow moves forward, the vortex grows
and begins interacting with the upstream sections of the diffuser.
Vortex growth elevates the fluid flow upstream of diffuser dump
region and results in high loss and poor pre-diffuser and CDC
performance.
[0004] As a result, there is a need for improved systems and
apparatus that trap the vortex and arrest its growth in the dump
cavity of the diffuser, thus reducing overall losses and ensuring
robust diffuser performance.
BRIEF DESCRIPTION OF THE INVENTION
[0005] The present application thus describes a discharge diffuser
that includes: a forward section and a dump cavity, the forward
section being configured to direct discharge from the compressor to
the dump cavity; an inner diffuser wall that defines an inner
radial flowpath of the upstream section; and an outer diffuser wall
that defines an outer radial flowpath of the upstream section;
wherein at an aft lip of the inner diffuser wall, the discharge
diffuser comprises an overhanging step.
[0006] The present application further describes a discharge
diffuser that includes: a forward section configured to direct
compressor discharge from the compressor to a dump cavity; wherein:
the forward section includes an inner diffuser wall and an outer
diffuser wall, the outer diffuser wall flaring outwardly to define
a widening flowpath therethrough; the dump cavity comprises a
region of increased volume positioned downstream of the upstream
section, the dump cavity being configured to surround at least a
portion of a combustor; and at an aft lip of the inner diffuser
wall, the discharge diffuser comprises an overhanging step, the
overhanging step including a step wall that, from the aft lip,
slants radially inward and in an upstream direction so that the
step wall undercuts a portion of the inner diffuser wall.
[0007] These and other features of the present application will
become apparent upon review of the following detailed description
of the preferred embodiments when taken in conjunction with the
drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features of this invention will be more
completely understood and appreciated by careful study of the
following more detailed description of exemplary embodiments of the
invention taken in conjunction with the accompanying drawings, in
which:
[0009] FIG. 1 illustrates an exemplary discharge diffuser for a
compressor in a combustion turbine engine that includes a vortex
trap or over hanging step according to an embodiment of the present
application;
[0010] FIG. 2 illustrates an exemplary discharge diffuser that
includes a vortex trap or overhanging step according to an
alternative embodiment of the present application;
[0011] FIG. 3 depicts exemplary dimensions of the various parts of
the a vortex trap or overhanging step according to an exemplary
embodiment of the present application;
[0012] FIG. 4 illustrates a fluid flow pattern within a
conventional diffuser; and
[0013] FIG. 5 illustrates a fluid flow pattern within the discharge
diffuser having a vortex trap or overhanging step according to an
exemplary embodiment of the present application.
DETAILED DESCRIPTION OF THE INVENTION
[0014] As an initial matter, to communicate clearly the invention
of the current application, it may be necessary to select
terminology that refers to and describes certain parts or machine
components of a combustion turbine engine. Whenever possible,
common industry terminology will be used and employed in a manner
consistent with its accepted meaning. However, it is meant that any
such terminology be given a broad meaning and not narrowly
construed such that the meaning intended herein and the scope of
the appended claims is unreasonably restricted. Those of ordinary
skill in the art will appreciate that often a particular component
may be referred to using several different terms. In addition, what
may be described herein as a single part may include and be
referenced in another context as consisting of several component
parts, or, what may be described herein as including multiple
component parts may be fashioned into and, in some cases, referred
to as a single part. As such, in understanding the scope of the
invention described herein, attention should not only be paid to
the terminology and description provided, but also to the
structure, configuration, function, and/or usage of the component,
as provided herein.
[0015] Further, as used herein, "downstream" and "upstream" are
terms that indicate a direction relative to the flow of working
fluid through the turbine. As such, the term "downstream" refers to
a direction that generally corresponds to the direction of the flow
of working fluid, and the term "upstream" generally refers to the
direction that is opposite of the direction of flow of working
fluid. The terms "aft" and "forward" may be used to describe
relative position within the turbine engine. It will be appreciated
that the compressor is generally referred to as residing on the
"forward" side of the turbine engine while the turbine section
resides on the "aft" side. Accordingly, as used herein, "forward"
describes a position closer to the compressor and "aft" describes a
position closer to the turbine. The term "radial" refers to
movement or position perpendicular to an axis. It is often required
to describe parts that are at differing radial positions with
regard to an axis. In this case, if a first component resides
closer to the axis than a second component, it may be stated herein
that the first component is "radially inward" or "inboard" of the
second component. If, on the other hand, the first component
resides further from the axis than the second component, it may be
stated herein that the first component is "radially outward" or
"outboard" of the second component. The term "axial" refers to
movement or position parallel to an axis. Finally, the term
"circumferential" refers to movement or position around an
axis.
[0016] FIG. 1 illustrates an exemplary compressor discharge
diffuser 100 in a combustion turbine engine that includes a vortex
trap or overhanging step according to an exemplary embodiment of
the present application. The discharge diffuser 100 may direct
compressed fluid from a compressor (not shown) to a combustor (not
shown). In general, air in the turbine engine leaves the compressor
with relatively high velocity and enters the diffuser 100, where it
is then decelerated.
[0017] As shown by arrows in FIG. 1, the compressed fluid initially
enters a forward section 101 of the discharge diffuser 100. The
forward section 101 may include an inner diffuser wall 102 and an
outer diffuser wall 104. It will be appreciated that the outer
diffuser wall 104 flares outwardly such that the diffuser walls
102, 104 define a widening flow path through the forward section
101, which decelerates the incoming compressed air. Further, an
annular splitter vane 105 may be included (as shown). The splitter
vane 105 splits the forward section 101 of the discharge diffuser
100 into two passages--a first passage 106 and a second passage
108, which direct the compressor discharge to a dump cavity 110.
(Note that only a portion of the dump cavity 110 is shown in FIGS.
1 through 3, whereas additional areas of the dump cavity 110 are
shown in FIGS. 4 and 5). In certain implementations of the
disclosure, the discharge diffuser 100 may include any number of
splitter vanes or, alternatively, may include a single widening
annular passage without splitter vanes.
[0018] Generally, the discharge diffuser 101 includes a dump cavity
110, which receives airflow from the forward section 101 (shown by
arrows). It will be appreciated that within the dump cavity 110,
air is directed into the annular channels surrounding the
combustor. FIG. 1 shows the dump cavity 110 as a region of
increased volume that is generally positioned downstream of the aft
termination points of the inner diffuser wall 102 and the outer
diffuser wall 104. The dump cavity 110 may include an inner cavity
wall 112 that defines an inner radial boundary of the dump cavity
110 and, as stated, the dump cavity 110 may surround at least a
portion of the combustor. The dump cavity 110 has a substantially
high diffusion gradient, which, in operation, typically leads to
the formation of a vortex or vortices (not shown). It will be
appreciated by those of ordinary skill in the art that the
formation of such vortices is a primary source of loss and
turbulence, which negatively impact the efficiency of the engine.
Typically, as the fluid flow moves downstream, the vortices grow
and begin interacting with the upstream section 101 of the
discharge diffuser 100, causing further efficiency losses.
[0019] The inner diffuser wall 102 terminates at an aft lip 113. As
used herein, the aft lip 113 is the downstream or aft termination
point of the inner diffuser wall 102, as indicated in FIGS. 1 and
2. In some embodiments, the inner diffuser wall 102 may include a
transition step 116 that is positioned just forward of the aft lip
113, as shown. It will be appreciated that the aft lip 113 marks
the transition point from the forward section 101 to the dump
cavity 110 of the discharge diffuser 100. Conventional design, as
shown in FIG. 4, provides a radial step at this location, with the
step having a step wall that is substantially aligned with the
radial direction.
[0020] According to embodiments of the present application, the
discharge diffuser 100 includes an overhanging step 116, which, as
discussed more below, serves to minimize or trap or arrest the
growth of vortices in this region. The overhanging step 116
generally includes a step wall 118 that slants radially inward and
in an upstream direction, thereby undercutting an aft portion of
the inner cavity wall 112, as shown in the cross-sectional views of
FIGS. 1 through 3. More specifically, the overhanging step 116
includes a step wall 118 that, from a beginning point at the aft
lip 113 of the inner diffuser wall 102, slants in a direction that
includes both an inboard directional component and an
axial-upstream directional component. At one end, the step wall 118
connects to the inner diffuser wall 102 and, at the other end,
connects to the inner cavity wall 112 at a forward edge (a location
that is referred to herein as the dump cavity forward edge 119). It
will be appreciated that, according to embodiments of the present
application, the axial position of the dump cavity forward edge 119
is forward of the axial position of the aft lip 113. Of course, it
is this configuration that creates the overhanging step 116, which,
in turn, produces the flow dynamics that reduce the formation of
vortices through the diffuser 100 during operation of the
engine.
[0021] The step wall 118, as shown, may be planar, and, in
cross-section, generally forms an angle 306 with a radial reference
line, which is specifically illustrated in FIG. 3. As used herein,
this angle will be referred to as the step wall angle 306.
Conventionally, as stated, the step wall 118 is aligned with the
radial reference line and, thus, the step wall angle 306 is
approximately 0.degree.. In other conventional arrangements (not
shown), the step wall 118 forms a positive angle with the radial
reference line, which, as used herein, refers to a configuration
wherein the step wall 118 slants inward radially in the aft
direction. As taught in the present application, however, the step
wall 118 creates a negative angle with the radial reference line,
which, as stated, creates an overhang or undercut. It has been
discovered that configurations having certain step wall angles 306
or step wall angles 306 within a certain range provide enhanced
performance. For example, in one preferred embodiment, the step
wall angle 306 comprises a range between approximately -20.degree.
and -60.degree.. More preferably, the step wall angle 306 comprises
a range between approximately -30.degree. and -50.degree.. In some
applications, an ideal step wall angle 306 comprises approximately
40.degree.. As discussed in more detail below, the slant of the
step wall 118 forms a vortex trap that arrests the growth of
vortices and prevents the vortices from interacting with the fluid
in the forward section 101 of the diffuser 100.
[0022] The aft lip 113 of the inner diffuser wall 102 may include
several preferred configurations. In one configuration, as shown in
FIG. 1, the aft lip 113 may have a smooth, rounded edge. In another
preferred embodiment, as shown in FIG. 2, the aft lip 113 may have
a sharp edge. In yet another preferred embodiment, as FIG. 3 shows,
the aft lip 113 includes a flat surface, aligned in a substantially
radial direction. These aft lip 113 alternatives have been proven
effective at trapping vortices and reducing aerodynamic losses.
While these described configurations for the aft lip 113 represent
preferred embodiments, it will be appreciated that other
configurations are possible.
[0023] In a preferred embodiment, the shape of the connection made
between the step wall 118 and the inner cavity wall 112, as shown,
includes a rounded, fillet region. As will be appreciated, this may
prevent stress concentrations. Other configurations are also
possible.
[0024] Further, it has been discovered through experimentation and
computer modeling of flow patterns that certain dimensions are
particularly more effective at controlling or limiting vortex
formation than others. FIG. 3 assists in describing the exemplary
dimensions of the various parts of an exemplary vortex trap 300
within the diffuser 100. For example, the radial height 312 of the
overhanging step 116 may be between approximately 4 and 6 inches.
More preferably, this radial height 312 may be approximately 4.4
inches. In some embodiments, the distance 302 between the
transition step 114 and the aft lip 113 may be approximately 3.5 to
4.5 inches. More preferably, this distance 302 may be about 4
inches. In some embodiments, the height 304 of the flat edge of the
aft lip 113 (see FIG. 3) may be between approximately 0 and 1
inches. More preferably, this height 304 may be approximately 0.5
inches. In some embodiments, the radius 308 of the arc formed
between the step wall 118 and the inner cavity wall 112 may be
between approximately 0.5 and 2 inches. More preferably, this
radius 308 may be approximately 1 inch. Further, the height 310 of
the transition step 114 may be between approximately 0.2 and 1
inches. More preferably, this height 310 may be around 0.5 inches.
The above dimensions are optimized for minimizing overall losses
due to vortex (not shown) growth and limiting vortex interaction
with upstream fluid flow. It will be appreciated that these
dimensions may be altered depending on the application and that
they represent only a preferred method of practice.
[0025] FIG. 4 illustrates a fluid flow pattern within a
conventional diffuser 400 and experimental results of same. The
conventional diffuser 400 includes the first passage 106 and the
second passage 108 through which the compressed fluid travels to
the dump cavity 110, as shown by arrows. A step 402, which has a
step wall oriented substantially in the radial direction, connects
the inner diffuser wall 102 to the inner cavity wall 112 of the
dump cavity 110, which is inboard in relation to the inner diffuser
wall 102. The dump cavity 110 has the highest diffusion gradient,
leading to vortex generation. A vortex 404 (which is represented by
the shaded region) forms in proximity to the step 402 as fluid
enters the dump cavity 110. The vortex 404 grows as the fluid moves
downstream and begins interacting with the fluid in the forward
section of the conventional diffuser 400. Fluid flow reversal in
the dump cavity 110 climbs the step 402, which is a substantially
vertical wall, and consequently, interacts with the upstream flow
and aids to the further growth of the vortex 404. The interaction
can be seen in FIG. 4, where the fluid is shown entering the second
passage 108. This growth in the vortex 404 elevates the flow
upstream of the dump cavity 110, leading to heavy loss and poor
pre-diffuser and CDC performance.
[0026] FIG. 5 depicts a fluid flow pattern within the diffuser 100
according to an embodiment of the present application and
experimental results of same. As discussed, the first leg 118 may
slant radially inward and in an upstream direction so that the
first leg 118 undercuts a portion of the inner diffuser wall 102.
Further, the aft lip 113 may have an axial position that is aft
relative to the axial position of the dump cavity forward edge 119.
FIG. 5 shows a mitigated vortex 502 formed in close proximity to
the step wall 118. The slant of the step wall 118 creates a vortex
trap in the dump cavity 110, arresting the growth of the mitigated
vortex 502 and preventing its interaction with the forward section
101 of the diffuser 100. FIG. 5 shows the mitigated vortex 502
being significantly disengaged from the second passage 108, as
compared to the vortex 404 in FIG. 4, which has significant
interaction with the second passage 108. This comparison
illustrates the manner in which the present design of the diffuser
100 may prevent the growth of the mitigated vortex 502 and may
substantially disengage the mitigated vortex 502 from the upstream
fluid flow.
[0027] It will be appreciated that the design of the diffuser 100
also facilitates uniform flow distribution across a transition
piece 504 and prevents the formation of hot spots. The resulting
flow field reduces overall losses and improves the diffuser 100
performance. Further, containment of the mitigated vortex 502
relieves the stringent need of having a uniform flow profile at the
compressor, without negatively affecting performance. The reduced
losses in the CDC may also allow a higher margin of loss during
compressor or combustor design, providing significant performance
and financial benefit.
[0028] Table 1 compares the performance of the conventional
diffuser 400 with that of the diffuser 100. Four scenarios are
considered, having different leakage levels set at the fourteenth
stator (S14) of the compressor, the leak being between the airfoil
at S14 and the CDC. 0.3% leak at S14 is the design point for the
present example. The pressure loss is measured according to the
following equation 1:
DPt Pt = ( Pressure at diffuser input - Pressure at diffuser output
Pressure at diffuser input ) ( 1 ) ##EQU00001##
TABLE-US-00001 TABLE 1 DPt/Pt for S14 Leak conventional diffuser
DPt/Pt for diffuser 100 (%) 400 (%) (%) 0.1 1.17 1.16 0.3 1.13 0.99
(design point) 0.4 1.19 1.03 0.8 1.42 1.3
[0029] It should be noted that, typically, significant effort is
invested in uniformly maintaining such low levels of leakage. The
reduced losses in the diffuser 100 may impart some flexibility
during compressor or combustor design and may further relax the
stringent requirements for maintaining leakage levels.
[0030] Table 1 shows that the diffuser 100 lowers the pressure loss
due to vortex growth compared to the conventional diffuser 400. It
should be noted that the claimed diffuser design provides robust
performance not only at design point, but also across various
operating conditions. Thus, the diffuser 100, according to the
embodiments of the present disclosure, restricts vortex growth and
limits upstream flow interaction with the vortex, leading to
substantial improvements in diffuser and CDC performance.
[0031] As one of ordinary skill in the art will appreciate, the
many varying features and configurations described above in
relation to the several exemplary embodiments may be further
selectively applied to form the other possible embodiments of the
present invention. For the sake of brevity and taking into account
the abilities of one of ordinary skill in the art, all of the
possible iterations is not provided or discussed in detail, though
all combinations and possible embodiments embraced by the several
claims below or otherwise are intended to be part of the instant
application. In addition, from the above description of several
exemplary embodiments of the invention, those skilled in the art
will perceive improvements, changes and modifications. Such
improvements, changes and modifications within the skill of the art
are also intended to be covered by the appended claims. Further, it
should be apparent that the foregoing relates only to the described
embodiments of the present application and that numerous changes
and modifications may be made herein without departing from the
spirit and scope of the application as defined by the following
claims and the equivalents thereof.
* * * * *