U.S. patent number 3,599,431 [Application Number 04/817,490] was granted by the patent office on 1971-08-17 for fluid-dynamic engine.
This patent grant is currently assigned to Carl Clement, Robert S. Estes, Royal M. Glavin, Jay Kurtz, James Linahan, Edward S. Merrill, Emmett Steel. Invention is credited to Giusto Fonda-Bonardi.
United States Patent |
3,599,431 |
Fonda-Bonardi |
August 17, 1971 |
FLUID-DYNAMIC ENGINE
Abstract
This invention relates to a fluid-dynamic engine wherein a gas
is accelerated through the engine at the speed of sound at the
sonic speed of the gas and imparting energy to the gas while
maintaining it at the sonic speed. The engine may comprise a duct
having a sonic duct section interposed between convergent and
divergent sections so that it is successively accelerated to the
sonic speed through the convergent section at the sonic speed. The
engine includes means for deriving power from the fluid stream by
coupling a fluid-responsive element to the stream and recompressing
the fluid of the fluid stream while moving at the sonic speed.
Inventors: |
Fonda-Bonardi; Giusto (Los
Angeles, CA) |
Assignee: |
Estes; Robert S. (Los Angeles,
CA)
Merrill; Edward S. (Palm Springs, CA)
Steel; Emmett (Los Angeles, CA)
Kurtz; Jay (Pacific Palisades, CA)
Linahan; James (Pacific Palisades, CA)
Clement; Carl (Pacific Palisades, CA)
Glavin; Royal M. (Pacific Palisades, CA)
|
Family
ID: |
25223198 |
Appl.
No.: |
04/817,490 |
Filed: |
April 18, 1969 |
Current U.S.
Class: |
60/645; 60/264;
60/772; 60/650 |
Current CPC
Class: |
F02C
3/00 (20130101); F02C 9/16 (20130101); F01D
1/06 (20130101) |
Current International
Class: |
F01D
1/00 (20060101); F02C 3/00 (20060101); F01D
1/06 (20060101); F02C 9/00 (20060101); F02C
9/16 (20060101); F01k 003/18 (); F02c 009/00 ();
F02k 001/00 () |
Field of
Search: |
;60/59,59T,39,39.02,39.75,39.14,39.53,264,270 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Claims
What I claim is:
1. A fluid-dynamic engine for the transformation of heat energy
into mechanical energy comprising
a fluid-conveying duct having a sonic duct section interposed
between a convergent section and a divergent section,
means for conveying fluid through each section of said duct so that
it moves in a fluid stream at the speed of sound in said fluid
through the sonic section,
means for heating the fluid stream while it is moving at said sonic
speed,
drive means including a rotatable shaft coupled to the downstream
side of the divergent section for deriving power from the
fluid-dynamic engine in the form of rotations of the shaft,
said fluid stream impinging on said drive means for imparting the
energy of the fluid stream to said drive means,
and means for controlling the coupling between said fluid stream
and said drive means for controlling the power extracted from the
engine and thereby the rotations of the shaft.
2. A fluid-dynamic engine as defined in claim 1 wherein the
divergent duct section is constructed and defined for recompressing
the fluid stream and redirecting the fluid stream into a path for
impingement onto said drive means.
3. A fluid-dynamic engine as defined in claim 2 wherein the
divergent duct section includes a solid terminal portion upon which
the fluid stream impinges and recompresses a portion of the fluid
stream to stagnation pressure and includes a ring of curved vanes
for redirecting the fluid stream.
4. A fluid-dynamic engine as defined in claim 3 wherein the drive
means carries turbine blades adapted for receiving the fluid stream
emerging from the curved vanes when coupled thereto.
5. A fluid-dynamic engine as defined in claim 4 including means for
controlling the coupling of the drive means to vary the extent of
impingement of the fluid stream with the turbine blades and thereby
the power derived from the engine.
6. A method of operating a fluid-dynamic engine including the steps
of
accelerating a fluid stream through an engine at the speed of sound
at the sonic speed of the fluid,
imparting energy to the fluid while maintaining it at said sonic
speed,
recompressing the fluid stream to stagnation pressure, and
deriving torque from the energy of the fluid stream.
7. A method for deriving energy from a fluid-dynamic engine
including the steps of
accelerating a fluid stream through an engine at the speed of sound
at sonic speed in the fluid,
imparting energy to the fluid stream while it is moving at said
sonic speed,
passing the fluid through a diffuser at subsonic speeds for
maintaining the fluid moving at sonic speed while energy is being
imparted to it,
coupling a fluid-responsive element to the stream for deriving
power therefrom, and
recompressing the fluid of the fluid stream passing through the
diffuser and deriving power from the fluid stream.
8. A method as defined in claim 7 including the step of redirecting
the path of the fluid stream in the diffuser prior to coupling to
the fluid-responsive element.
9. A method as defined in claim 7 wherein said diffuser is
represented by a solid surface shaped to coincide with the shape of
a selected streamline surface such as would naturally result in the
impingement of an otherwise unrestricted fluid stream of the same
characteristics stagnating against said solid terminal portion.
Description
This application is an improvement over the teachings of my earlier
filed copending application bearing Ser. No. 798,367 and entitled
"FLUID-DYNAMIC ENGINE." Briefly, the device therein described is
characterized by the process of heating a gas which is moving at
the speed of sound in a duct of suitable shape, and by the
utilization of the resulting increase of kinetic energy of the gas.
The shape of the duct is related to the rate of heat delivery to
the gas, so as to maintain the velocity of the gas equal to the
local speed of sound over substantially the entire length of duct
wherein the heat delivery process takes place. Conversely, this
means that, once a duct is built with a certain profile of cross
sections matched to a given profile of heat delivery rate, the heat
delivery rate cannot be changed much from the design profile
without causing the flow to deviate from the desired condition of
sonic velocity. As a consequence an engine of this type can be
designed to operate very efficiently for a fixed value of rate of
heat absorption and power output, but does not lend itself easily
to changes of power output.
There are two kinds of variation of power output that are of great
practical interest. One is the adjustment of operating conditions
to an optimum set of values resulting in the most efficient
operation for relatively long periods of time: an example of this
is the adjustment of operating conditions of an airplane engine for
most efficient cruise at a given altitude with a given gross
airplane weight. The other is the quick variation of power setting
required for maneuvers, e.g., takeoffs and landings. Here
responsiveness is more important than optimum utilization of
thermal energy in the engine. Similarly, a ship requires responsive
variations of propeller power for docking maneuvers independently
from the need for efficient propulsion during cruise. These two
distinct requirements can be separately met by two different
contrivances, which can, however, be both simultaneously applied to
the same engine. Accordingly, this invention refers to means for
quickly and responsively varying the power output of a
fluid-dynamic engine of the type described in the aforementioned
copending application, in the case in which the power output is
extracted from the engine in the form of mechanical power delivered
to a rotating shaft.
These and other features of the invention can be more fully
appreciated through reference to the drawings forming part of this
specification wherein:
FIG. 1 is a diagrammatic cross-sectional view of a fluid-dynamic
engine embodying the present invention;
FIG. 2 is an end view of the engine of FIG. 1 taken along the lines
2-2 and 2-A, and
FIGS. 3 and 4 show two positions of the power output device
corresponding respectively to maximum power output and zero power
output.
The structure and operation of the basic fluid-dynamic engine is
described in the aforementioned copending patent application and
the disclosure thereof is incorporated herein by reference and a
more detailed appreciation of the operation of the type of
fluid-dynamic engine under consideration may be had by reference to
said copending application. Briefly, for the purposes of the
present invention, the fluid-dynamic engine E comprises a duct D
for conveying a fluid stream thereto. The duct D has a convergent
section 10 where the fluid or gas is accelerated to Mach 1 by an
adiabatic expansion. The gas then enters the sonic section 11 of
the duct D wherein heat is delivered to the fluid while it is
moving at sonic speed. The fluid travelling at sonic speed then
enters the diffuser section 15. At this point the gas has a
pressure P equal to the critical pressure, conventionally indicated
by P*, related to the stagnation pressure P.sub.o by
P*=[ 2/(k+1 )].sup.k/(k.sup.- 1) P.sub. o
where k is the ratio of specific heats in the gas. This is a
general relationship and applies for all gases moving at the speed
of sound. For air, k=1.40 and P*=0.528 P .sub.0. The moving gas
contains kinetic energy, of which a part is used to compress the
gas in a subsonic diffuser to a pressure closer to P.sub.o, and a
part remains available for utilization. It is therefore important
that recompression be effected with a minimum of losses, in
particular frictional losses. Since frictional losses occur
predominantly in the boundary layer, where the moving gas is in
contact with a solid wall, and are proportional to the velocity of
the gas (which varies in a prescribed manner between two fixed
predetermined limits, i.e., between the speed of sound at the exit
of the sonic section and a preselected lower velocity at the end of
the diffuser), the total frictional loss is essentially
proportional to what is called the "wetted area," or the wall area
of the duct in contact with the boundary layer. This, for a given
diameter, is in turn proportional to the length of the diffuser. It
is therefore important to build the shortest diffuser possible
compatible with the requirement of effective recompression.
On the other hand, the adverse pressure gradient present in the
diffuser tends to increase the thickness of the boundary layer as
the gas progresses along the diffuser. If the pressure gradient is
too steep the boundary layer becomes detached, the diffuser stalls,
and no recompression is possible beyond the point of detachment.
Hence effective diffusers cannot be built shorter than a minimum
length imposed by the requirement that the pressure gradient be
less steep than that which causes boundary layer detachment. Within
these limitations, the most effective diffuser is the one which has
the least wall area in proportion to the cross-sectional area of
the duct.
An optimal diffuser, in this sense, can be built by taking
advantage of the fluid-dynamic properties of a free jet impinging
on a perpendicular flat plate. A free fluid stream, issuing at high
velocity from an orifice (assumed of circular shape) and impinging
on a flat plate perpendicular to the axis of the stream, is
deflected radially away from the center of impingement, which is a
point of stagnation. At this point the fluid is momentarily at rest
and full stagnation pressure P.sub.o is developed without any
frictional losses, because the moving gas arriving there is nowhere
in contact with any walls. The stagnation point is surrounded by a
region in which most of the original kinetic energy of the gas
arriving there is converted in pressure, whereby the gas comes
arbitrarily close to stagnation, again without being in contact
with any walls. This region is in turn surrounded by another in
which the pressure is lower and more unconverted kinetic energy
remains available and so on. The stream can be ideally subdivided
in concentric stream tubes, separated by ideal stream surfaces,
which are concentric surfaces of revolution each generated by a
typical streamline rotated about the axis of symmetry. Each
concentric stream tube is characterized by a maximum value of
recovered pressure, which occurs at the point where the streamline
in question is tangent to a surface of equal pressure in the fluid.
Each streamline (and each corresponding stream tube) can be labeled
with a characteristic value of the pressure ratio P.sub.e 1P.sub.
o, where P.sub.e is the maximum value of pressure recovered, and
P.sub.o is the stagnation pressure (which is fully recovered at the
center of the plate). If the wall of the diffuser is shaped to
coincide with that stream surface which corresponds to some desired
value of P.sub.e 1P.sub.o, and extended to the point where said
pressure ratio is developed in the fluid in contact with the wall
(i.e. to the line where said wall is tangent to the surface of
equal pressure P=P.sub.e), then the flow inside is unaffected by
the wall and the same pressure ratio P.sub.3 /P.sub.o appears at
all points of the surface of equal pressure, imbedded in the fluid,
for which P=P.sub.e. This surface intersects said plate along a
circular line concentric to the stagnation point: the plate must
extend at least to this line.
Under the simplifying assumption that the gas density does not
depend on pressure (which is valid in the neighborhood of the
stagnation point), the properties of the flow are best described in
terms of the velocity potential (see, for example, L. Prandt1 and
O. G. Tietjens, "Fundamentals of hydro- and aeromechanics," Dover,
N.Y. 1957, p. 143). It is easily found that the flow is axially
symmetrical and that all streamlines in each plane passing through
the axis are cubic hyperbolas described by the equation
R.sup.2 Z=C (1)
where R is the radius, Z is the distance from said plate, and, C an
arbitrary constant related to the pressure ratio P.sub. e /
P.sub.0. One such streamline is shown as arrow 101 in FIG. 1. All
streamlines are geometrically similar and any one of them can be
used to generate a surface of revolution which, together with a
plate 102, defines a possible and acceptable geometry for the
diffuser. The coordinates for the diffuser wall 103 are computed by
choosing an appropriate value for the arbitrary constant C in
equation 1. Within this envelope the gas recompresses to full
stagnation pressure P.sub.o at the central point 104 of plate 102.
The surfaces of equal pressure are portions of oblated ellipsoids,
each intersecting the plane of the paper of FIG. 1 along a ellipse,
for example as represented by the dotted lines 105 and 106, each
identified by a particular value of the pressure ratio P.sub.e
/P.sub.o. The line 106 is tangent to the diffuser wall 102 at point
107 and defines the exhaust compression ratio P.sub.e /P.sub.o for
which the diffuser is designed. Wall 103 is extended to point 107
and needs go no further to provide recompression to a pressure
ratio equal to P.sub.e /P.sub.o. Point 107 as shown in FIG. 1 is,
of course, the intersection with the plane of the paper of a
circular boundary concentric with the axis of the machine.
The above-described profile is rigorously correct only if the fluid
density is constant. This is very nearly true at the end of the
recompression process, but not so where the gas pressure P is still
close to the critical pressure P*, for which M=1. There is, in
fact, a substantial variation of density associated with the very
large pressure ratio P.sub.e /P* for which the diffuser must be
designed. This effect, called "compressibility effect," is
negligible in the neighborhood of plate 102, but is predominant in
the region immediately downstream of sonic section 11, where M=1
and P=P*.
Although it is possible to develop differential equations which
describe the stagnation of a compressible free jet against a
perpendicular flat plate, their solution is difficult and can be
best handled by a digital computer. The result is a profile quite
similar to that described by equation 1, but generally somewhat
wider and less tapered near the exit of sonic section 11. A very
good approximation of this rigorous profile can be obtained by
noting that compressibility effects are negligible by the time the
fluid is slowed down to a Mach number smaller than about 0.3. The
diffuser can be divided in two parts, of which part 108 is designed
on the basis of a constant pressure-ratio gradient, and part 109
which is designed in accordance with equation 1. The two parts are
joined at a point 111 where the Mach number M is approximately
equal to 0.3, and the duct profile is computed by imposing the
condition that all flow properties and their derivatives be
continuous across this point. A small correction is then applied to
the profile (whether rigorously generated by digital computer, or
approximated as described above), to allow for the growth of the
boundary layer: the correction consists of a displacement of the
wall outwards by an amount equivalent to the boundary layer
thickness at each point of the diffuser.
A diffuser designed in accordance with this disclosure has two
important properties which are needed in the implementation of this
invention:
a. It can recompress a gas from a pressure ratio P/ P.sub. o equal
to the critical pressure ratio P* /P.sub..sub.o (where M=1) to an
exhaust pressure ratio P.sub.e /P.sub. o arbitrarily close to unity
(for which the Mach number would be equal to zero), without
suffering boundary layer separation and with very low frictional
losses of kinetic energy.
b. It deflects the momentum vector associated with the moving fluid
from an axial direction (at the end of sonic section 11, where the
fluid is moving in an essentially parallel stream) to a
symmetrically radial direction at the exhaust of the diffuser
between plate 102 and the boundary 107 of the sidewall 103, as
indicated by the tip of the streamline arrow 101. The turning of
the momentum vector is causes by the radial component of the
pressure gradient between equal pressure surfaces (e.g. 105 and
106), and does not require any turning vanes in the stream, with
associated frictional and turbulent losses of kinetic energy.
It should be noted, parenthetically, that the diffuser here
described can be used in applications other than fluid-dynamic
engines, of the type under consideration, whenever a fluid must be
recompressed by converting part of its initial kinetic energy over
a large pressure ratio: if the fluid is incompressible (e.g. a
liquid), equation 1 may be used without compressibility
corrections.
The radially moving gas at the exhaust of the diffuser is imparted
angular momentum by a ring of curved vanes 120 mounted between
plate 102 and a flangelike extension 112 of the diffuser wall 103.
The curved vanes 120 are designed to have a radial extension such
that they do not protrude beyond an elliptical contour coincident
with the constant-pressure ellipsoid 106, which defines the exhaust
of the diffuser proper, and is also a surface of constant gas
velocity; and such that they terminate on a straight cylindrical
surface 113 on the outside. The curvature of the vanes is computed
to provide channels of constant area 121 between them, so as to
turn the momentum vector of the gas without changing its magnitude,
and to eject the gas at a constant angle .alpha. with the tangent
plane 126 to the cylindrical surface 113 at every point of the
surface. The gas impinges then on a ring of turbine blades 122
designed to utilize the angular momentum of the gas and having the
customary inlet and outlet angles appropriate to the velocity of
the gas and the tangential angle .alpha.. Since the gas emerges
uniformly from surface 113 and has everywhere the same velocity and
the same tangential angle .alpha., the turbine blades 122 have a
constant profile and no twist, and can be cheaply fabricated from
simple extruded bars of appropriate cross section. The blades are
oriented parallel to the axis of the machine and parallel to the
cylindrical surface 113. They are mounted between a support ring
114 and a wheel 115, carried by a hub 116.
The torque collected by the turbine is transmitted to the output
shaft 117 by means of a spline comprising an outer element 123
attached to wheel 115 and an inner element 124 attached to shaft
117. The spline permits the entire wheel, hub and blades assembly
to move axially while normally rotating and transmitting torque to
shaft 117. The axial position of the turbine assembly is
controlled, for example, by a control lever 118 engaged in a groove
119 cut around hub 116.
The extent of the axial movement of wheel 115 is sufficient to
place the turbine blades 122 across the entire width of the exhaust
of the diffuser (surface 113), or to retract them entirely clear of
the emerging stream of gas. FIG. 1 shows the turbine in an
intermediate position. FIG. 3 shows the blades fully engaged, and
intercepting the entire efflux from the diffuser. FIG. 4 shows the
blades fully retracted, and not touched by the emerging gas stream
125. It is clear that the device can pass from developing full
torque to zero, and vice versa, simply by translating axially wheel
115 from one extreme to the other of the travel on spline 123-124
and back. Intermediate values of the torque can be selected by
stopping the axial translation in an intermediate position.
When the wheel is in an intermediate position, as shown in FIG. 1
it extracts from the gas stream only the kinetic energy of that
fraction of the entire gas stream which engages blades 122. The
remainder, passing between flange 112 and ring 114, is not
utilized: the kinetic energy is eventually dissipated in turbulence
and is lost to the machine. For this reason the device here
described is best used when the loss of some kinetic energy is of
scarce importance compared with the need for quick changes of power
output. Since the power delivered by a rotating shaft is equal to
the product of the torque times the angular speed, and the torque
developed is proportional to the fraction of exhaust stream 125
engaged by blades 122, the power output can be changed without
changing the angular speed of the shaft, which is an advantage in
certain applications. This can be done by varying the torque,
simply by translating the wheel axially on spline 123-124. This is
contrasted with the slow change of power output which can be
obtained from other turbines in which the angular momentum of the
entire spinning assembly, sometimes very large, must be changed to
change the output power.
When quick changes of power output are not desired, a loss of
kinetic energy is avoided by leaving blades 122 fully engaged with
the exhaust gas stream as shown in FIG. 3. This is the normal
operating position for the device when the desired power output is
expected to remain constant or to change but slowly, and time is
available for adjusting the power level of the device by other
means.
* * * * *