U.S. patent number 3,802,801 [Application Number 05/222,845] was granted by the patent office on 1974-04-09 for method of and apparatus for operating an aerodynamic pressure-wave machine.
This patent grant is currently assigned to Aktiengesellschaft Brown Boveri & Cie. Invention is credited to Alfred Wunsch.
United States Patent |
3,802,801 |
Wunsch |
April 9, 1974 |
METHOD OF AND APPARATUS FOR OPERATING AN AERODYNAMIC PRESSURE-WAVE
MACHINE
Abstract
An aerodynamic pressure-wave machine which includes a rotor
provided with a circumferential array of longitudinally extending
open-ended cells rotates within the middle portion of a casing, the
end portions of the casing being provided with high-pressure
openings and low-pressure openings confronting the opposite ends of
the rotor cells for expansion of an energy-laden gas as it flows
through the cells which effects compression of another gas, such as
air, as it flows through the cells. Leakage gas flowing from the
high-pressure openings to the low-pressure openings is collected,
at least in part, and is fed back into the gas-dynamic process for
utilization of the energy still contained within them. The present
invention concerns a procedure for operating an aerodynamic
pressure-wave machine, the rotor of which is provided with cells
and moves in a casing comprising a middle portion and end portions,
such that the end portions each incorporate at least one
high-pressure inlet and one low-pressure outlet for a gas giving up
energy, and one high-pressure outlet and one low-pressure inlet for
a gas to be compressed, each end portion having at least one
high-pressure opening and one low-pressure opening, and leakage gas
flows from the high-pressure openings to the low-pressure openings;
it concerns further a device for effecting the procedure. In
aerodynamic pressure-wave machines, the pressure of one gas is
raised by expansion of another gas. The gas-dynamic process takes
place under the influence of compression and expansion waves in the
rotor cells, which are open at the ends and move past inlet and
outlet ducts in the end portions of the casing. The high-pressure
and low-pressure openings are separated from each other by a web
which is usually only narrow and to which seals can be fitted only
unsatisfactorily, if indeed at all. Leakage losses therefore occur
due to high-pressure gas flowing either in a circumferential
direction straight to a low-pressure opening, or radially, at first
into the space surrounding the rotor or into the gap between the
rotor shroud and the middle portion of the casing, and from there
to a low-pressure opening. A number of techniques for reducing the
leakage are known. All of them are intended to keep the clearance
between the rotor and the end portions of the casing small during
operation. However, these techniques have the disadvantage that
they are relatively costly and their reliability is not always
assured. The present invention adopts a completely different
approach. Its purpose is to exploit the unavoidable leakage in a
useful manner. In accordance with the invention this purpose is
achieved in that the quantities of leakage gas are at least
partially collected and fed to the gas dynamic process so that the
energy still contained in them can be utilized. A pressure-wave
machine for effecting this procedure contains at least one
leakage-gas recess which is located in one end portion of the
casing, the recess being open in the direction of the cells of the
rotor, and being fed from spaces filled with leakage gas. The
efficiency of the pressure-wave machine is raised by utilizing the
energy in the leakage gas. The characteristic of the machine then
alters in a beneficial manner, e.g. for charging road vehicle
engines, in that the pressure available for charging and scavenging
is increased more in the lower speed range than in the upper range.
A pressure-wave machine employing the above procedure is less
sensitive to the clearance between the rotor and the end portions
of the casing. If this clearance is small, the pressure-wave
machine inherently has a high efficiency which is only slightly
improved by utilizing the energy of the small quantity of leakage
gas. If the clearance is large, the effect of the leakage-gas
recess is more pronounced and compensates at least a part of the
losses.
Inventors: |
Wunsch; Alfred (Friedberg,
DT) |
Assignee: |
Aktiengesellschaft Brown Boveri
& Cie (Baden, CH)
|
Family
ID: |
4232247 |
Appl.
No.: |
05/222,845 |
Filed: |
February 2, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Feb 18, 1971 [CH] |
|
|
2373/71 |
|
Current U.S.
Class: |
417/64 |
Current CPC
Class: |
F02B
33/42 (20130101); F04F 13/00 (20130101) |
Current International
Class: |
F04F
11/02 (20060101); F02B 33/42 (20060101); F04F
11/00 (20060101); F02B 33/00 (20060101); F04f
011/00 () |
Field of
Search: |
;417/64 ;60/39.45 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Freeh; William L.
Assistant Examiner: Smith; Leonard
Attorney, Agent or Firm: Pierce, Scheffler & Parker
Claims
I claim:
1. An aerodynamic pressure-wave machine comprising a cylindrical
rotor provided with a circumferential array of longitudinally
extending open-ended cells and which is mounted for rotation about
its axis within the middle portion of a cylindrical casing with a
radial clearance gap therebetween, the end portions of said casing
facing the opposite ends of said rotor including at least one
high-pressure inlet opening and one low-pressure outlet opening for
an energy-laden gas giving up energy in the cells and at least one
high-pressure outlet opening and one low-pressure inlet opening for
a gas such as air to be compressed within the cells, each end
portion of said casing having at least one high-pressure opening
and at least one low-pressure opening which are spaced
circumferentially apart, means providing a gas-leakage collection
recess in at least one end portion of said casing opening in the
direction of and in communication with the cell ends and which
extends radially to the clearance gap between said rotor and casing
for collecting leakage-gas flowing in a circumferential direction
between a high-pressure opening and a low-pressure opening in a
axial clearance gap existing between the end portion of said casing
and the corresponding end of said rotor and flowing also in a
radially outward direction to said radial clearance gap existing
between the periphery of said rotor and the middle portion of said
casing, the leakage-gas so collected serving to charge said recess
and being thereafter discharged therefrom into said rotor cells to
give up its energy.
2. The invention as defined in claim 1 wherein the leakage-gas so
collected in said recess is discharged therefrom into said rotor
cells to achieve a pre-compression of the gas to be compressed.
3. The invention as defined in claim 1 wherein the leakage-gas so
collected in said recess is discharged therefrom into said rotor
cells to improve scavenging thereof in the low-pressure zone.
4. The invention as defined in claim 1 wherein the hub portion of
said rotor is provided with an axially extending cavity opening to
the end of the rotor at which said gas-leakage collection recess is
located, and said recess extends in a radially inward direction to
establish communication with said cavity which latter likewise
functions to receive gas leakage from said high-pressure opening.
Description
A number of examples of the invention are illustrated in the
accompanying drawings wherein:
FIG. 1 is a section through a pressure-wave machine;
FIG. 2 is an end portion of the casing viewed at II--II in FIG.
1;
FIGS. 3, 5 and 7 are schematic representations of parts of the
development of a cylindrical section at half the cell height
through the rotor and through the adjacent parts of the end
portions of the casing in different forms; and
FIGS. 4, 6 and 8 are the corresponding wave cycles shown in the
pressure/velocity diagram.
FIG. 1 shows the basic construction of an aerodynamic pressure-wave
machine with rotor 20 provided with longitudinal cells and mounted
in an overhung bearing, such that the rotor hub 21 incorporates
cavity 22 and the rotor turns in a casing composed of end portions
23 and 24 and middle portion 25. The energy-containing gas flows
into end portion 23 at 26, expends part of its energy in rotor 20
and leaves end portion 23 at 27. The gas to be compressed (usually
air, and therefore so termed in the following) flows into end
portion 24 at 28, is compressed in rotor 20 and leaves end portion
24 at 29, which is shown as a broken line because this outlet is
usually turned at 90.degree. to the plane of the drawing.
FIG. 2 shows end portion 23. Here can be seen the high-pressure
inlets 2v and low-pressure outlets 1n for the energy-expanding gas.
On leaving the high-pressure inlets 2v the greater part of the
energy-containing gas flows into the rotor, but smaller quantities
of leakage gas pass into the gap between the rotor and end portion
23. These dissipate, as indicated by arrows, partly in a peripheral
direction towards low-pressure outlets 1n, partly radially outwards
into the gap 30 between shroud 31 of rotor 20 (FIG. 1) and the
middle portion 25 of the casing, and partly radially inwards into
the cavity 22 in hub 21, and create a pressure within these
spaces.
The pressure in spaces 22 and 30 is lower than in high-pressure
inlets 2v because the narrow gap between the rotor and the end
portion throttles the flow of leaking gas. However, it is higher
than in low-pressure outlets 1n because the gap between rotor and
end portion closes off the flow in this direction also.
It is possible to connect pressurized spaces 22 and 30 with
leakage-gas recesses LT in end portion 23 by extending these
recesses radially beyond the high-pressure and low-pressure
openings as far as gap 30 and cavity 22. In the example shown, the
recesses LT are located between low-pressure and high-pressure
openings when viewed in the direction of rotation of the rotor
(indicated by a dashed arrow). They are charged by pressurized gas
from reservoir spaces 22 and 30 and in turn feed the rotor cells.
The effects of this measure can be seen from FIGS. 3 and 4.
FIG. 3 shows the development of a cylindrical section through the
rotor of the pressure-wave machine and a distance/time diagram,
while FIG. 4 is the corresponding pressure/velocity diagram as is
usually employed in the characteristics method of non-steady gas
dynamics.
FIG. 4 shows conditions during the course of the gas-dynamic
process, characterized by the pressure ratio (P/P.sub.o) (H-1/2H)
and the flow velocity referred to the acoustic velocity u/a.sub.o.
The states at the points of intersection of two characteristics are
numbered consecutively. In FIG. 3 the areas in which these states
exist are denoted by the same numbers. The rotor turns in the
direction of arrow U between the two end portions 23 and 24. In the
low-pressure zone, the cells are supplied with air from
low-pressure inlet lv. An expansion wave between areas 10 and 0
reduces the flow velocity to zero. As soon as a cell comes adjacent
to leakage-gas recess LT (which is linked with spaces 22 and 30
pressurized by the leakage gas flows and is also supplied by
leakage gas flowing in the peripheral direction) a pressure wave
occurs which pre-compresses the cell contents to state 1. Gas flows
from leakage-gas recess LT. The pressure wave is reflected from the
face of end portion 24 as a pressure wave and again reduces the
velocity to zero, so that the cell contents arrive at state 2.
Thus, in area 2 the cell contents are precompressed to a pressure
which is higher than the intake pressure and also higher than the
pressure in the leakage-gas recess.
Actual compression of the cell contents then begins from this
pressure level as soon as a cell becomes exposed to high-pressure
inlet 2v. The normal cycle of the pressure-wave machine then
follows. Compressed air flows through high-pressure outlet 2n,
expanded gas flows through low-pressure outlet 1n, and air is drawn
in through low-pressure inlet lv until state 0 is reached once
again. For a given exit velocity u.sub.2n of the compressed air,
the leakage-gas recess causes a higher pressure to be attained than
without pre-compression, i.e. if the principal compression were to
start direct from state 0.
Another possible comfiguration of the pressure-wave process with
utilization of leakage gas is shown in FIGS. 5 and 6. In this
example the pressure wave between states 10 and 0 is not an
expansion wave, but a compression wave. The inlet flow velocity of
the air at the end of low-pressure inlet lv is reduced to state 0
by the confronting face of end portion 23, whereupon leakage-gas
recess LT causes pre-compression by two pressure waves up to states
1 and 2. This reduction of the air inlet velocity creates a higher
pressure in leakage-gas recess LT and its effect is increased
accordingly.
Another possible way of utilizing the energy contained in the
leakage-gas is to use it to improve scavenging of the cells in the
low-pressure zone. The corresponding pressure-wave process is
illustrated in FIGS. 7 and 8. The leakage-gas recess LT, which
again is connected to pressurized spaces 22 and 30, is contained in
an additional web 32 twoards the end of the low-pressure outlet ln,
where the flow velocity is already low. Web 32 in end portion 23
must be supplemented by a further web 33 in end portion 24. By
introducing the leakage-gas into the gas-dynamic process, the
pressure in the cells rises to state 10, giving rise to a higher
flow velocity in areas 11 and 12, and hence to better scavenging in
the low-pressure zone.
The leakage-gas collecting recesses can also be located equally
effectively in end portion 24 or in both end portions. Furthermore,
the inlet and outlet for one gas must not always be at the same
end, i.e. in the same end portion. The leakage of the gases will
then tend to mix, in which case it is of no significance at which
end they are introduced into the gas process. It is only important
that the leakage-gas should not flow unchecked into the cells and
to impair the process, but should be fed to the cells with the aid
of the leakage-gas recesses at an accurately defined point, and in
this way improve the process.
The leakage-gas recesses can be employed in almost all aerodynamic
pressure-wave machines, and can be combined with special-purpose
devices, e.g. a deflecting recess in accordance with German patent
1 162 631.
* * * * *