This invention relates to a passive apparatus which lessens
the intensity of a back propagating pressure wave while having negligible impact
on forward pressure loss.
In existing pulse detonation devices a shock wave is produced
as a result of each detonation. This shock wave propagates both downstream, producing
thrust, and upstream toward the inlet of the device. The upstream propagation of
these shock waves can have detrimental effects to the operation of a pulse detonation
device. Specifically, in a valveless system, shock waves can enter the flow inlets,
which feed air and/or fuel into the device, thus causing high pressure spikes in
this structure, which can damage internal components or otherwise impede optimal
Several methods have been considered to prevent the propagation
of strong pressure waves including mechanically valved systems. However, such systems
require a number of moving parts, which increases the cost and complexity of such
systems. Additionally, the presence of a valve system reduces the operational reliability
of the detonation device.
Thus, a system or configuration that can be used in pulse
detonation (and similar) devices, which require no additional moving parts or complex
systems, and reduce the backflow of strong pressure waves, is desirable.
In an embodiment of the present invention, the detonation
chamber of a pulse detonation device is made up of a control region and a primary
region. The upstream propagating pressure wave is split into these two regions.
The control region is configured and structured such that the portion of the pressure
wave entering the control region is accelerated ahead of the pressure wave propagating
through the primary region. Further, the portion of the pressure wave passing through
the control region is redirected and channeled so as to form a high speed flow which
is directed into the backflow passing through the primary region. The mixing of
these two flows impedes the progress of the backflow passing through the primary
portion and redirects the flow, thus hindering the propagation of the pressure wave
further upstream. By preventing the pressure wave from moving upstream within the
device, reducing its size or magnitude and redirecting the flow, the operational
integrity and life of the system is increased. Furthermore, this type of passive
valving increases the net thrust of the pulse detonation device.
As used herein, a "pulse detonation chamber" (or "PD" chamber)
is understood to mean any combustion device or system where a series of repeating
detonations or quasi-detonations within the device cause a pressure rise and subsequent
acceleration of the combustion products as compared to the pre-burned reactants.
A "quasi-detonation" is a combustion process that produces a pressure rise and velocity
increase higher than the pressure rise produced by a deflagration wave. Typical
embodiments of PD chambers include a means of igniting a fuel/oxidizer mixture,
for example a fuel/air mixture, and a confining chamber, in which pressure wave
fronts initiated by the ignition process coalesce to produce a detonation wave.
Each detonation or quasi-detonation is initiated either by external ignition, such
as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing,
autoignition or by another detonation via cross-firing. The geometry of the detonation
chamber is such that the pressure rise of the detonation wave expels combustion
products out the PD chamber exhaust to produce a thrust force. As known to those
skilled in the art, pulse detonation may be accomplished in a number of types of
detonation chambers, including detonation tubes, shock tubes, resonating detonation
cavities and annular detonation chambers.
The advantages, nature and various additional features
of the invention will appear more fully upon consideration of the illustrative embodiment
of the invention which is schematically set forth in the figures, in which:
- FIG. 1 is a diagrammatical representation of a naturally aspirated flow control
device for redirecting strong pressure waves in accordance with an exemplary embodiment
of the present invention;
- FIG. 2 is a diagrammatical representation of a naturally aspirated flow control
device for redirecting strong pressure waves in accordance with an additional exemplary
embodiment of the present invention; and
- FIG. 3 is a diagrammatical representation of a naturally aspirated flow control
device for redirecting strong pressure waves in accordance with an alternative exemplary
embodiment of the present invention.
Various aspects and embodiments of the present invention
will be explained in further detail by making reference to the accompanying drawings,
which do not limit the scope of the invention in any way.
FIG. 1 is a cross-sectional side view of a portion of a
pulse detonation device 10 including a fixed geometry flow separator 14, which divides
a detonation chamber 12 of the device 10 into a primary region 18 and a control
region 16. FIG. 2 is a cross-sectional side view of a portion of pulse detonation
device 10, similar to the device 10 shown in FIG. 1, according to another embodiment
of the invention. FIG. 3 is a cross-sectional side view of a portion of an alternative
embodiment of pulse detonation device 30.
Turning now to FIG. 1, an exemplary embodiment of a pulse
detonation device 10 is shown. Within the device 10 a fuel-air mixture is detonated
in a detonation chamber 12, which is located downstream from both a fixed geometry
flow separator 14 and an upstream chamber portion 20. As a result of the detonation,
strong pressure waves and high-speed flows are generated which propagate both upstream
and downstream. The pressure waves and flow propagating downstream eventually exit
the device 10, thus producing thrust. The pressure waves and flow propagating upstream
impact the flow separator 14, which directs portions of the pressure waves into
the control region 16 and portions of the pressure waves into the primary region
18 of the chamber 12.
In a three-dimensional device 10, the flow separator 14
is formed as an annulus structure in the chamber 12, such that the outer control
region 16 is formed in a radially outward position from the flow separator 14, while
the inner primary region 18 is formed in a radially inward position from the separator
14. Further, the control region 16 is formed such that it converges in an upstream
direction, whereas the primary region 18 diverges in an upstream direction.
Moreover, the separator 14 is passive such that it maintains
a fixed geometry during detonation process. As such, there are no moving parts or
components to complicate the structure. The separator 14 is acting to direct the
flow with a fixed geometry configuration.
During operation, strong pressure waves impinge on the
downstream edge of the flow separator 14, where the pressure waves are separated
into the control flow Fo and primary flow Fi. Because the control region 16 is formed
in a converging manner, as the control flow Fo moves upstream pressure behind the
pressure waves increases. This increase in pressure causes the pressure waves and
flow to accelerate through the control region 16. Further, because the primary region
18 diverges in an upstream direction, pressure behind the pressure waves in the
primary flow Fi decreases, thus decelerating the pressure waves propagating in the
primary region 18.
Because of the speed differential between the primary flow
Fi and the control flow Fo, the pressure waves of the control flow Fo accelerate
ahead of the corresponding pressure wave of the primary flow Fi. Then, because of
the shape of a flow direction portion 26 and the upstream edge of the flow separator
14, the control flow Fo is directed toward a centerline CL of the device 10, thus
creating a jet of flow from the control region 16 into the flow from the primary
The control flow Fo exits the control region 16 at an angle
to the flow direction of the primary flow Fi. Because of this configuration, the
control flow Fo creates a barrier to the primary flow Fi, in addition to mixing
with the primary flow Fi, to reduce its strength, impede its progress upstream,
and redirect the primary flow. Such a configuration impedes the backflow in the
chamber 12, which prevents or impedes backflow into the secondary flow inlets 22
and primary flow inlets 25.
Fuel, air and/or a fuel/air mixture are injected into the
chamber 12, through the flow inlets 22 and primary flow inlets 25, prior to detonation,
from an upstream chamber 24. The structure and systems used to provide the flow
through the flow inlets 22 and primary flow inlets 25 can be sensitive to high and
frequent pressure rises, which are a side effect of upstream traveling pressure
waves, which result from a detonation. The flow separator 14, of this embodiment
of the present invention, acts to mitigate this backflow resulting in a reduction
of the stress on these components and systems. Further, this is accomplished with
no moving parts, but with the configuration of the control region 16, flow separator
14 and primary region 18.
Moreover, the configurations of the control region 16,
primary region 18 and flow separator 14 are optimized so as to maximize downstream
flow (minimize pressure loss), while minimizing the upstream flow (maximize pressure
loss). Thus, this configuration acts as a flow diode. More specifically, since this
device acts on pressure transients, the device is more likened to a flow induction
coil. Stated differently, the device provides a transient diode effect to provide
high impedance for backflow during a pressure pulse. However, the device may provide
a lower level of impedance to backflow during lower pressure backflows. Thus, providing
high impedance during high pressure pulses, while providing lower impedance during
steady state back-flow conditions.
During refill, a mixture of air and fuel is injected into
the chamber 12 via the primary flow inlets 25 and the secondary flow inlets 22.
The flow inlets 22 are positioned in the upstream chamber portion 20 and are intended
to provide additional cool air to purge the associated region of hot residual gases.
However, in an additional embodiment, the flow inlets 22 are positioned in the flow
direction portion 26. In a further embodiment, the flow inlets 22 are positioned
in the flow separator 14. In various embodiments, the present invention contemplates
that the flow inlets 22 are distributed as required based on system and operational
characteristics. For example, as shown in FIG. 1, the flow inlets 22 are positioned
on both the upstream chamber portion 20 and the flow separator 14. The flow inlets
22 inject fuel, air or a fuel/air mixture, depending on the operational needs of
In a further alternative embodiment, the flow inlets 22
are positioned on the flow separator 14 and/or the flow direction portion 26 so
as to flush out the control region 16 during the refill process. During operation,
after the pressure wave and flow behind the pressure wave from the detonation passes
through the control region 16, a secondary flow is directed into the control region
16 from the flow inlets 22 to flush the control region 16. In an additional embodiment,
this flow is used to provide cooling for the flow separator 14, in addition to providing
a flushing function.
In a further embodiment, a manifold structure (not shown)
is provided in the flow separator 14 and/or the flow direction portion 26 to provide
cooling of the components during operation.
FIG. 2 depicts a portion of another exemplary embodiment
of a device 10 similar to that shown in FIG. 1. In this embodiment, the flow separator
is secured in place with ribs 28. The ribs 28 are shaped such that they provide
minimal flow blockage of the control flow Fo.
Additionally, as shown in FIG. 2, an additional embodiment
of the present invention contains swirl vanes 29 positioned in the primary flow
inlets 25. The swirl vanes 29 impart a swirl or rotation to the flow coming from
the primary flow inlet 25. During the purge phase, where detonated gases are removed
from the chamber 12, the swirl vanes 29 impart a tangential momentum on the flow
entering from the primary flow inlets 25. Such momentum aids in turning the flow
around the flow separator 14 and the resulting centrifugal forces help the flow
expand past the divider 14 thus providing pressure recovery and a uniform flow.
In a further embodiment, the rotation also aids in directing at least some of the
flow back through the control region 16 to aid in purging this region before the
next detonation. Further, in an additional embodiment, the swirl vanes 29 are configured
and angled such that they provide additional shock wave reflection, to prevent or
inhibit the pressure wave from entering the primary flow inlet 25.
In an additional embodiment, a flow separator lip portion
46 is positioned on the upstream edge of the flow separator 14. This lip portion
46 extends a sufficient amount to direct some of the flow from the primary flow
inlet 25 back through the control region 16, so as to flush the control region 16
during a purge/refill process.
As indicated previously, the control region 16 directs
the control flow Fo into the chamber 12 at an angle with respect to the primary
flow Fi. The angle is optimized based on the desired operational characteristics
of the device. In one embodiment, the control flow Fo enters the chamber at an angle
less than 90 degrees to the angle of the primary flow Fi. In additional embodiments,
the control flow Fo enters the chamber at an angle 90 degrees to the angle of the
primary flow Fi, and more than 90 degrees to the angle of the primary flow Fi.
Additionally, the shape, size and orientation of the flow
separator is optimized based on the operational parameters and design criteria of
the device 10 in which it is used. Specifically, the flow separator 14 is optimized
to provide a minimal pressure loss in the downstream direction, while providing
a high impedance to upstream flows. This allows the separator 14 to act as a flow
diode, which provides optimal flow in the downstream direction, during the purge
and filling process, while inhibiting or preventing backflow after detonation. This
characteristic aids in the creation of a stagnation region in the vicinity of the
upstream chamber portion 20. This stagnation region generates high pressure for
the flow inlets 22 and 25, which aids in flushing the chamber 12 for the next detonation.
Additionally, in a further non-limiting embodiment the
overall effective area ratios of the control region 16 to the primary region 18
is optimized to provide the desired flow diode effect, where the downstream flow
and upstream flow impedance are optimized. In such a configuration, the effective
stopping power of the control flow Fo is increased with an increase in shock magnitude.
Stated differently, as the backflow magnitude increases, the magnitude of the control
flow Fo increases, thus increasing the power of the flow exiting the control region
16, impeding and/or redirecting the primary flow Fi.
FIG. 3 depicts a further, non-limiting, exemplary embodiment
of the present invention. In this embodiment, the pulse detonation device 30 is
configured such that the exit of the primary flow inlet 44 and the exit to the control
region 36 form a common channel 48 located in a downstream position from the flow
separator 34. Additionally, as shown, the flow separator 34 is positioned such that
a small portion, or none, of flow separator 34 is in the direct flow path of the
primary flow Fi. In the embodiments shown in FIGs. 1 and 2, the flow separator 14
is positioned within the primary flow path to redirect some of the flow into the
control region 16.
In the FIG. 3 embodiment, during the fill or purge phase,
flow is from left to right as depicted in FIG. 3. In an annular configuration, swirl
vanes, not shown, located in the control portions of the flow annulus impart tangential
momentum to the flow. This induces a centrifugal force which allows the fill or
purge gases to expand after the throat section 50, thus providing pressure recovery.
During the forward flow phases, through the primary region 38, the control region
36 is largely bypassed, but a sufficient amount of flow does enter this region,
thus purging any residual combustion gases.
In this embodiment, when a strong upstream pressure wave,
traveling right to left in FIG. 3, reaches the throat location 50 the flow is slightly
diverted away from the primary inlet 44. The pressure wave continues moving upstream
where it contacts the upstream chamber portion 40, and at least a portion of the
flow enters the control region 36. The pressure wave travels through the control
region 36 and is redirected onto itself, thus reducing the intensity of the flow.
The exit of the primary flow inlet 44 is shaped so as to impede any upstream flow
entering that region while allowing forward flow to progress unimpeded.
As the control flow Fo flows through the control region
36 it is directed back into the primary flow Fi, to impede the upstream flow of
the primary flow Fi. Although this embodiment shows the upstream chamber portion
40 having a planar surface, the present invention is not limited to this embodiment.
For example, the portion 40 may also be shaped with two converging shapes. The shape
of the upstream chamber portion 40 is optimized to provide maximum flow impedance
in the upstream direction, while providing little flow resistance in the downstream
direction during purge and refill.
Further, in an alternative embodiment a flow of air, fuel
or a fuel/air mixture is supplied via the primary flow inlet 44 such that the control
flow Fo is prevented from entering the primary flow inlet 44. Further, as the control
flow Fo passes beyond the primary flow inlet 44, the flow from this inlet begins
to enter the common channel 48 and begin the purge and refill process.
In yet an additional embodiment (not depicted), a single
flow deflector 14 and upstream chamber portion 20 is coupled to a plurality of detonation
chambers 12. In this embodiment, portions of the shock waves from the chambers 12
pass through the control region 16, while remaining portions pass through the primary
region. In an alternative configuration, the entire shock wave and flow from one,
or more, of the chambers 12 is directed into the control region 16, such that the
entire backflow from these chamber(s) 12 is used as the control flow Fo, whereas
the entire flow from the remaining chambers 12 passes through the primary region
18. In this configuration a manifold structure is used to direct the respective
flows as required.
While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that the invention
can be practiced with modification within the spirit and scope of the claims.
- Pulse Detention Device
- Detention Chamber
- Flow Separator
- Control Region
- Primary Region
- Upstream Chamber Portion
- Secondary Flow Inlets
- Upstream Chamber
- Primary Flow Inlets
- Flow Direction Portion
- Support Ribs
- Swirl Vanes
- Pulse Detonation Device
- Detonation Chamber
- Flow Separator
- Control Region
- Primary Region
- Upstream Chamber Portion
- Flow Inlets
- Primary Flow Inlets
- Flow Separator Lip Portion
- Common Channel
- Throat Section