Non-contact seal for positive displacement capture device

A positive displacement capture device contains a rotor portion positioned inside a casing portion to act as a least area rotor which captures a volume and moves the volume along the length of the separator. The rotor portion contains a plurality of lobes which interact with grooves in the casing portion, such that the interaction of the lobes and grooves create barriers which capture the volume. The creation of the volume creates a flow barrier between a downstream end of the separator and an upstream end of the separator. The flow separator is coupled to a combustion portion to provide a flow of material to the combustion portion. There is a non-contact seal between the lobes and the grooves, and the lobes have channels or depressions at their ends.

BACKGROUND OF THE INVENTION

This invention relates to positive displacement capture devices, and in particular to positive displacement capture devices for use with pulse detonation engines and other devices, and a method and structure for providing a non-contact seal of positive displacement flow separators.

With the recent development of pulse detonation combustors (PDCs) and engines (PDEs), various efforts have been underway to use PDCs in practical applications, such as combustors for aircraft engines. However, there has been difficulty in incorporated PDCs and PDEs in practical applications because of the nature of the operation of pulse detonation devices. Namely, unlike the operation of normal gas turbine engines or Brayton cycle engines, in pulse detonation devices when the transition to detonation occurs a strong shock wave is created. Not only does this shock wave travel downstream, but it also travels upstream. The upstream travel of a shock wave can cause damage to upstream devices, such as compressors and fuel injection components, as well as temporarily stopping/reversing inlet air flow. All of these problems, as well as others, are to be avoided.

Various efforts have been attempted to address these problems, such as using mechanical flow control valves and fluidic valves. However, to date, these methods have been inadequate. For example, mechanical valves are required to have high frequency operation, which requires highly complex and costly structure. Further, high frequency valves create their own pressure waves, due to the rapid opening and closure of the valve. Further, although fluidic valves divert the backflow and shockwave against itself (thus reducing the strength of the back pressure wave), they can not completely prevent backflow.

Therefore, because of these difficulties, there exists a need to provide a device which is less complex than traditional mechanical valves, while providing 100% diodicity, to separate the upstream air and components from the combustion chamber of the pulse detonation device. Further, there is a need to provide such a device which minimizes wear and avoids undue heat and friction loads.

SUMMARY OF THE INVENTION

In an embodiment of the invention, a positive displacement capture device is provided which has a casing portion with a plurality of grooves formed on an inner surface of the casing portion, and a rotor portion having a plurality of lobes formed on an outer surface of the rotor portion. The rotor portion is positioned adjacent to the inner surface of the casing portion such that the lobes interact with the grooves. The interaction of the lobes with the grooves creates a plurality of contact points between the lobes and grooves which travel around a perimeter of, and along a length of, the rotor portion as the rotor portion rotates about an axis relative to said casing portion. The above described interaction captures a volume of material and moves the volume along a length of the device due to the relative rotation. In an embodiment of the invention, the “contact points” are non-contact points and a portion of either of the lobes or the grooves has a plurality of depressions on a surface thereof where the contact points occur.

As used herein, a “pulse detonation combustor” PDC (also including PDEs) is understood to mean any device or system that produces both a pressure rise and velocity increase from a series of repeating detonations or quasi-detonations within the device. A “quasi-detonation” is a supersonic turbulent combustion process that produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. Embodiments of PDCs (and PDEs) include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a detonation 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, auto ignition or by another detonation (i.e. cross-fire).

DETAILED DESCRIPTION OF THE INVENTION

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. 1depicts a diagrammatical representation of an exemplary embodiment of the positive displacement capture device100of the present invention. In the context of the present application, the term “flow separator” and “capture device” will be used interchangeable, and are not intended to affect the scope of the present invention. The device100provides a continuous positive flow rate from an upstream end to the downstream end, with minimal pressure loss. The device100contains a rotor portion10, which rotates inside a casing portion12. Together, the rotor portion10and the casing portion12acts as a least area rotor which closes off a volume so as to provide 100% flow blockage from a downstream end19of the device100to an upstream end18of the device100. For the purposes of this application a “least area rotor” is a first geometric shape (e.g. a rotor), which is inscribed by a second geometric shape (e.g. a casing) in such a way that the rotor has one contact point with every side or face of the casing regardless of orientation of the rotor as either one or both of the shapes rotate about an axis. A common example of a least area rotor includes, but is not limited to a Reuleaux triangle.

The rotor portion10has a plurality of lobes14which are continuous along the length of the rotor portion10. The lobes14ride in continuous grooves16which are in the inner surface of the casing portion12. The interaction of the lobes14of rotor10and the lobes of the casing12create a barrier between the upstream portion18and downstream portion19which move down the length of the device100as the rotor portion10and/or the casing portion12are turned. Basically, the interaction between the lobes14and the grooves16create barriers (which can also be described as contact points, regardless of whether physical contact is made or not) that move along the length of the device100based on the pitch and rotational speed of the components. The contact points according to an embodiment of the invention will be discussed more fully below.

Because the rotor portion has a triangular cross-section, there are three lobes14in the embodiment shown inFIG. 1. In the embodiment shown inFIG. 1, there are two grooves16in the casing portion12. However, the present invention is not limited to this embodiment. As will be discussed in more detail below, the number of lobes/grooves will vary depending on the configuration employed. For example, in a further embodiment of the present invention there are more grooves16then there are lobes14. As indicated above, in the embodiment shown inFIG. 1, there is one less groove16than lobe14. However, the present invention is not limited in this regard. The combination of the rotor portion10and the casing portion form a least area rotor.

Further, in the embodiment shown inFIG. 1there are three lobes14on the rotor10and one fewer groove16on the casing12. In this configuration, the casing12rotates faster than the rotor10(in the embodiment where both components rotate). However, it is also contemplated that the casing12may have one more groove16than lobes14of the rotor12, and in such an embodiment the rotor10rotates faster than the casing12.

Because the overall operation of the invention is similar to that of a least area rotor, each lobe14makes contact with all sides of the casing portion12(via the grooves16) regardless of the orientation or angle of rotation of the rotor portion10within the casing portion12. An example of this type of mathematical geometry is known as a Reuleaux Triangle, which is known to those of ordinary skill in the art. Of course, it is noted that the present invention is not limited to the application of this geometry, but it is referenced merely as an example. To attain the least area rotor performance of the present invention, the number of contact points between rotor portion10(via the lobes14) and the casing portion12(via the grooves16) is N+1, where N is the number of lobes14on the rotor portion10. Further, regardless of the orientation of the rotor portion10the number of contact points for any one lobe14will be N+1, with N being the number of lobes14present on the rotor portion. Therefore, in the embodiment shown inFIG. 1there are four (4) contact points as there are three (3) lobes14.

Further, as shown, in the exemplary embodiment, the geometry of each of the rotor portion10and the casing portion12are swept along a helical axis. However, each of the rotor portion10and the casing portion12are swept at a different pitch. Because of this, the present invention “captures” a volume (which may include air, gases, fluids or solids) between the barriers formed by the interaction of the rotor lobes and casing grooves, and moves the volume downstream along the length of the device100until the volume opens at the downstream portion19of the device100. However, because of the geometries of the rotor portion10and the casing portion12, the downstream portion19of the device100is closed off from the upstream portion18of the device100, so that any pressures or backflows from any downstream component is blocked from any upstream components. It is these barriers (i.e. contact points) which form the boundaries of the captured volume, as such as the barriers (i.e. contact points) move along the device100the captured volume moves along as well.

In an embodiment of the invention, the ratio of the pitch of the rotor portion10to the casing portion12is proportional to the number of grooves16on the casing to the number of lobes14on the rotor. It is this difference in pitch which causes the grooves14and lobes16to interact with each other to form periodic barriers, which are moved along the axis of the device100.

Further, the geometries of the rotor portion10and the casing portion12are such that a cross-sectional area17is created between the two along the entire length of the device100. This area17has a different angular position along a length of the device100, and is used to create the volume.

Thus the present invention is ideal for applications where it is desirable to provide a flow of material (gas, liquid or solid) at a constant rate and protect upstream components from any downstream events or forces. For example, the present invention may be used as a flow device for a pulse detonation engine or combustor. It is known that the detonations created in pulse detonation engines/combustors create high pressure shock waves which tend to propagate upstream and can damage upstream components, or stall engine or compressor inlets. Therefore, it is desirable to block upstream components from this high pressure shock wave. The present invention accomplishes this by using the “least area rotor geometry” described herein. Of course, the present invention is not limited to this application, but can be used in many applications where the advantages of the present invention are desired.

In the present invention, the number of rotations needed to capture the volume depends on the ratio of lobes14on the rotor portion10to the grooves16on the casing portion12and the relative rotation angle between them. This will be discussed in more detail below. Further, the flow rate of the device100is a function of the rotational speed of the rotor portion10and casing portion12. One of the advantages of the present invention, is that the flow rate of the device100is not affected by the back pressure from any downstream device. Because the upstream portion18of the device100is completely isolated, and the volume is delivered to the downstream portion19via the rotation, the flow rate is not affected or reduced by downstream back pressure. Instead, the flow rate (or flow volume) is a function of factors such as rotational speeds and geometry of the rotor and casing portions.

In one embodiment of the present invention, both the rotor portion10and the casing portion12rotate. They rotate in the same direction as each other, but they rotate at different speeds. This will be explained in more detail below. In an embodiment such as this, because of the rotation of the casing portion12, the rotor portion10can rotate about its central axis. In another exemplary embodiment, the casing portion12is stationary and only the rotor portion10rotates. However, in this embodiment, not only does the rotor portion10rotate, but it also precesses about a central axis. This precession and rotation are needed to ensure the device acts as a least area rotor to capture a volume and provide 100% diodicity between the downstream portion19and the upstream portion18.

In an embodiment of the invention, the geometries of the rotor portion10and the casing portion12are such that no physical contact occurs between the lobes14and the grooves16. This greatly reduces the amount of wear and friction caused by the relative rotations of the rotor portion10and the casing portion12. With that said, the spacing between the tips of the lobes14and the deepest portions of the grooves16is to be such that flow is “choked.” Stated differently, the spacing is such that the resistance to the captured material (i.e. air, gas, liquid, or solid) flowing from one trapped volume to an adjacent volume is maximized. The spacing is to be minimal so as to inhibit any flow from passing between the lobes14and grooves16, at their closest points. Of course, it is understood that the size of the gaps between the tips of the lobes and grooves16is a function of the medium being conveyed and the pressures involved. For example, the size of the gaps would be smaller for when the medium is a gas (for example an engine oxidizer) than for a liquid or a solid (for example coal). Any known end or tip configuration or structure for the lobes14and/or grooves16may be used to minimize flow-through (maximize choke). The structure used is to have the ability to effectively seal and isolate the trapped volume within the device. In an alternative embodiment, contact is made between the lobes14and the grooves16to provide the barrier. In this embodiment a contact seal is made which captures the volume. A more detailed discussion of the contact points in an embodiment of the present invention is set forth below.

Further, in an exemplary embodiment of the present invention, the length and overall dimensions of the device100is to be determined based on the operational and performance criteria of the specific application. Further, the present invention contemplates that more than one volume can be trapped by the rotor portion10and casing portion12. The number of volumes trapped (or isolated) at any given time is a function of the length of the device100and the pitch/geometry of the helical lobes14and grooves16. In the present invention, the flow rate of the device100is a function of the helical pitch angle of the rotors and the rotational speed of the components.

In an embodiment of the present invention, the cross-sectional geometry and the pitch of the rotor10and casing12are constant throughout the length of the device100. In such a configuration, the present invention acts essentially as a pump or a valve, providing a desired flow rate from the upstream portion18to the downstream portion19of the device. This is essentially shown in the section A of the device100, inFIG. 1. Because of the nature of the device100, in such a configuration, the device100can consistently pump from a lower pressure to a higher pressure (on the downstream portion19) without exposing any upstream components to the higher downstream pressure or pressure spikes or transients.

In a further embodiment of the present invention, as shown inFIG. 1, the device100contains a reduced pitch portion B. The reduced pitch portion B is downstream of the upstream flow portion A, whereas the grooves16and lobes14are continuous from the upstream flow portion A, but have a decreased pitch. Because of the decreased pitch, the speed with which the barriers travel down the device100decreases, allowing the upstream barriers to “catch up.” Thus, the isolated volume is compressed. The degree of pitch in the reduced pitch portion B dictates the volumetric compression ratio, and thus the level of compression achieved for the isolated volume.

Thus, in the above described embodiment compression occurs at the transition between the upstream flow portion A and the reduced pitch portion B, as the upstream barriers “catch up” with the downstream barriers which have entered the reduced pitch portion B. By having the barriers “catch up” with each other the trapped volume is reduced, resulting in compression of the material trapped in the volume.

In an alternative embodiment, the device100can compress the volume in the compression portion B by changing the cross section of the rotor portion10and/or casing portion12. This will be discussed in more detail below.

In a further embodiment of the present invention, not shown, the device100contains a downstream portion with an increased pitch (i.e. replacing the reduced pitch portion B). The overall configuration is similar except that the increased pitch portion is downstream of the upstream flow portion A, whereas the grooves16and lobes14are continuous from the upstream flow portion A, but have an increased pitch. Because of the increased pitch, the speed with which the barriers travel down the device increases, allowing the downstream barriers to move ahead faster. Thus, the isolated volume is expanded. The degree of pitch in the increased pitch portion dictates the volumetric expansion ratio, and thus the level of expansion achieved for the isolated volume.

In the present invention, various variables can be used/adjusted to achieve the desired performance of the device100. For example, a larger pitch angle of the lobes/grooves will result in overall thinner lobe14structure, and thus provides weight savings, but a potentially weaker lobe. However, a larger pitch angle provides a relatively low volumetric flow rate, whereas a smaller pitch angle will create thicker, stronger lobes and provide a higher volumetric flow rate, but will provide more weight because the device100will be longer.

Further, in the present invention, as the number of lobes14increase, the number of volumes or chambers that are created in a given length of the device100are increased. Thus, the overall frequency of the device100is increased (i.e. more volumes being opened to the downstream portion19during a give time period). As such, a higher number of lobes provide a smoother flow.

Further, in the embodiment of the present invention, in which both the rotor portion10and casing portion12are rotated (so as to have the rotor portion10rotate along a fixed axis) the number of lobes14used will affect the relative rotational velocity of the rotor portion10and the casing portion12. As indicated above, the casing portion12rotates at a different speed than that of the rotor portion10in those embodiments where both components rotate. Their relative rotational velocities are a function of the number of lobes14on the rotor portion10, and the number of grooves16on the casing12.

In the exemplary embodiment of the present invention shown inFIG. 1, where the number of lobes14is higher than the grooves16(i.e. three lobes14to 2 grooves16), the casing portion12rotates at a higher rate than the rotor portion10, and as indicated above the relative rate between the components is a function of the number of lobes14. Thus, the relative rotational rate is a function of the number of lobes14on the rotor10and the number of grooves16in the casing12, where the number of grooves16is expressed relative to the number of lobes14. Stated differently, when N is the number of lobes14, then an expression of N−1 or N+1 will correspond to the number of grooves16. For example, in the embodiment shown inFIG. 1there are N−1 grooves16(i.e. one less groove16than lobe14). Therefore, in this embodiment the ratio of rotational speed between the casing12and the rotor10is N/(N−1). Likewise, if the casing12has one more groove16than lobe14on the rotor the ratio of rotational speed of the casing12to the rotor will be N/(N+1).

As indicated above, the configuration of the device100shown inFIG. 1is one where the number of lobes14is more than the number of grooves16. However, the present invention is not limited in this regard as further least area rotor geometries may be employed. This is shown for example inFIGS. 2 and 3, where the number of grooves is more than the number of lobes. In configurations such as these the rotor portion rotates at a speed which is faster than the outer portion. This relative rotational speed ensures that a least area rotor geometry and functionality is maintained. In these embodiments, the relative rotational speed of the casing portion to the rotor portion is defined by the expression N/N+1), where N is the number of lobes on the rotor portion.

FIG. 2depicts a device200of the present invention which has a configuration where there are four (4) lobes24on the rotor portion20and five (5) grooves26in the casing portion22. As with the above described embodiment one embodiment of this type can have both the rotor portion20and the casing portion22rotating, while another embodiment has only the rotor portion20rotating (and thus precessing also). In the embodiment, where both the rotor and casing portions rotate, the casing portion22rotates at a slower speed than the rotor portion20.

In an embodiment, the rotor and casing portions may be configured such that they rotate and precess through either a hypocycloidic or epicycloidic geometry path. Both of these geometries and the mathematical expressions therefore are known by those of ordinary skill in the industry. Therefore, a detailed discussion of these geometries will not be included herein. Thus, in embodiments of the present invention, the relative motion of the rotor portion20within the casing portion is either hypocycloidic or epicycloidic. The geometry chosen is a function of the operation parameters and desired performance criteria, and the present invention is not limited in this regard. Of course, it is also contemplated that additional geometries, such as a Reuleaux triangle geometry may be used, as long as the geometry results in the creation of a least area triangle which captures a volume and progress the volume along the length of the device200. Those of ordinary skill will recognize that other cross-sectional geometries may be employed for the present invention, and that a computer program may be used to numerically generate a cross-sectional profile which operates in a similar manner as that discussed above.

The hypocycloid geometry is that of a curve formed by a fixed point P on the circumference of a small circle having a radius b which is rolled around the inside of a larger circle with a radius a, where a>b. In an embodiment of the present invention, a set of hypocycloid curves are used where a/b=n, where n is an integer number and n>2. The Cartesian coordinates of the point P are defined by the following equations:

A geometric representation of how to construct a hypocycloid geometry is shown inFIG. 7a. Further,FIG. 7bshows several hypocycloid curves generated using various values for n=a/b. With a hypocycloid configuration, the offset of the rotor portion is a function of the number of lobes on the rotor portion and the radius a. The offset is defined by the ratio a/N, where N is the number of lobes. Therefore, for example, the offset ratio for the rotor portion20, inFIG. 2is defined by a/4 to ensure that the device200acts as a least area rotor.

The epicycloid geometry is that of a curve formed by a fixed point P on the circumference of a small circle having a radius b which is rolled around the outside of a larger circle with a radius a, where a>b. In an embodiment of the present invention, a set of epicycloid curves are used where a/b=n, where n is an integer number and n>2. The Cartesian coordinates of the point P are defined by the following equations:

A geometric representation of how to construct an epicycloid geometry is shown inFIG. 8a. Further,FIG. 8bshows several epicycloid curves generated using various values for n=a/b. With an epicycloid configuration, the offset of the rotor portion is a function of the number of lobes on the rotor portion and the radius a. The offset is defined by the ratio a/N, where N is the number of lobes. Therefore, for example, the offset ratio for the rotor portion10, inFIG. 1is defined by a/3 to ensure that the device100acts as a least area rotor.

In the embodiment shown inFIG. 2, the cross-sectional geometry of the rotor portion20and the casing portion22utilizes a hypocycloidic pattern. This rotational configuration allows for the creation of the least area rotor geometry resulting in trapping a volume for transmission from an upstream end28to a downstream end29. As with the embodiment shown inFIG. 1, this embodiment of the invention has an upstream flow portion A, which effectively acts as a pump. The reduced pitch section B allows the upstream barriers to catch up, thus compressing the volume before expelling to the downstream portion29. Of course, the embodiment is not limited to this and only a flow portion A may be used.

Additionally, an area27is created between the rotor portion20and the casing portion22. The area27, when summed along a length of the device200, creates the volume.

Similarly,FIG. 3discloses a flow control device300having a rotor portion30and a casing portion32, where the rotor portion30is shaped like a lens having two (2) lobes34and the casing portion32has three (3) grooves36. Again, a flow enters the upstream end38and a volume is captured and moved so as to exit the downstream end39. Further, the device300is shown with an upstream flow portion A and a reduced pitch portion B. Additionally, as with the previously discussed embodiments, an area37is created between the rotor portion30and the casing portion32.

As with the embodiment inFIG. 2, in the embodiment shown inFIG. 3, if both the casing portion32and the rotor portion30are rotated, then the casing portion32rotates at a speed slower than the rotor portion30. Additionally, to capture a volume in this embodiment, the rotor portion30makes contact at three (N+1) points on the casing portion32.

In an embodiment of the invention, the pitch ratio between the lobes of the rotor portion and the grooves of the casing portion are controlled so that the device acts as a least area rotor at all points along the axis of the device. The pitch ratio of the casing32to the rotor30is a function of the number of lobes and grooves and is defined by the ratio N/G, where N is the number of lobes and G is the number of grooves. For example, the pitch ratio of the embodiment shown inFIG. 1is 1.5 (i.e. 3/2), thus the pitch of the lobes14needs to be 1.5 times greater than then the pitch of the grooves16. In theFIG. 2embodiment, the pitch ratio is 0.8 (i.e. 4/5), and thus the pitch of the lobes24should be 80% of the pitch of the grooves26. As a final example, the pitch ratio of theFIG. 3embodiment is 0.67 (i.e. 2/3), and thus the pitch of the lobes34are to be 67% of the pitch of the grooves36.

Of course it is understood that for the purposes of the present invention, any lobe/groove ratio can be used as long as the overall cross-sectional geometry results in the creation of a least area rotor which allows for the capture of a volume and isolation of the upstream end of the flow device from the downstream end. In general, it is contemplated that embodiments of the present invention (in addition to those shown inFIGS. 1 to 3) have lobe to groove ratios of N/(N−1) and N/(N+1) where the actual number of lobes is dependant on the overall size and intended application of the device.

However, it is noted that in embodiments of the present invention, where the lobe/groove ratio is over 1, the geometries are such that more turns of the rotor portion are required before of a volume is captured (i.e. completely closed). For example, in the embodiment shown inFIG. 1(having a ratio of 3/2) it is necessary for the casing portion to make 2.5 revolutions before a volume is captured. However, in the embodiment shown inFIG. 2only one (1) revolution of the outer casing22is required for a volume to be captured. Depending on the operational and design parameters, either of these may be desirable, however, from a pure efficiency stand point the embodiment shown inFIG. 2would be more efficient than that ofFIG. 1as only a single revolution is required to capture the volume. Further, because of this relationship, the length of the embodiment shown inFIG. 1will be 2.5 times longer than the embodiment shown inFIG. 2to capture a volume.

The total number of contact points of the N/(N−1) configurations, such as the embodiment shown inFIG. 1, is the sum of the number of lobes14of both rotor10and the grooves16of the casing12(i.e. 2N−1). Also the number of turns of the casing12to capture a volume is 2+1/(N−1), where N is the number of lobes14on the rotor10. The situation is different for the N/N+1) embodiment shown inFIG. 2, however. For these configurations, the total number of contact points is (N+1) and the minimum number of turns of the outer casing to capture a volume is equal to 1. Exemplary embodiments are shown in the Table below:

The number of revolutions required by the casing portion required to capture a volume is referred to as the chamber cycle in the table above.

Finally, using the above information, the inner rotor offset (needed for the least area rotor geometry) can be determined. Specifically, the inner rotor offset is a function of the number of lobes and the radius “a” of the rotor portion (i.e. similar to the diameter “a” in the above discussion of the epicycloid and hypocycloid geometries). Namely, the inner rotor offset is defined by the relationship a/N, where N is the number of lobes.

The present invention is not limited to the above discussed embodiments, as it is contemplated that additional geometries may be used, as long as the employed geometries effectively form a least area rotor configuration so that a volume is captured and moved longitudinally along the device.

FIGS. 4A and 4Bdepict cross-sections of additional alternative embodiments of the present invention. In each figure, the cross-section of a positive flow control device400,400′ is shown. Each embodiment has a casing portion42,42′ and a rotor portion40,40′ positioned therein. Each of the rotor portions40,40′ have three (3) lobes44,44′, while each of the respective casing portions42,42′ have four (4) grooves46,46′. Accordingly, in each embodiment, if the casing portion42,42′ is rotated, its rotational speed is less than that of the rotor portion40,40′.

Further, as shown in each of the respective figures, an area47,47′ is created. InFIG. 4Athe area47is smaller than that inFIG. 4B, thus theFIG. 4Aembodiment captures a smaller volume, but because of the thickness of the lobes may provide additional durability, whereas the embodiment inFIG. 4Bcaptures more volume, but may provide less durability.

Further, the embodiment shown inFIG. 4Auses a epicycloid base geometry for its rotation and precession, whereas theFIG. 4Bembodiment uses a hypocycloid base geometry. The profile geometry of the embodiments shown inFIGS. 4A and 4Bwas generated by numerically creating a curve which was equidistant from the base geometry curve at all points. For the epicycloid based geometry, shown inFIG. 4A, the offset curve was generated inside the base geometry. For the hypocycloid based geometry, shown inFIG. 4B, the offset curve was generated outside the base geometry. For the purposes of the present invention, the actual amount of offset used is based on operational and design parameters of the device. Further, the amount of offset can be different, or change, along the length of the device.

By allowing the offset to change along the length of the device the thickness of the lobes can be increased in regions requiring greater strength. Further, changing the offset distance changes the cross sectional area, thus providing either compression or expansion independent of the rotor pitch. In an embodiment employing this feature the change in the cross-sectional area effectively causes compression or expansion of the captured volume similar to that described above. Therefore, compression or expansion can be achieved without changing rotor pitch. In an additional embodiment, the offset distances can be used to ensure that the tips of the lobes become rounded (similar to that shown inFIG. 4A, which are more durable, easier to manufacture, create greater flow resistance, thus increasing the sealing capacity of the device. Of course, it is contemplated that the offset distance can be selected to accommodate any desired operational or design characteristics and may allow for the lobes to be made having a relatively pointed end.

FIG. 5depicts a device500employing an embodiment of the present invention. Specifically, the device500includes a positive flow control device51which contains a rotor portion50and a casing portion51, having an upstream end54and a downstream end56. The detailed configuration of the flow control device51can be that of any of the above discussed types, or similar embodiments. As shown inFIG. 5, the rotor portion50is driven by motor58, whereas the casing portion is driven by motor59. Alternatively, one motor may be used where the rotor50and casing51are coupled together via a set of gears to achieve the required different rotational speeds. The present invention is not limited in this regard as each of the rotor and casing portions can be driven by any known or conventional means.

In a further embodiment, only the rotor portion50is driven by a motor58. In such an embodiment the rotor portion precesses as well as rotates. To accomplish this any known methodology or structure may be used, such as a cam structure, or the like.

Coupled to the upstream end54is an inlet plenum53which directs the medium or material to the upstream end54. The configuration and design of the inlet plenum53is dictated by the operational and design parameters of the device500and the present invention is not limited in this regard. Similarly, in the embodiment shown inFIG. 5an exhaust plenum55is coupled to the downstream end56into which the material or medium is flowed. Again, the present invention is not limited with regard to the configuration of the plenum55, as its construction is a function of the operational and design parameters of the device500.

Downstream of the plenum55is a device60which receives the material or medium that was flowed through the flow control device50. There is no limitation as to what the device60may be. For example, in a pulse detonation combustor application, the device60may be the combustor portion of the PDC and an oxidizer or oxidizer-fuel mixture is flowed through the flow control device50. In such an embodiment, the flow control device50blocks any backflow from the combustor of the PDC to any upstream components. In a further alternative embodiment, the device60may be a standard combustor for liquid fuel or coal, or simply may be a tank of some kind. Because the present invention provides 100% diodicity, the present invention may be employed in any situation, where it is desired to protect upstream components from downstream pressure increases or transients.

FIG. 6depicts a simplified trace of the rotor portion30(fromFIG. 3) and the area37. As shown, the trace begins at the upstream end38of the rotor portion30and the volume closes at a point downstream. In fact, in the embodiment shown, the chamber (i.e. volume) closes after a single rotation of the rotor portion30. Thus, the length of the flow control device must be such that at least one volume is captured. This ensures 100% diodicity.

For the purposes of calculating the volume created by the sum of the areas37, the volume may be calculated by integrating the cross-sectional area37along the Z-axis (i.e. the length of the rotor portion30).

FIG. 9depicts an embodiment of the present invention where there is no physical contact between the lobes14of the rotor portion10and the grooves16of the casing portion. As shown in this embodiment the tip of the lobe14contains a plurality of depressions901adjacent the groove16of the casing12. The depressions901increase the aerodynamic or hydrodynamic (depending on the medium in the device) resistance of the flow passing over the tips of the lobes14, such that flow can become choked. Stated differently, the depressions901aid in providing a significant pressure drop from one side of the lobe14to the other. This pressure drop allows the present invention to act as a positive displacement capture device which can provide 100% diodicity from one end of the device to the other.

In an embodiment of the invention, the depressions901are non-continuous, in that a single depression901does not run continuously along the length of the rotor10. In another embodiment, the depressions901are continuous along the length of the rotor901. However, it is noted that in some applications a fully continuous depression901could create a flow channel along the length of the rotor which could allow some of the medium to flow across boundaries, thus preventing the creation of a truly captured volume. In one embodiment, all of the depressions901have the same length, and in a further embodiment the depressions901have a varied or random length. The overall length of the depressions901is to be determined based on operational and performance parameters of the embodiment and should take into account the application and medium being captured within the device.

Further, the depressions901are not configured such that they follow the helical path of the rotor10construction. In an embodiment of the present invention, the depressions901are formed such that they are non-parallel with respect to the helical path of the rotor10.

In an embodiment of the invention, the depressions901are configured in a labyrinth type pattern on the tips of the lobes14along the length of the rotor10. In a further embodiment, the depressions901are configured in a hatched configuration, and in another embodiment the depressions901are configured in a herringbone type pattern. Such patterns aid in creating the needed pressure drop from one side of the lobe14to the other. The patterning to be used is determined based on operational and performance parameters of the embodiment and should take into account the application and medium being captured within the device.

The depressions901can be formed on the surface of the rotor10using any known or commonly used machining or etching practices.

In theFIG. 9embodiment, the depressions901are depicted as having a semi-circular cross-section. However, the present invention is not limited in this regard. Specifically, in a further embodiment of the invention the depressions901have a rectangular, square, polygonal or elliptical cross-section. In a further embodiment, depressions901have varying cross-sections depending on the depressions901respective location on the rotor10. For example, it is contemplated that a number of depressions901have a semi-circular cross-section, whereas other depressions901have a polygonal cross-section. Further combinations are contemplated. In an embodiment of the invention, the depressions901are extended in length (even though not continuous along the length of the rotor10) like channels, or the like. In a further embodiment, dimples or similar geometrical shapes are employed instead of, or in combination with, depressions901.

Additionally, it is noted that the overall dimensional geometry and cross-section of the depressions901is to be determined based on operational and performance parameters of the embodiment and should take into account the application and medium being captured within the device. Similarly the overall distance between the lobes14and the grooves16, at their closest points, is a function of design and performance parameters. However, the distance combined with the geometry and orientation of the depressions901is to be optimized taking into account the design and performance parameters along with the medium for which the device is being used.

The orientation and geometry of the depressions901take into account the respective aerodynamic and/or hydrodynamic forces and interactions involved in the specific design parameters to ensure that the pressure drop across the tip of the lobes14is large enough to capture the volume and provide the level of diodicity desired.

In a further embodiment of the present invention, instead of depressions901, protrusions are used which extend from the surface of the lobe14. In a further embodiment a combination or protrusions and depressions901employed to maximize pressure drop.

FIGS. 10athrough10dshow various exemplary embodiments of the depressions901of the present invention. It is note however, that these figures are exemplary in nature and the present invention is not limited to these embodiments. It is further noted that these figures show the depressions901as they would look with the lobe14of the rotor10laid out flat, and not in a helical pattern or the like. This is done for ease of visualization.

FIG. 10ashows the depressions901in a continuous and parallel configuration.FIG. 10bshows the depressions901in a discontinuous and random pattern. In this embodiment both the length of the depressions901and the gaps between the depressions901are random in size and distribution. Of course, it is contemplated that while the depression901length is random the gaps between them can be of a constant length, and vice versa.FIG. 10cshows the depressions901in a dashed configuration in which the depressions901are parallel. In this embodiment the gaps and lengths are fixed.FIG. 10dshows the depressions901on an angle in a parallel configuration. It is also contemplated that the depressions901can be dashed, etc.

It is further noted that althoughFIGS. 10athrough10dshow the depressions901in a parallel configuration, the present invention is not limited to this configuration. In an alternative embodiment the depressions901are angled randomly or are configured in a herringbone pattern, or the like.

The embodiment shown inFIG. 9depicts the depressions901in the lobe14of the rotor10. However, the present invention is not limited to this embodiment. In a further embodiment, the depressions901are located within the grooves16of the casing12, or otherwise on the inner surface of the casing12such that the same effect is obtained during operation. In a further embodiment, depressions901are located in both the surface of the rotor10and the casing12.

In an embodiment of the present invention, depressions901are located at all points on the rotor10and/or casing12which represent the points of minimum distance between the rotor10and the casing12. It is at these points of minimum distance in which the pressure drop is maximized. Accordingly, depressions901are positioned at these locations. In various embodiments of the present invention, the geometry of the rotor10and casing12are such that the point of minimum distance between these components is not at the same location on any one lobe14at each time. Stated differently, the point of minimum distance (i.e. the point of maximum pressure drop) between any one lobe14and the casing12will vary depending on the rotational position and orientation of the lobe14with respect to the casing12. Accordingly, in an embodiment of the present invention, the depressions901are distributed on the rotor10(e.g. lobe14) and/or casing12in such a manner so as to provide the maximum pressure drop over the lobe14at each of the respective points of minimum distance.

In an embodiment of the invention, the point of minimum distance on a lobe14varies between +/−60 degrees from a line extending from the center of the rotor10through the tip of the lobe14. In such an embodiment the angle A is 60 degrees. As shown inFIG. 9, the point903represents the end point of the radius of the tip of the lobe14. The point903is located on a line (not shown) extending from the center of the rotor10to the outermost tip of the lobe14. The point903represents the inner end point of the radius of curvature at the outermost end point of the tip of the lobe14. The angle A represents an angle from that radius line and in an embodiment of the present invention is 60 degrees. The angle A will vary depending on the geometric and design parameters of the rotor10and casing12.

In the embodiment shown inFIG. 9, the depressions901are present only at the tips of the lobes14on the rotor10. However, the present invention is not limited to this embodiment. In an alternate embodiment of the present invention, depressions901are also located in the grooves of the rotor10and the lobes of the casing12as these areas can also represent points of minimum distance between the rotor10and lobe12, i.e. “contact points.”

In a further alternate embodiment, the depressions901are additionally located in the distributed in the over the entire surface of the rotor10. In an alternate embodiment, the depressions901are distributed over the entire inner surface of the casing12, and in a further alternate embodiment the depressions901are distributed over both the entire surface of the rotor10and the inner surface of the casing12.

It is noted that although the present invention has been discussed above specifically with respect to aircraft applications, the present invention is not limited to this and can be employed in any application which experiences varying operational/performance conditions that require upstream components to be effectively isolated from downstream operations.