Patent ID: 12196223

DETAILED DESCRIPTION

Aspects of the present disclosure include turbomachines having one or more flow guiding features designed to increase the performance of the turbomachine. In some examples, flow guiding features are designed and configured to bias a circumferential pressure distribution at a diffuser inlet toward circumferential uniformity, or otherwise account for such low-frequency spatial pressure variations. In some examples, a diffuser having a row of vanes that include a plurality of first vanes and at least one second vane having a different characteristic than the first vanes are disclosed. In some examples, diffusers having an aperiodic section including one or more biased passages for biasing a flow field are disclosed. In some examples, turbomachines having flowwise elongate recesses in one or both of a hub and shroud surface are disclosed. As described herein, the present disclosure includes various combinations of flow guiding features that may be incorporated in a turbomachine to account for flow field characteristics, including but not limited to circumferential asymmetries, to thereby improve the performance of the turbomachine.

FIGS.1-5are graphs of static pressure versus circumferential angle for various diffuser types and operating conditions, each of the diffusers operably arranged downstream of a centrifugal compressor. Each ofFIGS.1-5shows time-averaged static pressure at several circumferential locations around the machines, all at a streamwise location between impeller exit and diffuser inlet.FIG.1shows time averaged static pressures for various flowrates102-116, with curve104being the lowest flow rate and102the highest, all at the same impeller rotational speed, here 120,000 RPM. The data inFIG.1is from a flat plate diffuser having 14 vanes. Vane location lines118show the approximate location of each of the vanes with respect to the static pressure measurements. As shown inFIG.1, each of pressure curves102-116has a sawtooth pattern, with peaks corresponding to each vane location118, such sawtooth pattern being mostly due to the natural vane-to-vane pressure field that exists in vaned diffusers or any cascade of turbomachinery vanes. Thus, the pressure curves102-116have a first spatial frequency that is substantially the same as the spatial frequency of the vanes of the flat plate diffuser. Pressure curves102-116, however, also have a lower-frequency wave type variation superposed on the sawtooth shape, the lower-frequency wave having a primary spatial frequency that is less than the spatial frequency of the vanes.FIG.2shows a subset of the pressure curves fromFIG.1—curves102,104, and112.FIG.2also includes mean pressure curves202,204, and206, which, in this example, are 6thorder polynomial curves. The low-frequency spatial variation in time-averaged circumferential static pressure can be seen in the mean pressure curves202,204, and206, in this example, each flow rate resulting in a low-frequency pressure variation with two maxima and two minima around the circumference of the machine.

FIGS.1and2indicate that, contrary to the common assumption made in turbomachinery design that the time averaged circumferential flow and pressure distribution at the diffuser inlet is substantially axisymmetric, the static pressure in fact varies around the circumference of the machine. In regions where the pressure is high, the velocities may be generally low and vane incidence may be closer to one extreme, e.g., low or high, depending, for example, on phase angle. And in regions where the pressure is low, the velocities may be generally high and vane incidence may be closer to the other extreme, e.g., high or low. Consequently, in regions where the incidence at the diffuser inlet due to this distortion is high, early stall may be more likely and losses may be relatively high. The flow field in these cases may be developing high flow and low flow regions with different pressures in order to pass the asymmetric impeller flow into a fixed number of diffuser passages.

FIG.3shows static pressure test data at three flow rates302,304,306with the same flat plate diffuser asFIGS.1and2, but with the compressor operating at a different speed, here 135,000 RPM, with curve304being the lowest flow rate and302the highest. Mean pressure curves308,310, and312show a similar low-frequency variation as shown inFIG.2, and also shows a circumferential shift in local maxima and minima as flow rates decrease and the system approaches surge.

FIGS.4and5similarly show a time-averaged circumferential distribution of static pressure at diffuser inlet for a double-divergence channel diffuser operably coupled to a centrifugal compressor impeller operating at 100,000 RPM (FIG.4) and 135,000 RPM (FIG.5). InFIG.4, pressure curves402and404and mean pressure curves408,410show a low-frequency circumferential variation having a primary spatial frequency distribution that is less than the spatial frequency distribution of the diffuser channels, as indicated by vane locations406. UnlikeFIGS.1-3, pressure curves402and404do not have the same number of higher-frequency local maxima in the sawtooth pattern as the number of vanes at locations406. Instead, a pocket412exists in the data, which shifts with flow rate. Pocket412suggests an offset or relief process may be occurring to allow the non-uniform flow to enter the fixed diffuser passages, and indicates potential underperforming diffuser passages, at least in the region of pocket412.FIG.5includes pressure curves502,504,506, and508and mean pressure curves512,514,516, and518corresponding to four different flow rates, all at 135,000 RPM. As inFIG.4, pockets510appear at each flowrate.

Extensive testing and analysis of circumferential pressure data for various diffuser types have shown that the low-frequency circumferential pressure distribution shown inFIGS.1-5do not originate from an asymmetric flow path located upstream or downstream of the diffuser.FIG.6shows an example of an asymmetric flow path in the form of a volute600located downstream of diffuser602. It is well known that volutes such as volute600create an asymmetry in the flow field of a diffuser, such as diffuser602, proximate cutwater604, (also referred to as a volute tongue604) e.g., creating a volute distortion zone606extending between locations A and B. In the illustrated example, volute distortion zone extends from approximately 90 degrees upstream of cutwater604(location “A”) to approximately 45 degrees downstream of the cutwater (location “B”).FIG.7shows circumferential pressure versus flow rate for a compressor or pump having a volute. As shown inFIG.7, the volute creates strong circumferential distortions in impeller exit pressures at low flows due to strong diffusion in the volute at that condition, which diminishes as flow rate increases and the volute flow state switches from diffusion to acceleration. Pressure curves 1 and 2 inFIG.7are in volute distortion zone606(FIG.6).

Various diffuser designs have been developed to improve diffuser performance in machines with asymmetric flow paths such as volutes that try to account for the large circumferential distortions caused by the volute or other asymmetric flow path. Other examples of such asymmetric flow paths located upstream or downstream of the diffuser include a side inlet in front of the impeller, an asymmetric collector, etc. Rather than localized bulk pressure distortions caused by an asymmetric flow path such as a volute, the low frequency pressure variations shown inFIGS.1-5extend around the entire circumference of the machine, are an active phenomena that shift in location with operating condition, and exist whether or not asymmetric flow paths are present. The present paper discloses a variety of diffusers having biased passages designed and configured to improve diffuser performance in light of these low-frequency spatial pressure variations. In some embodiments, biased passages are provided that are located, configured, and dimensioned to bias a low-frequency circumferential pressure distribution at a diffuser inlet, such as the low-frequency variations shown inFIGS.1-5, toward circumferential uniformity. In other examples, biased passages are designed and configured to also, or alternatively, improve the performance of a turbomachine, including increasing the controllability of spatial flow field variations, modifying flow field variations, and improving the performance of the turbomachinery in light of flow field variations.

The present paper includes a variety of diffuser design variables or characteristics that may be combined in any number of different combinations to develop a diffuser with biased passages tailored for particular performance and flow fields. Non-limiting examples of such diffuser design variables or characteristics include, but are not limited to, vane leading edge location, vane trailing edge location, a radial distance of a vane from a diffuser centerline, vane chord length, a maximum thickness of a vane, a vane height, a vane flowwise shape distribution, a vane stagger angle, vane wedge angle, channel divergence angle, vane pitch, vane lean, vane twist, vane leading edge shape, e.g., leading edge chevron, swallowtail or scallop, etc., fixed or moveable vanes, a passage height between hub and shroud surfaces, a circumferential location of a biased passage, a number of biased passages, and one or more flowwise channels located in one or both of hub and shroud surfaces extending upstream and/or downstream of a diffuser passage. One or more diffuser design variables may be adjusted for a subset of vanes in a diffuser vane row to create one or more biased passages having a cross-sectional flow area distribution in a flowwise direction that is different than a cross-sectional flow area distribution of a plurality of other diffuser passages in the same vane row. Such diffuser design variable combinations may be applied to any type of diffuser, including, for example, any type of vaned diffuser, including flat plate, airfoil, straight channel, conical, single row or tandem, single or multiple vane type per row, and any solidity, and may also be applied to vaneless diffusers.

In yet other examples, diffusers made in accordance with the present disclosure include multi-vane groupings, wherein each vane grouping includes two or more vanes each having one or more different characteristics than other ones of the vanes in the grouping. The groupings may be arranged in a periodic arrangement around the circumference of the machine, or may be arranged in an aperiodic arrangement, thereby resulting in one or more biased passages. Diffusers made in accordance with the present disclosure may include any combination of vane groupings disclosed herein and biased passages disclosed herein. For example, a diffuser may include a periodic section of one or more vane groupings, and one or more aperiodic sections including one or more biased passages. The one or more characteristics that may vary among vanes in a vane grouping may include, but are not limited to, vane leading edge location, vane trailing edge location, a radial distance of a vane from a diffuser centerline, vane chord length, a maximum thickness of a vane, a vane height, a vane flowwise shape distribution, a vane stagger angle, vane wedge angle, channel divergence angle, vane pitch, vane lean, vane twist, vane leading edge shape, e.g., leading edge chevron, swallowtail or scallop, etc., fixed or moveable vanes, and a passage height between hub and shroud surfaces. One or more of such characteristics may be varied. Such groupings may be designed, configured, and located to improve the performance of a turbomachine, including increasing the controllability of spatial flow field variations, modifying flow field variations, and improving the performance of the turbomachinery in light of flow field variations, such as the circumferential pressure variations discussed above.

Examples of vaneless diffusers with biased passages include vaneless diffusers with flowwise recesses, e.g., channels, grooves, or other recesses located in the hub or shroud surface for varying a passage height in one or more circumferential locations. As described more below, elongate recesses include, but are not limited to, flowwise channels having substantially square edges and flowwise grooves having rounded edges. In some examples, vaneless diffusers may have an aperiodic arrangement of flowwise recesses. The flowwise length of such recesses may vary, from longer recesses extending upstream of the diffuser into the impeller and downstream of the diffuser, to shorter recesses located at any flowwise location in the diffuser and of any shorter length. Biased passages disclosed herein may have a cross-sectional area that is greater than a cross-sectional area of other passages in a diffuser row. Such increased flow area passage(s) may provide a biased relief passage that may be designed and configured to accept an asymmetric portion of an impeller exit flow and cause a more uniform distribution of flow into other non-biased passages. In other examples, biased passages disclosed herein may have a reduced cross-sectional area as compared to the cross-sectional area of other non-biased passages, including fully blocked passages. Thus, as used herein, a reduced area biased passage includes fully blocked passages, or the absence of a diffuser passage in a location where a passage would be for a fully periodic diffuser passage arrangement. Such decreased flow area biased passages may be designed and configured to redistribute or otherwise influence an asymmetric impeller exit flow field, thereby providing a more uniform distribution of flow in the non-biased passages.

The present disclosure also includes experimental and computational methods of designing flow structures for turbomachines to improve performance. In one example, a computational model of a turbomachine and/or diffuser may be developed. A circumferential pressure distribution may be calculated at one or more operating conditions and the performance of the diffuser may be analyzed. In some cases, a low-frequency circumferential variation in pressure will be calculated at the diffuser inlet. The computational model of the diffuser may be iteratively adjusted with the addition of one or more biased passages, and a circumferential pressure distribution and diffuser performance may be calculated for each case to identify an optimized biased passage design. In other examples, rather than calculating a circumferential pressure distribution, a seeded perturbation in the diffuser inlet pressure or other equivalent approach may be applied to the computational model for various diffuser designs to determine an optimized biased passage arrangement. In yet other examples, experimental methods of determining biased passage designs may be implemented, including instrumenting a testing platform with sufficient pressure measurements around the circumference of a diffuser inlet to fully characterize the primary components of any circumferential pressure variation. The circumferential pressure variation for various diffuser designs with and without biased passages may be measured and improved biased passage designs determined.

FIGS.8-20illustrate exemplary embodiments of vaned diffusers having one or more biased passages.FIG.8shows a portion of an exemplary vaned flat plate low solidity diffuser800that has a row of vanes802extending between a hub804and shroud806and extending in a flowwise direction between a diffuser inlet808and exit810. Row802includes a plurality of first vanes812and at least one second vane814. Although only three are shown, first vanes812are equally spaced around one or more portions of diffuser800. As shown, second vane814has a different characteristic than first vanes812, here a different height, with second vane814being a partial height vane affixed to hub804. The partial height of second vane814results in a biased passage816that has a different cross-sectional area distribution in the flowwise direction than passage816between first vanes812. Thus, diffuser800has a plurality of passages located around a circumference of the diffuser, including at least one periodic section of passages816extending between first vanes812, wherein the section is periodic because the first vanes812are equally spaced at regular intervals around a diffuser centerline. Diffuser800also includes at least one aperiodic section including biased passage818, the section being aperiodic because there is a discontinuity in the periodic nature of first vanes812, here, biased passage818having a larger cross-sectional flow area than passages816. Exemplary diffuser800is designed and configured for receiving a flow field having a circumferential pressure distribution and biased passage816is located, configured, and dimensioned to bias the circumferential pressure distribution toward circumferential uniformity, e.g., bias a low-frequency spatial pressure variation, such as the ones shown inFIGS.1-5. Biased passage may also be located, configured, and dimensioned to improve the performance of a turbomachine, including increasing the controllability of spatial flow field variations, modifying flow field variations, and improving the performance of the turbomachinery in light of flow field variations. Diffuser800may have one or more of biased passages816located at any location around the circumference of the diffuser.FIG.9shows a diffuser900that is substantially the same as diffuser800, including first vanes902extending between hub904and shroud906, and at least one second vane908, wherein second vane is partial height and results in biased passage. Unlike diffuser800, second vane908is affixed to the shroud906, rather than hub904. Alternative embodiments may include combinations of second vanes814and908, e.g., a single diffuser with one or more partial-height vanes affixed to the shroud surface and one or more partial-height vanes affixed to the hub surface.

FIG.10shows an exemplary diffuser1000that has a plurality of first vanes1002and at least one second vane1004having a different characteristic, here radial distance from a centerline1005of diffuser1000and stagger angle, thereby forming biased passage1006. Broken line1008shows where one of first vanes1002would have been located if the periodic nature of first vanes had been continued, e.g., a periodic first vane location, as is the case with existing diffusers. Broken lines1010illustrate the stagger angle may be varied +/− from a first vane stagger angle. Although only a portion of diffuser1000is shown, the diffuser may include one or more biased passages1006. First and second vanes1002,1004may all be full height, or one or both may be partial height. As shown, exemplary second vane1004is slid back along a flowwise direction as compared to periodic first vane location1008, resulting in leading edge1012and trailing edge1014both being a greater radial distance from centerline1005than leading and trailing edges1016,1018of first vanes1002. Biased passage1006creates an aperiodic section in diffuser1000in the form of a larger cross-sectional flow area at inlet1020of diffuser1000.

FIG.11shows an exemplary diffuser1100that has a plurality of first vanes1102and at least one second vane1104having a different characteristic, here thickness, thereby forming biased passages1106. Although only a portion of diffuser1100is shown, the diffuser may include two or more biased passages1106. First and second vanes1102,1104may all be full height, or one or both may be partial height. As shown, exemplary second vane1104is thinner than first vanes1102, resulting in biased passages1106that have a different cross-sectional area distribution than passages1108, creating an aperiodic section in diffuser1100in the form of a larger cross-sectional flow area adjacent second vane1104.

FIG.12shows an exemplary diffuser1200, which is similar to diffuser1100(FIG.11) and has a plurality of first vanes1202and at least one second vane1204having a different characteristic, here maximum thickness, thereby forming biased passages1206. Although only a portion of diffuser1200is shown, the diffuser may include two or more biased passages1206. First and second vanes1202,1204may all be full height, or one or both may be partial height. As shown, exemplary second vane1204is thicker than first vanes1202, resulting in biased passages1206that have a different cross-sectional area distribution than passages1208, creating an aperiodic section in diffuser1200in the form of a smaller cross-sectional flow area adjacent second vane1204.

FIG.13shows an exemplary diffuser1300, which is similar to diffusers1100and1200(FIGS.11and12) and has a plurality of first vanes1302and at least one second vane1304having a different characteristic, here chord length, thereby forming biased passages1306. Although only a portion of diffuser1300is shown, the diffuser may include two or more biased passages1306. First and second vanes1302,1304may all be full height, or one or both may be partial height. As shown, exemplary second vane1304is longer than first vanes1302, resulting in biased passages1306that have a different flowwise cross-sectional area distribution than passages1308, creating an aperiodic section in diffuser1300proximate second vane1304.FIG.14shows diffuser1400, which is substantially the same as diffuser1300with equivalent components having the same name and same reference numeral suffix. Unlike diffuser1300, second vane1404may have a different stagger angle than first vanes1402, as indicated by broken line1410, showing one possible alternative stagger angle. The particular stagger angle of second vane1404may be varied, including both positive and negative angles with respect to the first vane1402stagger angle.

FIG.15shows an exemplary diffuser1500, which is similar to diffusers1100-1400(FIGS.11-14) and has a plurality of first vanes1502and at least one second vane1504having a different characteristic, here pitch, resulting in a different circumferential spacing between second vane1504and adjacent vanes than the spacing between adjacent first vanes1502, thereby forming biased passages1506aand1506b. Biased passage1506ahas a smaller cross-sectional area and1506bhas a larger cross-sectional area than passages1508. Although only a portion of diffuser1500is shown, the diffuser may include two or more biased passages1506a, b. First and second vanes1502,1504may all be full height, or one or both may be partial height. As shown, exemplary second vane1504has the same pitch, shape, and chord length as first vanes1202, but is located at a different circumferential location than a periodic first vane location, resulting in an aperiodic section and diffuser1500having a non-uniform and aperiodic circumferential vane pitch distribution.

FIG.16shows exemplary diffuser1600, which has a plurality of first vanes1602(only two of twelve labeled) and two second vanes1604a,1604beach having a different characteristic, here maximum thickness and chord length, than the first vanes, resulting in biased passages1606aand1606b. Second vane1604ahas the same thickness as the first vanes1602, but a longer chord length, resulting in biased passages1606ahaving a different flowwise cross-sectional area distribution than passages1608. Second vane1604bhas a greater thickness than first vanes1602, resulting in biased passages1606bhaving a different flowwise cross-sectional area distribution, including a smaller cross-sectional area, than passages1608. First and second vanes1602,1604a,1604bmay all be full height, or one or more may be partial height. As shown, second vanes1604a,1604band associated biased passages1606a,1606bare spaced approximately 180 degrees around the circumference of diffuser1600. First vanes1602are equally spaced from adjacent first vanes, providing two periodic sections1610and second vanes1604a,1604bresult in two aperiodic sections1612.

FIG.17shows exemplary diffuser1700, which has a plurality of first vanes1702(only two of seven labeled) and a plurality of second vanes1704(only two of seven labeled), each having a different characteristic from first vanes1702, here chord length. Unlike diffuser1600, diffuser1700has an equal number of first vanes1702and second vanes1704and a fully periodic arrangement of passages1706a,1706b. First vanes1702and second vanes1704may all be full height, or one or more may be partial height. First and second vanes1702,1704are arranged in vane groupings, here two vanes per grouping, where diffuser1700has a periodic arrangement of multi-vane groupings, and wherein each vane grouping includes first and second vanes1702,1704, each having a different characteristic than other ones of the vanes in the grouping.FIG.18shows diffuser1800, which is substantially the same as diffuser1700, including a plurality of first vanes1802(only two of seven labeled) and a plurality of second vanes1804(only two of seven labeled), each having a different characteristic from first vanes1802, here chord length. Unlike diffuser1700, each of second vanes1804also have a different flowwise location than first vanes1802, with a location of leading edge1812being at a different radial distance, here a greater distance, from diffuser centerline1814, than a radial distance of first vane leading edges1816from the diffuser centerline. For example, each of second vanes1804are slid back in a flowwise direction as compared to a periodic first vane location. As with diffuser1700, diffuser1800includes first and second vanes1802,1804that are arranged in multi-vane groupings, here two vanes per grouping, where diffuser1800has a periodic arrangement of multi-vane groupings. In other examples, one or more characteristics of one or more of first and/or second vanes1702,1802,1704,1804may be varied to create one or more aperiodic sections having biased passages that are configured to address asymmetric pressure fields, for example, the asymmetric pressure fields shown inFIGS.1-5. The one or more characteristics may include, for example, any of the characteristics described herein, such as vane height, stagger angle, pitch, vane shape, vane leading and trailing edge location, and chord length, etc.

FIG.19shows exemplary diffuser1900, which has a plurality of first vanes1902(only two of seven labeled) and a plurality of second vanes1904(only two of seven labeled), each having a different characteristic from first vanes1902, here chord length and stagger angle. Diffuser1900has an equal number of first vanes1902and second vanes1904and when second vanes1904are all at the same stagger angle, a fully periodic arrangement of passages1906a,1906b. First vanes1902and second vanes1904may all be full height, or one or more may be partial height. First and second vanes1902,1904are arranged in vane groupings, here two vanes per grouping, where diffuser1900has a periodic arrangement of multi-vane groupings. As indicated by broken lines1910, the stagger angle of second vanes1904may be the same as first vanes1902, or may be varied in a positive or negative direction from the first vane stagger angle. In some embodiments, the stagger angle of the second vanes1904may be varied, and may be arranged to form an aperiodic arrangement with one or more biased passages. For example, all but one of the second vanes1904may have the same stagger angle as first vanes1902, with one of the second vanes having an alternate stagger angle, thereby providing two biased passages on either side of the altered-angle full height second vane. In other examples, the stagger angle of other numbers of second vanes1904may be varied.

FIG.20shows exemplary diffuser2000, which is substantially the same as diffuser1900with equivalent components having the same name and same reference numeral suffix. Unlike diffuser1900, where the stagger angle of second vanes1904may be varied, in diffuser2000, the stagger angle of first vanes2002may be varied, as indicated by broken lines2010. As with diffuser1900, the stagger angle of less than all of first vanes2002may be different than other ones of the first vanes, thereby resulting in an aperiodic arrangement and one or more biased passages. First and second vanes2002,2004are arranged in vane groupings, here two vanes per grouping, where diffuser2000has a periodic arrangement of multi-vane groupings. In other examples, characteristics of diffusers1900and2000may be combined, including varying the stagger angle of select ones of both the first and second vanes, or the stagger angle of a subset of first vanes1902,2002, or a subset of second vanes1904,2004.

In another embodiment, an exemplary diffuser may include a plurality of vane groupings, wherein each vane in the grouping has a different height. For example, a vane grouping may include two partial-height vanes, including a first partial height vane affixed to a hub or shroud surface and a second, adjacent partial height vane affixed to the hub or shroud surface. The diffuser may include a periodic arrangement of such groupings, e.g., in one example the first and second partial height vanes may all be equally spaced around the circumference of the machine. In one example, the first partial height vane may have a different height than the second partial height vane. For example, the first partial height vane may have a height between approximately 15% and approximately 65% of a passage height, and in some examples, approximately 50% of the passage height. The second partial height vane may have a height between approximately 5% and approximately 45% of the passage height, and in some examples, approximately 15%. In one example, the first and second partial height vanes in each vane grouping may be affixed to opposite sides of the passage, e.g., the first partial height vane may be affixed to the shroud and the second partial height vane may be affixed to the hub. Such partial-height vane groupings may reduce leading edge metal blockage and increase passage area, and allow for flow reorganization especially near choke, thereby improving performance. In yet other examples, vane groupings may include three or more vanes, such vane groupings repeated around the perimeter of the diffuser. In yet other examples, one or more biased passages may be formed by locating such vane groupings adjacent periodic sections. For example, in a diffuser with 14 vanes, a two vane grouping with first and second partial height vanes may be used in the place of 2 to 12 of the 14 vanes in one or more circumferential locations resulting in one or more biased passages.

FIG.21shows a prior art channel-type diffuser2100andFIGS.22-33show exemplary embodiments of channel-type diffusers made in accordance with the present disclosure. As shown inFIG.21, prior art channel-type diffuser2100includes a plurality of vanes2102(only one labeled) defining passages2104(only one labeled) in the form of channels. Diffuser2100is similar to the diffuser used to generate the test data shown inFIGS.4and5. Diffuser2100is fully periodic and symmetric, with each of vanes2102having the same stagger angle S and wedge angle W, and each passage2104having the same divergence angle D.

FIG.22shows an exemplary channel diffuser2200having a plurality of passages2202(only one labeled) extending between a first vane2204(only one labeled). Unlike prior art diffuser2100, however, each passage2202also includes a second vane2206located between adjacent first vanes2204. Exemplary second vanes2206are flat plates, each have a leading edge2208that is downstream from diffuser inlet2210, and a trailing edge2212that is positioned upstream of diffuser exit2214. Second vanes2206are full height. In other examples, one or more of first and/or second vanes2204,2206may be partial height. In the illustrated example, second vanes2206have a shorter chord length than a length of passages2202, and are substantially centered in the passages in both circumferential and flowwise directions. First and second vanes2204,2206are arranged in vane groupings, here two vanes per grouping, where diffuser2200has a periodic arrangement of multi-vane groupings. Exemplary passages2202are periodic, however, one or more characteristics of one or more of first vanes2204and/or second vanes2206may be varied to create one or more biased passages. One or more characteristics of one or more of first and/or second vanes2204,2206may be varied to create one or more aperiodic sections having biased passages that are configured to address asymmetric pressure fields, for example, the asymmetric pressure fields shown inFIGS.1-5. The one or more characteristics may include, for example, any of the characteristics described herein, such as vane height, stagger angle, pitch, vane shape, vane leading and trailing edge location, and chord length, etc. For example, second vanes2206may be of any type including airfoil type and need not all be centered in passages2202; at least one may be relocated or resized to create a biased passage including partial height design.

FIG.23shows an exemplary channel diffuser2300, which is similar to channel diffuser2200with equivalent components having the same name and same reference numeral suffix. Diffuser2300includes a plurality of passages2302(only one labeled) extending between first vanes2304(only one labeled). Each passage2302also includes a second vane2306located between adjacent first vanes2304. Exemplary second vanes2306are flat plates. As compared to second vanes2206(FIG.22), second vanes2306are narrower and positioned farther upstream, in this example with leading edge2308located at diffuser inlet2310, and trailing edge2312located farther upstream of diffuser exit2314. Second vanes2306are full height. In other examples, one or more of first and/or second vanes2304,2306may be partial height. In the illustrated example, second vanes2306have a shorter chord length than a length of passages2302, and are substantially centered in the passages in a circumferential direction and located upstream of a passage2302midpoint in the flowwise direction. First and second vanes2304,2306are arranged in vane groupings, here two vanes per grouping, where diffuser2300has a periodic arrangement of multi-vane groupings. Exemplary passages2302are periodic, however, one or more characteristics of one or more of first vane2304and/or second vanes2306may be varied to create one or more biased passages. One or more characteristics of one or more of first and/or second vanes2304,2306may be varied to create one or more aperiodic sections having biased passages that are configured to address asymmetric pressure fields, for example, the asymmetric pressure fields shown inFIGS.1-5. The one or more characteristics may include, for example, any of the characteristics described herein, such as vane height, stagger angle, pitch, vane shape, vane leading and trailing edge location, and chord length, etc. For example, second vanes2306may be of any type including airfoil type and need not all be centered in passages2302; at least one may be relocated or resized to create a biased passage including partial height design.

FIG.24shows an exemplary channel diffuser2400that is the same as prior art diffuser2100(FIG.21) except that diffuser2400includes a plurality of first vanes2402and one second vane2404that has a characteristic that is different than first vanes2402, here, wedge angle. In the illustrated example, diffuser2400includes a single second vane2404located in a first vane2402periodic location, or where a first vane2402would have been located in a prior art arrangement. Second vane2404has a lower wedge angle W2than first vane2402wedge angle W1. The smaller wedge angle W2of second vane2404results in two biased passages2406. Diffuser2400includes a periodic section2408of first vanes2402and associated passages2410and an aperiodic section2412including the two biased passages2406. In other examples, one or more additional first vanes2402may be replaced with second vanes2404that may have one or more characteristics that are different than first vanes2402, thereby creating one or more additional biased passages.

FIG.25shows an exemplary channel diffuser2500that is similar to diffuser2400(FIG.24) with equivalent components having the same name and same reference numeral suffix. Diffuser2500includes a plurality of first vanes2502and one second vane2504that has a characteristic that is different than first vanes2502, here, wedge angle. Unlike diffuser2400, second vane2504has a larger wedge angle than first vanes2502. In the illustrated example, diffuser2500includes a single second vane2504located in a first vane2502periodic location, or where a first vane2502would have been located in a prior art arrangement. Second vane2504has a larger wedge angle W2than first vane2502wedge angle W1. The larger wedge angle W2of second vane2404results in two biased passages2506that have a smaller cross-sectional area than passages2510. Diffuser2500includes a periodic section2508of first vanes2502and associated passages2510and an aperiodic section2512including the two biased passages2506. In other examples, one or more additional first vanes2502may be replaced with second vanes2504that may have one or more characteristics that are different than first vane2502, thereby creating one or more additional biased passages.

FIG.26shows an exemplary channel diffuser2600that is similar to diffusers2400(FIG.24) and2500(FIG.25) with equivalent components having the same name and same reference numeral suffix. Diffuser2600includes a plurality of first vanes2602and one second vane2604that has a characteristic that is different than first vane2602, here, chord length. In the illustrated example, diffuser2600includes a single second vane2604located in a first vane2602periodic location, or where a first vane2602would have been located in a prior art arrangement. The longer length of second vane2604results in two biased passages2606that have a different flowwise cross-sectional area distribution than passages2610, and result in the trailing edge of second vane2604acting as an additional flow guide at diffuser exit to reduce losses at the diffuser exit. Diffuser2600includes a periodic section2608of first vanes2602and associated passages2610and an aperiodic section2612including the two biased passages2606. In other examples, one or more additional first vanes2602may be replaced with second vanes2604that may have one or more characteristics that are different than first vanes2602, thereby creating one or more additional biased passages.

FIG.27shows an exemplary channel diffuser2700that is similar to diffusers2400(FIG.24),2500(FIG.25), and2600(FIG.26) with equivalent components having the same name and same reference numeral suffix. Diffuser2700includes a plurality of first vanes2702and one second vane2704that has a characteristic that is different than first vane2702, here, vane stagger angle, resulting in alternate passage divergence angles. In the illustrated example, diffuser2700includes a single second vane2704located approximately where a first vane2702would have been located in a prior art arrangement. As indicated by the broken lines, the stagger angle of second vane2704may be varied in a +/− direction relative to the stagger angle of first vanes2702, resulting in two biased passages2706that have a different flowwise cross-sectional area distribution than passages2710. Diffuser2700includes a periodic section2708of first vanes2702and associated passages2710and an aperiodic section2712including the two biased passages2706. In other examples, one or more additional first vanes2702may be replaced with second vanes2704that may have one or more characteristics that are different than first vanes2702, thereby creating one or more additional biased passages.

FIG.28shows an exemplary channel diffuser2800that is similar to diffusers2400(FIG.24),2500(FIG.25),2600(FIG.26), and2700(FIG.27) with equivalent components having the same name and same reference numeral suffix. Diffuser2800includes a plurality of first vanes2802and one second vane2804that has a characteristic that is different than first vane2802, here, vane pitch, thereby altering vane circumferential location and spacing. In the illustrated example, diffuser2800includes a single second vane2804in the place of one of first vane2802. As shown, the pitch of second vane2804is different than the pitch of first vanes2802, resulting in two biased passages2806a,2806bthat have different flowwise cross-sectional area distributions than passages2810. Diffuser2800includes a periodic section2808of first vanes2802and associated passages2810and an aperiodic section2812including the two biased passages2806a,2806b. In other examples, one or more additional first vanes2802may be replaced with second vanes2804that may have one or more characteristics that are different than first vane2802, thereby creating one or more additional biased passages.

FIG.29shows an exemplary diffuser2900, which combines the characteristics of diffusers2500(FIG.25) and2600(FIG.26). As shown, diffuser2900includes a plurality of first vanes2902and two second vanes2904a,2904bthat each have a characteristic that is different than first vanes2902. Second vane2904ahas a greater chord length than first vanes2902and second vane2904bhas a greater wedge angle W2than wedge angle W1of first vanes2902, resulting in biased passages2906aand2906bthat have different flowwise cross-sectional area distributions than passages2910. Diffuser2900includes periodic sections2908a,2908bof first vanes2902and associated passages2910and aperiodic sections2912a,2912bincluding biased passages2906a,2906b, respectively. In other examples, one or more additional first vanes2902may be replaced with second vanes2904that may have one or more characteristics that are different than first vanes2902, thereby creating one or more additional biased passages.

FIG.30shows an exemplary channel diffuser3000which has a plurality of first vanes3002(only one labeled) and a plurality of second vanes3004(only one labeled), each of the second vanes having a different characteristic from first vanes3002, here chord length. Diffuser3000has an equal number of first vanes3002and second vanes3004and a fully periodic arrangement of passages3006a,3006b. As with any of the channel diffusers disclosed herein, first vanes3002and second vanes3004may all be full height, or one or more may be partial height.FIG.31shows diffuser3100, which is similar to diffuser3000, including a plurality of first vanes3102(only one labeled) and a plurality of second vanes3104(only one labeled), each of the second vanes having a different characteristic from first vanes3102, here chord length and flowwise location. Each of second vanes3104have a different flowwise location than first vanes3102, with a location of leading edge3112being at a different radial distance, here a greater distance, from diffuser centerline3114, than a radial distance of first vane leading edges3116from the diffuser centerline. For example, each of second vanes3104are slid back in a flowwise direction as compared to a periodic first vane location. One or more characteristics of one or more of first and/or second vanes3002,3102,3004,3104may be varied to create one or more aperiodic sections having biased passages that are configured to address asymmetric pressure fields, for example, the asymmetric pressure fields shown inFIGS.1-5. The one or more characteristics may include, for example, any of the characteristics described herein, such as vane height, stagger angle, pitch, vane shape, vane leading and trailing edge location, and chord length, etc.

FIG.32shows an exemplary channel diffuser3200which is substantially the same as diffuser3000(FIG.30) with equivalent components having the same name and same reference numeral suffix. Unlike diffuser3000, where the wedge angle, vane stagger, and channel divergence angles of first and second vanes3002,3004are the same, the stagger angle of first vane3202and associated channel diverge angles of adjacent passages3206may be varied in either direction from a stagger angle of second vanes3204. In some examples, the stagger angle of less than all of first vanes3202may be different than other ones of the first vanes, thereby resulting in an aperiodic arrangement and one or more biased passages3206.FIG.33shows diffuser3300, which is substantially the same as diffuser3200, except that rather than varying the stagger angle of first vanes3302, the stagger angle of one or more second vanes3304and associated channel divergence angles of adjacent passages3306may be varied. In some examples, the stagger angle of less than all of second vanes3304may be varied, resulting in diffuser3300having one or more aperiodic sections having one or more biased passages. In other examples, any one or more of the vane characteristic variations illustrated inFIGS.22-33may be combined in any combination.

FIG.34is an isometric view of a turbomachine3400, including impeller3402and vaneless diffuser3404. Diffuser3404extends between shroud3406and hub3407. Shroud3406extends from an impeller inlet3408, across an impeller exit/diffuser inlet3410to diffuser outlet3412.FIGS.35and36are additional views of shroud3406and hub3407. As shown inFIGS.35and36, exemplary shroud3406includes a plurality of flowwise grooves3502(only one labeled) that extend in a flowwise direction from a location upstream of diffuser inlet and adjacent impeller3402, to a location downstream of the diffuser inlet, in this example to diffuser outlet3412(FIG.34). Flowwise grooves3502are located in the surface of shroud3406and have rounded edges3504, giving the shroud wall a circumferential profile that approximates a periodic waveform. Exemplary grooves3502may be designed and configured to guide a portion of fluid flow in impeller3402into diffuser3404at a preferred angle, thereby increasing the performance of turbomachine3400.FIGS.37-39show turbomachine3700, which is substantially the same as turbomachine3400with equivalent components having the same name and same reference numeral suffix. Unlike turbomachine3400, turbomachine3700has flowwise grooves3802that are more closely spaced than flowwise grooves3502(FIG.35), with edges3804of adjacent grooves3802substantially touching at a leading edge region of the grooves.

FIGS.40-42show an exemplary turbomachine4000, which has the same impeller3402and shroud3406as turbomachine3400(FIGS.34-36), but an alternative hub4002, that, as can be best seen inFIG.42, also has flowwise grooves that extend in a flowwise direction, in this example, from diffuser inlet4204to diffuser outlet4206. In the example shown, diffuser4004has the same number of grooves4202as grooves3502in shroud3406, and similarly has grooves with rounded edges4208. Grooves4202are circumferentially aligned with grooves3502. As with grooves3502, hub-side grooves4202may be designed and configured to guide a portion of working fluid in a preferred direction to improve the performance of diffuser4004.FIGS.43and44show an alternate configuration fromFIGS.40-42, wherein a circumferential location of hub-side grooves4202are clocked with respect to shroud-side grooves3502. In this example, each of hub-side grooves4202are aligned with a midpoint between adjacent shroud-side grooves3502. In other examples, any other relative circumferential positioning may be used.

FIGS.45and46show an exemplary shroud4502and hub4504, each having flowwise grooves4506and4508, respectively. Unlike the embodiments shown inFIGS.40-44, shroud4502and hub4504also include biased passages4510,4512, in the form of enlarged flowwise grooves that have a larger cross-sectional area than grooves4506,4508. Such biased passages may be located, configured, and dimensioned to bias a circumferential pressure distribution toward circumferential uniformity, and/or provide other performance enhancements described herein. In other examples, one or both of shroud4502and hub4504may have additional biased flowwise grooves, or one or more biased flowwise grooves may be located in only the shroud or hub. The examples shown inFIGS.45and46include a periodic portion of passageways in the form of flowwise grooves and an aperiodic portion, in the illustrated example, having one biased passageway.

FIG.47is a cross-sectional elevation view of a biased diffuser passage4702disposed between passages4704. Biased passage4702has an increased passage height H1from recesses4706located in shroud4708and recess4710located in shroud4712. Recesses4706and4710may be similar in shape and location to grooves3502(FIG.35),4202(FIG.42), or may have other configurations, e.g., different leading and/or trailing edge location, width, flowwise length, etc. For example, in some embodiments, recesses4706and4710may have a leading edge located at a diffuser inlet. In the example shown inFIG.47, only one recess4706,4710is located in the hub and shroud4708,4712, thereby creating an aperiodic portion having a biased passage with a larger cross-sectional area than other passages in diffuser4700. In other examples a plurality of diffuser passages may have an increased height from one or more recesses located in the hub and/or shroud.

FIG.48is an isometric view of a turbomachine4800, including impeller4802and vaneless diffuser4804. Diffuser4804extends between shroud4806and hub4807. Shroud4806extends from an impeller inlet4808, across an impeller exit/diffuser inlet4810to diffuser outlet4812.FIG.49is an additional view of shroud4806and hub4807. As shown inFIGS.48and49, exemplary shroud4806and hub4807each include a plurality of flowwise channels4820,4822, respectively (only one of each labeled) that extend in a flowwise direction. Channels4820,4822as well as flowwise grooves3502(FIG.35),3802(FIG.38), and4202(FIG.42) are all flowwise elongate recesses. Channels4820and4822differ from grooves3502,3802,4202, by the cross-sectional shape of the recess, with the channels having a substantially square edge4902(FIG.49) and the grooves having a rounded edge3504(FIG.35). Shroud surface channels4820extend from a location upstream of diffuser inlet4810and adjacent impeller4802, to a location downstream of the diffuser inlet, in this example to diffuser outlet4812. Hub surface channels4822extend across the entire length of hub4807from diffuser inlet4810to diffuser outlet4812. Flowwise channels4820are located in the surface of shroud4806and have substantially square edges4902giving the shroud wall a circumferential profile that approximates a periodic square waveform. Similarly, flowwise channels4822are located in the surface of hub4807and have substantially square edges4904giving the hub wall a circumferential profile that approximates a periodic square waveform. Exemplary channels4820and4822may be designed and configured to guide a portion of fluid flow in impeller4802into diffuser4804at a preferred angle, thereby increasing the performance of turbomachine4800. In other embodiments, the characteristics of one or both of channels4820,4822may be varied, such as a depth, width, and number of channels. In the example shown inFIGS.48and49, channels4820and4822are circumferentially aligned, however, in other examples, the relative positions may be clocked such that the hub and shroud channels are not aligned.

FIGS.50and51show an alternative diffuser5000that is similar to diffuser4804(FIG.48) and includes hub5002and shroud5004having hub flowwise channels5006and shroud flowwise channels5008. Unlike diffuser4804, one of each of channels5006and5008have a characteristic that is different than the other channels5006,5008, here, a channel5006aand5008aeach having an enlarged depth, resulting in a biased passage. In other examples, a characteristic of just hub channels5006or just shroud channels5008may be varied from other ones of the hub and shroud channels to create a biased passage. In some examples, characteristics other than depth may be varied, such as cross-sectional shape (e.g., groove versus channel), width, length, leading edge location, and trailing edge location). In some examples, more than one of hub and/or shroud channels5006,5008may be varied to create a larger aperiodic section having more than one biased passage, or more than one aperiodic section. In yet other examples, diffusers made in accordance with the present disclosure may have a smaller number of flowwise recesses located at select circumferential locations, rather than a plurality of flowwise recesses equally spaced around the entire circumference of the machine. For example, diffusers made in accordance with the present disclosure may have only one, two, three, etc. flowwise recesses located in select locations around the circumference of the machine.

FIGS.52and53show an exemplary vaned diffuser5200having a shroud5202and hub5204, the shroud extending from an impeller inlet5206, across a diffuser inlet5208to a diffuser exit5210. Shroud5202includes flowwise channels5212extending to locations upstream and downstream of diffuser inlet5208and are separated by upper legs5214of a leading edge5216of vanes5218. In the illustrated example, leading edges5216have a scalloped, also referred to herein as a swallowtail shape. In the illustrated example, hub5204does not include any flowwise recesses. In other examples, hub5204may include flowwise recesses, such as channels or grooves.

As shown inFIGS.52and53, a biased channel5212ahas a different characteristic than the other channels5212, here, a leading edge location5220that is farther upstream than a leading edge location5222of channels5212(best seen inFIG.52) and a depth that is greater than a depth of channels5212(best seen inFIG.53). Biased channel5212acreates a biased passage in a aperiodic section of diffuser5200.

The foregoing has been a detailed description of illustrative embodiments of the invention. It is noted that in the present specification and claims appended hereto, conjunctive language such as is used in the phrases “at least one of X, Y and Z” and “one or more of X, Y, and Z,” unless specifically stated or indicated otherwise, shall be taken to mean that each item in the conjunctive list can be present in any number exclusive of every other item in the list or in any number in combination with any or all other item(s) in the conjunctive list, each of which may also be present in any number. Applying this general rule, the conjunctive phrases in the foregoing examples in which the conjunctive list consists of X, Y, and Z shall each encompass: one or more of X; one or more of Y; one or more of Z; one or more of X and one or more of Y; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y and one or more of Z.

Various modifications and additions can be made without departing from the spirit and scope of this invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present invention. Additionally, although particular methods herein may be illustrated and/or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.

Further alternative exemplary embodiments of the present invention are described in the paragraphs below.

In one example, a diffuser for a turbomachine includes a plurality of diffuser passages located around a circumference of the diffuser for receiving a flow field having a circumferential pressure distribution; the diffuser passages include at least one periodic section and at least one aperiodic section, the at least one aperiodic section including at least one biased passage that is located, configured, and dimensioned to bias the circumferential pressure distribution toward circumferential uniformity. Such an exemplary embodiment may also include one or more of the following features:The plurality of diffuser passages have a first spatial frequency, the circumferential pressure distribution including a time averaged low frequency component that has a lower spatial frequency than the first spatial frequency, the at least one biased passage configured to bias the low frequency component toward a circumferentially uniform pressure distribution.The at least one periodic section includes a plurality of first vanes and the at least one biased passage includes at least one second vane, the first and second vanes each having a plurality of vane characteristics including one or more of a leading edge located at a leading edge location, a trailing edge located at a trailing edge location, a radial distance from a diffuser centerline, a chord length, a maximum thickness, a height, a flowwise shape distribution, a stagger angle, vane pitch, vane wedge angle, vane lean, vane twist, vane leading edge shape, and channel divergence angle, at least one of the plurality of vane characteristics of the at least one second vane is different from at least one of the plurality of vane characteristics of the plurality of first vanes.The at least one of the plurality of second vane characteristics that are different from the first vane characteristics include differences in any of the plurality of vane characteristics in any combination.The leading edge of the at least one second vane is located at a different radial distance from the diffuser centerline than the leading edges of the plurality of first vanes.The trailing edge of the at least one second vane is located at a different radial distance from the diffuser centerline than the trailing edges of the plurality of first vanes.The at least one second vane is located at a different radial distance from the diffuser centerline than the first vanes.The second vane chord length is different than the first vane chord length.The second vane maximum thickness is different than the first vane maximum thickness.The second vane height is different than the first vane height.The diffuser includes hub and shroud surfaces, the plurality of diffuser passages extending between the hub and shroud surfaces, the second vane is a partial height vane affixed to either the hub or shroud surface.The second vane flowwise shape distribution is different than the first vane flowwise shape distribution.The second vane stagger angle is different than the first vane stagger angle.The at least one biased passage is blocked.The stagger angle of the at least one second vane is fixed.The stagger angle of the at least one second vane is adjustable.The second vane pitch is different than the first vane pitch.The plurality of diffuser passages each have a passage height, the passage height of the at least one biased passage being different than the passage height of the diffuser passages in the periodic section.The diffuser includes a hub surface, a shroud surface, and a flowwise recess located in at least one of the hub and shroud surfaces, the flowwise recess extending upstream of and aligned with the at least one biased passage.The diffuser includes a hub surface, a shroud surface, and at least one elongate flowwise recess located in at least one of the hub and shroud surfaces.The diffuser includes a plurality of elongate flowwise recesses, the plurality of elongate flowwise recesses having an aperiodic arrangement around the circumference of the diffuser.The circumferential pressure distribution does not originate from an asymmetric flow path located upstream or downstream of the diffuser.The circumferential pressure distribution does not originate from an asymmetric flow path located upstream or downstream of the diffuser, the asymmetric flow path selected from the group consisting of a side inlet, an asymmetric collector, and a volute.The at least one biased passage is not located in a volute distortion zone proximate a volute tongue or proximate a location 180 degrees from the volute distortion zone.The diffuser is configured for use in a centrifugal compressor or pump, the at least one biased passage is configured and dimensioned to limit or reduce a variation in a magnitude of the circumferential pressure distribution so as to improve a stage efficiency by more than 0.2 percentage points, to cause a more uniform impeller exit flow distribution, to improve a maximum through-flow at a given speed by more than 0.1%, to reduce a surge line by more than 0.2%, or to reduce vibratory stress levels on an impeller or diffuser vanes by more than 0.2%.The diffuser is configured for use in a centrifugal compressor or pump, the periodic section having a spatial frequency and the circumferential pressure distribution having a primary spatial frequency that is less than the spatial frequency of the periodic section, the at least one biased passage is configured and dimensioned to reduce a maximum variation in a magnitude of the circumferential pressure distribution over a design operating range of the compressor or pump by more than 1%.The diffuser is configured for use in a centrifugal compressor or pump having an impeller configured to generate a pressure rise, the periodic section having a spatial frequency and the circumferential pressure distribution having a primary spatial frequency that is less than the spatial frequency of the periodic section, the at least one biased passage is configured and dimensioned to limit a maximum variation in a magnitude of the circumferential pressure distribution over a design operating range of the compressor or pump to less than 30% of an impeller pressure rise.The first and second vanes are located in the same row.

In another example, a diffuser including a plurality of first vanes arranged in a row around a portion of a circumference of the diffuser, each of the first vanes spaced a first circumferential distance from an adjacent first vane; and at least one second vane located between ones of the first vanes, the at least one second vane having a different characteristic than the first vanes, the different characteristic resulting in a biased passage proximate the at least one second vane for biasing a circumferential pressure distribution of a flow field entering the diffuser toward a circumferentially uniform pressure distribution. Such an exemplary embodiment may also include one or more of the following features:The different characteristic is selected from the group consisting of a radial distance of a leading or trailing edge from a diffuser centerline, a radial distance from a diffuser centerline, a chord length, a maximum thickness, a height, a flowwise shape distribution, a stagger angle, vane pitch, vane wedge angle, vane lean, vane twist, vane leading edge shape, and channel divergence angle.The plurality of first vanes have a spatial frequency, the biased diffuser passage being configured to bias a time averaged circumferential pressure distribution having a low frequency component that has a lower spatial frequency than the first vane spatial frequency, the biased passage configured to bias the low frequency component toward a circumferentially uniform pressure distribution.

In another example, a diffuser includes a hub and a shroud; a plurality of first vanes extending from the hub to the shroud and arranged in a row around a portion of a circumference of the diffuser; and at least one second vane located between ones of the first vanes, the at least one second vane extending from the hub to the shroud and having a different characteristic than the first vanes. Such an exemplary embodiment may also include one or more of the following features:The different characteristic is selected from the group consisting of a radial distance of a leading or trailing edge from a diffuser centerline, a radial distance from a diffuser centerline, a chord length, a maximum thickness, a height, a flowwise shape distribution, a stagger angle, vane pitch, vane wedge angle, vane lean, vane twist, vane leading edge shape, and channel divergence angle.

In yet another example, a diffuser includes a hub and a shroud; and a plurality of vane groupings each including at least two vanes, each of the at least two vanes having a different characteristic than other ones of the at least two vanes. Such an exemplary embodiment may also include one or more of the following features:The diffuser has a circumference, the vane groupings located around the circumference of the diffuser in a periodic arrangement.The at least two vanes are partial-height vanes, one of the at least two vanes affixed to the shroud and a second one of the at least two vanes affixed to the hub.A height of the at least two vanes are not the same.

In still another example, a method of designing a diffuser having an inlet and a plurality of vanes to reduce a circumferential pressure variation proximate the inlet, the pressure variation having a primary spatial frequency that is less than a spatial frequency of the vanes. The method includes providing a plurality of diffuser passages each having an inlet and located around a circumference of the diffuser; and locating at least one biased diffuser passage between ones of the plurality of diffuser passages, the biased diffuser passage having a different cross-sectional area than the plurality of diffuser passages for minimizing the circumferential pressure variation at the inlets of the plurality of diffuser passages.

In another example, a method of designing a diffuser including developing a computational model of an axisymmetric diffuser; calculating a performance of the diffuser when a circumferential pressure distribution having a time averaged low-frequency circumferential variation is present at an inlet to the diffuser; modifying the computational model to add at least one biased flow passage to the diffuser; calculating a performance of the modified diffuser; and comparing the diffuser performance from the two calculating steps to determine if the biased flow passage improved diffuser performance.

In a further example, a method of designing a diffuser including measuring a circumferential pressure distribution at an inlet to a first diffuser having periodic diffuser passages; replacing the first diffuser with a second diffuser having at least one aperiodic section with at least one biased diffuser passage; measuring a circumferential pressure distribution at an inlet to the second diffuser; and comparing the pressure distributions from the two measuring steps to determine whether the second diffuser reduced an undesired variation in a magnitude of the measured circumferential pressure distribution by a predetermined amount. Such an exemplary embodiment may also include one or more of the following features:calculating a performance of the first diffuser;calculating a performance of the second diffuser; andcomparing the performance from the two calculating steps to determine whether the second diffuser improved diffuser performance by a predetermined amount.

In another example, a vaneless diffuser including an inlet and an exit; a hub surface and a shroud surface each extending between the inlet and the exit; and a plurality of flowwise recesses in at least one of the hub and shroud surfaces, the plurality of recess being aperiodic. Such an exemplary embodiment may also include one or more of the following features:The plurality of flowwise recesses include one or more first flowwise recesses and one or more second flowwise recesses, the one or more second flowwise recesses having at least one characteristic that is different than the first flowwise recesses.The at least one characteristic that is different is selected from the group consisting of a length, width, leading edge location, trailing edge location, depth, and cross-sectional shape.

In another example, a diffuser for a turbomachine, including a plurality of diffuser passages located around a circumference of the diffuser for receiving a flow field, the flow field has a circumferential pressure distribution; the diffuser passages include a first set of passages each having a first effective cross-sectional area distribution along a flow-wise direction and at least one biased passage having a second effective cross-sectional area distribution along the flowwise direction, the first and second effective cross-sectional area distributions being different, the at least one biased passage located, configured, and dimensioned to bias the circumferential pressure distribution toward circumferential uniformity.

Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.