Patent Description:
In rotary equipment such as fans, compressors and turbines, air flow past the rotating elements is influenced by the flow channel as defined by the casing structure surrounding the rotor. Rotor efficiency, and its impact on fuel consumption and performance, is influenced by the area near the rotor tips and the surrounding structure. Clearance around the rotor tips may be the source of significant losses. The rotor tip clearance losses may be magnified when the flowing gas does not follow its intended path and negatively impacts output due to interactions with the surrounding structure's boundary layer. For example, operating conditions may result in reduced surge margin and lower efficiency potential. Complex structures at the rotor-stator interface may improve performance but may be prohibitively difficult to fabricate using conventional manufacturing techniques.

Various types of articles may be created using additive manufacturing processes. Additive manufacture includes processes such as those that create a component or item by the successive addition of particles, layers or other groupings of a material onto one another. The article is generally built using a computer controlled machine based on a digital representation, and includes processes such as <NUM>-D printing. A variety of different additive manufacturing processes are used such as processes that involve powder bed fusion, laser metal deposition, material jetting, or other methods.

<CIT> discloses a method of manufacturing a rotor system comprising designing a casing with stall enhancement features; constructing the casing to be configured to fit over a rotor so that tips of the rotor blades are proximate the casing, and forming, by additive manufacturing, the casing with a series of recirculation channels in the casing to provide stall enhancement; optimizing, by analysis, aerodynamic performance of the recirculation channels wherein the method comprises: forming a section of the casing that contains the recirculation channels as a number of separate segments and fitting the segments to the casing to encircle the rotor, and forming, integrally during the additive manufacturing, a manifold in the section, wherein the manifold includes the recirculation channels and an annular channel connecting with each of the recirculation channels.

It is desirable to create rotor systems using effective, efficient and economical manufacturing methods of rotor system parts. It is also desirable to manufacture rotor systems that have extended performance ranges and for handling increased aerodynamic loadings. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.

In a first aspect, the invention is put in practice with the method of manufacturing a rotor system according to claim <NUM>.

In a further aspect, the invention is put in practice with the rotor system according to claim <NUM>.

The annular channel <NUM> connecting with each of the grooves <NUM> according to the invention can only be seen in <FIG>, <FIG>, <FIG> and <FIG>.

In the following description, features such as grooves, passages and channels are created by using an additive manufacturing process such as direct metal laser sintering (DMLS) to extend the performance characteristics of a rotor system by enabling complex geometry at the rotor-stator interface. Casing treatment with grooves oriented to extend longitudinally at an acute angle, including those with recirculation passageways are disclosed herein to provide beneficial performance characteristics. Additive manufacturing has been identified as an enabler for creating these complex parts, which otherwise may be prohibitively difficult to manufacture. In the examples given herein, details may be associated with a specific rotor and engine type, but the disclosure is not limited in application to any specific rotor or any particular type of engine but rather may be applied to any rotor where improved or extended performance is desired. In addition, the disclosure is not limited to any specific additive manufacturing process.

In embodiments of the present disclosure as further described below, systems, structures and methods of manufacturing relate to forming grooves and other features in a casing for a rotor, such as for an engine. Objectives include improving aerodynamic stall margin, efficiency and mechanical requirements. The casing or shroud is formed to fit over the rotor so that blade tips of the rotor are configured to pass proximate a section of the casing when the rotor rotates about an axis. The section is formed in segments to facilitate manufacture. A series of grooves is formed in the segmented section of the casing. The grooves extend into the casing radially outward from the axis and are oriented such as to extend at angles relative to the axis. Aerodynamic performance as influenced by the grooves is optimized by evaluating alternative depths, orientations and shapes of the grooves to avoid stall and possible engine surge. The segmented sections of the casing are fabricated by additive manufacturing with the grooves and other features incorporated. The rotor is assembled to rotate within the segmented sections of the casing with the grooves extending a distance upstream from the blade tips and over at least a portion of the blade tips so that the blade tips pass across the grooves when the rotor rotates.

The embodiments disclosed herein enable increased cycle pressure ratios and improved engine performance with higher aerodynamic loadings. Operational stability is extended at narrower surge margins. Stall in state of the art rotors may occur when system surge results in flow that leaks forward through the rotor's tip gap and causes local reverse flow. Reverse axial flow over the tip of a rotor (momentum flux), is a phenomenon associated with the onset of stall. This reverse flow is inhibited in the embodiments disclosed where grooves are employed to create resistance to the reverse flow over the rotor tip and allow the rotor to stably operate with significant increases in range from the operating line to stall. It has been found that additional benefits are realized when the grooves are generally axially oriented so that their longest dimension (length) is generally oriented in the axial direction. This axial orientation is made economically viable by the embodiments described herein, including by utilizing additive manufacturing processes.

As noted above, the grooved casing rotor systems and methods described herein may be employed in a variety of applications, including in a number of embodiments involving an engine. By way of an exemplary embodiment, an engine <NUM> will be described with reference to <FIG>. In this embodiment, the engine <NUM> is configured as a gas turbine engine for aircraft propulsion. The engine <NUM> includes an intake <NUM>, with a fan section <NUM> that has a rotor disposed in a fan case <NUM>. The fan section <NUM> draws air into the engine <NUM>, accelerates the air within the engine <NUM>, and may assist in providing propulsion. The air is directed through two paths that include a core flow through the engine core <NUM> channeling a flow stream <NUM>, and a bypass flow through a bypass duct <NUM> channeling another flow stream <NUM>. A compressor section <NUM> includes a rotor that compresses the air delivered to the engine core <NUM> and sends it to a combustion section <NUM>. In the combustion section <NUM> the air is mixed with fuel and ignited for combustion. Combustion air is directed into a turbine section <NUM>, which may include single or plural turbine stages. The hot, high-speed air flows within the turbine case <NUM> and over the turbine rotors <NUM>, <NUM> which spin on shafts <NUM>, <NUM> about an axis <NUM>. The axis <NUM> defines an axial direction <NUM>, with a radial direction <NUM> projecting from the axis <NUM> and normal thereto. The air from the turbine section <NUM> rejoins that from the bypass duct <NUM> and is discharged through an exhaust section <NUM> including through a propulsion nozzle <NUM>.

The turbine section <NUM> includes one or more turbine stages. In the depicted embodiment, the turbine section <NUM> includes two turbine stages, a high-pressure turbine <NUM>, and a power turbine <NUM>. However, it will be appreciated that the engine <NUM> may be configured with a different number of turbine stages. As the turbines <NUM>, <NUM> rotate, their rotors <NUM>, <NUM> drive equipment in the engine <NUM> via concentrically disposed shafts or spools. Specifically, the high-pressure turbine rotor <NUM> drives the compressor rotor <NUM> via a high-pressure spool including the shaft <NUM>, and the power turbine rotor <NUM> drives the fan rotor <NUM> via a low-pressure spool including the shaft <NUM>. Clearance is provided between each of the rotors <NUM>/<NUM>, <NUM>, <NUM> and their respective casings <NUM>, <NUM>, <NUM> including to avoid blade incursions during rotation.

Referring to <FIG>, which shows an example which is not according to the claimed invention, a meridional view of a part of the rotor <NUM> of the compressor <NUM> shows the radially outermost part of one blade <NUM> of the rotor <NUM>. The blade <NUM> includes a leading edge <NUM> on its upstream side, a trailing edge <NUM> on its downstream side and a tip <NUM>. The casing <NUM> is disposed across a radial clearance gap (i.e. blade running clearance) <NUM> from the tip <NUM>. It will be appreciated that the casing <NUM> defines an annular opening within which the rotor <NUM> is disposed. The radial gap <NUM> is typically very small, for example, in a range of about <NUM> to about <NUM> and may be non-dimensionalized by chord. The flow stream <NUM> from the perspective of <FIG> moves from left to right, which coincides with the axial direction <NUM>. In incipient stall conditions, flow may leak through the gap <NUM> in an upstream direction through the gap <NUM>, which would cause local reverse flow. In this embodiment, reverse flow is inhibited, including by the inclusion of grooves <NUM> that are formed into the casing <NUM> from the inner surface <NUM> and outward in the radial direction <NUM>. The grooves <NUM> are disposed to extend with their length disposed generally in the axial direction <NUM> from an upstream end <NUM> to a downstream end <NUM>. A portion of each groove <NUM> is disposed radially outward from a portion of the blades <NUM> and another portion is disposed radially outward from the flow stream <NUM> upstream from the blades <NUM>. Specifically, the upstream end <NUM> is disposed a distance <NUM> upstream from the leading edge <NUM>. The downstream end <NUM> is disposed a distance <NUM> downstream from the leading edge <NUM> and a distance <NUM> upstream from the trailing edge <NUM>. The distance <NUM> is greater than the distance <NUM> and the distance <NUM> is greater than the distance <NUM>. The stall inhibiting benefits of the grooves <NUM> has been found to be maximized by the axial orientation where the length of the grooves <NUM> in the axial direction is greater than their width in the circumferential direction (into the view of <FIG>).

Referring to <FIG>, a view of the grooves <NUM> is provided from a perspective point located radially outward from the blades <NUM> and toward the blade tips <NUM>. As shown, the grooves <NUM> span across the leading edges <NUM> of the blades <NUM> in the axial direction <NUM>. The blades <NUM>, which have an airfoil shape, are generally disposed at an angle <NUM> relative to the axis <NUM> so that the leading edges <NUM> are disposed before the trailing edges <NUM> in the rotation direction <NUM>. The grooves <NUM> are skewed relative to the axis <NUM> and are disposed at an acute angle <NUM> relative thereto. The angle <NUM> is negative relative to the angle <NUM> and the upstream ends <NUM> of the grooves <NUM> are offset further from the axis <NUM> than the downstream ends <NUM>. As a result, a blade <NUM> takes a longer period of time to traverse a given groove <NUM> as compared to if the grooves <NUM> were disposed axially straight and a right-to-left (as viewed) flow through the grooves <NUM> is induced. <FIG> illustrates the area of the rotor <NUM> from a perspective point located downstream from the blades <NUM> and directed into/against the direction of flow stream <NUM>. The grooves <NUM> are inclined in the rotation direction <NUM> so that the entry <NUM> is offset relative to the bottom <NUM> in a direction against the rotation direction. For example, the leading edge <NUM> passes the entry <NUM> of a given groove <NUM> prior to passing the bottom <NUM> of that groove <NUM>. The edges of the grooves <NUM>, for example edges <NUM>, <NUM> at the entry <NUM> are beveled or rounded to avoid sharp steps that would otherwise disturb airflow. The effect is that a passing blade <NUM> pushes air through each groove <NUM> from its downstream end <NUM> to its upstream end <NUM>. The resulting pressurization works against the formation of counterflow in the gap <NUM> and extends the surge threshold to higher pressure ratios. The result is that the performance of the rotor <NUM> is extended, enabling higher efficiencies and power outputs.

The location, orientations and features of the grooves support these performance enhancements. More specifically, the location relative to the blades <NUM>, the skewed and inclined dispositions and the shape each affect the improvements. Volumes of the grooves <NUM> are adjusted to control the frequency of the inflow/outflow to manage the rotor tip flow-field and to enhance range to stall. The grooves <NUM> are optimized, such as by modeling and through testing analysis. For example, aerodynamic performance of the grooves <NUM> is evaluated by testing alternative depths, widths, orientations and shapes of the grooves <NUM> to avoid compressor stall where flow may otherwise surge forward. For example, the grooves <NUM> may have curved or complex shapes.

Referring to <FIG>, a process <NUM> for manufacturing a rotor casing with complex treatments is defined. The process <NUM> includes defining, evaluating and iterating <NUM> advanced stall enhancement features. Aerodynamic performance as influenced by the grooves is optimized by evaluating alternative depths, orientations and shapes of the grooves to extend or enhance range to stall and possible engine surge. By using additive manufacturing, design limitations that may otherwise apply are avoided. For example, machining features into a casing carries limitations associated with the ability to efficiently remove material. Designs may be created using computer aided design software and evaluated using computational fluid dynamics software tools. Development parts may be fabricated using additive manufacturing and tested in an operating environment. Iterations of design, evaluation and testing may be carried out efficiently using additive manufacturing.

When the stall enhancement feature design meets aerodynamic stall margin, efficiency and mechanical requirements, the process <NUM> proceeds to integration/interfacing <NUM>. The casing treatment with stall enhancement features is integrated into the engine's shroud around the rotor section including attachment features and segment interfaces. Manufacturability is balanced with a need to ensure the segments with casing treatment are securely contained. For example, interlocking structure may be used to prevent segment shifting, such as during surge. In addition, features may be formed by additive manufacturing to prevent leakage between the segments during engine operation.

The process <NUM> proceeds to defining <NUM> the specifics of the additive manufacturing process. For example, the type of additive manufacturing is selected. The current embodiment uses DMLS due to its applicability to forming complex geometries for parts with strength and durability. In addition, DMLS may be used to form the fine details of the casing treatment designs with high accuracy and quality. The build orientation of the segments is determined. The need for build supports and their structure is defined. Iterations of test builds may be carried out to choose a final orientation and support arrangement. The build arrangement is defined including determining whether segments will be manufactured individually or with several on a common build plate. Evaluations <NUM> are carried out to maximize weight reduction, manufacturing time and cost. For example, voids may be designed into the segments to reduce weight and material use. Test build iterations may be carried out to minimize support structure volume. Any potential for material collapse during build is evaluated.

The process <NUM> includes determining <NUM> whether weight or cost reductions may be made. For example, whether segment width or thickness may be reduced. When the determination is positive, the process <NUM> proceeds to evaluating redesign <NUM> of the stall enhancement features. For example, the size or orientation of grooves or passageways may be changed. The stall enhancement feature design is evaluated to ensure it meets aerodynamic stall margin, efficiency and mechanical requirements. When the redesign is complete, the process <NUM> proceeds through steps <NUM>-<NUM> again. Any number of iterations of steps <NUM>-<NUM> may be carried out to finalize the design. When the determination <NUM> is negative, the design is released <NUM> and manufacturing may begin. Providing an optimal shape and disposition of the grooves <NUM> is simplified through the use of additive manufacturing processes, which lowers manufacturing cost and fabrication complexity. In addition, using additive manufacturing processes enables forming the grooves with the shape that is determined to be optimized, including complex shapes.

Referring to <FIG>, the area of the compressor rotor <NUM> at the compressor section <NUM> is shown removed from the engine <NUM>. The rotor <NUM> includes the blades <NUM> and is disposed within the casing <NUM>. The grooves <NUM> are spaced from one another and disposed around the entire perimeter of the casing <NUM>. The grooves <NUM> are formed in a number of segments <NUM> that abut one another at joints <NUM> and that are formed using the process <NUM>. Together, the segments <NUM> form a ring <NUM> that extends completely around the rotor <NUM> and that is fit into the casing <NUM>. The ring segments <NUM> are individually fabricated using an additive manufacturing process such as DMLS to form complex axial skewed and inclined grooves <NUM> of any shape. As shown in <FIG>, the grooves <NUM> extend into the ring <NUM> which is separate from and fitted into an annular cavity <NUM> in the casing <NUM>. Pitch of individual blades of the rotor <NUM> is the preferred minimum circumferential length of each segment <NUM>.

According to the invention, as illustrated in <FIG>, the grooves <NUM> are an integrally formed part of a manifold <NUM> formed in the ring <NUM>, and specifically in the segments <NUM>. The manifold <NUM> includes an annular channel <NUM> that is embedded in the ring <NUM> and encircles the rotor <NUM>. The channel <NUM> joins with each of the grooves <NUM> to balance their internal pressures to assist in attenuating surge conditions by allowing for additional aft to forward flow communication to improve range to stall. DMI,S is beneficial in forming both the grooves <NUM> and the channel <NUM> during a build and in forming the internal channel <NUM> as an unsupported structure. The diameter of the channel <NUM> may be limited to approximately <NUM> for proper formation, or a non-circular cross section is used for larger cross sections.

As illustrated in <FIG>, the grooves <NUM> and the channel <NUM> join together with the grooves open into the gap <NUM> and the area of flow stream <NUM>. The channel <NUM> is located proximate the downstream ends <NUM> (also shown in <FIG>), and further inhibits the formation of counterflow in the gap <NUM> and thereby extend the range to stall. <FIG> shows the general direction of the flow <NUM> through the grooves <NUM> is from their aft to forward generally in a direction from their downstream end <NUM> to their upstream end <NUM> inhibiting reverse flow in the gap <NUM> and maintaining flow <NUM>.

In a number of embodiments as illustrated in <FIG>, recirculation passages <NUM> are defined in the casing <NUM> and distributed around its perimeter. Each recirculation passage <NUM> has a forward end <NUM> that opens forward of the leading edge of the rotor <NUM> and upstream from the grooves <NUM>. Each recirculation passage <NUM> has a rearward end <NUM> that opens downstream from the rotor <NUM>. The recirculation passages <NUM> further enhance range to stall. In other embodiments, the forward end <NUM> of each recirculation passage <NUM> may open into the manifold <NUM> or into a groove <NUM>. Flow will move from the high pressure rearward end <NUM> to the lower pressure forward end <NUM>. In <FIG>, which does not show the inventive annular channel <NUM>, the segments <NUM> abut one another at the joint <NUM> with retention and sealing features <NUM>. The segment <NUM> interlock with a rabbet <NUM> at the end of one, that mates with a cantilevered segment <NUM> of the other. The rabbet <NUM> is a step-like area at the inward facing corner of the one segment <NUM> and the cantilevered segment <NUM> extends into the step-like area a sufficient distance for retention and sealing. It should be understood that each segment <NUM> will have a rabbet <NUM> at one of its ends and a cantilevered segment at its other end for j oining a number of the segments <NUM> in a ring. The retention and sealing features <NUM> may be formed with their respective segment <NUM> during additive manufacturing. Each segment <NUM> includes a void <NUM> formed on its side opposite the blades <NUM> and facing the casing <NUM>. The voids <NUM> are closed by the casing <NUM>. The void <NUM> is maximized to reduce material use and weight. A wall <NUM> between the void <NUM> and the grooves <NUM>/passages <NUM> is maintained at a minimum thickness for self-support during additive manufacturing.

Claim 1:
A method of manufacturing a rotor system comprising a casing and a rotor, the method comprising:
designing the casing (<NUM>) with stall enhancement features;
fabricating the rotor (<NUM>) with a number of blades (<NUM>), each blade having a tip, the rotor configured to rotate in a flow stream (<NUM>);
constructing the casing to be configured to fit over the rotor so that tips (<NUM>) of the blades are configured to pass proximate the casing when the rotor rotates about an axis (<NUM>);
forming, by additive manufacturing, the casing with a series of grooves (<NUM>) in the casing, wherein the grooves extend into the casing radially outward relative to the axis and are oriented to extend longitudinally at an acute angle (<NUM>) relative to the axis to provide stall enhancement;
optimizing, by analysis, aerodynamic performance of the grooves to avoid stall; and
assembling the rotor in the casing with the grooves extending over at least a portion of the blade tips so that the blade tips are configured to pass across the grooves when the rotor rotates, wherein the method comprises:
forming a section of the casing that contains the grooves as a number of separate segments (<NUM>);
fitting the segments to the casing to encircle the rotor; and
forming, integrally during the additive manufacturing, a manifold (<NUM>) in the section, wherein the manifold includes the grooves and an annular channel (<NUM>) connecting with each of the grooves.