Fuel nozzle having aerodynamically shaped helical turning vanes

A fuel nozzle for a gas turbine engine is disclosed which includes a nozzle body having a longitudinal axis, an elongated annular air passage defined within the nozzle body, and a plurality of circumferentially spaced apart axially extending swirl vanes disposed within the annular air passage, wherein each swirl vane has multiple joined leads and a variable thickness along the axial extent thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention is directed to fuel nozzles for gas turbine engines, and more particularly, to an air swirler for fuel nozzles having aerodynamically shaped helical turning vanes for efficiently turning the air flow passing through the swirler while minimizing the risk of separation.

2. Description of Related Art

In a fuel nozzle for a gas turbine engine, compressor discharge air is used to atomize liquid fuel. More particularly, the air provides a mechanism to breakup a fuel sheet into a finely dispersed spray that is introduced into the combustion chamber of an engine. Quite often the air is directed through a duct that serves to turn or impart swirl to the air. This swirling air flow acts to stabilize the combustion reaction.

There are many ways to develop swirl in a fuel nozzle. Historically, helical vanes were used because of their ability to effectively turn the air flow. These vanes generated acceptable air flow characteristics for many engine applications. However, when a higher swirl factor was desired for certain engine application, there was a tendency for the air flow to separate from the helical vanes. This was generally associated with a reduction in the effectiveness of the geometric flow area of the nozzle.

To mitigate separation, vanes were designed with multiple joined leads that could aid in turning the air flow. These vanes were typically associated with a higher effectiveness of the geometric flow area of the nozzle. Such improvements resulted in a more effective use of the air velocity for atomization.

Air swirlers have also been developed that employ aerodynamic turning vanes, as described in U.S. Pat. No. 6,460,344 to Steinthorsson et al., the disclosure of which is incorporated herein by reference in its entirety. These airfoil shaped turning vanes are effective to impart swirl to the atomizing air flow. However, they provide a substantially uniform velocity profile at the nozzle.

It would be beneficial to provide an air swirler for a fuel nozzle having turning vanes that incorporate the beneficial aspects of multiple joined helical leads and an aerodynamic shape. In so doing, air flow through the swirler could be efficiently turned while the risk of separation would be minimized.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful fuel nozzle for a gas turbine engine. The novel fuel nozzle includes a nozzle body having a longitudinal axis, an elongated annular air passage defined within the nozzle body, and a plurality of circumferentially spaced apart axially extending swirl vanes disposed within the annular air passage, each swirl vane having multiple joined leads and a variable thickness along the axial extent thereof.

Each swirl vane includes an upstream vane section having a leading edge surface and a downstream vane section having a trailing edge surface. The leading edge surface of the upstream vane section of each vane is disposed at an angle relative to the longitudinal axis of the nozzle body. The angle of the leading edge surface of each vane defines an initial pitch along the axial extent of the upstream vane section. The pitch of the downstream vane section of each vane varies from the pitch of the upstream vane section of each vane, forming a vane having multiple joined leads.

In one embodiment of the subject invention, the pitch of the downstream vane section varies continuously along substantially the entire axial extent of the downstream vane section. In another embodiment of the subject invention, the pitch of the downstream vane section remains constant for a certain axial vane segment or for substantially the entire axial length of the downstream vane section. In yet another embodiment of the subject invention, two or more contiguous axial vane segments of the downstream vane section have different but constant pitches, such that the downstream vane section has multiple joined leads along the axial extent thereof. In each instance, each vane includes a transitional vane section that smoothly blends the upstream vane section into the downstream vane section.

Each vane has a maximum normal thickness associated with the transitional vane section. In one embodiment of the subject invention, the normal vane thickness changes or otherwise decreases from the transitional vane section to the trailing edge surface of the vane. Preferably, the normal vane thickness also changes or otherwise decreases from the transitional vane section to the leading edge surface of the vane. However, it is envisioned that the lead-in vane section that extends from the leading edge to the transitional vane section could have a constant vane thickness. It is also envisioned that any axial vane segment along the axial extent of the vane could have a constant vane thickness. In any case, the resulting airfoil shaped helical vanes of the subject invention function to effectively impart a high degree of swirl while minimizing the risk of separation.

The subject invention is also directed to a new and useful air swirler for a fuel nozzle. The novel air swirler includes a central hub defining a longitudinal axis, and a plurality of circumferentially spaced apart axially extending aerodynamically shaped swirl vanes extending radially outwardly from the hub, wherein each swirl vane has multiple joined leads along the axial extent thereof.

These and other features of the fuel nozzle and air swirler of the subject invention will become more readily apparent to those having ordinary skill in the art form the following detailed description of the invention taken in conjunction with the several drawings figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals identify or otherwise refer to similar structural features or elements of the various embodiments of the subject invention, there is illustrated inFIG. 1a fuel injector for a gas turbine engine. Fuel injector10includes an elongated feed arm12having an inlet portion14for receiving fuel, a mounting flange16for securing the fuel injector10to the casing of a gas turbine engine, and a nozzle assembly20at the lower end of the feed arm12for issuing atomized fuel into the combustion chamber of a gas turbine engine.

Referring toFIG. 2, the nozzle assembly20of fuel injector10includes, among other things, an on-axis fuel circuit30and an outer air swirler40located radially outward of the fuel circuit30. The axial fuel circuit30issues fuel from an exit orifice32. The air swirler40is bounded by an outer air cap42and an inner hub44. Air swirler40includes a plurality of circumferentially disposed, equidistantly spaced apart turning vanes50forming a plurality of air flow channels48. The turning vanes50are adapted and configured to impart swirl to the airflow, which is directed toward fuel issuing from exit orifice32. The swirling air impacting the fuel acts to stabilize the combustion reaction and enhance fuel atomization. The number of spaced apart turning vanes50in the air swirler40can vary depending upon the nozzle and/or engine application. It is envisioned that air swirler40can include between three and fifteen turning vanes, but may have more depending upon the application.

As best seen inFIG. 3, each turning vane50in air swirler40has an aerodynamic or airfoil shaped cross-sectional profile. That is, the thickness or width of each turning vane50changes over the axial length of the vane. Consequently, each turning vane50has a suction side or low pressure side PLand an opposed high pressure side PH. The relative pressure differential on the opposed vane surfaces functions to advantageously keep the swirling airflow across the swirler attached to the vane walls. As a result, air flows efficiently through the air swirler40without separating from the vanes.

Referring now toFIG. 4, there is illustrated an exemplary air swirler40constructed in accordance with the subject invention. This exemplary air swirler has four airfoil shaped turning vanes50. Each turning vane50in air swirler40includes three axially extending vane sections ranging from the leading edge52of the vane to the trailing edge54of the vane. These three vane sections include an upstream vane section56that typically has little or no helical pitch associated therewith, a downstream vane section58that has a varying helical pitch associated therewith and a transitional vane section60located between the upstream and downstream vane sections56and58that serves to smoothly blend the upstream and downstream vane sections together to form a turning vane having multiple joined leads.

With regard to the varying pitch of the downstream vane section58, in one embodiment of the subject invention, the pitch varies continuously along substantially the entire axial extent of the downstream vane section58. In another embodiment of the subject invention, the pitch of the downstream vane section58differs from the pitch of the upstream vane section56and it is held constant along substantially the entire axial extent of the downstream vane section58. In yet another embodiment of the subject invention, two or more contiguous axial segments of the downstream vane section58have different but constant pitches, such that the downstream vane section58has multiple joined leads along the axial extent thereof.

The transitional vane section60is defined by a Fillet Factor FF, which is a dimensionless value (e.g., 1.2) related to vane thickness and selected to blend the edges of vane sections56and58together as smoothly as possible. The leading edge52of each vane50is preferably radiused (e.g., 0.012 in.) and may be oriented at an angle with respect to the longitudinal axis of the swirler40. The angle of the leading edge52of each vane50(i.e., the inlet vane angle) essentially defines the pitch of the upstream vane section56. Preferably, the angle of the leading edge52is oriented to accommodate any directional bias of the air flow into the swirler40. For example, if the air flowing into the air swirler40has a 5° bias, the angle of the leading edge52of each vane50would be set at 5°, and thus the upstream vane section56would have a 5° lead associated therewith. Typically, the angle at the leading edge of the vane is 0° and in such cases the upstream vane section56has no helical pitch associated therewith. In an embodiment of the subject invention, the base55of each vane50at the inner hub44is radiused (e.g., 0.1 in.).

As described above, each turning vane50has a downstream helically pitched vane section58. It is envisioned that the lead direction of the helically pitched vane section can be left-handed or right-handed depending upon the overall nozzle design. For example, the pitch direction of the vanes50can be the same as or opposite to the pitch direction of an inner air swirler, another outer air swirler or a fuel swirler associated with the on-axis fuel circuit30shown inFIG. 2.

As described above, in one embodiment of the subject invention, the pitch of the downstream vane section58varies continuously along the axial extent of the turning vane50. In such a case, the lead or helical pitch of each vane50in swirler40at any given point x along the axial extent of the vane, referred to as the Instantaneous Lead ρx, is defined by the following equation:

ρx=Ømean⁢πtan⁡(βx*)
where Ømeanis the mean or mid-span diameter of the vane (e.g., 0.30 in.) and is defined with respect to the major and minor diameters of the swirler by the equation:

Ømean=Ømajor+Øminor2
and β*xis the Instantaneous Vane Angle defined by the equation:
β*x=β*TE−(β*TE−β*i)(1−Δ)LF
where: β*TEis the Trailing Edge Vane Angle at the Mid-Span (e.g., 45°); β*iis the Leading Edge to Turning Blend Angle at Mid-Span (e.g., 10°); Δ is the Vane Length Ratio, which is a dimensionless quantity defined below; and LF is the Aerodynamic Loading Factor.

The Vane Length Ratio Δ, which is also used below to define the Instantaneous Vane Thickness txat any given point along the axial extent of the vane, is defined by the following equation:

Δ=L-xL-l
where: L is the Total Length of the Vane (e.g., 0.4 in.); x is the Axial Vane Position along the axial extent of the vane; and l is the Aerodynamic Lead-In.

The Aerodynamic Lead-In l, which is the lengthwise extent of the vane from the leading edge of the vane to a point at which the vane helix changes value from the lead-in section, is defined by the following equation:
l=γ(tmax−2rLE)
Where: γ is the Aerodynamic Lead-In Factor (e.g., 2.3); tmaxis the Maximum Normal Vane Thickness (e.g., 0.06 in.); and rLEis the Leading Edge Radius (e.g., 0.012 in.). A smaller value for the Aerodynamic Lead-In Factor results in a shorter upstream lead-in section before turning starts, whereas a larger value results in a longer upstream lead-in section with a shorter downstream turning section.

Those skilled in the art will readily appreciate that the greater the Aerodynamic Loading Factor LF the greater the amount of turning that will occur toward the lead-in section of the vane. Conversely, the lesser the Loading Factor LF the greater will be the amount of turning that occurs at the trailing edge of the vane. The risk associated with defining a higher Loading Factor is that the air flow can separate from the suction surface of the vane. The risk associated with defining a lower Loading Factor is that there can be inconsistent turning of the air flow through the swirler with the exit air greatly deviating from the exit vane angle. A proper balance must therefore be achieved to ensure that the airflow remains attached to the vane walls throughout the extent of the swirl passage48.

As mentioned above, each turning vane50has an aerodynamic or airfoil shape. Thus, the width or thickness of each turning vane50varies along its axis. In one embodiment of the subject invention, the thickness and pitch varies continuously along the axial extent of the downstream vane section58. In this regard, the thickness of a vane50at any given axial position x is expressed as the Instantaneous Normal Vane Thickness txwhich is defined by the following equation:
tx=tmax−(tmax−tTE)(Δ)TF
where: tmaxis the Maximum Normal Vane Thickness (e.g., 0.08 in.); tTEis the Trailing Edge Vane Thickness (e.g., 0.025 in.); and TF is the Thickness Factor, which is a dimensionless quantity (e.g., 1.6) that controls the distribution of the change in the thickness of the turning vane in the transition from the leading edge of the vane to the trailing edge of the vane.

The Maximum Normal Vane Thickness tmaxarises in the transitional vane section60between the upstream vane section56and the downstream vane section58. The Trailing Edge Vane Thickness tTEis the thickness or width of the vane at the trailing edge54. It is envisioned that the trailing edge54of each vane50can be formed with or without a radius. Furthermore, the trailing edge vane thickness tTEcan be minimized to an acceptable balance between manufacturability and a tendency to shed downstream vortices, which can negatively impact the atomization process.

As described above, Thickness Factor TF controls the change in the thickness of each vane50. Accordingly, a greater Thickness Factor will delay the thickness change along the axial extent of the downstream vane section58to the trailing edge54. In contrast, a lesser Thickness Factor will rapidly change the width of the vane from a maximum thickness to a minimum thickness closer to the transitional vane section60.

As described above, in one embodiment of the subject invention, the pitch of the downstream vane section58differs from the pitch of the upstream vane section56and is held constant along substantially the entire axial extent of the downstream vane section58. In another embodiment of the subject invention, two or more contiguous axial vane segments of the downstream vane section58have different but constant pitches, such that the downstream vane section58has multiple joined leads along the axial extent thereof.

In such cases, the Instantaneous Vane Angle over a certain axial vane segment extending from an initial axial location to a final axial location is defined by the equation:
β*x=β*f−(β*f−β*i)(1−Δl)LF
where: Δlis the Vane Length Ratio for that axial vane segment and is defined by the following equation:

Δl=lf-lxlf-li
Furthermore, the Instantaneous Normal Vane Thickness txover a certain axial vane segment extending from an initial axial location to a final axial location is defined by the following equation:
tx=ti−(ti−tf)(Δi)TF
where: Δiis the Vane Thickness Ratio for that axial vane segment and is defined by the following equation:

In view of each of the preceding equations, those skilled in the art will readily appreciate that the unique aerodynamic vane geometry described herein is highly variable. That is, for any given axial vane segment along the length of the turning vane, vane thickness could vary while pitch remains constant, vane thickness could remain constant while pitch varies, or both vane thickness and pitch could vary.

It is envisioned and well within the scope of the subject disclosure that the airfoil geometry of the helical turning vanes50of air swirler40can be defined using the National Advisory Committee for Aeronautics (NACA) 4-digit definitions, 5-digit definitions, or the modified 4-/5-digit definitions. In each case, the airfoil shape is generated using analytical equations that describe the camber (curvature) of the mean line (geometric centerline) of the air foil section, as well as the thickness or width distribution along the length of the airfoil. Once the coordinates of the airfoil are defined, they would be converted to helical definitions to form the turning section of the vane. In this regard, a diameter would be selected and the lead would then be found at that diameter. The thickness would then be added to either side of the camber line, and the resulting values would be projected to the major and minor diameters of the vane.

Those skilled in the art will readily appreciate that over the height of each vane in the air swirler of the subject invention, the chordal axis of the vane and the turning angle associated therewith continuously changes. Furthermore, as a result of the novel vane geometry described herein, the angular velocity profile of the air flow through the swirler increases over the height of the vanes for enhanced atomization. Thus, the air velocity at the exit of the swirler is not uniform.

While the subject invention has been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications may be made thereto without departing from the spirit and/or scope of the subject disclosure.

For example, while the air swirler of the subject invention has been shown and described with respect to a particular fuel nozzle design, those skilled in the art will readily appreciated that the novel air swirler of the subject invention can be employed with a variety of different types of atomizing fuel nozzles. These could include airblast fuel nozzles, dual or multiple air blast nozzles, air-assisted fuel nozzles, simplex or single orifice fuel nozzles, duplex or double orifice fuel nozzles, or piloted airblast fuel nozzles where the air swirler could be used for main fuel atomization, pilot fuel atomization or both. It is also envisioned that the aerodynamically shaped helical turning vanes disclosed herein could be used to efficiently turn fluid or gas passing through a fuel swirler or injector.