BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial longitudinal sectional view of a gas turbine engine.
FIG. 2 is a partial longitudinal sectional view of a high pressure compressor of the engine of FIG. 1.
FIG. 3 is a view of a compressor vane of the engine of FIG. 1.
FIGS. 4A-4D are sectional views of the vane of FIG. 3.
FIG. 5 is an aft view of the vane of FIG. 3.
FIG. 6 is a side view of the vane of FIG. 3.
FIG. 7 is an aft partial view of a stator ring.
FIG. 8 is an isometric view of a reengineered vane airfoil and a baseline rear airfoil superposed.
FIG. 9 is a profiled view of the superposed airfoils of FIG. 8.
FIG. 10 is a top (radially inward) view of the superposed airfoils of FIG. 8.
FIG. 11 is a front view of the superposed airfoils of FIG. 8.
FIG. 12 is a graph of total pressure loss against span for the baseline and reengineered airfoils of FIG. 8.
Like reference numbers and designations in the various drawings indicate like elements.
DETAILED DESCRIPTION
FIG. 1 shows a gas turbine engine 20 having a high speed/pressure compressor (HPC) section 22 receiving air moving along a core flowpath 500 from a low speed/pressure compressor (LPC) section 26 and delivering the air to a combustor section 28. High and low speed/pressure turbine sections (HPT, LPT) 30 and 32 are downstream of the combustor along the core flowpath. The engine may further include a fan 34 (optionally transmission-driven) and an augmentor (not shown) among other systems or features.
The engine 20 includes low and high speed shafts 40 and 42 mounted for rotation about an engine central longitudinal axis or centerline 502 relative to an engine stationary structure via several bearing systems (not shown). Each shaft may be an assembly, either fully or partially integrated (e.g., via welding). The low speed shaft carries LPC and LPT rotors and their blades to form a low speed spool. The high speed shaft carries the HPC and HPT rotors and their blades to form a high speed spool.
FIG. 1 shows an HPC rotor stack 44 mounted to the high speed shaft 28. The exemplary rotor stack 44 includes, from fore to aft and upstream to downstream, a plurality of blade disks 46A, 46B, 46C, and 46D (FIG. 2, further downstream stages not shown) each carrying an associated stage of blades 48. Between each pair of adjacent blade stages, an associated stage of vanes 50A, 50B, 50C, and 50D (downstream stages not shown) is located along the core flowpath 500. The vanes have airfoils 52 extending radially inward from roots 54 at outboard platforms 56 formed as portions of a core flowpath outer wall 58. The airfoils 52 extend to inboard airfoil tips 60 adjacent interdisk spacers 62 forming portions of a core flowpath inboard wall 64. Exemplary spacers may be as disclosed in the of the Suciu et al. '863 application. The exemplary spacers are of a generally concave-outward arcuate longitudinal cross-section in a static condition but may tend to straighten due to centrifugal loading.
The vane airfoils 52 extend from a leading edge 70 to a trailing edge 72. The apparent leading edge concavity of FIG. 2 reflects a bow and sweep profile/distribution discussed below. Swept blade airfoils are generally discussed in U.S. Pat. No. 5,642,985 of Spear et al. (the '985 patent). Blade airfoils are disclosed in U.S. Pat. No. 5,088,892 of Weingold et al. (the '892 patent). The disclosures of the '985 and '892 patents are incorporated by reference herein as if set forth at length.
FIG. 3 shows a vane-carrying shroud segment 280. The exemplary segment 280 includes an outboard shroud portion 282 extending between fore and aft longitudinal ends 284 and 286 and first and second longitudinally-extending circumferential ends 288 and 290. The longitudinal ends may bear engagement features (e.g., lips) for interfitting and sealing with adjacent case components. The circumferential ends may include features for sealing with adjacent ends of the adjacent shroud segments 280 of the subject stage (e.g., feather seal grooves). The exemplary shroud segment is a singlet, with a single vane airfoil 52 extending radially inward therefrom. The airfoil may be unitarily formed with the shroud such as by casting or may be integrated therewith such as by a stablug connection. Doublets and other multi-airfoil segments are possible as are continuous ring shrouds (such as unitarily cast members).
FIGS. 4A-4D show the pressure and suction sides 92 and 94 of the airfoil extending between the leading and trailing edges 70 and 72. FIGS. 4A-4D further show a direction of rotation 504 of the rotor relative to the stator. FIGS. 4A-4D also show a local chord line 100 having a centerpoint 102. FIGS. 5 and 6 also show a local radial line 506 intersecting the chord centerpoint 102 at the airfoil outboard root. FIGS. 5 and 6 also show a line 508 formed by the centerpoints 102 along the entire root-to-tip span of the airfoil. The line 508 is locally off-radial by an angle θ whose transverse and longitudinal projections are respectively marked at the root in FIGS. 5 and 6. FIG. 6 also shows a local radial line 510 intersecting the airfoil leading edge at the root and a line 512 intersecting the leading edge at the root and tip.
FIG. 6 further shows an abrasive coating layer 200 on the spacer 62 to preferentially wear by contact an abradable coating layer 202 on the stator airfoil tips. An exemplary layer 200 may be formed of cubic boron nitride (CBN) having a thickness of about 8 mil (0.2 mm). In broader exemplary thicknesses 0.1-0.3 mm. An exemplary layer 202 may be formed of zirconium oxide (ZrO) having a thickness of about 20 mil (0.5 mm). A broader exemplary thickness is 0.3-1.0 mm.
FIG. 7 shows a portion of a continuous stator ring 300 having a continuous one-piece outer shroud 302 from which the airfoils extend inward.
The foregoing principles may be applied in the reengineering of an existing engine configuration or in an original engineering process. Various engineering techniques may be utilized. These may include simulations and actual hardware testing. The simulations/testing may be performed at static conditions and one or more non-zero speed conditions. The non-zero speed conditions may include one or both of steady-state operation and transient conditions (e.g., accelerations, decelerations, and combinations thereof). The simulation/tests may be performed iteratively, varying parameters such as spacer thickness, spacer curvature or other shape parameters, vane sweep, dihedral, and bow profiles or vane tip curvature or other shape parameters, and static tip-to-spacer separation (which may include varying specific positions for the tip and the spacer). The results of the reengineering may provide the reengineered configuration with one or more differences relative to the initial/baseline configuration. The baseline configuration may have featured similar spacers or different spacers (e.g., frustoconical spacers). The reengineered configuration may involve one or more of eliminating outboard interdisk cavities, eliminating inboard blade platforms and seals (including elimination of sealing teeth on one or more of the spacers), providing the area rule effect, and the like.
For one exemplary reengineering, FIG. 8 shows the superposition of a reengineered vane airfoil 400 and a baseline vane airfoil 400′. The airfoil 400 has an outboard end 402 and an inboard end 404. The airfoil 400′ has an outboard end 402′ and an inboard end 404′. In an exemplary reengineering, the inboard end 404 is a free end whereas the outboard ends 402 and 402′ and inboard end 404′ are merely at junctions of the airfoil with the adjacent ID or OD platform or shroud. The airfoils 400 and 400′ have respective leading edges 406 and 406′ and trailing edges 408 and 408′.
The addition of tip-localized leading edge forward sweep and/or negative dihedral in the reengineered airfoil relative to the baseline airfoil may improve overall performance. Specifically, it may decrease the impact of the tip-to-spacer clearance on performance. Losses may be reduced. The radial distribution of stator vane exit velocity and stagnation pressure may be improved, maintaining higher momentum near the tip region. The effect on axial momentum may be particularly large when the vane stage is throttled toward a stall condition and the angle of incidence to the next downstream blade row is reduced.
FIG. 9 shows a leading edge tip region 420 of the airfoil 400 having a terminal sweep angle α. With the airfoil treated as a spanwise series of stacked airfoil sections, sweep is characterized by displacements of the sections parallel to their chord lines. Thus, the view of FIG. 9 is essentially normal to the chord line at the tip 404. The exemplary baseline airfoil is essentially unswept in the corresponding region 420′. The exemplary regions 420 and 420′ depart along a region of radial span S1. The transition to the sweep α may be gradual. In the exemplary reengineering, however, the sweep is essentially α over a span S2. Exemplary S1 is 20-40% of total span and S2 is 10-20% of total span. Exemplary α is 25-45°, more narrowly 30-40°. Along a majority of the remainder of the span, more narrowly, a majority of the total span, the airfoil may extend substantially radially (e.g., within 10°, more narrowly 5° of radial).
There may be dihedral departures along the same region 420. FIG. 11 shows a terminal dihedral β. Dihedral is characterized by displacement of the airfoil sections normal to their chord lines. Dihedral may be measured at the center of gravity of the airfoil section or as the intersection of datum parallel to the airfoil stacking line and suction side surface. For reference, positive dihedral decreases the angle between the suction side surface and the adjacent surface (e.g., outer surface of the spacer or outer surface of an adjacent platform). Exemplary β are 30-60°, more narrowly 35-55°. In a computational fluid dynamics (CFD) analysis, the exemplary forward sweep and negative dihedral have the effect of pulling more airflow to the tip region and strengthening the flow profiles at the tip. This reduces turbulent kinetic energy resulting in reduced pressure loss and increased flow. FIG. 12 plots pressure loss 450 of the airfoil 400 and 450′ of the airfoil 400′. Significant reduction in loss is observed in a region from approximately 4-30% of span. Below that, there may be a local increase in loss due to increased flow. However, the effect of this local loss increase is offset by the loss decrease elsewhere (e.g., demonstrated when this pressure loss is integrated across the airfoil total span to create a performance/loss parameter). Net leakage flow through the vane clearance gap may also be reduced due to the dihedral increasing non-radial flow.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when applied as a reengineering of an existing engine configuration, details of the existing configuration may influence details of any particular implementation. Among other factors, the size of the engine will influence the dimensions associated with any implementation relative to such engine. Accordingly, other embodiments are within the scope of the following claims.
Patent Application
20080063520
