Sealing for vane segments

TECHNICAL FIELD

0001The described subject matter relates generally to gas turbine engines and more particularly, to an arrangement for vane segments of gas turbine engines.

BACKGROUND OF THE ART

0002A gas turbine engine includes typically a segmented vane ring configured with outer and inner annular duct walls connected by a plurality of airfoils. The circumferential gaps between the segments usually are sealed by feather seals, but may still be a source of cooling air leakage into the hot gas path and/or hot gas ingestion from the hot gas path, if these circumferential gaps between the segments are not adequately sealed. Thus, there is room for improvement.

0003Accordingly, there is a need to provide an improved vane arrangement.

SUMMARY

0004In one aspect, the described subject matter provides a gas turbine engine comprising a segmented vane array disposed radially between annular outer and inner engine cases and including a segmented annular outer duct wall, a segmented annular inner duct wall, and a plurality of hollow airfoils radially extending between the outer and inner duct walls, a plurality of seals extending between adjacent segments on the inner and outer duct walls to thereby provide a gas path between the inner and outer duct walls, the gas path extending in an axial direction; and an annular seal housing extending axially substantially along an entire axial length of one of the duct walls, the seal housing spaced apart from said duct wall and from an adjacent one of the inner and outer engine cases to thereby provide an annular case cavity between said case and the seal housing and an annular duct cavity between the seal housing and said duct wall, the case cavity in fluid communication with an engine source of pressurized cooling air, the seal housing sealingly mounted within the engine to in use permit said cooling air to provide a pressure differential in the case cavity relative to the duct cavity.

0005In another aspect, the described subject matter provides a gas turbine engine comprising a mid turbine frame (MTF) disposed axially between first and second turbine rotors, the MTF including an annular outer engine case, an annular inner engine case and a plurality of load spokes radially extending between and interconnecting the outer and inner engine cases to transfer loads from the inner engine case to the outer engine case; an annular inter-turbine duct (ITD) disposed radially between the outer and inner engine case of the MTF, the ITD including an annular outer duct wall and annular inner duct wall, thereby defining an annular hot gas path between the outer and inner duct walls for directing hot gases from the first turbine rotor to the second turbine rotor, a plurality of hollow struts radially extending between and interconnecting the outer and inner duct walls, the load spokes radially extending through at least a number of the hollow struts, the ITD being assembled from a plurality of circumferential duct wall segments, each having at least one strut interconnecting a circumferential section of the outer duct wall and a circumferential section of the inner duct wall; a first annular case cavity defined between the annular outer engine case and outer duct wall and a second annular case cavity defined between the annular inner duct wall and inner engine case, the first and second case cavities being in fluid communication with an inner space within the respective hollow struts; and an air sealing system for the first and second case cavities and the hollow struts against cooling air leakage through gaps between the circumferential segments of the ITD, the system including an annular first seal housing disposed in the first annular case cavity and extending axially along a substantial length of the outer duct wall; an annular second seal housing disposed in the second annular case cavity and extending axially along a substantial length of the inner duct wall, the first and second seal housings having a plurality of openings to allow the respective load spokes to radially extend therethrough; and a plurality of insulation tubes aligning with the openings in the respective first and second seal housings, to surround the respective load spokes and to be attached to the first and second seal housings.

0006Further details of these and other aspects of the described subject matter will be apparent from the detailed description and drawings included below.

DESCRIPTION OF THE DRAWINGS

0007Reference is now made to the accompanying drawings depicting aspects of the described subject matter, in which:

0008<figref idrefs="DRAWINGS">FIG. 1</figref> is a schematic cross-sectional view of a turbofan gas turbine engine according to the present description;

0009<figref idrefs="DRAWINGS">FIG. 2</figref> is a partially cut away cross-sectional view of a mid turbine frame having an air sealing system according to one embodiment;

0010<figref idrefs="DRAWINGS">FIG. 3</figref> is a partially exploded perspective view of the mid turbine frame of <figref idrefs="DRAWINGS">FIG. 2</figref>, showing circumferential segments of a segmented inter-turbine duct to be installed in the mid turbine frame;

0011<figref idrefs="DRAWINGS">FIG. 4</figref> is a somewhat schematic cross-sectional view of the mid turbine frame system similar to that of <figref idrefs="DRAWINGS">FIG. 2</figref>;

0012<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates a circled area <b>5</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing the attachment of a flange of an insulation tube with a first annular seal housing of the air scaling system;

0013<figref idrefs="DRAWINGS">FIG. 6</figref> illustrates a circled area <b>6</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing the attachment of the insulation tube with a second annular seal housing of the air sealing system;

0014<figref idrefs="DRAWINGS">FIG. 7</figref> illustrates a circled area <b>7</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing a seal disposed between an outer engine case and the first seal housing of the air sealing system;

0015<figref idrefs="DRAWINGS">FIG. 8</figref> illustrates a circled area <b>8</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing an axial retention of the outer engine case and the first seal housing at an axial rear end of the outer engine case;

0016<figref idrefs="DRAWINGS">FIG. 9</figref> illustrates a circled area <b>9</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing a resilient element included in a seal between the axial front ends of the respective inner duct wall and the second seal housing;

0017<figref idrefs="DRAWINGS">FIG. 10</figref> illustrates a circled area <b>10</b> of <figref idrefs="DRAWINGS">FIG. 2</figref> in an enlarged scale, showing a thermal expansion joint to position an axial rear end of the second seal housing;

0018<figref idrefs="DRAWINGS">FIG. 11</figref> is a schematic top view illustration of a circumferential portion of the segmented inter-turbine duct of <figref idrefs="DRAWINGS">FIG. 3</figref>, showing a position of holes defined in the seal housings (not shown); and

0019<figref idrefs="DRAWINGS">FIG. 12</figref> is a view similar to <figref idrefs="DRAWINGS">FIG. 11</figref> showing another position for holes defined in the seal housings (not shown).

DETAILED DESCRIPTION

0020Referring to <figref idrefs="DRAWINGS">FIG. 1</figref>, a bypass gas turbine engine includes a fan case <b>10</b>, a core casing <b>13</b>, a low pressure spool assembly which includes a fan assembly <b>14</b>, a low pressure compressor assembly <b>16</b> and a low pressure turbine assembly <b>18</b> connected by a shaft <b>12</b> and a high pressure spool assembly which includes a high pressure compressor assembly <b>22</b> and a high pressure turbine assembly <b>24</b> connected by a turbine shaft <b>20</b>. The core casing <b>13</b> surrounds the low and high pressure spool assemblies to define a main fluid path therethrough. In the main fluid path there is provided a combustor <b>26</b> which generates combustion gases to power the high pressure turbine assembly <b>24</b> and the low pressure turbine assembly <b>18</b>. A mid turbine frame (MTF) <b>28</b> is provided between the high pressure turbine assembly <b>24</b> and the low pressure turbine assembly <b>16</b> and includes a bearing housing <b>50</b> to support bearings around the respective shafts <b>20</b> and <b>12</b>. The mid turbine frame <b>28</b> includes an inter-turbine duct (ITD) <b>30</b> to define an annular hot gas path <b>32</b> for directing hot gases from the high pressure turbine assembly <b>24</b> to pass into the low pressure turbine assembly <b>18</b>.

0021Referring to <figref idrefs="DRAWINGS">FIGS. 1-3</figref>, the mid turbine frame <b>28</b> includes an annular outer engine case <b>33</b> which has mounting flanges (not numbered) at both ends for connection to other components which cooperate to provide the core casing <b>13</b> of the engine. The outer engine case <b>33</b> may thus be a part of the core casing <b>13</b>. An annular inner engine case <b>34</b> is coaxially disposed within the outer engine case <b>33</b> and a plurality of (at least three) load spokes <b>36</b> radially extend between the outer engine case <b>33</b> and the inner engine case <b>34</b>. The inner engine case <b>34</b> is coaxially connected to a bearing housing <b>50</b> (see <figref idrefs="DRAWINGS">FIG. 1</figref>) which supports the bearings.

0022The load spokes <b>36</b> are each affixed at an inner end thereof to the inner engine case <b>34</b>, for example by welding. The load spokes <b>36</b> may be either solid or hollow. Each of the load spokes <b>36</b> is connected at an outer end thereof to the outer engine case <b>33</b>, for example by a plurality of fasteners (not shown). Therefore, the load spokes radially extend between and interconnect the outer and inner engine cases <b>33</b>, <b>34</b> to transfer the loads from the bearing housing <b>50</b> and the inner engine case <b>34</b> to the outer engine case <b>33</b>.

0023The annular ITD <b>30</b> is disposed radially between the outer engine case <b>33</b> and the inner engine case <b>34</b> of the MTF <b>28</b>. The ITD <b>30</b> includes an annular outer duct wall <b>38</b> and an annular inner duct wall <b>40</b>, thereby defining the annular hot gas path <b>32</b> between the outer and inner duct walls <b>38</b>, <b>40</b> for directing hot gases to pass therethrough. A plurality of hollow struts <b>42</b> (also referred to as airfoils) which are in an aerodynamic profile, radially extend between and interconnect the outer and inner duct walls <b>38</b> and <b>40</b>. Each of the hollow struts <b>42</b> defines an inner space <b>48</b>. The load spokes <b>36</b> radially extend through the respective hollow struts <b>42</b>, or at least through a number of the hollow struts (when the number of load spokes <b>36</b> is less than the number of hollow struts <b>42</b>).

0024The MTF <b>28</b> therefore defines a first annular cavity <b>44</b> between the annular outer engine case <b>33</b> and the annular outer duct wall <b>38</b> and a second annular cavity <b>46</b> between the annular inner duct wall <b>40</b> and the annular inner engine case <b>34</b>. The annular first and second cavities <b>44</b> and <b>46</b> are in fluid communication with the inner space <b>48</b> in the respective hollow struts <b>42</b>.

0025The ITD <b>30</b> is a segmented configuration which is assembled from a plurality of circumferential duct wall segments <b>52</b>. Each duct wall segment <b>52</b> has at least one strut <b>42</b> which interconnects a circumferential section of the outer duct wall <b>38</b> and a circumferential section of the inner duct wall <b>40</b>. The circumferential section of the respective outer and inner duct walls <b>38</b>, <b>40</b> has circumferentially opposed side edges <b>54</b>. A circumferential gap <b>54</b><i>a </i>is defined between the adjacent side edges <b>54</b> of adjacent duct wall segments <b>52</b> when the ITD <b>30</b> is assembled.

0026A first annular seal housing <b>56</b>, which may be, for example, a monolithic ring of sheet metal, is disposed in the first annular cavity <b>44</b> and extends axially along a substantial length of the outer duct wall <b>38</b> to form a heat shield for protecting the outer engine case <b>33</b> from heat radiating from the hot gas path <b>32</b>. Therefore, the first seal housing <b>56</b> divides the first cavity <b>44</b> into an annular case cavity between the outer engine case <b>33</b> and the first seal housing <b>56</b> and a duct cavity between the first seal housing <b>56</b> and the outer duct wall <b>38</b>. A second annular seal housing <b>58</b>, which may be, for example, a monolithic ring of sheet metal, is disposed in the second annular cavity <b>46</b> and extends axially along a substantial length of the inner duct wall <b>40</b> to form a heat shield for protecting the inner engine case <b>34</b> from heat radiating from the hot gas path <b>32</b>. Therefore, the second seal housing <b>58</b> divides the second cavity <b>46</b> into a case cavity between inner engine case <b>34</b> and the second seal housing <b>58</b> and an annular duct cavity between the second seal housing <b>58</b> and the inner duct wall <b>40</b>. The first and second seal housings have in this example a plurality of openings <b>60</b>, <b>62</b> to allow the respective load spokes <b>36</b> to radially extend therethrough.

0027Optionally, a plurality of insulation tubes <b>64</b>, which may be made for example from sheet metal, are aligned with the openings <b>60</b>, <b>62</b> defined in the respective first and second seal housings <b>56</b>, <b>58</b>. Each of the insulation tubes <b>64</b> surrounds one of the load spokes <b>36</b> and are attached to the first and second seal housings <b>56</b>, <b>58</b>.

0028If the number of load spokes <b>36</b> is less than the number of hollow struts <b>42</b>, the hollow struts <b>42</b> which do not have load spokes <b>36</b> extending therethrough, may be completely covered at the opposed ends thereof by the respective first and second seal housings <b>56</b>, <b>58</b> without corresponding openings <b>60</b>, <b>62</b> at those particular locations. Therefore, there is no insulation tube <b>64</b> to be provided within such hollow spokes. Alternatively, insulation tubes <b>64</b> may be provided in every hollow spoke <b>42</b> aligning with corresponding openings <b>60</b>, <b>62</b> defined in the respective first and second seal housing <b>56</b>, <b>58</b>, regardless of whether or not a load spoke <b>36</b> extends through a particular hollow strut <b>42</b>.

0029The first and second seal housings <b>56</b>, <b>58</b> are installed in the respective first and second cavities <b>44</b>, <b>46</b> with a plurality of annular seals which will be further described hereinafter, in order to form an air sealing system (not numbered) for the first and second cavities <b>44</b> and <b>46</b> and the hollow struts <b>42</b> against cooling air leakages through the gaps <b>54</b><i>a </i>(see <figref idrefs="DRAWINGS">FIG. 3</figref>) between the circumferential duct wall segments <b>52</b> of the ITD <b>30</b>. The gaps <b>54</b><i>a </i>are formed between the adjacent side edges <b>54</b> of the adjacent ITD duct wall segments <b>52</b> in each of the outer and inner duct walls <b>38</b> and <b>40</b>. The cooling air leakage through the gaps between the segments of the ITD <b>30</b> will be further described with reference to <figref idrefs="DRAWINGS">FIG. 4</figref> below. The first and second seal housings <b>56</b>, <b>58</b> in combination with the insulation tubes <b>64</b>, substantially isolate the axial gaps <b>54</b><i>a </i>in the respective outer and inner duct walls <b>38</b>, <b>40</b>, from the first and second cavities <b>44</b>, <b>46</b> and the inner space <b>48</b> of the respective hollow struts.

0030In one embodiment, the outer engine case <b>33</b> may define a cooling air inlet <b>66</b> in fluid communication through an external passage (not shown) with a pressurized cooling air source. Therefore, cooling air may be introduced from inlet <b>66</b> to enter the second cavity <b>46</b> through respective annulus <b>63</b> between the insulation tube <b>64</b> and the load spokes <b>36</b>. The sealing system formed by the first and second seal housings <b>56</b>, <b>58</b> with insulation tubes <b>64</b>, maintains the first and second cavities <b>44</b>, <b>46</b> substantially pressurized with the cooling air introduced from the inlet <b>66</b>. Hollow cross arrows <b>69</b> indicate the pressurized state in the first and second cavities <b>44</b> and <b>46</b>.

0031Alternative to the arrangement of introducing cooling air into the first cavity <b>44</b>, the inlet <b>66</b> defined in the outer engine case <b>33</b> may be positioned to align with one or more load spokes <b>36</b> which are hollow and define a radial passage <b>67</b> such that cooling air may be introduced radially and inwardly through the radial passage <b>67</b> into the inner engine case <b>34</b> which is in fluid communication with the second cavity <b>46</b>. Therefore, the cooling air in the second cavity <b>46</b> enters the first cavity <b>44</b> through the respective annulus <b>63</b> between the insulation tube <b>64</b> and the load spoke <b>36</b>. Similarly, the first and second cavities <b>44</b> and <b>46</b> are pressurized with the cooling air.

0032Optionally, the first and second seal housings <b>56</b>, <b>58</b> may be spaced apart from the respective outer and inner duct walls <b>38</b>, <b>40</b> and a plurality of holes <b>68</b> (see <figref idrefs="DRAWINGS">FIG. 11</figref>) may be provided in the respective first and second seal housings <b>56</b>, <b>58</b> such that air streams under the air pressure indicated by arrows <b>69</b>, eject from the holes <b>68</b>, resulting in impingement cooling on the respective outer and inner duct walls <b>38</b>, <b>40</b>.

0033Optionally, feather seals <b>70</b> may be provided on the respective outer and inner duct walls <b>56</b>, <b>58</b> to cover the gaps <b>54</b><i>a </i>between the circumferential duct wall segments <b>52</b> of the ITD <b>30</b>. Some of the holes <b>68</b> defined in the respective first and second seal housings <b>56</b>, <b>58</b> may be positioned to align with the respective gaps <b>54</b><i>a </i>between the circumferential duct wall segments <b>52</b> of the ITD <b>30</b> for directing cooling air streams directly upon the feather seals <b>70</b> against the respective outer and inner duct walls <b>38</b>, <b>40</b> in order to avoid hot gas ingestion from the gaps <b>54</b><i>a. </i>

0034The feather seals <b>70</b> which cover the individual gaps <b>54</b><i>a </i>between the circumferential duct wall segments <b>52</b> in either of the outer and inner duct walls <b>38</b>, <b>40</b> of the ITD <b>30</b>, may be formed as a single annular seal, for example by a plurality of feather components circumferentially extending between and interconnecting adjacent feather seals <b>70</b>.

0035As shown in <figref idrefs="DRAWINGS">FIG. 4</figref>, arrows <b>72</b> indicate the air leakage from the first and second cavities <b>44</b>, <b>46</b> through the gaps <b>54</b><i>a </i>(see <figref idrefs="DRAWINGS">FIGS. 3</figref>, <b>11</b> and <b>12</b>) between the segments of the ITD <b>30</b>. The feather seals <b>70</b> may be placed on the respective outer and inner duct walls <b>38</b>, <b>40</b>, to cover the respective gaps <b>54</b><i>a </i>(see <figref idrefs="DRAWINGS">FIGS. 3</figref>, <b>11</b> and <b>12</b>) in order to prevent or minimize air leakage <b>72</b>, which is also shown in <figref idrefs="DRAWINGS">FIGS. 11 and 12</figref>.

0036Referring to <figref idrefs="DRAWINGS">FIGS. 1-2</figref> and <b>7</b>-<b>8</b>, The annular outer duct wall <b>38</b> may include front and rear hooks <b>74</b> and <b>76</b> at opposed axial ends thereof for connection with the annular outer engine case <b>33</b>. Therefore, the first cavity <b>44</b> is also defined axially between the front and rear hooks <b>74</b> and <b>76</b>. The annular front and rear hooks <b>74</b>, <b>76</b> may be positioned as far as possible to the respective front and rear axial ends of the annular outer duct wall <b>38</b> in order to allow the first cavity <b>44</b> to extend along the substantial axial length of the outer duct wall <b>38</b>. According to one embodiment, the annular outer engine case <b>33</b> may be integrated with a rear housing <b>78</b> of the high pressure turbine assembly <b>24</b> in order to allow the front hook <b>74</b> of the outer duct wall <b>38</b> to be positioned further upstream.

0037An annular front end <b>80</b> (see <figref idrefs="DRAWINGS">FIG. 7</figref>) of the annular first seal housing <b>56</b> is positioned adjacent a radial surface (not numbered) of the outer engine case <b>33</b> at the axial front end thereof. A seal device, such as a “W” seal <b>82</b> may be provided between the radial surface of the outer engine case <b>33</b> and the axial front end <b>80</b> of the first seal housing <b>56</b>. The rear book <b>76</b> of the annular outer duct wall <b>38</b> as shown in <figref idrefs="DRAWINGS">FIG. 8</figref>, in combination with a low turbine module (not shown) of the low pressure turbine assembly <b>18</b> (see <figref idrefs="DRAWINGS">FIG. 1</figref>) provides an axial retention of the ITD <b>30</b> and the sealing of the first cavity <b>44</b>.

0038Referring to <figref idrefs="DRAWINGS">FIGS. 1-2</figref> and <b>9</b>, a seal device such as a crush seal <b>84</b> which includes a resilient component, is provided between an axial front end <b>86</b> of the second seal housing <b>58</b> and an axial front end (not numbered) of the annular inner duct wall <b>40</b> to allow an axial expansion of the inner duct wall <b>40</b> with respect to the second seal housing <b>58</b>. The axial front end <b>86</b> of the second seal housing <b>58</b> is also sealingly connected with an axial front end (not numbered) of the inner engine case <b>34</b>, thereby sealing the second cavity <b>46</b>.

0039Referring to <figref idrefs="DRAWINGS">FIGS. 1-2</figref> and <b>10</b>, an annular seal <b>88</b> which may include a thermal expansion joint, is positioned between an axial rear end <b>90</b> of the second seal housing <b>58</b> and an axial rear end (not numbered) of the annular inner duct wall <b>40</b>, in order to allow radial expansion of the inner duct wall <b>40</b> with respect to the second seal housing <b>58</b>. The axial rear end <b>90</b> of the second seal housing <b>58</b> is also sealingly connected with an axial rear end (not numbered) of the inner engine case <b>34</b>, thereby sealing the second cavity <b>46</b>.

0040Referring to <figref idrefs="DRAWINGS">FIGS. 2 and 5</figref>, each of the insulation tubes <b>64</b> includes a flange <b>92</b> integrally and outwardly extending from a radial outer end (not numbered) of the insulation tube <b>64</b>. The flange <b>92</b> of the insulation tube <b>64</b> overlaps a peripheral edge (not numbered) of the opening <b>60</b> which receives the insulation tube <b>64</b>, defined in the first seal housing <b>56</b>. The overlapped flange <b>92</b> of the insulation tube <b>64</b> is secured to the first seal housing <b>56</b> by a fastener <b>94</b> which, for example is a pin-typical spring washer as shown in <figref idrefs="DRAWINGS">FIG. 5</figref>.

0041Referring to <figref idrefs="DRAWINGS">FIGS. 2 and 6</figref>, the insulation tube <b>64</b> includes a radial inner end <b>96</b> which is inserted into a corresponding opening <b>62</b> defined in the second seal housing <b>58</b>. An annular seal <b>98</b> such as a compliance seal of any suitable type may be provided to make the seal between the radial inner end <b>96</b> of the insulation tube <b>64</b> and the second seal housing <b>58</b>.

0042The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departure from the scope of the present description. For example, the approach may be applied to any suitable vane configuration in the engine. The described subject matter may be applied to any suitable gas turbine engines type. Any suitable sealing arrangement may be employed. Still other modifications which fall within the scope of the present description will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.