Patent Description:
A turbine engine such as a gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.

The propulsive efficiency of a gas turbine engine depends on many different factors, such as the design of the engine and the resulting performance debits on the fan that propels the engine. As an example, the fan may rotate at a high rate of speed such that air passes over the fan airfoils at transonic or supersonic speeds. The fast-moving air creates flow discontinuities or shocks that result in irreversible propulsive losses. Additionally, physical interaction between the fan and the air causes downstream turbulence and further losses. Although some basic principles behind such losses are understood, identifying and changing appropriate design factors to reduce such losses for a given engine architecture has proven to be a complex and elusive task.

<CIT> discloses an airfoil with a total chord length curve increasing from <NUM>% span to a first peak between <NUM>% and <NUM>% span and then being constant to <NUM>% span.

<CIT> discloses a fan blade airfoil having a relationship between a total chord length and a span position corresponding to a curve having an increasing total chord length from <NUM>% span to a peak, the curve having a decreasing total chord length from the peak to the <NUM>% span position.

Further airfoil configurations having a variable total chord length along span are shown in <CIT>, <CIT> and <CIT>.

In one aspect there is provided an airfoil for a turbine engine according to claim <NUM>.

Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

Alternative engines might include an augmenter section (not shown) among other systems or features. That is, the disclosed airfoils may be used for engine configurations such as, for example, direct fan drives, or two- or three-spool engines with a speed change mechanism coupling the fan with a compressor or a turbine sections.

The exemplary engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis X relative to an engine static structure <NUM> via several bearing systems <NUM>.

The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate via bearing systems <NUM> about the engine central longitudinal axis X which is collinear with their longitudinal axes.

In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). The geared architecture <NUM> may be an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>.

The example gas turbine engine includes the fan <NUM> that comprises in one non-limiting embodiment less than about twenty-six (<NUM>) fan blades. In another non-limiting embodiment, the fan section <NUM> includes less than about twenty (<NUM>) fan blades. Moreover, in one disclosed embodiment the low pressure turbine <NUM> includes no more than about six (<NUM>) turbine rotors schematically indicated at <NUM>. In another non-limiting example embodiment the low pressure turbine <NUM> includes about three (<NUM>) turbine rotors. A ratio between the number of fan blades <NUM> and the number of low pressure turbine rotors is between about <NUM> and about <NUM>. The example low pressure turbine <NUM> provides the driving power to rotate the fan section <NUM> and therefore the relationship between the number of turbine rotors <NUM> in the low pressure turbine <NUM> and the number of blades <NUM> in the fan section <NUM> disclose an example gas turbine engine <NUM> with increased power transfer efficiency.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM>). The flight condition of <NUM> Mach and <NUM>,<NUM> ft (<NUM>,<NUM>), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>. In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>. In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>. In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>. In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>. In another non-limiting embodiment the low fan pressure ratio is from <NUM> to <NUM>. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]<NUM> (where °R = K × <NUM>/<NUM>). The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second. The "low corrected fan tip speed" as disclosed herein according to another non-limiting embodiment is less than about <NUM> ft / second (<NUM>/s).

Referring to <FIG>, the fan blade <NUM> is supported by a fan hub <NUM> that is rotatable about the axis X. Each fan blade <NUM> includes an airfoil <NUM> extending in a radial span direction R from a root <NUM> to a tip <NUM>. A <NUM>% span position corresponds to a section of the airfoil <NUM> at the inner flow path (e.g., a platform), and a <NUM>% span position corresponds to a section of the airfoil <NUM> at the tip <NUM>.

The root <NUM> is received in a correspondingly shaped slot in the fan hub <NUM>. The airfoil <NUM> extends radially outward of the platform, which provides the inner flow path. The platform may be integral with the fan blade or separately secured to the fan hub, for example. A spinner <NUM> is supported relative to the fan hub <NUM> to provide an aerodynamic inner flow path into the fan section <NUM>.

The airfoil <NUM> has an exterior surface <NUM> providing a contour that extends from a leading edge <NUM> aftward in a chord-wise direction H to a trailing edge <NUM>, as shown in <FIG>. Pressure and suction sides <NUM>, <NUM> join one another at the leading and trailing edges <NUM>, <NUM> and are spaced apart from one another in an airfoil thickness direction T. An array of the fan blades <NUM> are positioned about the axis X in a circumferential or tangential direction Y. Any suitable number of fan blades may be used in a given application.

The exterior surface <NUM> of the airfoil <NUM> generates lift based upon its geometry and directs flow along the core flow path C. The fan blade <NUM> may be constructed from a composite material, or an aluminum alloy or titanium alloy, or a combination of one or more of these. Abrasion-resistant coatings or other protective coatings may be applied to the fan blade <NUM>.

One characteristic of fan blade performance relates to the fan blade's total chord relative to a particular span position (R direction). Referring to <FIG>, span positions a schematically illustrated from <NUM>% to <NUM>% in <NUM>% increments. Each section at a given span position is provided by a conical cut that corresponds to the shape of the core flow path, as shown by the large dashed lines. In the case of a fan blade with an integral platform, the <NUM>% span position corresponds to the radially innermost location where the airfoil meets the fillet joining the airfoil to the platform. In the case of a fan blade without an integral platform, the <NUM>% span position corresponds to the radially innermost location where the discrete platform meets the exterior surface of the airfoil. In addition to varying with span, total chord varies between a hot, running condition and a cold, static ("on the bench") condition.

The total chord corresponds to a chord length L extending from the leading edge <NUM> to the trailing edge <NUM> at a given span position, as shown in <FIG>. The chord length L changes along the span of the airfoil <NUM> to achieve a desired aerodynamic performance for the fan blade. The total chord may also be expressed as a ratio to the span distance Rd, where Rd is the radial distance from hub's rotational axis X to the tip of the leading edge <NUM> and where the ratio is L/Rd. Rd as disclosed herein according to one non-limiting embodiment is about <NUM>-<NUM> inches (<NUM> - <NUM> meters). In another non-limiting embodiment Rd is about <NUM>-<NUM> inches (<NUM> - <NUM> meters). In another non-limiting embodiment Rd is about <NUM> - <NUM> inches (<NUM> - <NUM> meters). One example prior art airfoil has an Rd of about <NUM>-<NUM> inches (<NUM> - <NUM> meters).

In one example prior art airfoil, a peak between positive and negative slopes is provided in a range of <NUM>% span to <NUM>% span at which point the curve includes an L/Rd ratio of <NUM> - <NUM>. The total chord L at <NUM>% span is around <NUM> inches (<NUM> - <NUM>).

Example relationships between the total chord length L and the span position (PERCENT AVERAGE SPAN), which is the average of the radial position at the leading and trailing edges <NUM>, <NUM>, are shown in <FIG> for several example fan blades, each represented by a curve. Only one curve in each graph is discussed for simplicity. Each relationship starts with a total chord length at the <NUM>% span position in the range of <NUM>-<NUM> inches (<NUM>-<NUM>). The fan blades include a maximum differential between the maximum and minimum chord lengths along the entire span in the range of <NUM>-<NUM> inches (<NUM>-<NUM>). The curves have an increasing total chord length (positive slope from the <NUM>% span position to a first peak. The first peak occurs in the range of <NUM>-<NUM>% span position, after which the curve either remains generally constant (no slope/no change in total chord length) or has a decreasing total chord length (negative slope). The example curves are at least a third order polynomial with a generally S-shaped curve having an initial positive slope. Some notable points are indicated by an "x" on the curve.

Referring to <FIG>, which discloses an embodiment not falling within the scope of the claims, the peak is provided by a critical point in a range of <NUM>-<NUM>% span position. The critical point has an L/Rd ratio in the range of <NUM> to <NUM>. A negative slope extends from the critical point to a second critical point in a range of <NUM>-<NUM>% span position. The second critical point has an L/Rd ratio in the range of <NUM> to <NUM>. A positive slope extends from the second critical point to the <NUM>% span position, and the total chord length at the <NUM>% span position less than the total chord length at the peak.

Referring to <FIG>, which discloses an embodiment according to the invention, the peak is provided by a critical point in a range of <NUM>-<NUM>% span position. A slope from the critical point to an inflection point is substantially zero. The inflection point in a range of <NUM>-<NUM>% span position. A positive slope extends from the inflection point to the <NUM>% span position. The <NUM>% span position has an L/Rd ratio in the range of <NUM> to <NUM>. The positive slope extending from the inflection point to the <NUM>% span position is generally constant.

Referring to <FIG>, which discloses an embodiment not falling within the scope of the claims, the peak is provided by a critical point in a range of <NUM>-<NUM>% span position. A negative slope extends from the critical point to the <NUM>% span position. The negative slope is generally constant from about a <NUM>% span position to the <NUM>% span position. The critical point has an L/Rd ratio in the range of <NUM> to <NUM>.

The total chord in a hot, running condition along the span of the airfoils <NUM> relate to the contour of the airfoil and provide necessary fan operation in cruise at the lower, preferential speeds enabled by the geared architecture <NUM> in order to enhance aerodynamic functionality and thermal efficiency. As used herein, the hot, running condition is the condition during cruise of the gas turbine engine <NUM>. For example, the total chord in the hot, running condition can be determined in a known manner using numerical analysis, such as finite element analysis.

It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations.

Claim 1:
An airfoil (<NUM>) for a turbine engine (<NUM>) comprising:
pressure and suction sides (<NUM>, <NUM>) extending in a radial direction (R) from a <NUM>% span position at an inner flow path location to a <NUM>% span position at an airfoil tip (<NUM>), wherein the airfoil (<NUM>) has a relationship between a total chord length (L) and a span position corresponding to a curve having an increasing total chord length (L) from the <NUM>% span position to a first peak, the first peak occurs in the range of <NUM>-<NUM>% span position, wherein the total chord length at the <NUM>% span position is in the range of <NUM>-<NUM> inches (<NUM>-<NUM>), the first peak is provided by a critical point in a range of <NUM>-<NUM>% span position, a slope from the critical point to an inflection point is substantially zero, the inflection point is in a range of <NUM>-<NUM>% span position and a positive slope extends from the inflection point to the <NUM>% span position.