Patent Application
20100266385
This application discloses articles having surfaces for achieving improved aerodynamic performance and particularly describes a turbomachinery airfoil that resists fluid separation.
Gas turbine engines employ compressors and turbines each having having arrays of blades and vanes. Each blade or vane includes an airfoil having a suction surface and a pressure surface. During engine operation, a stream of working medium fluid flows over the airfoil surfaces. Under some conditions the airfoil surfaces, especially the suction surface, are susceptible to undesirable fluid separation that compromises the aerodynamic performance of the airfoil. Turbine airfoils that are highly loaded and operate at low Reynolds Number are particularly susceptible to fluid separation. Such highly loaded airfoils are attractive because their use allows an engine designer to reduce airfoil count and thus reduce the weight, cost and complexity of the engine. It is, therefore, desirable to impart separation resistance to such airfoils so that they can be employed effectively.
One known technique for combating separation is to use vortex generator jets (VGJ's). An airfoil designed for VGJ operation includes an internal plenum and a series of spanwisely distributed passages extending from the plenum to the suction surface. During engine operation, pressurized fluid flows into the plenum and through the passages. Each passage discharges a jet of the pressurized fluid (a vortex generator jet) into the working medium fluid flowing over the suction surface. Each jet penetrates through the fluid boundary layer on the suction surface and interacts with the free stream portion of the working medium fluid to create a pair of counterrotating, streamwisely extending vortices in the free stream. The vortices transport higher momentum free stream fluid into the lower momentum boundary layer, thereby counteracting any proclivity for fluid separation. Although this approach is successful, the pressurized fluid used in conventional VGJ arrangements is air extracted from the engine compressor. The air extraction diminishes engine efficiency: Moreover, the supply system required to convey the compressed air to the airfoil plenum introduces mechanical complexity into the engine.
It is, therefore, desirable to devise an airfoil capable of taking advantage of VGJ's without being encumbered by efficiency losses and mechanical complexity.
An airfoil disclosed herein comprises a pressure surface exposed to a stream of fluid, a suction surface exposed to the stream of fluid and a passage extending from a passage intake end to a passage discharge end. The intake end has an intake opening penetrating the pressure surface for extracting fluid from the fluid stream. The discharge end has a discharge opening penetrating the suction surface upstream of a natural separation point. The discharge end is configured to inject the extracted fluid into the fluid stream at a jet angle whose components include at least one of a nonzero streamwise angle in a prescribed angular range and a nonzero cross-stream angle.
The foregoing and other features of the various embodiments of the airfoil described herein will become more apparent from the following detailed description and the accompanying drawings.
Referring to
Referring to
The airfoil also includes a passage 56 having a meanline 58 for conveying fluid from the pressure side 42 of the airfoil to the suction side 40 of the airfoil. The passage 56 has an intake end 60 with an intake opening 62 that penetrates the pressure surface 42 for extracting fluid from the fluid stream FP. The intake end includes a fillet 64. The intake end is oriented so that it faces upstream (i.e. toward) the oncoming fluid stream FP, i.e. the local velocity vector V forms an acute angle δ with the meanline 58. The intake opening may penetrate the pressure surface at any convenient location. However because the static pressure of the fluid stream FP decreases as it flows along the pressure surface, particularly aft of about 50% of the axial chord CX, it may be desirable to locate the intake opening within the first 50% of axial chord, and as far upstream as practicable. The illustrated passage is substantially linear and defines a substantially linear pathway between the pressure surface and the suction surface. The passage may also be nonlinear, however a linear passage with a correspondingly short length is desirable to minimize aerodynamic losses in fluid flowing through the passage.
The passage 56 also has a discharge end 66 with a discharge opening 68 that penetrates the suction surface. The opening 68 is located upstream of the point 52 of separation onset by a distance D, which is typically no more than about 20% of the axial chord C. The term “upstream”, as used herein to describe and claim the location of the opening 68 relative to separation point 52, includes a location at the separation point itself. In the illustrated variant of the airfoil, the discharge opening 68 is chordwisely aft or downstream of the intake opening 62. The pressure gradient between the pressure surface and the suction surface extracts working medium fluid from the pressure side of the airfoil and drives it through the passage. The extracted fluid is injected as a jet 72 into the fluid stream flowing along the suction side of the airfoil. The discharge end is configured to inject the jet at a jet angle whose components include at least one of a nonzero streamwise angle α in a range of about 45° to about 110° and a nonzero cross-stream angle β.
Referring now to
The cross-stream angle β is an acute angle measured in a plane PC perpendicular to plane PS. The angle β is measured as shown from the reference plane PT. The angle β is in the range of about 30° to about 60°.
The discharge end of the passage may be configured to inject the jet 72 at a prescribed jet angle by merely orienting the entire passage 56, including the discharge end, at that same angle as suggested in
The passage 56 may be installed in the airfoil by any suitable means, such as laser drilling or electro-discharge machining. For cast airfoils, the passage may also be created during the airfoil casting process.
As seen best in
Although this disclosure refers to specific embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the subject matter set forth in the accompanying claims.
