Patent Application
20070297916
Referring now to the drawings,
It has been found that trip strips are desirable to provide adequate cooling of the leading edge, especially at the nose portion 36 of the airfoil portion 32 adjacent to the external stagnation region 38. The trip strip arrangement which will be discussed hereinafter provides high heat transfer to the leading edge 30 of the airfoil portion 32.
As shown in
Referring now to
The orientation of the trip strips 40 and 44 in the cavity 34 also increases heat transfer at the leading edge 30 of the airfoil portion 32. If desired, the trip strips 40 and 44 may be oriented at an angle α of approximately 45 degrees relative to the flow direction 48. The leading edges 54 and 56 of the trip strips 40 and 44 are positioned in the region of highest heat load, in this case the leading edge nose 36. This trip strip orientation permits the creation of a turbulent vortex 49 in the cavity 34. The cooling fluid initially hits the leading edges 54 and 56 of the trip strip and separates from the airfoil surface. The flow then re-attaches downstream of the trip strip leading edges 54 and 56 and moves toward the divider rib 60 between the leading edge cavity 34 and the adjacent cavity 62. As the flow approaches the divider rib 60, it is forced toward the opposite airfoil wall. The flow is directed perpendicular to the pressure side and suction side walls 42 and 46, and meets at the center of the cavity 34. The flow is now forced back towards the leading edge 30 of the airfoil portion 32. The result of this flow migration causes a large vortex 49 that drives flow into the leading edge of the cavity, acting as an impingement jet which also enhances heat transfer at the leading edge nose 36.
Using the trip strip configuration of the present invention, radial flowing leading edge cavities of turbine engine components will see an increase in convective heat transfer at the leading edge nose of the cavity.
The particular orientation of the trip strip configuration allows for cooling flow to impinge on the leading edge nose 36, further enhancing heat transfer. The leading edge of the trip strips 40 and 44 is located near the nose 36 of the leading edge cavity 34.
The trip strips 40, although skewed at an angle a with respect to the direction of flow 48 along the pressure-side wall 42, become normal to the direction of flow 48 as they wrap around the nose 36 of the leading edge cavity 34, increasing the turbulent vortex 49 generated by the trip strips 40 and 44, and subsequently increasing the heat transfer coefficient.
The trip strips 40 and 44 may overlap with the trip strip 40 extending underneath the trip strip 44, and vice-versa.
While the trip strips 40 have been described as being on the pressure side wall 42 of the airfoil portion, they could instead be mounted to the suction side wall 46 if desired. In such a situation, the trip strips 44 would be mounted to the pressure side wall 42.
Away from the leading edge nose 36, the staggered and 45 degree angled trip strips generate a vortex that impinges flow onto the nose 36 of the leading edge cavity.
The trip strip configuration of the present invention maintains a P/E ratio between 3 and 25 where P is the radial pitch in between trip strips and E is trip strip height. Further, the trip strip configuration described herein maintains an E/H ratio of between 0.15 and 1.50 where E is trip strip height and H is the height of the cavity 34.
Airflow testing has shown that the heat transfer coefficients at the leading edge of the airfoil adjacent to the external stagnation region when using the staggered trip strips of the present invention are enhanced by approximately two times, greatly increasing airfoil oxidation and thermo-mechanical fatigue cracking life.
It is apparent that there has been provided in accordance with the present invention leading edge cooling using staggered-chevron trip strips that wrap around the nose of the leading edge cavity which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other unforeseeable alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing detailed description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
