Premixer assembly and mechanism for altering natural frequency of a gas turbine combustor

Abstract

A system and method are provided for altering the natural frequency of a dome plate portion of a premixer assembly of a gas turbine combustor. The plate assembly has a dome plate with a central pilot mixer and a plurality of extension tabs extending radially outward from the pilot mixer. A plurality of radially extending struts are secured to the extension tabs in order to alter the natural frequency of the dome plate.

1 . A plate assembly for a gas turbine combustor comprising:
 a dome plate having a central opening therein and a plurality of openings arranged in an annular array about the central opening;   a pilot mixer assembly extending from the central opening, the pilot mixer assembly having an outer wall, a center ring located within the outer wall, a plurality of pilot vane swirler vanes extending therebetween, and a pilot cone surrounding a portion of the outer wall;   a plurality of extension tabs extending from the outer wall of the pilot mixer assembly and through the pilot cone; and,   a plurality of radially extending struts secured to the plurality of extension tabs and the dome plate.   
     
     
         2 . The plate assembly of  claim 1 , wherein the plurality of openings in the dome plate are each sized to receive a swirler assembly. 
     
     
         3 . The plate assembly of  claim 2  further comprising a plurality of swirler assemblies, each comprising a premix tube, a premix swirler positioned within the premix tube, the swirler having a plurality of turning vanes for imparting a swirl to a passing flow, and a plurality of mounting of mounting blocks positioned on the outer wall of the premix tube; 
     
     
         4 . The plate assembly of  claim 1 , wherein the dome plate further comprises a plurality of air holes extending through the dome plate. 
     
     
         5 . The plate assembly of  claim 1 , wherein the plurality of extending tabs are secured to the outer wall of the pilot mixer assembly. 
     
     
         6 . The plate assembly of  claim 1 , wherein the pilot cone extends through the dome plate and transitions into a divergent portion. 
     
     
         7 . The plate assembly of  claim 4 , wherein the radially extending struts have an interrupted surface in contact with the dome plate such that each of the struts are secured to the dome plate at multiple locations. 
     
     
         8 . The plate assembly of  claim 1 , wherein the radially extending struts are positioned between adjacent plurality of openings. 
     
     
         9 . A system for stiffening a premixer assembly comprising:
 a generally circular dome plate having a central opening, an upstream face, an opposing downstream face, and a plurality of cooling holes;   a pilot mixer assembly located within the central opening, the pilot mixer assembly having an outer wall and a pilot cone surrounding a portion of the outer wall;   a plurality of extension tabs extending from the outer wall of the pilot mixer assembly and through the pilot cone; and,   a plurality of struts extending between the plurality of extension tabs and the dome plate and radially outward from the outer wall of the pilot mixer assembly, the plurality of struts being fewer than the plurality of extension tabs;   wherein the plurality of struts are positioned about the pilot mixer assembly in order to provide a desired natural frequency to the generally circular dome plate.   
     
     
         10 . The system of  claim 9 , wherein the generally circular dome plate further comprises a plurality of swirler assemblies oriented in an annular array about the pilot mixer assembly. 
     
     
         11 . The system of  claim 9 , wherein the plurality of extension tabs are welded to both the outer wall and the plurality of struts. 
     
     
         12 . The system of  claim 11 , wherein each of the plurality of struts are secured to the dome plate at multiple locations. 
     
     
         13 . The system of  claim 12 , wherein each of the plurality of struts, further comprise a recessed portion between the multiple locations where the plurality of support plates are secured to the dome plate. 
     
     
         14 . The system of  claim 1 , wherein the plurality of struts are positioned in between the plurality of openings in the dome plate. 
     
     
         15 . The system of  claim 1 , wherein the pilot cone has a diffuser section extending from proximate the downstream face of the dome plate. 
     
     
         16 . The system of  claim 15  further comprising an outer cone enveloping a portion of the pilot cone, the outer cone spaced a distance from the pilot cone so as to maintain a gap therebetween. 
     
     
         17 . A method of altering natural frequency of a premixer assembly comprising:
 providing a dome plate having a central opening therein and a plurality of openings arranged in an annular array about the central opening, a pilot mixer assembly located within the central opening and having an outer wall, and a pilot cone surrounding a portion of the outer wall, and a plurality of extension tabs extending from the outer wall of the premixer and through the pilot cone;   securing the quantity of radially extending struts to the plurality of extension tabs and the dome plate; and,   securing additional radially extending struts to the plurality of extension tabs and the dome plate upon a determination to increase the natural frequency of the dome plate.   
     
     
         18 . The method of  claim 17 , wherein the quantity of radially extending struts equals the plurality of openings arranged in an annular array about the central opening. 
     
     
         19 . The method of  claim 17 , wherein the natural frequency of the premixer assembly is increased upon securing additional radially extending struts to the plurality of extension tabs and the dome plate. 
     
     
         20 . The method of  claim 17 , wherein the natural frequency of the premixer assembly is decreased by removing radially extending struts from the premixer assembly such that the struts do not contact the plurality of extension tabs and the dome plate.