Mitigating instability by actuating the swirler in a combustor

Abstract

The present disclosure relates to a method and apparatus to mitigate thermo-acoustic instabilities in combustor of gas turbine engines using a lean premixed flame; and provides a dynamic control strategy for mitigating thermo-acoustic instability in a swirl stabilized, lean premixed combustor by rotating the otherwise static swirler meant for stabilizing the lean premixed flame. The swirler is subjected to a controlled rotation for imparting increased turbulence intensity and higher tangential momentum to the premixed reactants towards mitigating thermo-acoustic instability. The rotating swirler induces vortex breakdown and increased turbulence intensity to decimate periodic interactions found during a particular phase of the instability cycle on account of periodic collision of diverging flame base with the flame segment above the dump plane in the combustor. This prevents flame-flame interactions and emergence of strongly positive Rayleigh indices which contribute as sources of acoustic energy to drive the self-excited instability.

We claim: 
     
         1 . A combustor configured to receive fuel and air, and burn the fuel-air mixture, the combustor comprising:
 (a) at least one swirler in feeding path of the fuel-air mixture and configured to create turbulence by swirling of the air; and   (b) means to rotate the at least one swirler at different rotational speeds;   wherein rotation of the at least one swirler at different rotational speeds results in mitigating thermo-acoustic instabilities.   
     
     
         2 . The combustor of  claim 1 , wherein the combustor is configured to receive air pre-mixed with fuel and burn the fuel-air mixture; and the at least one swirler is in feeding path of the air pre-mixed with fuel. 
     
     
         3 . The combustor of  claim 1 , wherein the at least one swirler is a vane swirler. 
     
     
         4 . The combustor of  claim 1 , wherein the combustor further comprises means to detect thermo-acoustic instabilities. 
     
     
         5 . The combustor of  claim 4 , wherein the means to detect thermo-acoustic instabilities includes one or more pressure sensors for sensing pressure in the combustor and a processor to process sensed pressure signals to detect occurrences of thermo-acoustic instabilities. 
     
     
         6 . The combustor of  claim 5 , wherein the combustor further comprises controller to actuate the means to rotate the at least one swirler at a desired rotational speed based on detection of occurrence of thermo-acoustic instability. 
     
     
         7 . The combustor of  claim 1 , wherein the means to rotate the at least one swirler at different rotational speeds is at least one motor operatively coupled to the at least one swirler through at least one shaft. 
     
     
         8 . The combustor of  claim 7 , wherein the at least one motor is a variable speed motor to facilitate rotation of the at least one swirler at different rotational speeds. 
     
     
         9 . A method for mitigating thermo-acoustic instabilities in a combustor, the method comprising steps of:
 (a) providing at least one swirler in feeding path of fuel-air mixture to stabilize the premixed flame in the combustor.   (b) providing means to rotate the at least one swirler at different rotational speeds;   (c) providing means to detect the occurrence of thermo-acoustic instability; and   (d) rotating the at least one swirler, on detection of thermo-acoustic instability, at a desired rotational speed;   (e) wherein rotation of the at least one swirler at different rotational speeds results in a change in swirl number and change in turbulence intensity by further swirling the fuel-air mixture thereby mitigating thermo-acoustic instabilities.   
     
     
         10 . The method of  claim 9 , wherein the air is pre-mixed with fuel.