ABSTRACT
The present work numerically investigates the effect of secondary air conditions on
the combustion of natural gas/air mixture in a gas turbine combustor. Secondary air
is introduced normally at the combustor first half. Secondary air test conditions
include its flow rate, entry position, and its arrangement around the combustor
periphery and the total number of inlet ports. Secondary air inlet ports are located at
different levels along the combustor length. Each level includes a number of inlet
ports uniformly distributed around the combustor periphery. The number of ports
levels varied from four to sixteen and the number of ports in each level varied from
four to sixteen ports. Thus, the total number of ports varied from 16 up to 256. The
primary air swirl number is kept constant during tests taking the value of 0.87. A
three dimensional (SST k-omega) model is used to simulate the turbulent isothermal
flow and the non-premixed combustion model was used to simulate the turbulent
reacting flow using a CFD package Fluent 12. For validation of the models used, a
comparison between the calculated axial temperature distributions with the
measured results of other investigators was made and showed a satisfactory
agreement. Secondary air showed a remarkable effect on temperature distribution
inside the combustor. For secondary to primary air mass ratio (SPAR) above 0.3, the
flame becomes wider in diameter and longer in length when SPAR is increased. The
NO increases by about 58% and 12 % when the SPAR increases from 0 to 90 % for
the ports arrangement of 4x4.