Investigation Of Fluid Flow Behaviour On A New Generation DLE Combustor

Dry low emissions(DLE)combustion technology is currently the most commonly used low-emissions combustion technology.This combustion technology keeps the combustion reaction at relatively dilute fuel concentrations in order to reduce thermodynamic NOx formation.At present,DLE gas turbines have been able to reduce the NOx emissions to 15 ppmvd(15% O2)under natural gas fuel conditions.In this paper,the model DLE combustor is designed based on the combustion chamber of Siemens SGT750 unit.The combustor structure in this unit consists of three nozzles,RPL(Rich-Pilot-Lean)nozzle,duty Pilot nozzle and main nozzle(Main1 and Main2).In this paper,the structure and flow characteristics of the new generation DLE combustor were studied.A model combustor was designed in this paper.The commercial numerical software FLUNT was used to do non-reaction simulation of the model combustor.Comparison was made on the different combinations of main swirlers.The result shows: The length of the main recirculation zone of the counter-rotating conditions is longer than that of the co-rotating conditions,and the vortex core of the mainstream is shifted to the downstream;The air inlet flow condition has no significant effect on the normalized flow characteristics of this combustion chamber.Then,based on the PIV visualization measurement technology,a non-reaction experimental test was set up to visualize the exit position of the swirlers.2?m smoke particles were selected as tracer particles.There were 2 sets of shooting cross sections,the longitudinal section through the axis,and 3 transverse sections.The experimental result shows: The vortex core of the mainstream is shifted to the downstream;The counter-rotation conditions show a larger axial velocity gradient near the outlet of swirlers,while the co-rotating conditions show a larger axial velocity gradient downstream,and there exists a critical plane in which the axial velocity distributions in the radial direction are basically the same;The axial pulsation velocity increases first and then decreases along the radial direction,and the peak value of the axial pulsation velocity is radially shifted with the increase of the axial position;There exist two shear layers near the outlet of the swirlers in the case of the counter-rotation conditions;The normalized characteristics of different inlet flow conditions are basically the same.Finally,a simplified model combustion was designed.Pre-mixed air-gas boundary conditions were given for each nozzle's inlet directly.The result shows: The combustion reaction mainly occurs at the head of the RPL section,the position where the mixing of RPL's high-temperature gas jet and the Pilot premixed gas occurs,and the location of the mainstream nozzle outlet;The vortex core of the mainstream is shifted to the downstream compared with non-reaction conditions,and shifting characteristics for co-rotating conditions and counter-rotating conditions are similar with that of non-reaction conditions.The axial velocity distribution profiles of reaction conditions show similar peak features with non-reaction conditions,as the velocity of RPL outlet is larger,the main recirculation zone is impacted,and the left stagnation point position at the axis line is shifted to the downstream;The RPL equivalent ratio mainly affects the combustor head area,while the swirling direction mainly affects the flow field downstream of the swirlers' outlet.