Numerical Investigation on the Cavity Implementation Methods in Trapped Vortex Combustor

Well-stabilized vortices inside a physical cavity using direct injection of reactants can be used to provide stable combustion with performance benefits. The adaptation of the Trapped Vortex Combustion (TVC) concept involves the placement of the cavity-based flame stabilization device in the main duct of the combustor using annular or planar geometric configurations. In this work, we compare the performance of inner annular, outer annular and planar arrangements of the cavity with dual-vortex structure configuration enabled by a single injection port on the upstream wall of the cavity. The comparison is done using Reynolds Averaged Navier-Stokes (RANS) simulations. The effect of cavity implementation methods on the flame stabilization, temperature distribution at the exit of the combustor and pollutant emissions are analyzed with three combustor operating conditions based on the flow parameters. Significant differences in the flame stabilization are observed in the combustors due to the dissimilarity of the velocity and fuel distribution. The parameter, jet momentum flux ratio, denoted by J, is defined based on the inlet conditions and the estimate of actual cavity flow velocity from numerical results. This parameter is used to correlate the combustor performance among the various configurations studied. The inner annular combustor can be scaled to higher power by increasing the combustor radius (R) with same cavity size, flow parameters and chemical parameters, however, the flame stabilization and performance are affected by the geometric parameters, combustor radius (R) and cavity depth (D). Strategies to scale-up the combustor to obtain the required performance are discussed along with the challenges faced in comparing results of the various configurations studied.

Development and Atmospheric Testing of a High Hydrogen FlameSheet™ Combustor for the OP16 Gas Turbine

Gas turbines with a combustion system for hydrogen operation offer a low carbon solution to support the stability of the energy grid. This provides a solution capturing the needs for energy storage, in the form of hydrogen, and flexible power generation. Fuel flexibility is a key requirement to reduce the operational risks in case hydrogen is not available, whereby hydrogen can be combined with other conventional or alternative fuels. A key issue to achieve 100% hydrogen combustion with low emissions is to prevent flashback. To address the challenges, a project consortium was set-up consisting of gas turbine equipment manufacturers, academia and end-users. The major objective is to develop a cost-effective, ultra-low emissions (sub 9 ppm NOx and CO) combustion system for gas turbines in the 1–300 MW output range, including the 1.85 MWe OPRA OP16 gas turbine. At the center of this innovative high-technology project is the patented and novel aerodynamic trapped vortex FlameSheet™ combustion technology platform. Burner concepts based on an aerodynamically trapped vortex flame stabilization have a higher resistance towards flame blowout than conventional swirl stabilized burners. This paper will present the results of the first phase of the project, whereby atmospheric testing of the upgraded FlameSheet™ combustor has been performed operating on natural gas, hydrogen and mixtures thereof. The optimized combustor configurations demonstrated a wide load range on 100% hydrogen, and these results will be presented.

Passive flow control of shock-induced dynamic stall via surface-based trapped vortex generators

A novel passive approach for controlling the flow in a 2D dynamic stall at variabl freestream is investigated. 2D computational fluid dynamics simulations of an SC1095 airfoil with surface-based trapped vortex generator (STVG) type passive flow control were conducted. The airfoil was exposed to a fluctuating freestream of Mach 0.537 ± 0.205 and Re = 6.1 × 106 (based on the mean Mach number) and experienced a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz. These conditions were selected as an approximation to the flow experienced by a UH-60A helicopter rotor airfoil section in an actual fast forward flight test case. The baseline simulations were cautiously validated with experimental data for both transonic flow and dynamic stall under the variable freestream. Then, 20 different local STVGs type geometry modifications were investigated as a means of passive flow control. Modifications were examined on both the airfoil’s upper and lower surfaces. Results showed that the STVGs were able to mitigate the negative effects of shock-induced dynamic stall. The best geometries could reduce the peak negative pitching moment by as much as 9–23% during the transonic phase of a cycle and by as much as 19–71% during the dynamic stall phase. Also, they were able to reduce peak drag by 8–20% in the transonic phase and by 15–44% in the dynamic stall phase. On the other hand, the lift-to-drag ratio was significantly increased by 3–28% per one rotor cycle. All the above advantages came at virtually no penalty in the lift.