The Trapped Vortex Combustor (TVC) potentially offers numerous operational advantages over current production gas turbine engine combustors. These include lower weight, lower pollutant emissions, effective flame stabilization, high combustion efficiency, excellent high altitude relight capability, and operation in the lean burn or RQL modes of combustion. The present work describes the operational principles of the TVC, and extends diffuser velocities toward choked flow and provides system performance data. Performance data include EINOx results for various fuel-air ratios and combustor residence times, combustion efficiency as a function of combustor residence time, and combustor lean blow-out (LBO) performance. Computational fluid dynamics (CFD) simulations using liquid spray droplet evaporation and combustion modeling are performed and related to flow structures observed in photographs of the combustor. The CFD results are used to understand the aerodynamics and combustion features under different fueling conditions. Performance data acquired to date are favorable compared to conventional gas turbine combustors. Further testing over a wider range of fuel-air ratios, fuel flow splits, and pressure ratios is in progress to explore the TVC performance. In addition, alternate configurations for the upstream pressure feed, including bi-pass diffusion schemes, as well as varia-tions on the fuel injection patterns, are currently in test and evaluation phases.

The adequacy and accuracy of the constant Schmidt number assumption in predicting turbulent scalar fields in jet-in-crossflows are assessed in the present work. A round jet injected into a confined crossflow in a rectangular tunnel has been simulated using the Reynolds-Averaged Navier-Stokes equations coupled with the standard k-ε turbulence model. A semi-analytical qualitative analysis was made to guide the selection of Schmidt number values. A series of parametric studies were performed, and Schmidt numbers ranging from 0.2 to 1.5 and jet-to-crossflow momentum flux ratios from 8 to 72 were tested. The principal observation is that the Schmidt number does not have an appreciable effect on the species penetration, but it does have a significant effect on species spreading rate in jet-in-crossflows, especially for the cases where the jet-to-crossflow momentum flux ratios are relatively small. A Schmidt number of 0.2 is recommended for best agreement with data. The limitations of the standard k–ε turbulence model and the constant Schmidt number assumption are discussed.

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17.SECURITY CLASSI FICATION

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Numerical simulations are performed to predict the flow properties in a liquid spray droplets fueled Trapped Vortex Combustor (TVC) sector rig. The quantities studied include aerodynamics, pressure drop, spray droplets trajectories, evaporation, mixing and combustion, and combustor exit temperature distributions. Previous numerical simulations of this TVC configuration have identified basic flow patterns and performance characteristics, and were generally in good agreement with experimental data. In the current effort, more detailed investigations were performed to understand the sensitivity of the TVC combustor to variations in the liquid fuel injection parameters. The computational model is described, including combustor geometry, boundary conditions for all combustion and cooling air injections, and spray droplets inlet conditions. A key finding is that liquid fuel injection boundary conditions for different types of downstream flows (cavity, high velocity cross flow) require different treatments, even though similar fuel injectors are used. This is evident in the large differences observed in the combustor exit plane pattern factor due to only minor differences in the fueling schemes. Combustor exit temperature profile strongly affects the design for turbine durability. With small changes in the temperature distribution, design modifications for the first turbine vane cooling schemes are required.

Transonic strong blade-vortex interaction is numerically analyzed by solving the unsteady 2-D Navier–Stokes equations using an iterative implicit second order scheme. The dominant processes during the interaction are the development of large transverse pressure gradients in the upper leading edge region and the development of disturbances at the root of the lower surface shock wave. As a result of this interaction, high pressure pulses are emitted from the leading edge, and acoustic waves are radiated from the lower surface in a region originally occupied by a supersonic pocket. In addition, severe load variations occur when the vortex is within one chord length of the blade.