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.

Laser-Doppler anemometry is applied to study the dynamics of small-diameter carbon dioxide and air bubbles rising in a quiescent liquid. Primary data include bubble velocity and diameter as functions of position above a generating nozzle. Direct observation of decreasing bubble diameter provides instantaneous mass transfer results for carbon dioxide bubbles, presented in terms of Sherwood versus Reynolds and Peclet numbers. The range of velocity measured is 1.0 to 35.0 cm/sec, and the range of diameter measured is 0.07 to 1.20 mm, corresponding to a Reynolds number range from less than unity to over 500. Bubble oscillations, observed through direct diameter measurements, are recorded for bubbles with initial diameter greater than 0.80 mm. Fourier transforms of the instantaneous diameter profiles result in a frequency of oscillation of about 10 Hz for most test runs. Drag studies indicate that bubbles with Reynolds number greater than 40 follow correlations developed for fluid spheres with attached boundary layers and wakes. Transition from solid-sphere to fluid-sphere drag behavior is observed for increasing Reynolds number in the range 10 to 40.

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