Low-velocity ows in the cavities of a combustor can aid in establishing stable ames. However, unsteady ows in and around cavities may destabilize these ames. By proper cavity design it is possible to lock (trap) the vortices spatially and, thereby, stabilize the ames. The spatially locked vortices restrict the entrainment of main air into the cavity. For obtaining good performance characteristics with a trapped-vortex combustor, a suf cient amount of fuel and air must be injected directly into the cavity. This mass injection can alter the dynamic characteristics of the ow inside and around the cavity. The present study employed a numerical simulation to investigate the vortex dynamics of a cavity into which uid mass is directly injected through jets. A third-order-accurate, time-dependent, computational uid dynamics with chemistry code was used for simulating the dynamic ows associated with an axisymmetric, centerbody trapped-vortex combustor under nonreacting and reacting conditions. It was found that mass injection increases the optimum size (width-to-diameter ratio) of the cavity. Injection of small amounts of uid into a nonoptimum cavity increases the unsteadiness of the ow. Fluid injected into the optimumsize cavity is transported along the outer core of the vortex, providing more ef cient mixing and a longer residence time for the fuel/air mixture. It was also found that use of thinner afterbodies results in the cavity ow being more dynamic. Calculations made with a global-chemistry model revealed that at higher annulus air velocities, combustion is limited to the cavity region. As in the case of cold ows, the injection jets in reacting ows are pushed outward from the center when the cavity size is small.
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Katta et al. (1998) studied this question.
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