Analysis of unsteady cavity flows for scramjet applications

A passive scalar-based method for numerical combustion

“…When calculating the cavity residence time, it is found that there is not a single exponential decay curve which can fit the mass decay history very well, thus a three-segment exponential fit method [7] is adopted. The calculated residence time together with the previous results for non-reacting cases [8] is displayed in Fig.…”

“…Due to the difficulty in measuring this complex unsteady process experimentally, numerical simulation appears as a powerful complementary tool. Nonreacting cavity [7] and jet-cavity flows [8] have been studied numerically regarding the cavity/mainstream mass exchange characteristics for scramjet applications. In these nonreacting cases, each species was divided into two nominal species (in or out of the cavity) when the flow reached a periodic steady state, and the transport equations for all nominal species were solved simultaneously.…”

Cavity-based flameholding for chemically-reacting supersonic flows

“…5 via the computational results obtained by Gruber et al [30]. Beyond a certain length vortex breakdown occurs and multiple trapped vortices are likely to be present within the recirculation zone [4]. Length-to-depth ratio has also been shown to affect the mode -transverse or longitudinal -in which the vortices oscillate about their mean positions, which can affect the extent of mass exchange between them [98].…”

“…The mean residence time is defined as the time scale associated with the rate of decay of cavity fluid due to mass exchange with the freestream [4], and is governed by the coupled behavior of the shear layer and recirculation zone flowfield. Results from experiments performed by Winterfeld [93] on turbulent transport in the wakes of bluff body flameholders in subsonic flows, suggest that the following relationship between exchange rate and mean residence time can be applied to subsonic cavity recirculation zones embedded in supersonic flows:…”

Mixing Effects of Pylon-Aided Fuel Injection Located Upstream of a Flameholding Cavity in Supersonic Flow

“…22 More modern research has investigated how to reduce unwanted oscillations in a cavity designed for flameholding. [23][24] Another variation of cavity geometry is the closed cavity. This is one in which the shear layer has ample distance with which to reattach on the cavity floor, negating the need for a back wall found in open cavities.…”