Hybrid Reynolds-Averaged/Large-Eddy Simulation of a Scramjet Cavity Flameholder

Abstract

.J055339Steady-state and scale-resolving simulations have been performed for flow in and around a model scramjet combustor flameholder. Experimental data available for this configuration include velocity statistics obtained from particle image velocimetry as well as a limited number of scalar measurements using laser-induced breakdown spectroscopy. Several turbulence models were used for the steady-state Reynolds-averaged simulations, which included both linear and nonlinear eddy viscosity models. The scale-resolving simulations used a hybrid Reynoldsaveraged/large-eddy simulation strategy that is designed to be a large-eddy simulation everywhere except in the inner portion (log layer and below) of the boundary layer. Hence, this formulation can be regarded as a wall-modeled largeeddy simulation. This effort was undertaken to not only assess the performance of the hybrid Reynolds-averaged/ large-eddy simulation modeling approach in a flowfield of interest to the scramjet research community but also to begin to understand how this capability can best be used to augment standard Reynolds-averaged simulations. The numerical errors were quantified for the steady-state simulations and at least qualitatively assessed for the scaleresolving simulations before making any claims of predictive accuracy relative to the measurements. The steady-state Reynolds-averaged results displayed a high degree of variability when comparing the flameholder fuel distributions obtained from each turbulence model. This prompted the consideration of applying the higher-fidelity scale-resolving simulations as a surrogate "truth" model to calibrate the Reynolds-averaged closures in a nonreacting setting before their use for the combusting simulations. In general, the Reynolds-averaged velocity profile predictions at the lowest fueling level matched the particle imaging measurements almost as well as was observed for the nonreacting condition. However, the velocity field predictions proved to be more sensitive to the flameholder fueling rate than was indicated in the measurements.

Analysis of combustion modes in a cavity based scramjet

“…A much smaller secondary anti-clockwise recirculation area is found at the front of the cavity with lower speed. The shape of the recirculation areas is similar to the one found in the work of Baurle [28], and the velocity of the primary recirculation zone is very close to the experimental data of Tuttle et al [6]. A variety of averaged flow properties for non-reactive case are displayed in Fig.…”

“…A strong reattachment shock system where the pressure reaches 90 kPa is identified at the aft wall of the cavity. This system of shocks is also present at the same position in the RANS/LES performed by Baurle [28]. This shock system is actually responsible of the temperature increase inside the cavity as the temperature rise which is initiated at the base of the shock structure, is brought to the front and the middle of the cavity due to the recirculation effect.…”

“…The upper and lower walls of the scramjet are modelled either with an adiabatic non-slip condition or with a mixed adiabatic/fixed temperature non-slip condition following the approach from Baurle [28]. For this latter wall condition, adiabaticity is enforced if the wall temperature is below 800 K, but set to 800 K if the wall temperature reaches 800 K. The adiabatic condition can lead to very high temperature levels at the cavity wall which are a priori not observed in the experiment.…”

“…without accounting for potential subgrid scale effects. A reduced kinetic scheme of 22 species and 206 reactions [34] for ethylene is used as retained in the simulations from Baurle [28].…”

“…Baurle [28] for his RANS simulations. Averaged temperature profiles in the injector centerplane at different locations are displayed Fig.…”