Experimental studies have been performed to investigate the effects of hydrogen addition on the combustion characteristics of Chinese No.3 jet fuel (RP-3 kerosene/air premixed flames. Experiments were carried out in a constant volume chamber and the influences of the initial temperatures of 390 and 420 K, initial pressures of 0.1 and 0.3 MPa, equivalence ratios of 0.6–1.6 and hydrogen additions of 0.0–0.5 on the laminar burning velocities, and Markstein numbers of Hydrogen (H₂)/RP-3/air mixtures were investigated. The results show that the flame front surfaces of RP-3/air mixtures remain smooth throughout the entire flame propagation process at a temperature of 390 K, pressure of 0.3 MPa, equivalence ratio of 1.3 and without hydrogen addition, but when the hydrogen addition increases from 0.0 to 0.5 under the same conditions, flaws and protuberances occur at the flame surfaces. It was also found that with the increase of the equivalence ratio from 0.9 to 1.5, the laminar burning velocities of the mixtures increase at first and then decrease, and the highest laminar burning velocity was measured at an equivalence ratio of 1.2. Meanwhile, with the increase of hydrogen addition, laminar burning velocities of H₂/RP-3/air mixtures increase. However, the Markstein numbers of H₂/RP-3/air mixtures decrease with the increase of hydrogen addition, which means that the flames of H₂/RP-3/air mixtures become unstable with the increase of hydrogen addition.

A new hybrid RANS/LES approach with scale-adaptive capabilities is developed. The blending function in the SST model is adopted to prevent the invasion of the von Karman length scale to the RANS region, and the compressibility correction proposed by Wilcox is incorporated to produce a realistic shear layer development in compressible flows. The new model is validated for a subcritical flow past a circular cylinder and a supersonic base flow. Time-averaged turbulent statistics predicted by the new model show fairly good agreement with the experimental data, slight improvements over DES simulations, and are much better than SAS results. The main advantage of the new model over the DES method is that the distribution of the blending function reflects local vortex structures instead of grid spacing in the turbulent wake. The sequence of the effect intensity of the compressibility correction from strong to weak is SAS, the new model and DES.

The minimum ignition equivalence ratio of the strut stabilizer is an important parameter in the design of integrated afterburners. The ignition location significantly affects the ignition equivalence ratio and flame propagation, and therefore, it should be deeply studied. The ignition equivalence ratio and flame propagation at different axial ignition locations downstream of the strut stabilizer are studied in this paper. When the ignition distance is approximately the bluff body trailing edge width, a lower ignition equivalence ratio is required for ignition, and the flame propagates faster through the entire combustion chamber. For different ignition locations, the generated flame kernel at different locations all first propagates to the shear layer. Subsequently, the unilateral flame rapidly extends, ultimately igniting the entire combustion chamber. The flame propagation trajectory depends on the ignition location controlled by the non-reacting flow field and the distribution of kerosene concentration. The flame propagation trajectory mainly includes three paths: (1) the flame kernel is directly downstream the shear layer when the ignition location is close to the tail edge of the stabilizer, (2) the flame propagates upstream into the shear layer in a U-shape when the ignition location is far from the stabilizer but still in the recirculation zone, and (3) the flame propagates upstream into the recirculation zone and shear layer in a U-shape when the ignition location is outside the recirculation zone. In addition, the time for flame propagation to the shear layer is directly related to the ignition performance when the ignition location is within the recirculation zone. If the flame reaches the shear layer in a longer time, there will be more energy loss during the flame propagation process, and the ignition performance will deteriorate. The speed of the flame-trailing edge extension is directly related to the ignition fuel-air ratio, and the downstream extension of the flame is mainly affected by the turbulence velocity in the shear layer.