No abstract

To examine the impact of oxidative jets on the thrust vector angle, secondary combustion efficiency, and combustion chamber pressure, inert gas (nitrogen) and pure oxygen are injected into the primary flow, which includes combustible components, at various locations in the divergence section and throat using different injection techniques. The simulations utilize Reynolds-averaged Navier-Stokes equations coupled with the SST k - ω turbulence model in two-dimensional numerical simulations and large-eddy simulation in three-dimensional studies. The numerical method is validated through schlieren experiments, and the vortex is identified using the Liutex-Omega method. The vortex structures and flow characteristics are analyzed. The results indicate that, at the same flow rate, the vector control effect of pure oxygen is superior to nitrogen only in the divergence section, but inferior to nitrogen in both the divergence section and throat. However, with improved vector control, the peak of the vector angle is achieved at a lower flow rate in the case of pure oxygen. When the secondary flow is introduced only in the divergence section, the flow ratio corresponding to the peak point in the pure oxygen case is approximately 14.3% earlier than that in the nitrogen case. The introduction of the pure oxygen jet enhances the secondary combustion efficiency of the primary flow, but to a limited extent. Additionally, when the jet is introduced at the throat, the effect of the pure oxygen case on adjusting the combustion chamber pressure is inferior to that of the nitrogen case. Concerning flow details, the trailing lower vortex replaces the trailing major vortex to become the highest magnitude vortex when the momentum flux ratio is small.

Multiresolution models such as the wavelet-domain hidden Markov tree (HMT) model provide a powerful approach for image modeling and processing because it captures the key features of the wavelet coefficients of real-world data. It is observed that the Laplace distribution is peakier in the center and has heavier tails compared with the Gaussian distribution. Thus we propose a new HMT model based on the two-state, zero-mean Laplace mixture model (LMM), the LMM-HMT, which provides significantly potential for characterizing real-world textures. By using the HMT segmentation framework, we develop LMM-HMT based segmentation methods for image textures and dynamic textures. The experimental results demonstrate the effectiveness of the introduced model and segmentation methods.

To develop an effective suction slot arrangement, computational fluid dynamics simulation software and a high subsonic compressor cascade were used to simulate different suction slots. Based on the effects of various suction slots on the cascade performance under various operating conditions, a novel segmented suction slot structure Seg3 was proposed. The results of the study revealed that in the vicinity of the operating conditions ( incidence ≤ 4 ° ), a full-blade height suction slot should be installed at least 5% of the chord length downstream of the corner separation point to effectively remove the separation. For small and medium incidences, the best performance was observed for suction slot SS5, which was located at 60% of the chord length downstream of the leading edge. Analyzing the effects of SS5 and Seg3 on the cascade performance revealed that when the incidence was less than 4°, the reductions in the total pressure loss coefficients for ζsuc of SS5 and Seg3 both exceeded 8.2%. When the incidence was 4° or greater, the ζsuc increased slightly for SS5, whereas it decreased for Seg3, and the ζsuc was reduced. For a 3° incidence, for example, Seg3 reduced the ζsuc and passage blockage by 12.74% and 8.41%, respectively, and increased the static pressure rise coefficient by 18.55% from the baseline values. Thus, the segmented suction slot proposed in this paper outperformed conventional full-blade height suction slots.