Jianguo Tan

Multiobjective Design Optimization of a Cantilevered Ramp Injector Using the Surrogate-Assisted Evolutionary Algorithm

AbstractThe mixing efficiency of the fuel and the supersonic freestream has a great impact on the operation of the scramjet engine because of the very short residence time. In the current study, the cantilevered ramp injector was used to promote mixing of the fuel and the supersonic flow, and the injector’s configuration was optimized by the surrogate-assisted evolutionary algorithm—namely, the nondominated sorting genetic algorithm coupled with the Kriging surrogate model. In the optimization process, the swept angle, the ramp angle, the compression angle, the length of the step, and the diameter of the injector were considered as the design variables, and the mixing efficiency, the total pressure recovery efficiency, and the drag force were taken as the objective functions. Finally, the Pareto front for the multiobjective design optimization results was obtained, and the relationship between the objective functions was explored. The results show that optimized drag force increases with increased mixing ...

Visualization of flow structures and mixing characteristics induced by forced vibration in supersonic mixing layer

Graphical abstract

Numerical and Experimental Investigation of Computed Tomography of Chemiluminescence for Hydrogen-Air Premixed Laminar Flames

Computed tomography of chemiluminescence (CTC) is a promising technique for combustion diagnostics, providing instantaneous 3D information of flame structures, especially in harsh circumstance. This work focuses on assessing the feasibility of CTC and investigating structures of hydrogen-air premixed laminar flames using CTC. A numerical phantom study was performed to assess the accuracy of the reconstruction algorithm. A well-designed burner was used to generate stable hydrogen-air premixed laminar flames. The chemiluminescence intensity field reconstructed from 37 views using CTC was compared to the chemiluminescence distributions recorded directly by a single ICCD camera from the side view. The flame structures in different flow velocities and equivalence ratios were analyzed using the reconstructions. The results show that the CTC technique can effectively indicate real distributions of the flame chemiluminescence. The height of the flame becomes larger with increasing flow velocities, whereas it decreases with increasing equivalence ratios (no larger than 1). The increasing flow velocities gradually lift the flame reaction zones. A critical cone angle of 4.76 degrees is obtained to avoid blow-off. These results set up a foundation for next studies and the methods can be further developed to reconstruct 3D structures of flames.

Flow characteristics of supersonic mixing layer under forced vibration

Supersonic mixing layer is one of the most important phenomenon of turbulent flow, which occurs in scramjet, ejector and supersonic airfoil. With the development of efficient propulsion systems, rapid mixing of two high-speed streams in a short distance always receives a great deal of attention all over the world. There are a lot of literatures that investigated flow characteristics and mixing efficiency of supersonic mixing layer. To evaluate the compressibility level of mixing layer, convective Mach number ( Mc ) was proposed by Papamoschou, their experimental study revealed that Mc had an important effect on the growth rate of mixing layer. By employing Schlieren and PLIF techniques, Rossmann found that with the value of Mc risen, the thickness of mixing layer had strong reduction. Considering the low mixing efficiency of supersonic mixing layer, many methods were proposed to control supersonic flow and increase mixing efficiency. By introducing chevrons to supersonic flow, Callende et al. found that the mixing efficiency was strongly enhanced, while the pilot loss could not be ignored. The experiments done by McLaughlin et al. revealed that an effective way to promote mixing was to use glow discharge excitation system in a supersonic mixing layer. In their experimental study, a high oscillating signal was passed through the copper electrode insulted from the aluminum trailing edge, which produced a glow between the copper and the aluminum when a threshold voltage was reached. This glow brought about a very high temperature disturbance locally, slightly perturbing the flow adjacent to the electrodes. However, flow fields of supersonic mixing layer under conditions of vibration have not been thoroughly researched, partly because of the complexity of fluid-structure interaction (FSI). Flutter of airfoil is one example of vortex induced vibration, and can cause severe damage. By employing PIV technique, Kim et al. investigated the flow structures induced by the vibration of cantilever, the contours of velocity field were displayed with the Reynolds numbers of 101, 126 and 146 respectively. However, due to the equipment limitations, they could not get the characteristics of turbulent flow. In the present study, forced vibration which decouples the FSI is applied in the supersonic mixing layer through a vibration shaker, and flow characteristics under different vibration conditions are experimentally and numerically investigated. Besides, through employing edge detection technology, the thickness of supersonic mixing layer along the flow direction is displayed, which demonstrates that forced vibration is responsible for the increase of growth rate.

Numerical Simulation of the Auto Ignition Process in Inlet-Injection Shock-Induced-Combustion Scramjet Engines

Fuel injection in the inlet surface of the scramjet engine can promote the fuel/air mixing process, resulting in a decrease in skin friction as well as vehicle length and structural weight. In the current study, the two-dimensional Reynolds-averaged Navier-Stokes (RANS) equations and the SST k-ω turbulence model have been employed to simulate the auto-ignition process in a shock-induced-combustion scramjet engine. Combustion is simulated by a one-step hydrogen-air mechanism and the Laminar Finite-Rate reaction model. The numerical approach has been validated through a grid independency analysis and a comparison with the available experimental data in the open literature. The influences of the injection angle and jet–to–crossflow pressure ratio on the auto–ignition process of the shock–induced–combustion scramjet engine have been investigated. The predicted results show good agreement with the experimental data, and the grid scale has only a slight impact on the wall pressure distribution of the scramjet engine. The cases with an injection angle of 90° are more beneficial to the auto-ignition process, and the reaction process occurs mainly at the entrance of the combustor when the jet-to-crossflow pressure ratio is 2 and 3. At the same time, two large separation regions are formed on the upper and lower walls of the scramjet engine, and their sizes increase with the increase of the jet-to-crossflow pressure ratio. However, when the jet-to-crossflow pressure ratio is 4.0, the flame is pushed forward, and the reaction process occurs mainly upstream of the injection port. This may be induced by the intensive combustion.Copyright