| Trapped vortex combustor (TVC) is a very potential and promising new concept combustor forits demonstrated advantages over conventional swirl-stabilized combustors: wide operation range,high combustion efficiency (η) and low emissions. Now, TVC has become one of the most importantcandidates for the future high temperature rise combustor of military aero engine. This paper presentsthe aerodynamic, fuel/air scheme and geometry design of a high fuel/air ratio (FAR) trapped vortexcombustor, as well as numerical and experimental results of aerodynamics, some key technique inves-tigations and combustion characteristics.Particle imaging velocimetry (PIV) measurement and numerical simulation were carried out toinvestigate the cold flow characteristics of the model combustor. The results show that single-vortexand dual-vortex cavity flow patterns were obtained in the radial strut plane and in the middle planebetween two radial struts, respectively. The cavity/mainstream mixing mechanism and mixing degreeof different planes are different, this difference is believed to be helpful in enhancing the three dimen-sional effect of the flow. It is also observed that the flow remains self-similar with the range of inletMach number from0.1to0.25, the vortices become more intense at higher inlet Mach number, whichimplies the ability for the TVC to operate at high inlet velocities. A comparison between the numericalresults and the experimental results demonstrates the superiority of the standard k-ε turbulence modelin TVC flow prediction. The data obtained by PIV measurements in this paper can be used as a benchmark for cold flow CFD simulations of TVC.Key techniques were investigated in terms of flow optimization and fuel supply. A passive flowcontrol technique is proposed to optimize the cavity flow, it is found that streamwise vortexes aresuccessfully induced in cavities by local block area settled in the slots of the cavity fore walls, whichwould result in enhanced heat and mass transfer in circumferential direction. The geometry of radialstrut was varied to check its effect on TVC performance, the results reveal that the geometry of radialstruts has very strong impact on flow field and combustion characteristics of cavities in addition to itsimpact on "flame transportation", the optimum width and inclination angle are20mm and0°respec-tively in present work. Also, the relative position of radial struts and cavity injectors in circumferentialdirection are proved to be a critical issue in TVC, the best performance was achieved when a radialstrut was located in the middle plane of two adjacent cavity injector planes. Partially pre-mixedpre-vaporized multi-injection concept was proposed for the fuel injection in main stage of TVC, the effect of hole diameter, the area ratio and the inlet Ma number on performance were investigated ex-perimentally. The feasibility of this fuel injection technique was validated preliminarily by combus-tion tests. It is shown that combustion performance varies nonmonotonicly with increasing spray an-gle of cavity swirl-pressure injectors, the performance curve peaks at the spray angle of60°, also,better performance is observed with hollow spray cone rather than solid spray cone.The combustion characteristics of the high FAR TVC both in cavity-only mode and in cav-ity+main mode were investigated at atmospheric pressure. The lowest lean blowout fuel/air ratioachieved at the inlet temperature of473K is0.0042, which indicates encouraging flame stability. Incavity-only mode, combustion efficiency over98%were obtained for most of the tested cases. In cav-ity+main mode, noticeable decrease of η is observed as the cavity fuel percentage increases from20%to50%, the highest η at the over fuel air ratio of0.04is96.7%, however, a higher value of η can beexpected at realistic engine conditions of higher temperature and higher pressure. The overall tem-perature distribution factor (OTDF) varies in the range of0.14～0.18. |
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