Numerical study of guide vane effects on reacting flow characteristics in a trapped vortex combustor

Secondary flow characteristics like horseshoe vortices and related total pressure losses decrease turbine efficiency. Computerized simulations of potentially favorable modifications in turbine systems could provide a fast, numerical and inexpensive method of evaluating their effects on flow properties: This paper consists of a comparative numerical study of the flow characteristics of a domain containing a vertical cylinder subjected to cross flow and upstream endwall modifications. Analyzing the flow around a turbine nozzle guide vane (NGV) could be simplified by modeling it as a vertical cylinder with a diameter proportional to the leading edge diameter of the blade, and adding upstream endwall fences of varying dimensions and alignments could attenuate the development of a horseshoe vortex. A commercial computational fluid dynamics (CFD) software package, Fluent, was used for the numerical analysis. To validate the modeling strategy, experimental data previously reported in the literature for conventional cylinders in cross flow were compared to the current predictions. A grid independence study was also performed. The lateral distance between the two legs of the horseshoe vortex downstream of the cylinder was decreased by 7% to 14%. All fence types effectively changed the location of the main horseshoe vortex roll-up. The height of the fence was more influential than the length of the fence in modifying flow characteristics. The existence of the fences slightly increased the mass-averaged total pressure loss far downstream of the cylinder; however, beneficial near-fence flow characteristics were observed in all cases. Also, it was noted that an endwall fence could possibly result in decreased interaction between the horseshoe vortices created by consecutive blades in a row of NGV blades, which would be expected to result in improved flow conditions within actual turbine passages.

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Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

Volume 2: Combustion, Fuels and Emissions, Parts A and B ◽

10.1115/gt2011-45263 ◽

2011 ◽

Cited By ~ 1

Author(s):

Dipanjay Dewanji ◽

Arvind G. Rao ◽

Mathieu Pourquie ◽

Jos P. van Buijtenen

Keyword(s):

Flow Field ◽

Swirling Flow ◽

Numerical Study ◽

Reverse Flow ◽

Direct Injection ◽

Flow Characteristics ◽

Droplet Breakup ◽

Reacting Flow ◽

Lean Direct Injection ◽

Wide Range

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.

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Effect of structure parameters of the flow guide vane on cold flow characteristics in trapped vortex combustor

Journal of Hydrodynamics ◽

10.1016/s1001-6058(15)60535-2 ◽

2015 ◽

Vol 27 (5) ◽

pp. 730-737 ◽

Cited By ~ 5

Author(s):

Zhi-kai Wang ◽

Zhuo-xiong Zeng ◽

Kai Li ◽

Yi-hua Xu

Keyword(s):

Guide Vane ◽

Flow Characteristics ◽

Structure Parameters ◽

Cold Flow ◽

Trapped Vortex ◽

Flow Guide ◽

Effect Of Structure

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Numerical Studies on Trapped-Vortex Concepts for Stable Combustion

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2818088 ◽

1998 ◽

Vol 120 (1) ◽

pp. 60-68 ◽

Cited By ~ 33

Author(s):

V. R. Katta ◽

W. M. Roquemore

Keyword(s):

Drag Coefficient ◽

Reacting Flow ◽

Flow Conditions ◽

Third Order ◽

Cold Flow ◽

Flow Simulations ◽

Numerical Studies ◽

Dynamic Flows ◽

Experimental Findings ◽

Trapped Vortex

Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.

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