Shusheng Zang

Technical Brief: Predictions of Flow Field for Circular-Disk Bluff-Body Stabilized Flame Investigated by Large Eddy Simulation and Experiments

The objective of the current work is to shed light on simulating the flow features of nonpremixed flame stabilized by a circular-disk bluff-body with large eddy simulation technique. Two subgrid scale (SGS) models (Smagorinsky and Germano), combined with a constrained chemical equilibrium model, are applied to simulate this turbulent flame. Validation is made through the particle image velocimetry measurements. The comparison between the numerical simulation and experimental data shows that both models perform well and reproduce most of the significant features of the bluff-body flame, while the Germano SGS model performs better in prediction of turbulent fluctuations. These investigations show that it is possible to describe such flows with relatively simple turbulence and combustion models with moderate grids.

Experimental Study of Nitrogen Dilution Effects on a Double-Swirled Non-Premixed Syngas Burner

The development of integrated, coal-gasification combined cycle (IGCC) systems provides cost-effective and environmentally sound options for meeting future coal-utilizing power generation needs in the world. The combustion of gasified coal fuel significantly influences overall performance of IGCC power generation. This study focuses on investigating the nitrogen dilution effects on a double-swirled non-premixed syngas flame. As the references, investigations on the H2 and CO double-swirled flames with N2 dilution are presented. Planar laser-induced fluorescence (PLIF) of OH-radical measurement is adopted to identify main reaction zones and burnt gas regions. Together with temperature and emission measurement during exhaust section, some important characteristics of the syngas flame are overall investigated. Experimental result shows that syngas flame root near the burner exit demonstrates double flame front structure. The existence of N2 expands the flame opening angle and enlarges the main reaction zone, and it may lead to lower NO emission and higher CO emission in exhaust gas.Copyright

Experimental and Numerical Investigations of Low-Swirl Multi-Nozzle Combustion in a Lean Premixed Combustor

This paper presents large-eddy simulations (LES) and laser diagnostic experiments of low-swirl lean premixed methane/air flames in a multi-nozzle combustor including five nozzles with the same structure. OH Planar Laser Induced Fluorescence (PLIF) is used to observe flame shapes and identify main reaction zones. NOx and CO emissions are also recorded during the experiment. The flows and flames are studied at different equivalence ratios ranging from 0.5 to 0.8, while the inlet velocity is fixed at 6.2 m/s. Results show that the neighboring swirling flows interact with each other, generating a highly turbulent mixing zone where intensive reactions take place. The flame is stabilized above the nozzle rim and its liftoff height decreases with increasing equivalence ratio. The center flow is confined and distorted by the neighboring flows, resulting in instabilities of the center flame. Mean OH radical images reveals that the center nozzle flame is extinguished when equivalence ratio is equals to 0.5, which is successfully predicted by LES. In addition, NOx emissions show log-linear dependency on the adiabatic flame temperature, while the CO emissions remain lower than 10 ppm. NOx emissions for multi-nozzle flame are less sensitive to the flame temperature than that for single nozzle. These results demonstrate that the low-swirl multi-nozzle concept is a promising solution to achieve stable combustion with ultra-low emissions in gas turbines.Copyright

Comparative Study of Impinging Jet Array Heat Transfer on a Flat Plate Cooled by Superheated Steam and Air

In modern gas turbine, using superheated steam to cool the vane and the liner of combustion chamber is a promising alternative to traditional compressor air. Infrared camera was applied to measure the spatial distribution of the impingement heat transfer coefficient on a flat plate cooled by superheated steam and air in this paper. The experimental study revealed the distribution of local heat transfer coefficients over a flat plate cooled by steam and air in an array of 3×5 impinging jets module. Results showed that the impingement cooling heat transfer is enhanced by the increase of mass flow rate, and the superheated steam cooling could improve area averaged heat transfer performance 35.3∼83.0% more than air cooling in the same mass flow rate conditions in the experiment. The influence of the jet-to-plate spacing ratio (Zn/d) and the jet-to-jet spacing ratio (Yn/d) on heat transfer were also investigated. It was concluded that the heat transfer is enhanced with the increase of Yn/d or the decrease of Zn/d based on the same area. Furthermore, three-dimensional and steady state computations had been carried out for experimental operating conditions. The Numerical results and experimental data have good agreements with each other for both the area averaged Nu and the local Nu, so results of the numerical model are expecting reliable. Results based Numerical models showed detailed characteristics of the distribution of the velocity and turbulence level, which revealed underlying mechanisms of pressure loss and flow structure for steam cooing and air cooling respectively.© 2014 ASME

LES and Experimental Study of Flow Features in Humid-Air Combustion Chamber With Non-Premixed Circular-Disc Stabilized Flames

Sydney/Sandia bluff-body flame series [1] has been world-widely studied based on a simple-geometry bluff-body. This study focuses on a turbulent piloted non-premixed methane jet flame with circular-disc which is used in a humid-air combustion chamber without a swirler. Large eddy simulation has been performed to investigate the flow features. Meanwhile, in order to validate the simulation results, an experimental study is also conducted, where the instantaneous velocity and temperature fields are measured using PIV and high temperature thermocouples, respectively. Compared to Sydney/Sandia flame series, the enlarged simulation area effectively eliminates the boundary effects on flow field. Comparisons with experimental data also show that for high resolution of grids, comparatively good agreement is obtained for the flow field. Unlike Sydney/Sandia flame series, central jet tends to break up early in this case because of the existence of the circular disc. It has also been found that the shear layer between the co-flow and the bluff-body wake is captured by LES as well as by PIV. Because of the difference in geometry between Sydney/Sandia and circular-disc bluff-bodies, it needs to be further studied how to apply the conclusions based on the former to the latter. However, current and future LES and experimental study can help to illustrate the tradeoffs among the degree of swirl and the choice of bluff-body shapes in devices such as industrial burners and gas turbines.© 2008 ASME