A numerical model for turbulent reacting flow is described and applied for predictions in an industrial gas turbine combustor operating on low-Btu coal gas. The model, based on fast-reaction limit, used Favre averaged conservation equations with the standard k-c model of turbulence. Effects of turbulent fluctuations on chemistry are described statistically in terms of the mean, variance and probability density function (assumed to be fldistribution) of the mixture fraction.Two types of geometric approximations, namely axisymmetric and three-dimensional, were used to model the combustor. Computations were performed with (a) no swirl (b) weak swirl and (c) strong swirl at the fuel and primary air inlets. Essentially, the same bulk mean temperature distributions were obtained for axisymmetric and three-dimensional calculations while the computed pattern factors and the liner wall temperatures for the two differed significantly. Complete combustion was predicted with strong swirl, a result supported by the available test data. The maximum liner wall temperature predicted for three-dimensional calculations compared favorably with the experimental data while the predicted maximum exhaust gas temperature differed by =120 K . The difference was attributed to measurement uncertainties, model assumptions and lack of accurate data at the inlets. The maximum flame temperature was below 1,850 K indicating that thermal NOx may be insignificant.

AIAA JOURNAL approximation. 3) The pilot pressure distributions together with the distributions of the cross components of the local velocity indicate that the inboard shock wave, starting perpendicularly from the wing surface, extends into the central region (i.e., the region where the influence of both halves of the delta wing is felt). 4) The measurements strongly suggest that the inboard shock wave ends with zero strength in the point where the conical sonic line starts. The way in which this transition occurs has not been clarified by the present measurements. 5) The measurements are in very good agreement with numerical calculations using a shock capturing technique.A turbulent boundary-layer flow from along a fixed surface and on to a moving surface is described and analyzed. Analysis of experimentally measured velocity profiles is used to justify the use of the boundary-layer equations in this flow situation. A calculation technique for moving wall boundary layers based on the Cebeci-Smith method is presented. A new correlation for eddy viscosity in the outer layer suitable for use with the moving wall analysis is given. This correlation is based on the average shear velocity and the boundary-layer thickness. Experimental data of streamwise minimum boundary-layer velocities and a velocity profile presented compare favorably with the calculation technique. Based on the experimental data available it is concluded that the boundary-layer equations are applicable to the flow situation and the calculation technique is satisfactory. Nomenclature/ = dimensionless stream function k j, k 2 = constants in eddy-viscosity formulas P = dimensionless pressure R e = Reynolds number, V e 0/v U e = external flow velocity U t = external flow velocity along the stationary wall U p -wall velocity u,v -x and y components of velocity, respectively A 6 Y] = friction velocity (i/p) 1/2 = average absolute friction velocity in the outer layer -VJV. -integral boundary-layer thickness = boundary-layer thickness = transformed y coordinate = momentum boundary-layer thickness = kinematic viscosity = density = shear stress Subscripts e = outer edge of boundary layer w = wall p = moving wall _ = beginning of moving wall (underline) Downloaded by UNIVERSITY OF ARIZONA on February 4, 2015 | http://arc.aiaa.org |

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This paper presents an experimental/computational study of cold flow in the combustor-diffuser system of industrial gas turbines to address issues relating to flow interactions and pressure losses in the pre- and dump diffuses. The present configuration with can annular combustors differs substantially from the aircraft engines which typically use a 360 degree annular combustor. Experiments were conducted in a one-third scale, annular 360-degree model using several can combustors equispaced around the turbine axis. A 3-D computational fluid dynamics analysis employing the multidomain procedure was performed to supplement the flow measurements. The measured data correlated well with the computations. The airflow in the dump diffuser adversely affected the prediffuser flow by causing it to accelerate in the outer region at the prediffuser exit. This phenomenon referred to as the sink-effect also caused a large fraction of the flow to bypass much of the dump diffuser and go directly from the prediffuser exit to the bypass air holes on the combustor casing, thereby, rendering the dump diffuser ineffective in diffusing the flow. The dump diffuser was occupied by a large recirculation region which dissipated the flow kinetic energy. Approximately 1.2 dynamic head at the prediffuser inlet was lost in the combustor-diffuser system; much of it in the dump diffuser where the fluid passed through the narrow gaps and pathways. Strong flow interactions in the combustor-diffuser system indicate the need for design modifications which could not be addressed by empirical correlations based on simple flow configurations.

This paper presents a procedure for the design and the performance prediction of axially symmetrical contoured wall diffusers employing suction boundary layer control. An inverse problem approach was used in the potential flow design of the diffuser wall contours. Three short (L/l ≤ 5.15), high area ratio (2.5 and 3) diffusers were tested in the study and were found to have effectiveness values in excess of 90 percent (comparable straight wall diffusers have effectiveness <40 percent) while requiring suction flows of less than 10 percent of the inlet flow. The experimentally observed flow characteristics, the stability of flows within the diffusers, are also described. Because of their high effectiveness and short length these diffusers appear to be ideally suited for use as gas turbine combustor diffusers and as turbine discharge diffusers.