Numerical-Experimental Research of Ultra Compact Combustors containing Film and Effusion Cooling

Abstract

A novel Ultra-Compact Combustor (UCC) that operates as a main combustor in a gas turbine engine is modeled with the Trapped Vortex Combustor (TVC) incorporating three inlet guide vanes (IGVs), containing no radial vane cavities (RVC), and three deswirler vanes located further downstream (Configuration 1). This geometry is compared with another configuration containing three IGVs with a full-through RVC (Configuration 2e). The steady threedimensional equations of continuity, momentum, turbulence, total enthalpy (H), C-progress variable (C), Favre mixture fraction (f), and Favre mixture fraction variance (f ` ) in Eulerian reference frame as well as the n-dodecane liquid-fuel droplet trajectory, and heat and mass exchange with the continuum phase in a Lagrangian frame are solved using FLUENT. This combustion model is referred as a partially premixed combustion (PPC) model. The PPC flamelets are calculated by solving the laminar n-dodecane/air counterflow non-premixed flame equations in a mixture fraction (f) space using the JetSurf-ls-1.0 chemical reaction mechanism containing 100 species and 856 Arrhenius reactions. A -shape probability density function (PDF) table containing density (ρ), species (Y ), and temperature (T) as function of f, f ` , H,  , and C is generated. Turbulence is modeled using the Realizable k- RANS governing equations. Liquid fuel is injected through the TVC (which contains air driver jets and effusion and film cooling jets) with a local TVC equivalence ratio of TVC1.39 (excluding cooling air) and TVC0.84 (including cooling air). The global equivalence ratio is Global= 0.066 (without cooling air), or Global= 0.059 (with cooling air). The jets involved in film cooling are resolved, whereas the effusion cooling jets are modeled as source terms because there are thousands of tiny injections with geometrical sizes comparable to that of the cells near the boundary conditions. Therefore, meshing these tiny design features would be prohibitive. Nevertheless, accurate numerical predictions call for inclusion of these effusion cooling jets in the simulated approached adopted here because their total air mass flow rate constitutes a substantial fraction of the total overall mass flow rate. Consequently, the effusion cooling jets are introduced in the model as volumetric mass flow rate and momentum source terms in the cells adjacent to the relevant boundary conditions. Simulations are compared with measurements conducted at the High Pressure Combustor Research Facility (HPCRF) located at Wright-Patterson AFB (WPAFB). This paper presents flow/flame structure, exit temperature profiles, and global performance parameters of the two UCC-TVC-IGV configurations operating at 514,762.6 Pa. Numerical results indicate that liquid fuel that is injected in the TVC as a conical spray of droplets evaporates and boils almost immediately after injection within the TVC cavity. A turbulent triple flame containing multiple reaction zones, viz., rich premixed (RPRZ), nonpremixed (NPRZ), and lean premixed (LPRZ), is attached to the TVC. Both UCC-TVC-IGV configurations show a single dominating vortex in the TVC cavity rotating in opposite direction to the mainstream flow. Generally, hightemperature regions correspond to near-stoichiometric fuel/air mixtures, whereas low temperature regions are associated with off-stoichiometric fuel/air mixtures. Increasing scalar dissipation ( ), enhancing heat losses, and flame front regions (0.0<C<1.0) reduce the temperature (T) below its corresponding adiabatic equilibrium temperature. Configuration 1 shows a more uniform temperature flow field in comparison with Configuration 2e. For the former the temperature is more equally distributed in the spanwise direction within the TVC cavity than for the latter configuration. In addition, for Configuration 1 the temperature decreases in the normal direction whereas for Configuration 2e the temperature increases in the normal direction away from the TVC cavity. However, in both configurations the Mach number does not exceed 0.5, and it is maximum downstream the TVC cavity along the IGV suction sides, and peaks at the deswirler vane leading edges. Good comparison between the measured IGV heat signature and the predicted temperature contours on the IGV was achieved. The model predicts good effusion cooling. However, where film cooling is used there is a temperature distribution such as in the aft wall of the TVC 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 07 10 January 2013, Grapevine (Dallas/Ft. Worth Region), Texas AIAA 2013-1045