Computation of Two-Phase Flows in Low-NOx Combustor Premix Ducts Utilizing Fuel Film Evaporation

Abstract

For aircraft gas turbines as well as for industrial gas turbines current and future developments aim at the implementation of lean premixed-prevaporized (LPP) combustor techniques. For the development and optimization of these combustors powerful CFD-codes are required. A new code developed at the Institut für Thermische Strömungsmaschinen (ITS), University of Karlsruhe, provides detailed information on the gas flow as well as on the propagation and evaporation characteristics of liquid wall films inside combustors. The flow characteristics of the gas phase are predicted using a Finite-Volume 3D-Navier-Stokes code with k-ε turbulence modeling. To calculate the evaporation characteristics of a propagating wall film, a two-dimensional wall film model based on the boundary layer equations is proposed. The present paper comprises a comparison between calculations and experiments for the verification of the code and a detailed study on the evaporation characteristics of fuel films. The results obtained allow judgement to be made on the risk of coke formation on the prefilming surface and suggest that in some operating points a LPP combustor can be operated utilizing solely film evaporation. In addition, the computer code developed also accounts for many familiar types of shear driven film flows such as internal prefilming air blast atomizer flows for example.

Effect of the Shear Driven Liquid Wall Film on the Performance of Prefilming Airblast Atomizers

“…This leads to the new heat transfer model which is shown in Figure 8. (1998) and Rosskamp et al (1998). For shear driven liquid films with three dimensional wave pattern, the model parameters may be taken as constant with reasonable accuracy (Table 1) AT (19) I an effective Nusselt number for the wavy film may be defined which reads: .44 (20) This means that the wavy flow pattern enhances the wall heat…”

“…This resulting set of coupled ordinary differential equations is solved by a Runge-Kutta algorithm with self-adapting step size. For the details of the model the reader is referred to Rosskamp et al (1997a). The air flow and the heat transfer on the back side of the prefilming wall (in this case the secondary swirl channel) may be calculated by conventional means.…”

“…Even though this atomizer type became well investigated (Lefebvre 1989, Rizk et al 1987, Sattelmayer et al 1989, still no general quantitative relationship between atomizer design and spray quality could be established since the fuel state at the atomizer edge cannot be precisely predicted yet. In extending earlier experimental and theoretical work on airblast atomizers (Sattelmayer et al 1989, Himmelsbach et al 1994 and recent advances in the numerical modeling of wall film flows (Rosskamp et al 1997a), this paper presents a numerical approach to judge the effect of fuel mass flow, air flow and the film length (i. e. length of atomizer lip) on the temperature of the liquid at the atomizer edge. The computer code developed provides detailed information on the wall film flow and the nozzle wall temperature.…”