Predictions of misruns using three-phase coupled mold-filling and solidification simulations in low pressure turbine (LPT) blades

Abstract

New alloy developments such as γ-TiAl aim at weight reduction and improvement of performance capabilities of aircraft engines. A drawback of TiAl is its low fluidity, which easily leads to misruns during the casting process. In this work a three-phase mold filling and solidification simulation methodology has been established and validated against casting trials. It uses the finite-volume method and arbitrary polyhedral control volumes to solve the governing equations. A High-Resolution Interface-Capturing (HRIC) scheme has been established as state-of-the-art for modeling multiphase flows with sharp interfaces using the so called Volume-of-Fluid (VOF) model. This multiphase model has been extended to casting processes to predict velocity, pressure and temperature distribution for all three phases, namely the gas, melt and solidified phase. Since LPT blades for aircraft engine applications are of widely differing in geometry with less than 1 mm thickness at the trailing edges, the effect of surface tension and wetting angle is dominant in these wall-bounded flows during the filling stage. These effects can only be calculated correctly if the interface between the phases is sharp and mesh quality is high. For the later automatically generated body-fitted polyhedral meshes with thin prism layers are used. In addition resistance of the dendrite network to melt flow must be adequately modeled. Here, an additional source term in the momentum equation based on Kozeny-Carman relation for permeability estimation is used. A detailed analysis of filling and solidification is presented to study the performance of the simulation method. © Published under licence by IOP Publishing Ltd.