Computational Modeling of High Temperature Deposition in Gas Turbine Engines with Experimental Validation

Abstract

Four deposition models--critical velocity, critical viscosity, and two forms of elastoviscoplasticity--were studied to determine their applicability to deposition in gas turbine engines. An experimental rig was constructed to determine the coefficient of restitution and sticking probability of bituminous ash particles. The coefficient of restitution was found to decrease for both increased particle temperature and increased particle impact velocity, matching the trends of similar tests performed with quartz particles. The sticking probability was observed to be highest at the lowest observed particle kinetic energies. These trends highlight the shortcomings of both the critical velocity and critical viscosity models. No results were found to discount either of the elastoviscoplasticity models, but more data must be analyzed to confirm if either of these models correctly describes ash particle impact physics in gas turbine engine environments. Nomenclature A= constant used to define critical viscosity model B = constant used to define critical viscosity model D = particle diameter E = effective modulus of elasticity ‫ܧ‬ = particle modulus of elasticity ‫ܧ‬ ௦ = surface modulus of elasticity e = coefficient of restitution KE = kinetic energy k = apparent plastic flow consistency m = particle mass n = apparent plastic flow index P S = probability of particle sticking r = particle radius T P = temperature of particle ‫ݒ‬ = normal critical velocity ‫ݒ‬ = final/rebound velocity ‫ݒ‬ = initial/impact velocity ܹ = work of adhesion ߛ = surface energy adhesion parameter η = ratio of initial tangential velocity to initial normal velocity ߟ = particle Poission's ratio ߟ ௦ = surface Poission's ratio µ = viscosity of particle µ crit = viscosity of particle at critical sticking temperature µ Tp = viscosity of particle at temperature ߩ = particle density ߪ ො = flow stress ߪ = yield stress ߪ = uniaxal yield stress