Two-Phase CFD-Calculations for the Design of Water-Based Turbine Cleaning Systems for Turbochargers

Abstract

Turbochargers operated with heavy fuel oil are subjected to deposition of combustion residues on stator vanes, the turbine rotor and turbine casing. Without appropriate measures the turbine stage efficiency drops. Moreover, in severely contaminated turbine stages clogging of whole stator channels can occur, which results in unwanted turbine excitation and ultimately failure. To assure a constantly high level of efficiency and mechanical integrity turbochargers operated with critical fuels are equipped with an online turbine cleaning system that is based on the injection of water. The water is injected such that the whole stator is evenly wetted with water and ultimately cleaned. The design of modern cleaning systems is based on two-phase computational fluid dynamics (CFD) simulations, where water-jets are tracked throughout the computational domain, commonly in a Lagrangian way. Multiple physical phenomena are considered, e.g. turbulent interaction with the gas phase and droplet break-up within the liquid spray, where the latter has a direct influence on spray penetration depth and finally the proper design of the cleaning system. This paper presents a validation of spray modeling in the relevant Weber and Reynolds number regime, with emphasis on the droplet break-up model. The numerical results are compared with LIF and laser diffraction measurements of the water spray in cross flow in terms of concentration and droplet size distribution. Finally, the validated and improved model is applied to re-calculate a real world application: the state-of-the-art cleaning system of a turbocharger again thoroughly validated against the test bench measurements.