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On-wing cleaning of engine compressors for commercial aircraft is a required maintenance task which results in greater operating efficiency and lower emission rates. It is typically carried out by injection of water and detergents into the intake of an engine while the engine is being cranked by the starter. Two drawbacks of this process are the risk of icing in cold weather and the collection and treatment of the water effluent. The dry-ice blasting process, a cleaning system which uses pressurized air and CO2 dry-ice particles as cleaning agent, has been proposed as an alternative method which does not suffer the above drawbacks but is potentially capable of efficient cleaning. In this context, such a cleaning system is currently being developed by Lufthansa Technik in association with Hochschule Darmstadt and DIT. This work focuses on the development and validation of a numerical model of this process, which can be used to improve the understanding of the complex multiphase flow phenomena involved and to assess the cleaning physics. Appropriate multiphase flow set-ups and new particle breakup and erosion models are developed. These new models will facilitate the numerical prediction of particle behaviour and defouling erosion rates during the defouling process.
An appropriate simulation set-up for the particle laden injection system flow simulations using the Euler-Lagrange method is investigated. Three possible injection systems with various air flow velocities and particle loading densities are considered. These systems are investigated by means of high-speed camera (HSC) experiments and the predicted results are compared to the experimental in order to find the best numerical set-up. An improvement to the particle drag force formulation is proposed for highly pressurized air-flows. A new particle breakup model for dry-ice in Euler-Lagrange simulations is developed. This model is theoretically derived from an energy balance and un-derpinned with data from HSC experiments. It includes velocity, impact angle and target temperature as factors determining breakup behaviour of dry-ice particles impinging solid walls. A new defouling erosion model utilizing an energy balance approach and based on a range of experiments with several types of actual and artificial fouling material is developed and tested. The particle breakup and the erosion model are implemented into the commercial CFD code Ansys CFX. Verification and validation studies of both new models are presented. The validation of the new models uses data acquired in a specially-designed wind-tunnel experiment. All main findings and models are used in a final application case study where the new dry-ice based cleaning procedure is applied to a GE-CF6-50 test engine. Comparison of numerical results to data from air-flow, particle tracking and defouling experiments is also presented for this case.
Rudek, A. (2018) Development and Validation of a Numerical Model of the CO2 Dry-ice Blasting Process for Aircraft Engine Cleaning Applications, Vols. 1 and 2. Doctoral thesis, DIT, 2018.