Engine durability tests are used by manufacturers to demonstrate engine life and minimum performance when subjected to doses of test dusts, often Arizona Road Dust. Grain size distributions are chosen to replicate what enters the engine; less attention is paid to other properties such as composition and shape. We demonstrate here the differences in the probability of interaction of a particle of a given particle Reynolds number on to a vane if particle shape, vane geometry, and flow Reynolds number are varied and discuss why the traditional definition of Stokes number is inadequate for predicting the likelihood of interaction in these flows. We develop a new generalized Stokes number for nozzle guide vanes and demonstrate its use through application to 2D sections of the General Electric E3 nozzle guide vane. The new Stokes number is used to develop a reduced-order probability curve to predict the interaction efficiency of spherical and nonspherical particles, independent of flow conditions and vane geometry. We show that assuming spherical particles instead of more realistic sphericity of 0.75 can lead to as much as 25% difference in the probability of interaction at Stokes numbers of around unity. Finally, we use a hypothetical size distribution to demonstrate the application of the model to predict the total mass fraction of dust interaction with a nozzle guide vane at design point conditions and highlight the potential difference in the accumulation factor between spherical and nonspherical particles.

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There have been several recorded mishaps of rotorcraft experiencing flame-out due to engine surge as a result of rapid accumulation of sand and dust on nozzle guide vanes. Minerals such as sodium chloride and albite have lower melting points than quartz and are found to constitute some of the loose sediment on unprepared landing sites in the Persian Gulf. Despite this, they are not found in great abundance, if at all, in many of the test dusts that are used to qualify engines operating in harsh environments. The consequence is an under-prediction of the time to failure due to vane deposit build-up. In the current work, we use a simple model to demonstrate the sensitivity of accumulation efficiency (the proportion of ingested dust that sticks) to mineral dust physico-chemical properties. We utilise the concept of thermal Stokes number to examine the relationship between time to equilibrate and residence time and how this varies as a function of constituent mineral, as well as particle size. The likelihood of impact increases with momentum Stokes number, while the likelihood of adhesion decreases with thermal Stokes number, yet the two both increase with the square of particle diameter. This leads to a peak in deposition rate at a certain particle size. However, dust mineralogy is shown to influence sticking efficiency more than impact efficiency owing to differences in melting point. Finally, we apply our simple model to estimate the mass of dust deposited during a single brownout landing of a Pave Hawk helicopter, using two different commercially-available test dusts.

Commercial aircraft operating in some regions of the world are subject to harsh atmospheric conditions that can affect the efficiency and integrity of modern aero-engines. Conditions that are investigated in this contribution are dusty atmospheres following sand storms. Specifically, the dust ingested by the engines of an Airbus A380-841 (Rolls-Royce Trent 900) operating out of Doha airport (IATA: HIA) is estimated by simulating climb-out trajectories over three separate calendar months during which a number of sand storms have been identified. The atmosphere model incorporates dust concentration hind-casts from the European Centre for Medium-Range Weather Forecasts (ECMWF) near real-time Copernicus Atmosphere Monitoring Service database. A total of 365 flights were considered. The average dust mass ingested into the engine core per flight is estimated as ∼8.5 g. Using a compressor fouling prediction model, the dust ingestion reduces the asymptotic deterioration rate time constant by a factor ∼8. The worst dust storm within the time frame considered is selected for further examination. This flight is flagged as a dust-flight, during which the total mass of dust ingested into the engine core exceeds the monthly mean by two standard deviations. A peak dust ingestion rate of 22 mg/s occurs shortly after take-off, midway through the first climb segment. A second peak presents as the aircraft transitions into the climb from 3,000 feet to 10,000 feet. Finally, the dust ingested during a 20-minute holding pattern over the Persian Gulf is estimated as ∼8g, which is approximately the same as the dust ingested during climb-out on a very dusty day. The results suggest that a mission-based approach may be more useful for determining aircraft engine durability in dusty environments.

A statistical analysis has been developed from the ICAO databank to predict aero-engines exhaust emissions during a landing and takeoff cycle (LTO). The ICAO databank contains updated emission indices for a vast number of turbojet and turbofan engines only, with thrust ratings greater than 26.7 kN. Correlations are developed and proposed for turboprop and turboshaft engines to overcome the difficulty of assessing exhaust emissions from these engines in absence of industry data. LTO emissions are predicted for a turbofan-powered commuter airplane (Embraer E195) using the surrogate model. It is demonstrated that the predictions are closer to the values extracted from the flight data recorder than to the emissions calculated with the ICAO method. Thus, approximate emissions indices applied to actual flight procedures are a better choice that a standard ICAO LTO emission estimate from the databank. The correlations are then applied to the prediction of LTO emissions of a turboprop airplane (Bombardier Q400).