Today, main hub airports are already at their capacity limit and hence, smaller airports have become more interesting for providing point-to-point connections. Unfortunately, the use of regional airports induces an increased environmental footprint for the population living around it. In an attempt to solve the related problems, the research project Coordinated Research Centre 880 aims to examine the fundamentals of a single-aisle aircraft with active high-lift configuration powered by two geared ultra-high bypass turbofan engines mounted over the wing. Low direct operating costs, noise shielding due to the over-wing configuration, and short runway lengths are the main advantages. Highlighting the performance, economical and noise benefits of a geared ultra-high bypass engine is the key aim of this paper. This assessment includes a correspondingly adjusted aircraft. Open literature values are applied to design the two investigated bypass ratios; a reference engine with a bypass ratio of 5 and 17 respectively. This study shows that a careful selection of engine mass flow, turbine entry temperature and overall pressure ratio determines the desirable bypass ratio. The aircraft direct operating costs drop by 5.7% when comparing the designed conventional with a future ultra-high bypass ratio engine. Furthermore, the sound at source for a selected mission and operating condition can be reduced by 7 dB. A variable bypass nozzle area for the ultra-high bypass ratio engine is analysed in terms of performance and operability. An increase of safety margin is shown for the turbofan engine with a variable bypass nozzle. It is concluded that this unconventional aircraft configuration with ultra-high bypass ratio engines mounted over the wing has the potential to relieve main hub airports and reduce the environmental impact.
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Jet engine maintenance is a very competitive field in terms of time and costs. To increase planning security and reduce turnaround time (TAT) of the maintenance process it is important to get as much engine data as possible before disassembly. Aero engines are especially subjected to environmental and operational influences. For the high pressure turbine (HPT), the following parameters have been identified to describe the deterioration of its nozzle guide vane (NGV): On-wing cycles, NGV material, airport region, engine wing position, thrust rating, vane repair history and customer business segment. The combined influences of the parameters are non-trivial and it is not possible to acquire them analytically. There are no known mathematical laws connecting the above-mentioned parameters. The linear regression method set limits for processing data in an adequate manner. This is confirmed by the analysis of the arithmetic means and standard deviations. Especially the standard deviation values fit in a broad spectrum due to various reasons. Thus, it is not feasible to make an appropriate forecast with a simple statistical method due to the multidimensional character of the parameters influencing the accuracy. For this reason, advanced methods need to be developed to derive a feasible forecast method. By applying a statistical hypothesis test, a bayesian belief network (BBN) has been designed. It allows the use of imprecise data without suffering a significant loss in forecast accuracy and additionally, the implementation of expert knowledge. The objective of this study is to develop an effective BBN in order to adequately predict the next repair of the first stage HPT NGV of the General Electric CF6-80C2 engine. The reason for selecting the NGV is due to its high susceptibility to different influences, combined with the significant costs and TAT during the maintenance process. Having poor forecasting quality by using a simple statistical method, the evaluation of the BBN provides very satisfactory accuracy of above 80 percent which is equivalent to 19 out of 23 vane segments. Furthermore, the developed BBN emphasises robustness when detecting the expected tendencies while having only a limited amount of input parameters. Further work includes application of this method on other engine components as well as establishing the business value of the developed method. In conclusion, BBN have tremendous potential for forecasting the repair of the entire jet engine.
The "Technische Universität Braunschweig" has commissioned a Propulsion Test Facility (PTF) for aspirated intake models of jet engines under off-design point conditions. For the commissioning of the unique facility, an aspirated intake test campaign has been carried out. Aim of the campaign was to compare the measured data in the PTF to numerical results and experimental data, which have already been measured in another test facility in the past using the same intake geometry. For the tests the Laminar Flow Reynolds Action (LARA) nacelle has been chosen. The LARA intake has been built and tested in the early 1990s at the "ONERA F1" wind tunnel during the work on hybrid laminar flow technology. At TU Braunschweig an Aspirated-Intake-Rig (ASI-Rig) with an in-house designed fan stage was worked out, whose fan is located far enough downstream to avoid interaction with the nacelle. For the results, the static pressure distribution at the inner and outer contour of the nacelle lip and the velocity distribution in the fan face during pure crosswind conditions have been compared and analysed. As seen in the results, the PTF pressure distribution at the lip is in good agreement with the numerical and the experimental data from the ONERA. Of particular note is the deviation between the achieved peak Mach number between the two experimental setups, analysed at the 0 • /180 • and 90 • section, which can be explained by the Reynolds number effect.
The lower atmosphere is known to be relatively more concentrated with airborne pollutant. Short-range aircrafts are particularly more affected due to the altitude they operate, making them more susceptible to compressor fouling degradation. This usually leads to the demand for more fuel that increases the emissions, to make up for the reduction in the thrust. Compressor fouling is therefore a concern for aircraft operators due to increasing fuel cost and emission-based landing fees which impact the direct operating costs of an aircraft. Highlighting the performance and economic benefits of compressor washing are the key aims of this study. An economic model is developed and the benefit is calculated for different wash intervals, which are based on the usual aircraft checks. The clean and fouled engine performance is simulated, indicating the impact of compressor fouling degradation on the twin-spool engine model. To emphasise the benefit of compressor washing, the degraded engine is compared to its new condition after washing. It was observed that it is impossible to fully recover the performance of a fouled compressor by an on-wing compressor wash. This study concludes that compressor washing has a significant improvement on engine performance, as well as cost benefit in monetary terms. The results also suggest that compressor washing can reduce the unwanted thrust loss and exhaust gas temperature increase due to fouling, by half. A gross recovery of almost £75,000 per year for a short-range engine is shown to be achievable with a marginal increase of the total washing cost.
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