Georgios Doulgeris

Computational analysis of the effects of a boundary layer ingesting propulsion system in transonic flow

Continuous requirements for more efficient aircrafts lead to the design and analysis of novel propulsion configurations, with an example being the boundary layer ingestion. The complexity and integration challenges in such aircraft synergistic propulsion system characterize the research in this field, driven by the potential benefits. The aim of this article is to investigate the effects of boundary layer ingestion on the aerodynamics of a transonic wing, together with the quality of the flow ingested by the propulsion system. A two-dimensional computational model of a transonic airfoil with boundary layer ingesting propulsion system is developed in order to assess boundary layer ingestion for a commercial air transport at cruise conditions and highlight the complex integration issues arising from such configuration. A parametric analysis of the effects of flight conditions, nacelle geometry and engine operating point, on lift, pressure recovery, distortion, total pressure and velocity distribution at the intake, comes to enhance understanding of the performance of this configuration. The pressure distribution around the airfoil and the boundary layer growth are both substantially affected by the engine operating condition, which is represented by the mass flow ratio, with a direct impact on pressure recovery and lift. Mach number and angle of attack influences on lift and drag ingested are also investigated. Intake size and position on the airfoil appear to have significant effects on lift and losses ingested. In general, the results of this study include several aspects related to wing aerodynamics and ingested flow quality, which may facilitate design and integration of the boundary layer ingestion propulsion system for future commercial aircraft.

Liquid hydrogen tank considerations for turboelectric distributed propulsion

Purpose – This article aims to investigate a selected number of liquid hydrogen storage tank parameters in a turboelectric distributed propulsion concept. Design/methodology/approach – In this research study, tank structure, tank geometry, tank materials and additional physical phenomenon such as hydrogen boil-off and permeation are considered. A parametric analysis of different insulation foams is also performed throughout the design process of a lightweight liquid hydrogen storage tank. Findings – Based on the mass of boil-off and foam weight, phenolic foam exhibited better characteristics amongst the five foam insulation materials considered in this particular study. Practical implications – Liquid hydrogen occupies 4.2 times the volume of jet fuel for the same amount of energy. This suggests that a notable tank size is expected. Nonetheless, as jet fuel weighs 2.9 times more than liquid hydrogen for the same amount of energy, this reduced weight aspect partly compensates for the increased tank size. O...

Turboelectric Distributed Propulsion System Modelling for Hybrid-Wing- Body Aircraft

(ABSTRACT) In 2005, NASA released plans of next generation commercial airplane for 2030, with a crossdisciplinary effort on: reduced fuel consumption, aviation reliability, fundamental noise reduction and shorter take-off length. Meeting these requirements will need a fundamental shift in aircraft and engine design. Turboelectric distributed propulsion system was chosen to achieve these targets. Different from traditional turbofan, distributed propulsion system employs a large number of fans embedded on upper surface of the airframe and two turbogenerators at wing tip. This novel configuration benefits from boundary layer ingestion and distributed fans to achieve higher bypass ratio but lower fuel burn. The N3-X hybrid-wing-body is used as a baseline aircraft for the study. This paper gives basic simulation methods, as well as computational models for turboelectric distributed propulsion system. Initially, a boundary layer ingesting model has been built from computational results for embedded propulsor at different inlet conditions. In a further step, a weight estimation model of propulsors was concluded to estimate propulsors’ weight and size. Then, thermal cycle model was built to calculate engine’s performance at both design point and off design conditions. Finally, effects of boundary layer ingestion on the propulsion system were examined. The boundary layer ingesting model showed mass-average inlet pressure and Mach number are function of flight Mach number and fan inlet mass flow, on the N3-X airframe. The weight estimation model shows the overall system weight decreased with increased number of propulsors, which also caused total inlet width of propulsors increasing. So for a given total inlet width, the propulsor should be used as many as possible to reduce weight. Thermal cycle results show that fan shaft speed should be chosen as high as possible before reaching the fan tip speed limitation, and fan pressure ratio (FPR) between 1.3 and 1.35 yields minimum thrust specific fuel consumption (TSFC) at the aerodynamic design point. A fan pressure ratio of 1.3 is chosen for its potential effects on noise control. In the end, a turboelectric distributed engine was simulated to satisfy NASA N+3 subsonic commercial airplane goals.

Development of a Method for Enhanced Fan Representation in Gas Turbine Modeling

A challenge in civil aviation future propulsion systems is expected to be the integration with the airframe, coming as a result of increasing bypass ratio or above wing installations for noise mitigation. The resulting highly distorted inlet flows to the engine make a clear demand for advanced gas turbine performance prediction models. Since the dawn of jet engine, several models have been proposed, and the present work comes to add a model that combines two well-established compressor performance methods in order to create a quasi-three-dimensional representation of the fan of a modern turbofan. A streamline curvature model is coupled to a parallel compressor method, covering radial and circumferential directions, respectively. Model testing has shown a close agreement to experimental data, making it a good candidate for assessing the loss of surge margin on a high bypass ratio turbofan, semiembedded on the upper surface of a broad wing airframe.

Enhanced Gas Turbine Performance Simulation Using CFD Modules in a 2D Representation of the Low-Pressure System for a High-Bypass Turbofan

The improvement of performance simulation for gas turbines has been approached in very different ways. In particular for high-bypass turbofans, efforts have been made to investigate radial flow distributions. The aim of the presented study was to combine a conventional characteristics-based performance code using a 2D representation of the fan with 2D representations of the adjoining intake and bypass system. Computational fluid dynamics (CFD) was the chosen tool to generate modules for the intake, bypass duct, and bypass nozzle. This approach required geometry data. A design procedure to generate these components in an axisymmetric meridional fashion and the numerical requirements for the CFD modules were developed. Typical component performances were predicted and the combined use of CFD and the performance code showed that in terms of performance, the inclusion of intake and bypass losses and the radial inlet distribution was worth considering. In particular, however, the required numerical effort was significant.

Effect of jet noise reduction on gas turbine engine efficiency

This article introduces a method for gas-turbine preliminary design, featuring jet-noise reduction as one of the main design objectives, or as the main objective. Selected methods have been implemented in an integrated systemic approach tool that includes gas turbine performance, aircraft performance and noise prediction. This tool enables the optimisation of the thermodynamic cycle for low noise, low fuel consumption, or a compromise between the two. Two case studies have been carried out for a 4000 nautical mile, 216-passenger aircraft: one targeting at minimum noise; and one for minimum fuel consumption. The parametric analysis approach enables the visualisation of the effect of cycle choices (overall pressure ratio, bypass ratio, combustor outlet temperature) on parameters such as engine size, weight, specific thrust, specific fuel consumption, noise and mission fuel. It is shown that noise reduction comes at the expense of fuel consumption, reducing the energy conversion efficiency of the system. Nevertheless the proposed tool allows the performance engineer to make appropriate choices for given design targets.

The Effect of Utilization Strategy on the CO2 Footprint of a Long Haul Aircraft

A study on the environmental impact of a long haul aircraft has been performed. Target of the study is to investigate the effect of flight mission characteristics on total emissions over the average lifetime of an airliner. This has been achieved using ‘Hermes’ aircraft performance model, developed in Cranfield University. The results show that a long range aircraft is expected to produce ~10000 times its weight in CO2, during a 20-year operating life. In a further step, the effect of the engine design has been assessed, where it has been shown that a ~2% improvement in fuel consumption and CO2 emissions can be achieved by matching the engine design point with the aircraft requirements.

Dynamic Response and High Cycle Fatigue Analysis of Fan Blades under Inlet Distortion

Continuous requirements for more efficient, greener aircrafts drive the design and analysis of novel propulsion configurations. A promising concept is expected to be the distribution of propulsion systems along the span of the wing. One of the benefits from distributed propulsion is the ingestion of the boundary layer that develops on the suction surface, with a direct effect on propulsive efficiency and fuel saving. However, the reenergization of low momentum boundary layer flow, introduces an inherent complexity to the design of the fan, as the flow that hits the fan face is characterized by highly distorted velocity profiles, due to low inlet velocity region at the lower part of the inlet circumference . As a result, each fan blade operates under varying inlet conditions during every revolution, something that has an impact on both aerodynamic performance but also mechanical integrity of the fan. The present paper focuses on the mechanical dynamic response of a fan blade operating under inlet distortion that could result from a boundary layer ingesting configuration.

Marine Gas Turbine Performance Model for More Electric Ships

This paper presents the benefits of the more electric vessels powered by hybrid engines and investigates the suitability of a particular prime-mover for a specific ship type using a simulation environment which can approach the actual operating conditions. The performance of a mega yacht (70m), powered by two 4.5MW recuperated gas turbines is examined in different voyage scenarios. The analysis is accomplished for a variety of weather and hull fouling conditions using a marine gas turbine performance software which is constituted by six modules based on analytical methods. In the present study, the marine simulation model is used to predict the fuel consumption and emission levels for various conditions of sea state, ambient and sea temperatures and hull fouling profiles. In addition, using the aforementioned parameters, the variation of engine and propeller efficiency can be estimated. Finally, the software is coupled to a creep life prediction tool, able to calculate the consumption of creep life of the high pressure turbine blading for the predefined missions. The results of the performance analysis show that a mega yacht powered by gas turbines can have comparable fuel consumption with the same vessel powered by high speed Diesel engines in the range of 10MW. In such Integrated Full Electric Propulsion (IFEP) environment the gas turbine provides a comprehensive candidate as a prime mover, mainly due to its compactness being highly valued in such application and its eco-friendly operation. The simulation of different voyage cases shows that cleaning the hull of the vessel, the fuel consumption reduces up to 16%. The benefit of the clean hull becomes even greater when adverse weather condition is considered. Additionally, the specific mega yacht when powered by two 4.2MW Diesel engines has a cruising speed of 15 knots with an average fuel consumption of 10.5 [tonne/day]. The same ship powered by two 4.5MW gas turbines has a cruising speed of 22 knots which means that a journey can be completed 31.8% faster, which reduces impressively the total steaming time. However the gas turbine powered yacht consumes 9 [tonne/day] more fuel. Considering the above, Gas Turbine looks to be the only solution which fulfills the next generation sophisticated high powered ship engine requirements.Copyright

Performance Evaluation of the CVC With Open Rotor Engine Technologies as Propulsion Systems for Subsonic Aircraft

This paper evaluates the constant volume combustion (CVC), the open rotor (OR) and constant volume combustion with open rotor (CVCOR) engine technologies as propulsion systems in subsonic aircraft. Available simulation codes are used to compare different engine technologies assuming the same level of technology investment, to identify the cycle optimum, to calculate the thrust specific fuel consumption (SFC) and to determine flight mission fuel burn for a short range and a long range aircraft. Compared to turbofans of current and of equal technology, it is concluded the novel cycles give better uninstalled SFC performance and better fuel burn performance installed for short and long range missions. Within the constraints of this study, it is concluded the novel cycles offer better thermal efficiencies, increasingly higher overall pressure ratios and yield a lower fuel burn compared to turbofans of current and of equal technology. The novel cycles would be viable as future propulsion systems if the primary design target is fuel consumption. The CVCOR and OR would be comparable based on SFC alone. However installation losses make the CVCOR a better prospect considering the effects of OPR and BPR. Against the impact of increasing fuel costs, it would be beneficial to use the novel cycles.Copyright