Showing papers on "Turbofan published in 2011"

Turboelectric Distributed Propulsion in a Hybrid Wing Body Aircraft

Abstract: The performance of the N3-X, a 300 passenger hybrid wing body (HWB) aircraft with turboelectric distributed propulsion (TeDP), has been analyzed to see if it can meet the 70% fuel burn reduction goal of the NASA Subsonic Fixed Wing project for N+3 generation aircraft. The TeDP system utilizes superconducting electric generators, motors and transmission lines to allow the power producing and thrust producing portions of the system to be widely separated. It also allows a small number of large turboshaft engines to drive any number of propulsors. On the N3-X these new degrees of freedom were used to (1) place two large turboshaft engines driving generators in freestream conditions to maximize thermal efficiency and (2) to embed a broad continuous array of 15 motor driven propulsors on the upper surface of the aircraft near the trailing edge. That location maximizes the amount of the boundary layer ingested and thus maximizes propulsive efficiency. The Boeing B777-200LR flying 7500 nm (13890 km) with a cruise speed of Mach 0.84 and an 118100 lb payload was selected as the reference aircraft and mission for this study. In order to distinguish between improvements due to technology and aircraft configuration changes from those due to the propulsion configuration changes, an intermediate configuration was included in this study. In this configuration a pylon mounted, ultra high bypass (UHB) geared turbofan engine with identical propulsion technology was integrated into the same hybrid wing body airframe. That aircraft achieved a 52% reduction in mission fuel burn relative to the reference aircraft. The N3-X was able to achieve a reduction of 70% and 72% (depending on the cooling system) relative to the reference aircraft. The additional 18% - 20% reduction in the mission fuel burn can therefore be attributed to the additional degrees of freedom in the propulsion system configuration afforded by the TeDP system that eliminates nacelle and pylon drag, maximizes boundary layer ingestion (BLI) to reduce inlet drag on the propulsion system, and reduces the wake drag of the vehicle.

Refined Exploration of Turbofan Design Options for an Advanced Single-Aisle Transport

Abstract: A comprehensive exploration of the turbofan engine design space for an advanced technology single-aisle transport (737/A320 class aircraft) was conducted previously by the authors and is documented in a prior report. Through the course of that study and in a subsequent evaluation of the approach and results, a number of enhancements to the engine design ground rules and assumptions were identified. A follow-on effort was initiated to investigate the impacts of these changes on the original study results. The fundamental conclusions of the prior study were found to still be valid with the revised engine designs. The most significant impact of the design changes was a reduction in the aircraft weight and block fuel penalties incurred with low fan pressure ratio, ultra-high bypass ratio designs. This enables lower noise levels to be pursued (through lower fan pressure ratio) with minor negative impacts on aircraft weight and fuel efficiency. Regardless of the engine design selected, the results of this study indicate the potential for the advanced aircraft to realize substantial improvements in fuel efficiency, emissions, and noise compared to the current vehicles in this size class.

Assessment of Future Aero-engine Designs With Intercooled and Intercooled Recuperated Cores

Abstract: Reduction in CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction in engine nacelle drag and weight. Conventional turbofan designs, however, that reduce CO2 emissions—such as increased overall pressure ratio designs—can increase the production of NOx emissions. In the present work, funded by the European Framework 6 collaborative project NEW Aero engine Core concepts (NEWAC), an aero-engine multidisciplinary design tool, Techno-economic, Environmental, and Risk Assessment for 2020 (TERA2020), has been utilized to study the potential benefits from introducing heat-exchanged cores in future turbofan engine designs. The tool comprises of various modules covering a wide range of disciplines: engine performance, engine aerodynamic and mechanical design, aircraft design and performance, emissions prediction and environmental impact, engine and airframe noise, as well as production, maintenance and direct operating costs. Fundamental performance differences between heat-exchanged cores and a conventional core are discussed and quantified. Cycle limitations imposed by mechanical considerations, operational limitations and emissions legislation are also discussed. The research work presented in this paper concludes with a full assessment at aircraft system level that reveals the significant potential performance benefits for the intercooled and intercooled recuperated cycles. An intercooled core can be designed for a significantly higher overall pressure ratio and with reduced cooling air requirements, providing a higher thermal efficiency than could otherwise be practically achieved with a conventional core. Variable geometry can be implemented to optimize the use of the intercooler for a given flight mission. An intercooled recuperated core can provide high thermal efficiency at low overall pressure ratio values and also benefit significantly from the introduction of a variable geometry low pressure turbine. The necessity of introducing novel lean-burn combustion technology to reduce NOx emissions at cruise as well as for the landing and take-off cycle, is demonstrated for both heat-exchanged cores and conventional designs. Significant benefits in terms of NOx reduction are predicted from the introduction of a variable geometry low pressure turbine in an intercooled core with lean-burn combustion technology.

Demonstrating the more electric engine: a step towards the power optimised aircraft

Abstract: Early in 2008, as part of the European funded power optimised aircraft (POA) technology project, Rolls-Royce ran a substantial engine test programme to demonstrate the feasibility of more electric engine technologies. This study outlines the technologies that were developed as replacements for conventional turbofan engine components, discussing the key features of the power electronics, generation and motor drive systems integrated within the aircraft engine and goes on to discuss outcomes from the test programme and draw conclusions to the applicability of more electric technologies for future applications. The main findings of systems-level modelling and simulation, which was employed to de-risk the engine electrical network design ahead of the hardware build, are also discussed. The study presents a summary of the major technical challenges faced in the development and operation of the engine system together with the solutions employed to overcome them. A selection of test results is provided to illustrate examples of the electrical system operation and to show a comparison between the modelled and tested results. The study concludes by exploring how the technical achievements of the engine demonstration and of the wider POA programme are providing the foundation for further work to realise the full potential of the more electric aircraft.

Conceptual Design and Mission Analysis for a Geared Turbofan and an Open Rotor Configuration

Abstract: In this multidisciplinary study a geared open rotor configuration is assessed and compared to an ultra high bypass ratio geared turbofan engine. Both designs assume a 2020 entry into service level of technology. The specific thrust level for minimizing block fuel and the resulting engine emissions for a given mission is sought. The tool used contains models that effectively capture: engine performance, mechanical and aerodynamic design, engine weight, emissions, aircraft design and performance as well as direct operating costs. The choice of specific thrust is a complex optimization problem and several disciplines need to be considered simultaneously. It will be demonstrated, through multidisciplinary analysis, that the open rotor concept can offer a substantial fuel saving potential, compared to ducted fans, for a given set of design considerations and customer requirements.

Bypass duct of a turbofan engine

Abstract: On a turbofan engine, at least one of the downstream guide vanes (1) of the downstream guide vane assembly (2) arranged behind the fan in the bypass duct, and a fairing element (3) arranged behind a downstream guide vane, are provided as a combined—one-piece and aerodynamically shaped—vane and fairing element (4) functioning as both a downstream guide vane and a fairing element for installations arranged in the bypass duct or an aerodynamically shaped supporting strut. The one-piece configuration of a fairing element with upstream vane, i.e. the integration of fairing elements provided with a specific outer contour into the downstream guide vane assembly, results in lower pressure losses and reduced fuel consumption as well as reduced pressure effect on the fan and, consequently, increased operating stability of the fan, higher fan efficiency and reduced sound emission.

Ultra High Bypass Ratio Engine Sizing and Cycle Selection Study for a Subsonic Commercial Aircraft in the N+2 Timeframe

Abstract: This paper presents an engine sizing and cycle selection study of ultra high bypass ratio engines applied to a subsonic commercial aircraft in the N+2 (2020) timeframe. NASA has created the Environmentally Responsible Aviation (ERA) project to serve as a technology transition bridge between fundamental research (TRL 1–4) and potential users (TRL 7). Specifically, ERA is focused on subsonic transport technologies that could reach TRL 6 by 2020 and are capable of integration into an advanced vehicle concept that simultaneously meets the ERA project metrics for noise, emissions, and fuel burn. An important variable in exploring the trade space is the selection of the optimal engine cycle for use on the advanced aircraft. In this paper, two specific ultra high bypass engine cycle options will be explored: advanced direct drive and geared turbofan. The advanced direct drive turbofan is an improved version of conventional turbofans. In terms of both bypass ratio and overall pressure ratio, the advanced direct turbofan benefits from improvements in aerodynamic design of its components, as well as material stress and temperature properties. By putting a gear between the fan and the low pressure turbine, a geared turbo fan allows both components to operate at optimal speeds, thus further improving overall cycle efficiency relative to a conventional turbofan. In this study, sensitivity of cycle design with level of technology will be explored, in terms of both cycle parameters (such as specific thrust consumption (TSFC) and bypass ratio) and aircraft mission parameters (such as fuel burn and noise). To demonstrate this sensitivity, engines will be sized for optimal performance on a 300 passenger class aircraft for a 2010 level technology tube and wing airframe, a N+2 level technology tube and wing air-frame, and finally on a N+2 level technology blended wing body airframe with and without boundary layer ingestion (BLI) engines.© 2011 ASME

Initial Assessment of Open Rotor Propulsion Applied to an Advanced Single-Aisle Aircraft

Abstract: Application of high speed, advanced turboprops, or propfans, to subsonic transport aircraft received significant attention and research in the 1970s and 1980s when fuel efficiency was the driving focus of aeronautical research. Recent volatility in fuel prices and concern for aviation s environmental impact have renewed interest in unducted, open rotor propulsion, and revived research by NASA and a number of engine manufacturers. Unfortunately, in the two decades that have passed since open rotor concepts were thoroughly investigated, NASA has lost experience and expertise in this technology area. This paper describes initial efforts to re-establish NASA s capability to assess aircraft designs with open rotor propulsion. Specifically, methodologies for aircraft-level sizing, performance analysis, and system-level noise analysis are described. Propulsion modeling techniques have been described in a previous paper. Initial results from application of these methods to an advanced single-aisle aircraft using open rotor engines based on historical blade designs are presented. These results indicate open rotor engines have the potential to provide large reductions in fuel consumption and emissions. Initial noise analysis indicates that current noise regulations can be met with old blade designs and modern, noiseoptimized blade designs are expected to result in even lower noise levels. Although an initial capability has been established and initial results obtained, additional development work is necessary to make NASA s open rotor system analysis capability on par with existing turbofan analysis capabilities.

Adaptive fan system for a variable cycle turbofan engine

Abstract: One embodiment of the present invention is a unique gas turbine engine. Another embodiment is a unique variable cycle gas turbine engine. Another embodiment is a unique adaptive fan system for a variable cycle turbofan engine having at least one turbine. Another embodiment is a unique method for operating a variable cycle gas turbine engine. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and related systems.

Control Volume Analysis of Boundary Layer Ingesting Propulsion Systems With or Without Shock Wave Ahead of the Inlet

Abstract: The performance benefit of boundary layer or wake ingestion on marine and air vehicles has been well documented and explored. In this article, a quasi-one-dimensional boundary layer ingestion (BLI) benefit analysis for subsonic and transonic propulsion systems is performed using a control volume of a ducted propulsion system that ingests the boundary layer developed by the external airframe surface. To illustrate the BLI benefit, a relationship between the amount of BLI and the net thrust is established and analyzed for two propulsor types. One propulsor is an electric fan, and the other is a pure turbojet. These engines can be modeled as a turbofan with an infinite bypass ratio for the electric fan, and with a zero bypass ratio for the pure turbojet. The analysis considers two flow processes: a boundary layer being ingested by an aircraft inlet and a shock wave sitting in front of the inlet. Though the two processes are completely unrelated, both represent a loss of total pressure and velocity. In real applications, it is possible to have both processes occurring in front of the inlet of a transonic vehicle. Preliminary analysis indicates that the electrically driven propulsion system benefits most from the boundary layer ingestion and the presence of transonic shock waves, whereas the benefit for the turbojet engine is near zero or negative depending on the amount of total temperature rise across the engine.

The Feasibility of High-Flow Nacelle Bypass for Low Sonic Boom Propulsion System Design

Abstract: A new supersonic design methodology has been developed by Gulfstream Aerospace Corporation for expanding the design space of a nacelle to reduce its contribution to an aircraft’s sonic boom signature. This method uses high-flow nacelle bypass to permit more latitude in the shaping of the nacelle’s surface, in particular the reduction of its axial slope at the intake entrance and nozzle exit. In doing so, the cowl shock strength and the aft nacelle’s expansion-reshock amplitude are both substantially reduced. The most significant unknown with this concept had been the practicality of internally bypassing a very large fraction of total captured airflow around the engine while avoiding unacceptable pressure loss. A unique curved channel arrangement was designed to divert the bypass flow around the massive blockage profile created by the engine gearbox. Internal choking and supersonic expansion combine to maintain a favorable pressure gradient through the length of the bypass. A configuration bypassing 40 percent of captured intake flow has been investigated through 16 separate computational and experimental campaigns conducted by Gulfstream, NASA Glenn Research Center, University of Illinois, Purdue University, and the University of Virginia. The culmination of the experimental work has been full-scale ground testing at Gulfstream using a Rolls-Royce Tay turbofan engine and, more recently, large-scale model testing at speeds to Mach 1.8 at NASA Glenn’s 8-by-6 ft wind tunnel. Excellent static and supersonic inlet performance was recorded during these tests, with outstanding robustness against crossflow effects. Buzz margin was large, and bypass flow pumping was shown to be stable and predictable at supersonic speeds. Selected results are presented in this report along with a summary of the development history of the bypass concept, with an emphasis on the work accomplished in the 8-by-6 ft tunnel. Results from six years of research and over twenty technical publications indicate that high-flow nacelle bypass is a feasible and valuable addition to the growing set of tools available for ultra-low sonic boom aircraft design.

Parametric Ideal Scramjet Cycle Analysis

Abstract: Parametric cycle analyses for the ideal ramjet, ideal turbojet, and ideal turbofan engines are well known and documented. The parametric mathematical descriptions of these ideal propulsion systems are useful for understanding the advantages and useful operation conditions when comparing these engines with one another and with mission requirements. It is also known that the scramjet engine is superior in producing specific thrust over these other engineswhen operating at hypersonicMachnumbers. The purpose of this work is to present a parametric cycle analysis for the ideal scramjet. This permits the description of the ideal scramjet via simple algebraic equations similar to that for the ideal ramjet, ideal turbojet, and ideal turbofan engines.

Aircraft engine control during icing of temperature probe

Abstract: Methods for controlling an aircraft turbofan engine during icing of a temperature probe and devices for carrying out such methods are described. The methods may comprise: using one or more signals representative of temperature received from a heated temperature probe to generate one or more control signals for use in controlling the engine; determining that an icing condition associated with the probe exists; and using data representing one or more substitute signals in place of signals representative of temperature received from the heated temperature probe to generate the one or more control signals for use in controlling the engine.

Adaptation of the Beveled Nozzle for High Speed Jet Noise Reduction

Abstract: The noise of high-speed jets, generated by nozzle exhaust systems that resemble typical jet engine installations on fighter aircraft, has been investigated with the main objective of developing noise reduction designs. To this end, the aeroacoustic characteristics of beveled nozzles have been examined in model scale tests and their performance relative to a conventional round nozzle system has been established. Two different physical models with appropriate area ratios to simulate the engine operating conditions at different power settings were tested; these correspond to 96% N1 (Military or MIL power) and 91% N1 (cutback power). Aeroacoustic measurements and analyses have been carried out for nozzles at bevel angles of 20o, 24o, 28o and 35o for MIL power, and 24o and 32o for cutback power. For the same plenum conditions, the mass flow rates for the beveled nozzles are identical to those of the baseline round nozzle, for a wide range of NPR. The thrust coefficients are higher for the beveled nozzles for both the nozzle geometries at typical MIL power and cutback power, respectively. The increase in the thrust coefficient ranges from ~0.75% for the bevel35 to ~2% for bevel28, in spite of the slight deflection of the jet plume. The reasons for this phenomenon are examined. The beveled nozzles produce at least the same or greater absolute thrust as the baseline nozzle. The beveled nozzles specifically reduce the noise in the peak polar radiation angles; the maximum noise benefit is observed in the azimuthal direction of the longer lip. The magnitude of noise reduction increases with increasing bevel angle, with the largest reduction for bevel35. An examination of the dBA metric, which is used in noise exposure studies, indicates that there is a noise benefit of ~3 dBA to ~4 dBA in the peak radiation sector. The noise benefit in the azimuthal direction of the shorter lip is only slightly lower than that in the direction of the longer lip. I. Introduction he noise of high-speed jets, as from the engines that power fighter aircraft, is a major concern for both military personnel and civilians living close to military bases. Military jets are powered by turbojets or very low bypassratio turbofan engines (BPR ≤ 0.3). The attendant high jet velocities produce extremely high levels of jet noise. This problem is severe for operations on aircraft carrier decks because military personnel are stationed very close to the aircraft during the launch and the landing of carrier-based fighter aircraft. Pilots perform training missions, called Field Carrier Landing Practice, at military bases that mimic the actual flights at the appropriate engine power settings, thereby creating a huge noise problem for the surrounding communities. The magnitude of the problem is first highlighted with a comparison of the noise footprints from the F/A-18 A/B and the Boeing 737-800 aircraft. The noise foot print is calculated as follows: first, A-weighted spectra are calculated from the measured spectra over a wide range of radiation angles. The A-weighting adjusts the full-scale spectrum measured by the microphone to account for the response of the human ear, with the low frequency levels decreased by several decibels, and the high-frequency portion of the spectrum relatively unmodified. The energy levels in the resulting spectrum at the different frequencies are logarithmically summed to produce one dBA number at each angle. The maximum dBA

Visual mining and statistics for a turbofan engine fleet

Abstract: Snecma, as a turbofan manufacturer, needs to deal with a wide fleet of more than thousands of engines. Every day, data from aircraft engines are broadcasted to the ground. Some airlines companies rely on their engine manufacturer to control the engines' behavior and help prepare for maintenance scheduling. The goal of the manufacturer is to detect abnormalities to help schedule maintenance operations. The advantage of the manufacturer as MRO operator is the registered memory of all past events that appears on its fleet of engines. If one opens the possibility to look in this huge amount of data for corresponding similar behaviors, which may have append in the past (for all engines of all customer companies), it becomes possible to make some targeted statistics of the future. This paper describes an algorithm to help engineers looking at some wear indicators and proposes a new full automatic method able to fetch information stored from many years of operations. This methodology is based on mathematic foundations. It uses a formalization of engine trajectories; creates a metric space where it becomes possible to compare time intervals of the evolution of engines. A generic maintenance application uses this methodology and finds in the fleet database engines that were similar in behavior to build future statistics. 1 2

Commercial Modular Aero-Propulsion System Simulation 40k

Abstract: The Commercial Modular Aero-Propulsion System Simulation 40k (CMAPSS40k) software package is a nonlinear dynamic simulation of a 40,000-pound (approximately equals 178-kN) thrust class commercial turbofan engine, written in the MATLAB/Simulink environment. The model has been tuned to capture the behavior of flight test data, and is capable of running at any point in the flight envelope [up to 40,000 ft (approximately equals 12,200 m) and Mach 0.8]. In addition to the open-loop engine, the simulation includes a controller whose architecture is representative of that found in industry. C-MAPSS40k fills the need for an easy-to-use, realistic, transient simulation of a medium-size commercial turbofan engine with a representative controller. It is a detailed component level model (CLM) written in the industry-standard graphical MATLAB/Simulink environment to allow for easy modification and portability. At the time of this reporting, no other such model exists in the public domain.

Design Drivers of Energy-Efficient Transport Aircraft

Abstract: The fuel energy consumption of subsonic air transportation is examined. The focus is on identification and quantification of fundamental engineering design tradeoffs which drive the design of subsonic tube and wing transport aircraft. The sensitivities of energy efficiency to recent and forecast technology developments are also examined. Background and Motivation Early development of the modern jet transport, starting with the DeHavilland Comet and Boeing 707 in the 1950’s, was strongly driven by range requirements. With the imperatives of rising fuel costs and increased environmental concerns, more recent developments have focused on fuel economy and also on noise. Of the three main drivers of fuel economy — aerodynamics, structures, and propulsion — the latter has seen the largest improvements, not surprisingly because in the 1950’s turbojet and turbofan engines were a very young technology. As engine technology maturation has now reached the levels of the other disciplines, further improvements will have to come from all technologies. The recent and ongoing NASA Aeronautics research, 1 in particular the N+1,2,3 programs 2 target a wide range of aerodynamic, structural, and propulsion technologies towards this goal.

Dynamic Loading on Turbofan Blades Due to Bird-Strike

Abstract: In the present paper, a hydrodynamic bird material model made up of water and air mixture is developed, which produces good correlation with the measured strain-gage test data in a panel test. This parametric bird projectile model is used to generate the time-history of the transient dynamic loads on the turbofan engine blades for different size birds impacting at varying span locations of the fan blade. The problem is formulated in 3-D vector dynamics equations using a non-linear trajectory analysis approach. The analytical derivation captures the physics of the slicing process by considering the incoming bird in the shape of a cylindrical impactor as it comes into contact with the rotating fan blades modeled as a pre-twisted plate with a camber. The contact-impact dynamic loading on the airfoil produced during the bird-strike is determined by solving the coupled non-linear dynamical equations governing the movement of the bird-slice in time-domain using a sixth-order Runge-Kutta technique. The analytically predicted family of load time-history curves enables the blade designer to readily identify the critical impact location for peak dynamic loading condition during the bird-ingestion tests mandated for certification by the regulatory agencies.Copyright © 2011 by ASME

The benefits of variable area fan nozzles on turbofan engines

Abstract: A variable area nozzle (VAN) on the bypass stream of a turbofan engine may prove to be necessary for a sufficient surge margin on an ultra-high bypass ratio fan. It is shown that such a nozzle also has benefits with respect to fuel burn and noise. The fuel burn will reduce typically about 10 % during departure and approach and likely 2 % in cruise. The noise reduction is in the order of 2 dB for sideline and flyover. Jet mixing noise in cruise is reduced by typically 1.0 dB, the reduction of broadband shock noise being larger. A VAN complements the fan rotational speed n with an additional parameter for controlling the working point on the fan performance map. The smallest nozzle area is needed only for a single flight condition, TOC, while for all other conditions, the nozzle exit area can be enlarged, yielding lower fan pressure ratios, higher mass flows and propulsive efficiencies, lower noise emissions and higher flutter margins for the fan. The benefits are studied for a UHBR fan with a pressure ratio of 1.5 at TOC. The optimal nozzle enlargement for this fan varies from small values in the range of a few percent during cruise to values larger than 15 % for take-off and approach, depending on the actual fan performance map.

Gas turbine engine with ejector

Abstract: The present inventions include a boundary layer ejector fluidically connecting boundary layer bleed slots from an external surface of an aircraft to reduce aircraft/nacelle/pylon drag, reduce jet noise and decrease thrust specific fuel consumption. In one embodiment a boundary layer withdrawn through the boundary layer bleed slots is entrained with an exhaust flow of a gas turbine engine. In another embodiment a boundary layer withdrawn through the boundary layer bleed slots is entrained with a flow stream internal to the gas turbine engine, such as a fan stream of a turbofan. Members can be provided near an outlet of a passageway conveying the withdrawn boundary layer air to locally reduce the pressure of the fluid in which the withdrawn boundary layer air is to be entrained. A lobed mixer can be used in some embodiments to effect mixing between the boundary layer and a primary fluid of the ejector.

A Wide-range single engine: operated from startup to hypersonic

Abstract: A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime is proposed for aircrafts and spaceships. A compression system of colliding super multijets is proposed instead of a traditional turbofan. Computational fluid dynamics with a chemical reaction model clarifies a large potential and stability of this system. This ultimate engine system can be extended with a special piston and scram jet systems to achieve an improved fuel consumption rate at various situations between the ground and the space, while maintaining a very low noise level with silent detonation. The present engine system will also solve the problem of the buzz at highersonic conditions.

Technology Insertion in Turbofan Engine and assessment of Architectural Complexity

Abstract: The design and development of a gas turbine engine is a highly integrated process, and requires the integration of efforts of large numbers of individuals from many design specialties. In the case that there are significant architecture changes due to technology insertion, customer requirements or component configuration for performance, integration of design efforts become more challenging. The analysis presented here compares a traditional two spool turbofan engine with a two spool engine incorporating a gear reduction between the fan and the driving spool. This is known as “Geared Turbofan” (GTF) engine architecture. The analysis presented here shows that the change in engine architecture represents a move to a more distributed and less modular architecture. The DSM shows a 20% increase in density of connectivity between components and 40% increase in terms of structural complexity. The impact of these changes suggests that the more distributed architecture of the newgeneration geared turbofan architecture likely will require more system integration effort than the traditional turbofan architecture.

Investigation of the Effects of Inlet Swirl on Compressor Performance and Operability Using a Modified Parallel Compressor Model

Abstract: Serpentine ducts used by both military and commercial aircraft can generate significant flow angularity and total pressure distortion at the engine face. Most low by-pass ratio turbofan engines with mixed exhaust are equipped with inlet guide vanes (IGV) which can reduce the effect of moderate inlet distortion. High by-pass ratio and some low by-pass ratio turbofan engines are not equipped with IGVs, and swirl can in effect change the angle of attack of the fan blades. Swirl and total pressure distortion at the engine inlet will impact engine performance, operability, and durability. The impact on the engine performance and operability must be quantified to ensure safe operation of the aircraft and propulsion system. Testing is performed at a limited number of discrete points inside the propulsion system flight envelope where it is believed the engine is most sensitive to the inlet distortion in order to quantify these effects. Turbine engine compressor models are based on the limited amount of experimental data collected during testing. These models can be used as an analysis tool to improve the effectiveness of engine testing and to improve understanding of engine response to inlet distortion. The Dynamic Turbine Engine Compressor Code (DYNTECC) utilizes parallel compressor theory and quasi-one-dimensional Euler equations to determine compressor performance. In its standard form, DYNTECC uses user supplied characteristic stage maps in order to calculate stage forces and shaft work for use in the momentum and energy equations. These maps were typically developed using experimental data or created using characteristic codes such as the 1-D Mean Line Code (MLC) or the 2-D Streamline Curvature Code. The MLC was created to calculate the performance of individual compressor stages and requires less computational effort than the 2-D and 3-D models. To improve efficiency and accuracy, the MLC has been incorporated into DYNTECC as a subroutine. Rather than independently developing stage maps using the MLC and then importing these maps into DYNTECC, DYNTECC can now use the MLC to develop the required stage characteristic for the desired operating point. This will reduce time and complexity required to analyze the effects of inlet swirl on compressor performance. The combined DYNTECC/MLC was used in the past to model total pressure distortion. This paper presents the result obtained using the combined DYNTECC/MLC to model the effects of various types of inlet swirl on F109 fan performance and operability for the first time.© 2011 ASME

Incorporating Risk into Control Design for Emergency Operation of Turbo-Fan Engines

Abstract: The paper describes a risk function based approach to constrained turbo-fan engine control to facilitate aircraft emergency maneuvering during take-off or landing. With this approach, the pontwise-in-time state and control constraints limiting the engine thrust response can be intelligently relaxed depending on the individual engine condition monitoring. The proposed control functionality uses the barrier Lyapunov functions, the predictive reference governor and functional limiters. The approach is illustrated using simulations on a linearized and on a fully nonlinear NASA C-MAPSS40k turbo-fan engine model. The capability and flexibility of the design approach to provide fast thrust response while handling multiple constraints, that may be time-varying and dynamically changing, by coordinating multiple engine actuators is demonstrated.

Towards Prediction of Dual-Stream Jet Noise: Database Generation

Abstract: The accurate prediction of jet noise from dual-stream nozzle exhaust geometries typical of high bypass ratio turbofan engines has practical relevance for aircraft design studies and in aircraft noise certification. Existing empirical methods do not provide good predictions against measured data; in addition, they are restricted to lower area ratio (secondary to primary) nozzle geometries and lower bypass ratios (BPR). The area ratio and BPR of newer engines have increased substantially, well beyond the range of validity of existing prediction methods. Therefore, there is a dire need to develop an accurate empirical prediction method that is valid over a wider range of jet operating conditions and nozzle geometries that are representative of current engines. A wind tunnel test has been completed and a comprehensive database from realistic geometries and operating conditions has been generated. The data have been analyzed and investigated with an eye towards modeling that would lead to an empirical prediction method. The area ratio and BPR cover wide ranges that encompass all current engines and potential ultra-high BPR engines of the future. The spectral characteristics have been examined and the effects of the following parametric variations are reported in this paper: (1) impact of area ratio with fixed, but over a range of, power settings; (2) at a given As/Ap, fixed primary jet and systematically varying secondary conditions; (3) at a given As/Ap, fixed secondary jet and systematically varying primary conditions; and (4) the effects of forward flight for the above situations. It is established that the characteristics of dual-stream jets with velocity ratio less than 0.5 are similar to those for a single jet, with the velocity ratio being the main controlling parameter and the area ratio playing a lesser role. At higher velocity ratios, contributions from the secondary shear layer is dominant at higher frequencies and the contributions from the mixed jet component controls the peak spectral levels in the peak radiation sector at large aft angles. At low inlet angles, the spectral shape remains invariant for all jet and geometric conditions.