Turbofan

About: Turbofan is a research topic. Over the lifetime, 4114 publications have been published within this topic receiving 39490 citations. The topic is also known as: fanjet & turbofan engine.

Stator bypass system for turbofan engine

Abstract: A nacelle for use with a turbofan engine for reducing both rotor and stator source noise emitting from the engine. The nacelle contains a ducted system which when in operation bypasses a portion of the flow in the fan duct around the fan stators causing unloading of the rotor, diffusion of the flow between the rotor and the stators, a reduction in the viscous flow at the rotor tips, and a substantial elimination of the rotor tip flow. Flow enters the duct system through openings in the interior walls of the nacelle located between the rotor and fan stators but downstream of the rotor at least a certain predetermined minimum distance. Flow through the system is controlled by doors or other means and it is normally operated only during approach and take-off, thus minimizing cruise penalty on engine performance.

Simplified Thrust and Fuel Consumption Models for Modern Two-Shaft Turbofan Engines

Abstract: Performance data of two-shaft turbofan engines have been used to investigate the validity of previously published models (empirical equations) that describe an engine's thrust variation as a function of Mach number and altitude during takeoff and climb. Where necessary, the constants and the format of the models have been revised. An updated model is presented that describes the takeoff thrust to within ±1% of that of the reference engines, for flight speeds up to Mach 0.4. This takeoff thrust model has been adapted to account for the impact of bleed air extraction and altitude effects. To describe the maximum climb thrust, a new approach has been devised in which the climb path has been divided into three segments and an equation developed for each segment, based on a reference thrust at 30,000 ft and typical climb/speed schedules. A widely used thrust specific fuel consumption power law model for cruise has been investigated, and new empirical constants determined. These results will allow a more realistic prediction of engine performance for the purpose of preliminary aircraft design or initial performance analysis.

Development of Methods for Analysis and Optimization of Complex Jet Engine Systems

Abstract: This thesis describes the development of GESTPAN (GEneral Stationary and Transient Propulsion ANalysis), a generalized system for the design, steady-state and transient simulation of gas turbine systems. Some of the main achievements in the thesis are related to the development of new algorithms or integration of existing numerics tailored to simplify the structure and use of generalized gas turbine simulation systems. In particular, a method for performing system design utilizing the analysis equations, i.e. an inverse design method, has been developed. Furthermore, attention is drawn to a number of advantages of using an implicit high order differential algebraic system solver for transient gas turbine system analysis. The simulation studies carried out with the GESTPAN system have focused on the performance optimization of the Selective Bleed variable cycle engine. In particular, a method for controlling the engine during mode transition was developed. Work with the implementation of a hybridized optimization method suitable for mission optimization of variable cycle engines is also described. The method couples the cycle selection and the control optimization of the engine variable geometry. Simulations performed with the method indicate that previously published designs of the Selective Bleed Variable cycle engine can be downsized considerably. Early work carried out in the research project concentrated on developing a method for optimizing the performance of variable geometry compressors integrated in gas turbine systems. Although the method was limited to subsonic operation of compressors, it was successfully used to simulate the core driven fan stage of the double bypass variable cycle engine.

Numerical studies of infrared signature levels of complete aircraft

Abstract: This paper begins with an outline of the procedure for predicting the infrared signature emissions from the airframe, engine casing, and the plume, and their attenuation by the intervening atmosphere. These emissions are contrasted against the background, to obtain the infrared signature levels. The infrared detector’s — noise equivalent flux density, is proposed as an operational constraint on the flight envelope. The shift of this newly imposed constraint on the flight envelope for several engine-operating conditions, and for turbojet and turbofan engines is studied. The signature levels from the casing and plume, of a turbofan and equivalent turbojet engine, are compared at different operating points on the flight envelope. Result in the form of a polar plot of infrared signature level variation with aspect is also examined for low flying missions. The results are analysed to direct stealth design and operation.

Rotor Interaction Noise in Counter-Rotating Propfan Propulsion Systems

Abstract: Due to their inherent noise challenge and potential for significant reductions in fuel burn, counter-rotating propfans (CRPs) are currently being investigated as potential alternatives to high-bypass turbofan engines. This paper introduces an integrated noise and performance assessment methodology for advanced propfan powered aircraft configurations. The approach is based on first principles and combines a coupled aircraft and propulsion system mission and performance analysis tool with 3-D unsteady, full wheel CRP CFD computations and aero-acoustic simulations. Special emphasis is put on computing CRP noise due to interaction tones. The method is capable of dealing with parametric studies and exploring noise reduction technologies. An aircraft performance, weight and balance and mission analysis was first conducted on a candidate CRP powered aircraft configuration. Guided by data available in the literature, a detailed aerodynamic design of a pusher CRP was carried out. Full wheel unsteady 3-D RANS simulations were then used to determine the time varying blade surface pressures and unsteady flow features necessary to define the acoustic source terms. A frequency domain approach based on Goldstein’s formulation of the acoustic analogy for moving media and Hanson’s single rotor noise method were extended to counter-rotating configurations. The far field noise predictions were compared to measured data of a similar CRP configuration and demonstrated good agreement between the computed and measured interaction tones. The underlying noise mechanisms have previously been described in the literature but, to the authors’ knowledge, this is the first time that the individual contributions of front-rotor wake interaction, aft-rotor upstream influence, hub-endwall secondary flows and front-rotor tip-vortices to interaction tone noise are dissected and quantified. Based on this investigation, the CRP was re-designed for reduced noise incorporating a clipped rear-rotor and increased rotor-rotor spacing to reduce upstream influence, tip-vortex, and wake interaction effects. Maintaining the thrust and propulsive efficiency at takeoff conditions, the noise was calculated for both designs. At the interaction tone frequencies, the re-designed CRP demonstrated an average reduction of 7.25 dB in mean SPL computed over the forward and aft polar angle arcs. On the engine/aircraft system level, the re-designed CRP demonstrated a reduction of 9.2 EPNdB and 8.6 EPNdB at the FAR 36 flyover and sideline observer locations, respectively. The results suggest that advanced open rotor designs can possibly meet Stage 4 noise requirements.Copyright © 2010 by ASME