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A three-dimensional linearized Euler model is developed for the interaction and scattering of unsteady incident disturbances by an annular cascade of unloaded blades. The model is first used to examine the validity of the popular two-dimensional strip theory for three-dimensional annular cascades at frequencies relevant to fan engine noise. It is then applied to investigate three methods of passive control for turbofan tonal noise, namely, blade lean, blade sweep, and mean flow acceleration. Because blade lean and sweep generally enhance the blade upwash radial phase variation, an analysis is carried out to examine the effects of the radial modulation of the incident disturbances on the annular cascade sectional lift and the modal acoustic response. Noise control by blade lean and sweep is then investigated for typical fans. The results show that blade lean or sweep can be designed to be effective noise reduction mechanisms; however, their effectiveness depends on the characteristics of the incident disturbances and the number of propagating duct modes. Converging ducts are also shown to be effective sound reduction mechanisms.

The traditional method for bearing and damper analysis usually involves a development of rather complicated numerical calculation programs that may just focus on a simplified and specific physical model. The application of the general CFD codes may make this analysis available and effective where complex flow geometries are involved or when more detailed solutions are needed. In this study, CFX-TASC flow is employed to simulate various fixed geometry fluid-film bearing and damper designs. Some of the capabilities in CFX-TASCflow are applied to simulate the pressure field and calculate the static and dynamic characteristics of hydrodynamic, hydrostatic, and hybrid bearings as well as squeeze film dampers. The comparison between the CFD analysis and current computer programs used in industry has been made. The results show reasonable agreement in general. Some of the possible reasons for the differences are discussed. It leaves room for further investigation and improvement on the methods of computation. [DOI: 10.1115/1.1807415]

Steady-state performance models can be used to evaluate a new engine's baseline performance. As a gas turbine accumulates operating time in the field, its performance deteriorates due to fouling, erosion, and wear. This paper presents the development of a model for predicting the performance deterioration of aircraft gas turbines. The model accounts for rotating component deterioration based on the aircraft mission profiles and environmental conditions and the engine's physical and design characteristics. The methodology uses data correlations combined with a stage stacking technique for the compressor and a tip rub model, along with data correlations for the turbine to determine the amount of performance deterioration. The performance deterioration model interfaces with the manufacturer's baseline engine simulation model in order to create a deteriorated performance model for that engine.

The jet engine modulation (JEM) phenomenon, observed in radar returns from the rotating structure of jet engines, has been successfully exploited for aircraft target identification in a number of experimental radar systems. We develop a parametric model based on the periodic modulation of the scattered return, motivated by the potential reduction in time-on-target for reliable target identification provided by parametric models, as well as gaining insight into the JEM phenomenon. We then compare the model with JEM measurements made with an experimental radar system. Finally, we discuss the implications for JEM-based target identification systems.

The paper describes a conceptual control system design based on advanced technologies currently in the exploratory development phase, and, in some cases, emerging into the advanced development phase. It explores future propulsion control systems that focus on improvements in three areas: (1) significantly reducing control system weight,- (2) enhancing engine performance (thrust, sfc, etc.); and (3) improving control system reliability and tolerance to high-threat environments (temperature, vibration, EMI, EMP, etc.). The factors that will influence the design and hardware configuration of future propulsion control systems are described. Design goals for future systems, based on the DOD/NASA IHPTET Initiative, and projections of emerging technology capability (and availability) form the basis for future propulsion control system design requirements and for estimating future hardware configurations., An experimental control system for tomorrow's jet fighter engines as envisioned in the Integrated High-Performance Turbine Engine Technology program is given. The proposed system has innovations in weight reduction, system performance and reliability. The lightweight construction is made possible by using advanced materials and systems integration. Better performance is achieved by using digital engine control. The system's adjustment to the environment is also improved.

Byline: Rajasekar Varadharajan, Nilesh J. Vasa, Y.G. Srinivasa A simplified, low order state-space approach for dynamic modelling of a twin spool turbofan gas turbine engine is proposed and investigated. The governing equations constituting the dynamic model of the engine are derived analytically by considering 1D mass, moment and energy balance equations at intermediate engine stations. Engine subsystems are modelled by using algebraic relationships, neural networks and experimental data collected through rig tests. Simulations are performed at various operation conditions for investigating the off-design and transient behaviour of the engine system. The simulation results are compared with the experimental time series data recorded during engine test runs. The responses of the model are found to be in good agreement with the experimental results for critical engine parameters such as shaft speeds, compressor delivery pressure, turbine inlet temperatures, etc. The proposed model may be extended for use in real-time engine simulation scenarios such as closed loop testing of engine control and condition monitoring systems.

This paper evaluates the potential impact of utilizing advanced engine technology for a limited life, combat capable, unmanned air vehicle (UAV) application. A study was conducted to define payoffs in terms of mission capability and system level life cycle costs (LCC) associated with implementing three different engine development approaches into a combat capable UAV design. The three different approaches considered were: a new, advanced technology engine; an existing (off-the-shelf) engine; and a derivative of an existing engine with limited technology insertion. A detailed vehicle configuration design was developed to conduct this assessment, including a low observable (LO), highly integrated engine/airframe layout for survivability and mission adaptable considerations. The vehicle is designed with multirole mission capability such as suppression of enemy air defense (SEAD), close air support (CAS), and battlefield air interdiction (BAI). A system level performance comparison is assessed with the three different engine approaches, specifically for the SEAD-type mission. For the cost analysis, the multirole mission capability is reflected in the overall assumptions such as in the number of aircraft needed to meet the mission requirements. A system level assessment such as in this study is essential in determining whether the additional costs associated with the development of a new, advanced engine is worth the investment. The results of this study suggest that advanced engine technology insertion can provide significant benefits in terms of mission range capability, vehicle weight/size, and overall life cycle costs versus an existing engine. [DOI: 10.1115/1.1362666]