Search Results

The study of Supercooled Large Droplets (SLD) has received greater attention in the Aviation industry since the ATR-72 accident in 1994, which was attributed to SLD. This type of icing cloud usually consists of droplets of up to a millimeter in diameter and mean volumetric diameter (MVD) greater than 40 microns1. The analyses of the ice accretion process with SLD have focused mainly on the wing and stabilizers, particularly on the leading edges where accretion can occur beyond the ice protected areas. There are several numerical and empirical models to predict the mass and shapes of ice accreted from SLD, but there are few published papers that focus on SLD accretion within aircraft turbofan engines2, 3, 4, 5, 6, 7, 8, 9. SLD droplets have higher inertia than conventional icing droplets, which leads to their trajectories being less influenced by the aerodynamic forces. However, large droplets are more likely to breakup than smaller droplets when subjected to highly shear flows.

Propulsion engine low-emission combustion technology evolution of the last 30 years is described with a special emphasis on the most recent development, namely Twin Annular Premixing Swirler, TAPS. TAPS mixer technology has been developed for potential application in Single and Dual Annular Combustors, SAC and DAC. Both SAC and DAC TAPS technology development efforts have gone through full-scale annular combustor demonstration for emissions, pressure and airflow distribution, combustor exit temperature quality, structure temperature levels and gradients, lean blowout and ignition characteristics. The SAC TAPS technology demonstration effort involved full-scale engine testing including sea-level emissions, performance, cyclic durability, operability in regard to ignition, acceleration and snap decel (throttle burst-chop transient) and operation under inclement weather conditions.

Current industry trends demonstrate aircraft electrification will be part of future platforms in order to achieve higher levels of efficiency in various vehicle level sub-systems. However, electrification requires a substantial change in aircraft design that is not suitable for re-winged or re-engined applications as some aircraft manufacturers are opting for today. Thermal limits arise as engine cores progressively get smaller and hotter to improve overall engine efficiency, while legacy systems still demand a substantial amount of pneumatic, hydraulic and electric power extraction. The environmental control system (ECS) provides pressurization, ventilation and air conditioning in commercial aircraft, making it the main heat sink for all aircraft loads with exception of the engine fuel thermal management system.

The optimal integration of vehicle subsystems is of critical importance in the design of future energy efficient fighter aircraft. The INVENT (INtegrated Vehicle ENergy Technology) program has been dedicated to this endeavor through modeling/simulation of thermal management, power generation & distribution, & actuation subsystems. Achieving dual cooling & power generation capability from a single subsystem would be consistent with current efforts in system integration optimization. In this paper, we present a reconfiguration of an archetypal closed-loop air cycle system for a modern fighter as an open-loop gas generator cycle operating interchangeably between refrigeration and auxiliary power modes. A numerical model was developed within NPSS to assess maximum power extraction capabilities of a system originally designed for cooling purposes under different operating conditions.

To obtain a system level, integrated perspective on vehicle energy management, the traditional methods for conducting preliminary design, gauging independent requirements, must be abandoned. This method does not capture critical interactions between the various aircraft subsystems. Instead, a more global appreciation for interactions across boundaries needs to be realized with a mosaic scheme, where models are integrated and co-simulated. The advantage of this approach is to enhance the preliminary design stage by predicting integration issues early in the development process. Legacy design practice involved gathering data from multiple vendors in order to produce design iterations. The ability to link models directly is extremely beneficial, as requirements no longer have to be executed independently. This approach reduces cumbersome iterations between model owners and accelerates trade studies.

An important part of future air vehicle design will be the development of a transient integrated aircraft system model. DC electric power system modeling poses particular challenges because they are highly dynamic and employ short time constant line replaceable units [1, 2, 3]. This paper describes an approach to modeling an aircraft's electric power system that uses simplified non-physics based models of the line replaceable units that are part of future 270VDC aircraft power systems. The model is an alternative to physics based models and is particularly useful for the initial phases of aircraft development before hardware development has occurred. A 270VDC aircraft power system model is constructed as an example using the unit models. Selected results will be presented.

A Distributed Engine Control Working Group (DECWG) consisting of the Department of Defense (DoD), the National Aeronautics and Space Administration (NASA)- Glenn Research Center (GRC) and industry has been formed to examine the current and future requirements of propulsion engine systems. The scope of this study will include an assessment of the paradigm shift from centralized engine control architecture to an architecture based on distributed control utilizing open system standards. Included will be a description of the work begun in the 1990's, which continues today, followed by the identification of the remaining technical challenges which present barriers to on-engine distributed control.

This article attempts to provide a big picture of systems engineering in both philosophy and engineering perspectives, discusses current status and issues, trends of systems engineering development, future directions and challenges, followed by certain examples.

It is typical in aircraft engine design to explore new configurations in a constant effort to achieve greater efficiency with respect to various considerations. An integral component of this process requires a complete and robust simulation of rotor dynamics. Tuning the design with results of rotor dynamics simulations can be made possible with a tool that has adequate modeling techniques to capture the physics associated with engine behavior under various operating conditions accurately.