Jonathan C. Gladin

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

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

Effects of Boundary Layer Ingesting (BLI) Propulsion Systems on Engine Cycle Selection and HWB Vehicle Sizing

A methodology for analyzing the boundary layer ingestion technology on a hybrid wing body aircraft has been developed using a simplified boundary layer analysis based on computation fluid dynamic results. With certain assumptions, a method for calculating the boundary layer velocity profiles across the flight envelope was shown using a log-wake velocity profile. This boundary layer profile was integrated over the surface of an assumed “D-shape” inlet to produce the inlet total pressure, temperature, and the ratio of the area averaged Mach number to the free-stream Mach number. The resulting curves were used within the EDS multi-disciplinary environment to analyze an HWB aircraft with BLI and other N+2 technologies over a range of cycle design parameters and for varying inlet aspect ratios. Aerothermodynamic engine cycle design explorations are performed that show that the candidate engine cycle selection that minimizes design mission fuel burn depends greatly on the assumed negative impacts BLI has on the engine performance.

Engine Design Strategy for Boundary Layer Ingesting Propulsion Systems With Multiple Non-Symmetric Engine Inlet Conditions

Boundary layer ingesting inlets for hybrid wing body aircraft have been investigated at some depth in recent years due to the theoretical potential for fuel burn savings. Such savings derive from the ingestion of a portion of the low momentum wake into the propulsor to reenergize the flow, thus yielding total power savings and reducing required block fuel burn.A potential concern for BLI is that traditional concepts such as “thrust” and “drag” become less clearly defined due to the interaction between the vehicle aerodynamics and the propulsive thrust achieved. One such interaction for the HWB concept is the lateral location of the inlet on the upper surface which determines the effective Reynolds number at the point of ingestion. This is an important factor in determining the amount of power savings achieved by the system, since the boundary layer, displacement, and momentum thicknesses are functions of the local chord length and airfoil shape which are all functions of the lateral location of the engine. This poses a design challenge for engine layouts with more than two engines as at least one or more of the total engines will be operating at a different set of changing inlet conditions throughout the flight envelope.As a result, the engine operating point and propulsive performance will be different between outboard and inboard engines at flight conditions with appreciable boundary layer influence including key flight conditions for engine design: takeoff, top of climb, and cruise. The optimal engine design strategy in terms of performance to address this issue is to design separate engines with similar thrust performance. This strategy has significant challenges such as requiring the manufacturing and certification of two different engines for one vehicle. A more practical strategy is to design a single engine that performs adequately at the different inlet conditions but may not achieve the full benefits of BLI.This paper presents a technique for cycle analysis which can account for the disparity between inlet conditions. This technique was used for two principal purposes: first to determine the effect of the inlet disparity on the performance of the system; second, to analyze the various design strategies that might mitigate the impact of this effect. It is shown that a single engine can be sized when considering both inboard and outboard engines simultaneously. Additionally, it is shown that there is a benefit to ingesting larger mass flows in the inboard engine for the case with large disparity between the engine inlets.Copyright

Hybrid Wing Body Engine Cycle Design Exploration for Boundary Layer Ingesting (BLI) Propulsion Systems Under Design Uncertainty

of the concept. The current paper presents a modeling approach that allows for the modeling of BLI at multiple design points and throughout the mission operating envelope. Furthermore, the paper presents a probabilistic engine cycle design space study for a 300 passenger HWB aircraft using the EDS design tool that explores the impacts of the various physical assumptions on the system level impacts. The results show that the system is particularly sensitive to the level of total pressure drop at the fan face. An engine sizing study shows that the level of assumed losses incurred by the engine has a large eect on the resultant size of the engine as well as on the performance of the sized engine at other assumed loss levels.

Propulsion Systems Modeling with Vehicle Sketch Pad

The design of advanced aircraft that simultaneously meet increasingly strict noise, emissions, and fuel burn requirements will require accurate analysis of propulsion-airframe integration effects even at the conceptual design level. To meet this requirement, there is a need for new, easy-to-use parametric-based geometry and modeling analysis methodologies. This paper presents a research strategy for integrating various levels of analytical fidelity for conceptual level engine design and integration and presents geometric parameterizations for engine components at the conceptual level. The parameterizations and design strategy are intended to be used with standard MDAO tools and include parameterizations of 3D geometry in order to facilitate more detailed analyses of the engine cycle and flow-path design for highly integrated propulsion-vehicle concepts. The primary tools utilized in this research include the NASA-developed programs Numerical Propulsion System Simulation (NPSS), Weight Analysis for Turbine Engines (WATE++), and Vehicle Sketch Pad (VSP).

Fundamentals of Parallel Hybrid Turbofan Mission Analysis with Application to the Electrically Variable Engine

This paper describes a basic analysis for mission performance of parallel hybrid turbofan systems. A series of equations is derived to illustrate the concept of parallel hybrid performance showing that there is an optimum range for a given battery size that corresponds to the exact usage of the battery capacity stored on the aircraft. The fundamental concepts were then demonstrated on a more detailed problem using a performance model of the Electrically Variable Engine developed by Rolls-Royce on a high aspect ratio vehicle. Trends from this study again demonstrate the concepts derived in the preliminary theoretical analysis. Finally, a standard method for presenting hybrid data is proposed called the “money chart” which is a means for showing all of the required performance parameters of a parallel hybrid system to compute other metrics of interest as desired.