Bryce Alexander Roth

Work Potential Perspective of Engine Component Performance

Presented at the 37th Joint Propulsion Conference and Exhibit, Salt Lake City, UT, July 2001.

Comparison of Thermodynamic Loss Models Suitable for Gas Turbine Propulsion

The description of Several e gures of merit for estimation of loss in work potential based on the second law of thermodynamicsandevaluationoftheirrelativemeritsforpropulsionsystemanalysisanddesignaretheobjectives. Thelosse guresofmeritexamined areexergy,gashorsepower,and thrustwork potential.Dee nitionsandsimplie ed expressions for evaluating each are presented and related via contours on a Temperature-Entropy diagram, and a working comparison is provided by way of a pedagogical example using the J-79 turbojet engine. It is shown that thrust work potential is a special case of gas horsepower, which is in turn a special case of exergy. Based on these results, a general taxonomy is suggested to classify the various work potential e gures of merit. The results of this analysis are then used to draw inferences as to what applications each work potential e gure of merit is best suited, the general conclusion being that they are complimentary, with each e gure of merit being well suited to a particular application. Finally, a general work exclusion principal is suggested as a guide to which of the various loss e gures of merit is most appropriate for a given application.

Adaptive Selection of Engine Technology Solution Sets from a Large Combinatorial Space

This paper describes a method to assist in selecting technology concepts from amongst a pool of candidates such that the resulting concepts yield the best compromise between conflicting objectives, such as design performance and technology risk. The heart of this method is a unique technology impact forecasting environment that is used in conjunction with a genetic algorithm as a tool to efficiently explore the technology combinatorial space. The technique is applied to a commercial turbofan engine technology selection problem of practical interest. A pool of forty technology concepts is proposed and evaluated, the objective being to determine which subset of technologies is the best candidate to go forward into development given conflicting objectives on performance, engine manufacturing cost and design risk (i.e. cumulative technology readiness).

A Work Availability Perspective of Turbofan Engine Performance

Presented at the 39th AIAA, Aerospace Sciences Meeting and Exhibit, Reno, NV, January 9-11, 2001.

A Generalized Model for Vehicle Thermodynamic Loss Management and Technology Concept Evaluation

Presented at the 5th World Aviation Congress and Exposition, San Diego, CA, October 10-12, 2000.

Probabilistic Matching of Turbofan Engine Performance Models to Test Data

This paper describes the development of an improved method for reliable, repeatable, and accurate matching of engine performance models to test data. The centerpiece of this approach is a minimum variance estimator algorithm with a priori estimates which addresses both deterministic and probabilistic aspects of the problem. Specific probabilistic aspects include uncertainty in the measurements, prior expectations on model matching parameters, and noise in the power setting parameters. The algorithm is able to produce optimal results using any number of measurements and model matching parameters and can therefore take advantage of all measured data to produce the best possible match. This improves on current matching algorithms which require that the number of measured parameters be equal to the number of model matching parameters. This algorithm has been implemented in the Numerical Propulsion System Simulation (NPSS) and tested on a generic high-bypass turbofan model typical of those used in commercial service. The baseline engine model and simulated test data are described in detail. Several exercises are discussed to illustrate results available from this algorithm including the matching of a typical power calibration data set and matching of a typical production engine data set.Copyright

Method for Propulsion Technology Impact Evaluation via Thermodynamic Work Potential

The task of propulsion technology concept selection and integration is one of the most challenging problems in aerospace systems design. This is because of the tightly-coupled and inherently multidisciplinary nature of the problem, as well as the multitude of performance constraints and requirements placed on modern propulsion systems. In addition, as the cost of developing new and improved propulsion systems continues to rise, the attendant risk to the developer increases also. This leads to an aversion to risk that stifles innovation, particularly when it involves the

High-Accuracy Matching of Engine Performance Models to Test Data

Matching of cycle models to test results for gas turbine engines is fundamentally an exercise in optimal robust parameter estimation. The problem is inherently nondeterministic in nature, so it stands to reason that probabilistic information can be used to secure improved match accuracy if properly employed. This paper proposes an approach to status matching that eliminates the need for parameter weightings, gives an intuitive feel for the results in terms of probabilistic parameters, utilizes all available information (probabilistic and deterministic), and yields high-accuracy matches between model prediction and experiment. The method development begins with a typical sum-squared errors approach and subsequently builds on this. A deviation penalty function formulation is introduced to improve solution conditioning and a multi-objective measure of fit based on the Z-score is introduced. Several measures of model fit are compared including summed-squared errors, minimax, and sum absolute error formulations. This approach is first demonstrated for a simple cantilever beam parameter-matching problem, and is later discussed in the context of turbofan engine matching.Copyright

A Probabilistic Design Methodology for Commercial Aircraft Engine Cycle Selection

Presented at the 3rd World Aviation Congress and Exposition, Anaheim, CA, September 28-30, 1998.

Generalized Model for Vehicle Thermodynamic Loss Management

A general-purpose loss management model to account for the usage of thermodynamic work potential in vehicles of any type is developed. The key to accomplishing this is the creation of a differential representation for vehicle loss as a function of operating condition. This differential model is then integrated through mission time to obtain an analytical estimate for total usage of work potential consumed by each loss mechanism present during vehicle operation. This leads to a better understanding of how the work potential initially present in the mission fuel is partitioned amongst all loss mechanisms present during the vehicles operation. This result can also be used in conjunction with cost accounting to gain a better understanding of underlying drivers on vehicle manufacturing and operating costs. The method is demonstrated for the analysis of a lightweight fighter aircraft