Date of Award

Fall 2025

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Luis Ferrer-Vidal Espana-Heredia

Committee Chair Email

ferrervl@erau.edu

First Committee Member

Luis Ferrer-Vidal Espana-Heredia

First Committee Member Email

ferrervl@erau.edu

Second Committee Member

Mark Ricklick

Second Committee Member Email

ridlickm@erau.edu

Third Committee Member

L.L. Narayanaswami

Third Committee Member Email

swami@erau.edu

College Dean

James W. Gregory

Abstract

Gas turbine performance modeling is essential for predicting engine behavior across design and off-design conditions. Yet the treatment of cooling or service flows remains inconsistent, as these streams interact with the main flow in complex ways and their contribution to turbine work depends on how they are represented in performance models. The challenge is especially present in “black-box” approaches, where only inlet and outlet conditions are known and engineers must decide whether to introduce cooling flows upstream (if performing useful work) or downstream (if not). This thesis examines how different definitions of isentropic power and cooling-flow treatment affect the apparent efficiency of a cooled two-stage axial turbine. A representative numerical model was developed to simulate several service-flow configurations and compare four modeling approaches. Results show that neglecting cooling contributions (Approach A) yields unrealistically high efficiencies, while more refined methods (Approach B, inlet-weighted enthalpy; Approach C, work-potential factors) capture the reduction in available work more accurately. The most rigorous formulation (Approach D, based on Hartsel) applies individual isentropic expansions to each cooling stream and establishes a theoretical lower bound. The study also quantifies the work potential of each cooling stream using literature-based, design-based, and CFD-derived formulations, illustrating how these factors guide the classification of flows as chargeable or non-chargeable in black-box models. Despite the simplified geometry employed, the results offer insight into the sensitivity of turbine efficiency to cooling-flow modeling choices. This work represents a step toward standardized, physically consistent methods for cooled-turbine performance prediction, with future efforts focusing on more realistic geometries, improved mixing models, and integration of the proposed criterion into advanced performance tools.

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