Manish Pokhrel
(Advisor: Prof. Dimitri Mavris]

will defend a doctoral thesis entitled,

A Framework for Fan Stage Conceptual Design Under Distortion

Induced by Boundary Layer Ingestion

Wednesday, October 14 at 12:00 p.m.
Meeting Link: https://bluejeans.com/424060103

Abstract
Various tightly integrated aircraft concepts have emerged as a result of aggressive performance goals set forth by various organizations. Most integrated aircraft system configurations exploit the concept of Boundary Layer Ingestion (BLI). While the potential benefits of BLI are huge, several significant challenges - both on the modeling and design fronts - appear due to BLI. This dissertation focuses on addressing the impacts of BLI induced circumferential flow distortion on the conceptual design of a fan stage.

Distortion introduces extra losses in both rotors and stators in addition to increased unsteady rotor response. In presence of incidence swings, conventional conceptual design tools are inadequate to design optimal rotor blades and generate non-axisymmetric stators, a concept that has shown promise in alleviating stage losses due to distortion. Besides, concerns of structural integrity also arise for rotor blades due to the unsteady loading they experience when rotating in a distorted flow field. Parametric effects of these phenomena with varying levels of distortion are quantified, and a significant portion of the fan stage losses are shown to be recoverable using the aero-structural design framework introduced and developed in this dissertation.

The aerodynamic design framework is developed through several extensions to the conventionally used multi-meanline method. The inclusion of additional features accounts for flow asymmetry, parametric blade angle optimization, rotor unsteady performance, and non-axisymmetric stator design. The model is verified, and experiments are performed to evaluate the effectiveness of each modeling element. Similarly, the Variational Asymptotic Method (VAM) is proposed as a computationally efficient technique to perform transient structural analysis of rotor blades. VAM is validated for a variety of loading scenarios and is leveraged to demonstrate the nature of vibratory stresses and highlight the concerns of resonance on a test case. The framework encapsulating both aerodynamic design and structural analysis is finally utilized to explore the design space to minimize vibratory stresses on the blades with a small trade-off in the stage efficiency. The fan stage design resulting from the framework proposed and formulated in this dissertation aims to serve as a starting point for the preliminary design of a distortion-tolerant fan.

Committee

1. Prof. Dimitri Mavris – School of Aerospace Engineering (Advisor and Committee Chair)
2. Prof. Lakshmi N. Sankar – School of Aerospace Engineering
3. Prof. Dewey H. Hodges – School of Aerospace Engineering
4. Dr. Jonathan Gladin – Research Engineer II, School of Aerospace Engineering
5. Dr. Mohit Gupta – Department of Aerospace Engineering Sciences, University of Colorado Boulder