Airfoil design framework for optimized boundary-layer integral parameters

Collazo Garcia III, Armando R.

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https://hdl.handle.net/2142/117734 Copy

Description

Title

Airfoil design framework for optimized boundary-layer integral parameters

Author(s)

Collazo Garcia III, Armando R.

Issue Date

2022-10-27

Director of Research (if dissertation) or Advisor (if thesis)

Ansell, Phillip J

Doctoral Committee Chair(s)

Ansell, Phillip J

Committee Member(s)

• Elliott, Gregory S
• Chamorro, Leonardo P
• Saxton-Fox, Theresa A
• Liebeck, Robert H

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• airfoil
• airfoil design
• airfoil optimization
• boundary layer
• integral boundary-layer parameter
• Stratford pressure recovery
• Squire-Young formula
• minimum drag
• laminar flow
• laminar flow airfoil
• LRN1015
• global hawk
• high altitude long endurance
• HALE, MSES, XFOIL

Abstract

A new airfoil design framework is proposed in which the boundary-layer integral parameters serve as the driving design mechanism. The method consists of a parameterization for generation of a pressure distribution capable of producing desired boundary-layer characteristics, which is then used to obtain a corresponding airfoil geometry through an inverse design process. Additionally, by deduction from the Squire-Young theory, the method allows to determine the pressure distribution that results in the minimum theoretical drag. As part of efforts to find a minimum drag solution, special consideration was given to the pressure recovery characteristics when defining the pressure distribution parameterization. Thus, the initial part of this study considered the boundary-layer state in compressible flow conditions associated with Stratford pressure recovery profiles, which represent the theoretical limit across which a given pressure differential can be recovered by a turbulent boundary layer in the shortest chordwise distance. Airfoil geometries with Stratford-like pressure distributions were designed and tested to show that both sub- and super-critical recoveries retain the classical marginally separated state across the recovery region, with the former showing a greater separation stability margin at off-design conditions. In the process of developing the design framework, the LRN1015 airfoil was considered as a seed geometry and modified based on the mission requirements of the RQ-4B Global Hawk aircraft. Several airfoils were developed considering different operating constraints and boundary-layer target conditions. Numerical results obtained using a viscous-inviscid solver of the integral boundary-layer and Euler equations showed that the optimized airfoils achieved profile drag reductions of 9.06% and 6.00%, respectively, for the α = 0° and L/Dmax design points considered. Additional airfoils were developed for high Reynolds number and incompressible flow applications to display the applicability of the design method across a broad range of operating conditions, which also resulted in significant benefits over the baseline geometry. Operation at off-design conditions displayed imminent separation at higher angles of attack, characteristic of Stratford-type recoveries, as well as the presence of laminar separation bubbles in free transition cases at lower angles of attack, which adversely affected the drag performance. The final part of this investigation consisted of an experimental campaign to validate the design methodology being proposed. Experimental models of the LRN1015 and CA5427-72 airfoils were fabricated and tested at their representative operating design conditions. The acquired data produced the expected pressure distribution characteristics and aerodynamic performance improvements, indicating that the airfoil successfully achieved the design objectives. Experimental results at the operating design condition displayed a 16.01% profile drag reduction when compared to the baseline geometry, showing even greater improvement than anticipated from the computational predictions.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 by Armando R. Collazo Garcia III. All rights reserved.

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