Computational Analysis of Circulation Control Airfoils

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Title: Computational Analysis of Circulation Control Airfoils
Author: McGowan, Gregory Zar
Advisors: Dr. Harvey Charlton, Committee Member
Dr. Ashok Gopalarathnam, Committee Chair
Dr. William Roberts, Committee Member
Abstract: Current projections for future aircraft concepts call for stringent requirements on high-lift and low cruise-drag. The purpose of this study is to examine the use of circulation control, through trailing edge blowing, to meet both requirements. This study was conducted in two stages: (i) validation of computational fluid dynamic procedures on a general aviation circulation control airfoil and (ii) a study of an adaptive circulation control airfoil for controlling lift coefficients in the low-drag range. In an effort to validate computational fluid dynamics procedures for calculating flows around circulation control airfoils, the commercial flow solver FLUENT was utilized to study the flow around a general aviation circulation control airfoil. The results were compared to experimental and computational fluid dynamics results conducted at the NASA Langley Research Center. This effort was conducted in three stages: (i) a comparison of the results for free-air conditions to those from previously conducted experiments, (ii) a study of wind-tunnel wall effects, and (iii) a study of the stagnation-point behavior. In general, the trends in the results from the current work agreed well with those from experiments, some differences in magnitude were present between computations and experiments. For the cases examined, FLUENT computations showed no noticeable effect on the results due to the presence of wind-tunnel walls. The study also showed that the leading-edge stagnation point moves in a systematic manner with changes to the jet blowing coefficient and angle of attack, indicating that this location can be sensed for use in closed-loop control of such airfoil flows. The focus of the second part of the study was to examine the use of adaptive circulation control on a natural laminar flow airfoil for controlling the lift coefficient of the low-drag range. In this effort, adaptive circulation control was achieved through blowing over a small mechanical flap that can be deflected up or down. Such a blown trailing-edge flap allows for control of the jet direction to be independent of the jet momentum coefficient. This study was performed in two stages. In the first study, a two-dimensional thin-airfoil thin-jet theory and accompanying computer program was developed. With this method, changes to the airfoil ideal lift coefficient were studied for various jet blowing rates and angles showing that the ideal lift coefficient could be adjusted by varying either the blowing rate or the flap angle. In the second stage, a hybrid computational study was conducted. This hybrid method involved the use of the CFL3D Reynolds-averaged Navier-Stokes code in conjunction with an integral boundary layer method. The surface pressure distributions for the airfoil were determined using CFL3D. Using these pressure distributions, the boundary layer transition locations were calculated using the integral boundary layer method. The transition-location data was then used to determine the lift-coefficient range in which extended laminar flow could be achieved for cases with and without blowing. The results of this study confirmed that, in addition to flap angle, blowing across the trailing edge flap can be used to adjust the range of lift coefficients over which extensive laminar flow can be achieved. The blown trailing-edge flap was shown to be more effective at altering the location of the low-drag range than a cruise flap with no blowing. In addition, the blown flap eliminates separation off the flap at high flap angles.
Date: 2004-10-26
Degree: MS
Discipline: Aerospace Engineering

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