Available at: http://digitalcommons.calpoly.edu/theses/283
Date of Award
MS in Aerospace Engineering
Dr. David Marshall
In recent years, airports have experienced increasing airport congestion, partially due to the hub-and-spoke model on which airline operations are based. Current airline operations utilize large airports, focusing traffic to a small number of airports. One way to relieve such congestion is to transition to a more accessible and efficient point-to-point operation, which utilizes a large web of smaller airports. This expansion to regional airports propagates the need for next-generation low-noise aircraft with short take-off and landing capabilities. NASA has attacked this problem with a high-lift, low-noise concept dubbed the Cruise Efficient Short Take-Off and Landing (CESTOL) aircraft. The goal of the CESTOL project is to produce aircraft designs that can further expand the air travel industry to currently untapped regional airports.
One method of obtaining a large lifting capability with low noise production is to utilize circulation control (CC) technology. CC is an active flow control approach that makes use of the Coanda effect. A high speed jet of air is blown over a wing flap and/or the leading edge of the wing, which entrains the freestream flow and effectively increases circulation around the wing.
A promising tool for predicting CESTOL aircraft performance is computational fluid dynamics (CFD,) due to the relatively low cost and easy implementation in the design process. However, the unique flows that CC introduces are not well understood, and traditional turbulence modeling does not correctly resolve these complex flows (including high speed jet flow, complex shear flows and mixing phenomena, streamline curvature, and other challenging flow phenomena). The recent derivation of the v2-f turbulence model shows theoretical promise in increasing the accuracy of CFD predictions for CC flows, but this has not yet been assessed in great detail. This paper presents a methodical verification of several variations on the v2-f turbulence model. These models are verified using simple, well-understood flows. Results for CC flows are compared to those obtained with more traditional turbulence modeling techniques (including the Spalart-Allmaras, k-ε, and k-ω turbulence models). Wherever possible, computed results are compared to experimental data and more accurate numerical methods.
Results indicate that the v2-f turbulence models predict some aspects of circulation control flow fields quite well, in particular the lift coefficient. The linear v2-f, nonlinear v2-f, and nonlinear v2-f-cc turbulence models have generated lift coefficients within 19%, 14%, and -26%, respectively of experimental values, whereas the Spalart-Allmaras, k-ε, and k-ω turbulence models produce errors as high as 85%, 36%, and 39%, respectively. The predicted stagnation points and pressure coefficient distributions match experimental data roughly as well as standard turbulence models do, though the modeling of these aspects of the flow do show some room for improvement. The nonlinear v2-f-cc turbulence model shows very non-physical skin friction coefficient profiles, pressure coefficient profiles, and stagnation points, indicating that the streamline curvature correction terms need attention. Regardless of the source of the discrepancies, the v2-f turbulence models show promise in the modeling of circulation control flow fields, but are not quite ready for application in the design of circulation control aircraft.