Analysis of Active Flow Control Concepts Using the 3D LES Vorcat Software
National Aeronautics and Space Administration (NASA)
The goal of this project is to produce a revolutionary computational methodology that is fast, reliable and accurate for predicting complex high Reynolds number, turbulent flows associated with advanced aerodynamic designs. The proposed work will focus on low-speed canonical flows that introduce challenging physics, e.g., separation, transition and turbulence onset/progression, vortex/viscous interactions, merging shear layers with strong curvature, juncture flows and jet-exhaust flows. The extension of our proposed methodology to compressible flows has already begun and will be pursued in Phase II and beyond after the incompressible capability is fully validated.
The Vorcat implementation of the gridfree vortex method is particularly attractive in this case since it efficiently represents near-wall vorticity producing motions while at the same time capturing the dynamics of the shed vorticity without numerical diffusion. An accurate and well resolved accounting of the boundary flow is crucial for controlling separation and other complex phenomena while unsteady free vortices are responsible for producing sound, downstream wing/vortex interactions and a range of other important phenomena.
A number of previous studies have established the unique benefits and accuracy of the Vorcat vortex filament method. These include computations of ground vehicle flows, isotropic turbulence, shear layers), coflowing round jets, and boundary layers. Additional validation studies have been conducted in such applied settings as wind turbines, rotorcraft and particulate flows. Collectively, these results establish the effectiveness of the vortex filament scheme in capturing the flow structure and statistics for complex spatially evolving flow fields in a way that has not been duplicated by alternative grid-based methodologies. In the realm of vortex structure the Vorcat approach has opened up a window into the dynamics of flow organization that is forcing a reassessment of some of the principal ideas concerning the physics of turbulent flow. Such insights are of great importance in efforts to predict transition, control turbulence, assess noise production and understand other facets of complex aerodynamic flow fields.
The proposed research is geared to accomplishing four tasks that will enable the use of Vorcat in numerous NASA applications:
developing optimal extensions of the current solver to account for features found in advanced applications (e.g., control jets, moving parts, vortex interaction),
optimizing the code by developing and implementing acceleration and memory management techniques,
testing the code on selected canonical flows and analyzing the results; and, finally
lay the ground work to the extension of the incompressible solver to a fully compressible technology.
This project brings to NASA a means for circumventing the persistent limitations of traditional turbulence modeling and simulation techniques that have delayed or prevented progress across a spectrum of innovative flow technologies. In particular, unlike RANS modeling, Vorcat requires no ad hoc model adjustments that must be fine tuned to the peculiarities of individual flows or extensive three-dimensional grid development that often requires a posteriori refinements to reduce numerical diffusion and/or capture missing details of detached vortices. Unlike grid-based schemes, Vorcat readily accounts for natural transition to turbulence without the use of special forcings. With Vorcat, the door is opened for NASA to more freely pursue design innovations without heavy reliance on corroborating physical tests.
Some particular examples where Vorcat can have high impact both for NASA and global aerospace industry include aerodynamic efficiency, aeroacoustics, vehicle design optimization, safety studies, and flows containing complex physics, turbulent mixing and heat transfer.