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Stephen D.S.,SimCenter National Center for Computational Engineering
41st AIAA Fluid Dynamics Conference and Exhibit | Year: 2011

Although modern turbulence models have been greatly improved in recent years by advances in sub-scale techniques, little has been done to address the interaction between turbulence modeling and aerodynamic shocks. Consequently, modern turbulence models are hampered by inadequate source terms and eddy viscosities that work well on a case by case basis. The objective of this study is to demonstrate straightforward modifications to the blended kεkω turbulence model that result in vastly improved computations for aerodynamic shocks. A flapped nozzle is chosen as the primary test case due to the complexities of the three dimensional flow field over a wide range of flow conditions. © 2011 by D. Stephen Nichols, SimCenter.

Druyor Jr. C.,SimCenter National Center for Computational Engineering | Karman Jr S.,SimCenter National Center for Computational Engineering
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

An adaptive hybrid mesh generation method is described to automatically provide spa-tial discretizations suitable for computational uid dynamics or other 2D solver applica-tions. This method employs a hierarchical grid generation technique to create a background mesh, an extrusion-type method for inserting boundary layers, and an unstructured tri-angulation to stitch between the boundary layers and background mesh. This method provides appropriate mesh resolution based on geometry segments from a file, and has the capability of adapting the background mesh based on a spacing field generated from solu-tion data or some other arbitrary source. By combining multiple approaches to the grid generation process, this method seeks to benefit from the strengths of each, while avoiding the weaknesses of each. Copyright © 2012 by University of Tennessee Chattanooga, SimCenter: National Center for Computational Engineering. Published by the American Institute of Aeronautics and Astronautics.

Pankajakshan R.,SimCenter National Center for Computational Engineering | Mitchell B.J.,SAIC | Taylor L.K.,SimCenter National Center for Computational Engineering
Computers and Fluids | Year: 2011

The present study details the implementation of a time accurate method for the tracking of particles being acted upon by a continuous gas phase and gravity. The Lagrangian particle tracking approach was implemented within the framework of a parallel, incompressible, unstructured, node-centered finite-volume flow solver. The paper gives a method for selecting time steps for individual particles such that interactions with the continuum phase are updated at particle locations nearest the continuum-phase nodes while constraining the particle from passing beyond boundaries of the relevant adjacent cell. An implementation of this technique for three-dimensional nonuniform multi-element unstructured grids is given in the context of domain decomposition for implementation on distributed-memory parallel computers. Results of simulations with and without particle-particle collisions compare favorably with experimental validation results. © 2010 Elsevier Ltd.

Taylor L.K.,University of Tennessee at Chattanooga | Taylor L.K.,SimCenter National Center for Computational Engineering | Sreenivas K.,University of Tennessee at Chattanooga | Sreenivas K.,SimCenter National Center for Computational Engineering | And 3 more authors.
44th AIAA Thermophysics Conference | Year: 2013

An implicit algorithm is presented for the unsteady three-dimensional incompressible Navier-Stokes equations including the thermal energy equation, formulated in a strongly coupled manner. Thermal buoyancy is addressed using the Boussinesq approximation. The method of artificial compressibility is introduced to cast the resulting equations into a time marching form. A finite volume discretization is applied for general unstructured grids with nonsimplical elements. Numerical flux formulations are presented for both Roe's approximate Riemann solver and an HLLC approach. A backward Euler scheme is utilized for temporal discretization. The resulting implicit nonlinear equation is solved at each time step using an approximate Newton iteration algorithm. All boundary conditions are applied implicitly. The resulting algorithm has been implemented in Tenasi, an in-house developed flow solver, and validated for canonical test cases from the three regimes (forced, natural, and mixed) of laminar heat transfer and one regime (mixed) of turbulent heat transfer. A final application of the current algorithm is the prediction of forced turbulent heat transfer in a two-pass ribbed turbulator. All computed solutions are in close agreement with analytical solutions, other benchmark simulations, or experimental data.

Ji L.,SimCenter National Center for Computational Engineering | Wilson R.,SimCenter National Center for Computational Engineering | Sreenivas K.,SimCenter National Center for Computational Engineering | Hyams D.,SimCenter National Center for Computational Engineering
28th AIAA Applied Aerodynamics Conference | Year: 2010

Many approaches for moving and deforming mesh have been developed, but the approach adopted often depends on both the meshing scheme and the proposed application. Approaches based on a spring analogy with linear torsional springs or solution of partial differential equations have been used, but are generally very expensive to solve at each time step and are not trivial to parallelize. Here, a universal approach to grid motion known as the algebraic interpolation method (AIM) is followed to manage deforming surfaces. This method is universal and applicable to any grid type. Also, it is perfectly suitable to a parallel platform and can be implemented efficiently. The original scheme has some difficulty handling two-node bending mesh deformation involved in various fluid-structure interaction problems and other cases in which mesh deformation is driven solely by the surface motion. Several modifications have been made for these applications. It is determined that the grid quality can be improved significantly by adding a smoothing algorithm. Extra connectivities can also help improve the grid quality. The current scheme is applied to several well known synthetic jet applications from a NASA Langley Workshop for validation. Results are presented for the mesh deformation of NACA0012 airfoil and Suboff body. Free surface evolution of S175 container ship is also included along with its two-node bending mesh deformation. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

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