Unsteady Analysis of Separated Aerodynamic Flows Using an Unstructured Multigrid Algorithm

39th Aerospace Sciences Meeting and Exhibit 02/2001; DOI: 10.2514/6.2001-860
Source: NTRS


An implicit method for the computation of unsteady flows on unstructured grids is presented. The resulting nonlinear system of equations is solved at each time step using an agglomeration multigrid procedure. The method allows for arbitrarily large time steps and is efficient in terms of computational effort and storage. Validation of the code using a one-equation turbulence model is performed for the well-known case of flow over a cylinder. A Detached Eddy Simulation model is also implemented and its performance compared to the one equation Spalart-Allmaras Reynolds Averaged Navier-Stokes (RANS) turbulence model. Validation cases using DES and RANS include flow over a sphere and flow over a NACA 0012 wing including massive stall regimes. The project was driven by the ultimate goal of computing separated flows of aerodynamic interest, such as massive stall or flows over complex non-streamlined geometries.

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    • "This discretization is secondorder accurate in space. The baseline steady-state solver is extended to an unsteady Reynolds-Averaged Navier-Stokes (URANS) solver, using a second-order accurate three-point backwaxds difference time discretization [2]. At each physical time-step, the parallel agglomeration multigrid algorithm is employed to drive the non-linear (unsteady) residual to convergence . "
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    ABSTRACT: This work is concerned with the development of an efficient parallel Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) capability using unstructured meshes. The advantages of unstructured meshes include flexible modeling of complex geometries, adaptive meshing capabilities, and homogeneous data structures well suited for massively parallel computer architectures. On the other hand, unstructured mesh techniques require additional computer resources as compared to cartesian or structured mesh methods, and the achievable accuracy of the particular unstructured mesh discretization must be carefully considered. The approach developed in this work is based on an existing steady-state unstructured mesh solver which relies on agglomeration multigrid for rapid convergence and has been shown to scale well on inexpensive personal computer (PC) clusters as well as on massively parallel supercomputers using thousands of processors1.
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    ABSTRACT: An overview of the current status of time dependent algorithms is presented. Special attention is given to algorithms used to predict fluid actuator flows, as well as other active and passive flow control devices. Capabilities for the next decade are predicted, and principal impediments to the progress of time-dependent algorithms are identified.


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