Unsteady flow simulations using unstructured sliding meshes

grid quality and therefore corrective measures have to be incorporated into the algorithms. However, for a large class of Techniques for numerical simulation of unsteady flow probproblems of practical interest, the direction of motion of the lems using translatingand/orrotatingunsuucturedmeshes are components is known a priori and remeshing can be avoided presented. These tcchniques are implemented in a generalby decomposing the domain into zones which move relative purpose unstructured grid based flow-solver. The procedure to each other along judiciously chosen boundaries. Viually can be used to solve a wide range of unsteady or time-periodic all rotating machinery problems fall into this class; examples flows resulting from interactions between multiple compoinclude axial and centrifugal turbomachinery, mixing tanks, nents in relative motion. Results for some demonstrative etc. Several other problems, such as vehicle/vehicle or vecalculations, such as as rotor-stator interactions in axial or hicle/tunnel interaction, can also be accommodated within a centrifugal turbomachinery and the unsteady interactions besliding mesh framework. tween high speed trains and tunnels are presented. Sliding meshes have been used in the past but usually only in conjunction with structured grids. Rai et al 15, 61 have employed patched and overlaid moving grids for the analysis Introduction of unsteady rotor-stator interactions. Both nonconservative as well as conservative interface schemes were investigated. An Unstructured grid-based methods have become increasingly popular over the last decade for computational simulations of can be found in [7]. Even though the meshes do not align fluid flow problems. The main advantage of these methods along the interfaces, the interpolation procedure is relatively over the traditional structured grid basedapproaches is in the easy to implement because of the structured nature of the flexibility in discretizing complex geometries. An equally grids. The procedure is simplified even further if the threeimponant benefit of an unstructured discretization is the reldimensional grids are generated by stacking two-dimensional ative me with which the grid can be dynamically adapted, grids since then interpolation is only required along lines. either in response to an evolving solution or to accommodate Unsmctured threc-dimensional grids, however, result in changes in geometry. The latter capability has been exploited interfaces which are also unstructured and therefore interface by several researchers in solving unsteady problems such as procedures become quite complex. In this paper we develop the oscillations of airfoils and store separation from aircraft techniques for fully conservative and efficient treatment of [ I , 2, 3.41. Techniques employed for remeshing the domain such boundaries. This discussion is preceded by a brief dehave ranged from simple spring-mass analogies to full regenscription of the flow-solver into which the procedures have eration of grids. been implemented. Finally, results for a couple of demonstraAlthough these techniques make it possible to allow fully tive problems are presented. general motion of Ihe components, the remeshing effort at every time step, even if confined to part of the domain, can incur a significant performance penalty. This is of particular Flow Solver concern in periodic problems where the solution time must often extend to several cycles in order to establish a periodic The steady-state. Continuous remeshing can also deteriorate the eeneral ournose nackarre for modeline fluid Row W n of work has been implemented in RAMPANT, a heat L . transfer marketed by Fluent Inc. The code is capable of bothcompressible as well as incompressibleflow simulations. 'Copynghr 0 1 9 9 4 by Nuen1 Inc. Published by thc American Inslilute of Aeronautics and Asironaulicn.lnc. with ocrmission. IEnginecr. Member AlAA In addition to the usual features of unstructured grid based 1 methods such as the ability to handle complex geometries and solution adaption. it also incorporates numerous physical models for turbulence, convective heat transfer, porous media