This manual describes the operation and use of Wind-US, a computational platform which may be used to numerically solve various sets of equations governing physical phenomena. Wind-US represents a merger of the capabilities of four CFD codes --- NASTD (a structured grid flow solver developed at McDonnell Douglas, now part of Boeing), NPARC (the original NPARC Alliance structured grid flow solver), NXAIR (an AEDC structured grid code used primarily for store separation analysis), and ICAT (an unstructured grid flow solver developed at the Rockwell Science Center and Boeing). [Wind-US is a product of the NPARC Alliance, a partnership between the NASA Glenn Research Center (GRC) and the USAF Arnold Engineering Development Center (AEDC) dedicated to the establishment of a national, applications-oriented flow simulation capability. The Boeing Company has also been closely associated with the Alliance since its inception, and represents the interests of the NPARC User's Association.] Currently, the code supports the solution of the Euler and Navier-Stokes equations of fluid mechanics, along with supporting equation sets governing turbulent and chemically reacting flows.
All terms are retained in the governing equations, including secondary flow, reversed flow convection, pressure gradients normal to a wall, streamwise diffusion, and unsteady flow. All heat transfer terms are retained. Several algebraic, one-equation, and two-equation turbulence models are available. Transition may be specified through the use of an external file. Modification of the effective heat transport coefficient due to turbulence is linked to the momentum diffusion coefficient by a turbulent Prandtl number, which is taken to be constant.
The fluid may be treated as a thermally and calorically perfect gas, a thermally perfect gas, equilibrium air, or a mixture undergoing a finite-rate chemical reaction. For an ideal gas, conventional values are given to the gas constant R and the ratio of specific heats γ, or they may be specified.
Wind-US uses externally generated computational grids. Therefore, all geometric input and capability depend on the grid generator. Wind-US has no geometric input. All analyses must be preceded by a grid generation run.
Wind-US uses multi-zone computational grids, and is capable of computing solutions on a wide variety of structured or unstructured grids. However, not all of the features of Wind-US are available for both types of grids. The individual keyword descriptions note when a specific capability is limited to structured or unstructured grids.
Because Wind-US is written to accommodate arbitrary grid topologies and boundary condition combinations, it may be used to obtain solutions about most of the geometric configurations for which a grid can be generated. The multi-zone approach makes it possible to decompose virtually any configuration into a number of manageable subregions, or zones. Zonal connectivity information is computed using a pre-processing code (either GMAN or MADCAP), and stored in the grid file used by Wind-US. During the course of a solution, Wind-US maintains continuity in flow properties across zone boundaries through a process known as zone coupling. [Romer, W. W., and Bush, R. H. (1993) "Boundary Condition Procedures for CFD Analyses of Propulsion Systems - The Multi-Zone Problem," AIAA Paper 93-1971.]
The solution is executed iteratively on the computational mesh. The flow equations are evaluated using second-order-accurate finite differences. The partial differential equations are modeled in their conservative form. Explicit terms are computed using either upwind or central differencing, and their order may be controlled through the use of keywords in the input data file. The implicit terms are computed using either an approximately factored or four-stage Runge-Kutta scheme, or they may be disabled altogether. Global Newton iteration or dual time stepping schemes are also available, and may be used for unsteady flows with large time scales or as a convergence acceleration technique for steady flows.
Wind-US is written almost entirely in ANSI Standard Fortran 90. The low-level library routines are generally written in Fortran 77 and/or in ANSI C. The production version of the code is known to run on a variety of systems, including Linux, Silicon Graphics, Hewlett-Packard, Sun, and Cray.