The ADPAC software is a computational fluid dynamics (CFD) code for analysis of flows in turbomachines. The outstanding feature of ADPAC is the ability to solve the Navier-Stokes equations for complex three-dimensional (3D) flow fields that include multiple flow paths, and the modeling of which typically involves multiple computational grid blocks. In addition, ADPAC can handle coupled calculations in which some portions of models are rotating and some are not, as in the case of the rotating blades and stationary vanes of a turbomachine. ADPAC was developed especially for use in analyzing the performances of short-duct, ultrahigh-bypass-ratio turbofan engines, both as uninstalled and as installed; however, ADPAC is applicable to a very broad range of other turbomachines and of other flow systems.
There are now several commercially available computer programs that offer capabilities similar to those of ADPAC. However, when the development of ADPAC began (circa 1989) 3-D Navier-Stokes CFD codes for turbomachinery could handle only single flow paths, and only a few codes could handle more than one component at a time. NASA had a need for a CFD code that could simultaneously handle multiple flow paths (through the core, through the bypass duct, and outside the cowl), multiple blade rows, and tightly coupled components of conceptual ultrahigh-bypass-ratio turbofan engines. Prior to the development of ADPAC, computational simulations of such complex flow fields were done in parts: In a typical case, each flow path and each blade row was split out, gridded, and run separately. Then the data at the interfaces between blocks were adjusted and the individual blocks run again until there was convergence. This decoupled-solution method proved to be inefficient and time-consuming.
The development of ADPAC involved rewriting of a prior 3D, viscous-flow CFD code that was capable of handling a single flow path with a single grid block. The rewriting included the incorporation of multiblock and multigrid capability, extra boundary conditions, and mathematical models of turbulence. The resulting ADPAC code is characterized by the following major features and capabilities:
- External Inflow: On-axis or off-axis for configurations at various angles of attack.
- Internal Inlet: Uniform (or plug) flow; distortion patterns with mixed radial and circumferential distributions of total pressure and total temperature.
- Boundary Conditions: Solid walls bounding inviscid or viscous flow; porous walls with inflow or outflow; and exit planes with constant static pressure or radial equilibrium.
- Grids: Multiple blocks; mixed C, H, I, and/or O grids (with some restrictions); mixed axisymmetric and/or three-dimensional grids with single or multiple blade passages; and multiblock binary (Cartesian) grids stored externally as PLOT3D files.
- Coupling Among Blocks: All boundary conditions must be given on a common face. Direct patch or interpolation is possible for mismatched grids with no relative movement. Mixing-plane or unsteady interpolation is possible for blocks with relative movement.
- Block Periodicity: Cylindrical (as for turbomachinery) or Cartesian (as for linear cascades or aircraft).
- Flow Paths: Multiple.
- Solver Algorithm: Finite-volume 4- or 5-stage Runge-Kutta explicit, dual time step implicit, multigrid acceleration, parallelized via message passing, APPL, PVM, or MPI libraries.
- Turbulence Models: Baldwin-Lomax with wall functions, restricted to the block with the wall; Goldberg's k-R; and Spalart-Allmaras.
- Time-Marching Throughflow Capability: Turbomachinery blade rows represented as 2-D axisymmetric surfaces with body forces to represent flow turning and profile losses.
- Inverse Design Capability: Turbomachinery blade row design based on time-marching throughflow simulation with user-specified tangential velocity and airfoil thickness distributions.
This work was done by Christopher J. Miller of Glenn Research Center and Edward J. Hall, Nathan J. Heidegger, Michael L. Koiro, and David A. Topp of Rolls Royce Allison Engine Division. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Mechanics category.