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PMARC 12

PMARC 12
Software for computing the potential flow field around complex threedimensional bodies



SOURCE CODE AVAILABLE


Panel method computer programs are software tools of moderate cost used for solving a wide range of engineering problems. The panel code PMARC 12 (Panel Method Ames Research Center, version 12) can compute the potential flow field around complex threedimensional bodies such as complete aircraft models.
PMARC 12 is a welldocumented, highly structured code with an open architecture that facilitates modifications and the addition of new features. Adjustable arrays are used throughout the code, with dimensioning controlled by a set of parameter statements contained in an include file; thus, the size of the code (i.e. the number of panels that it can handle) can be changed very quickly. This allows the user to tailor PMARC 12 to specific problems and computer hardware constraints. In addition, PMARC 12 can be configured (through one of the parameter statements in the include file) so that the code's iterative matrix solver is run entirely in RAM, rather than reading a large matrix from disk at each iteration. This significantly increases the execution speed of the code, but it requires a large amount of RAM memory. PMARC 12 contains several advanced features, including
 internal flow modeling,
 a timestepping wake model for simulating either steady or unsteady (including oscillatory) motions,
 a Trefftz plane induced drag computation,
 offbody and onbody streamline computations,
 and computation of boundary layer parameters using a twodimensional integral boundary layer method along surface streamlines.
In a panel method, the surface of the body over which the flow field is to be computed is represented by a set of panels. Singularities are distributed on the panels to perturb the flow field around the body surfaces. PMARC 12 uses constant strength source and doublet distributions over each panel, thus making it a low order panel method. Higher order panel methods allow the singularity strength to vary linearly or quadratically across each panel. Experience has shown that low order panel methods can provide nearly the same accuracy as higher order methods over a wide range of cases with significantly reduced computation times; hence, the low order formulation was adopted for PMARC 12.
The flow problem is solved by modeling the body as a closed surface dividing space into two regions: the region external to the surface in which an unknown velocity potential exists representing the flow field of interest, and the region internal to the surface in which a known velocity potential (representing a fictitious flow) is prescribed as a boundary condition. Both velocity potentials are required to satisfy Laplace's equation. A surface integral equation for the unknown potential external to the surface can be written by applying Green's Theorem to the external region. Using the internal potential and zero flow through the surface as boundary conditions, the unknown potential external to the surface can be solved for.
When the internal flow option, which allows the analysis of closed ducts, wind tunnels, and similar internal flow problems, is selected, the geometry is modeled such that the flow field of interest is inside the geometry and the fictitious flow is outside the geometry. Items such as wings, struts, or aircraft models can be included in the internal flow problem.
The timestepping wake model gives PMARC 12 the ability to model both steady and unsteady flow problems. The wake is convected downstream from the wakeseparation line by the local velocity field. With each time step, a new row of wake panels is added to the wake at the wakeseparation line. Time stepping can start from time t=0 (no initial wake) or from time t=t0 (an initial wake is specified). A wide range of motions can be prescribed, including constant rates of translation, constant rate of rotation about an arbitrary axis, oscillatory translation, and oscillatory rotation about any of the three coordinate axes.
Investigators interested in a visual representation of the phenomenon they are studying with PMARC 12 may want to consider obtaining the program GVS (ARC13361), the General Visualization System. GVS is a Silicon Graphics IRIS program which was created for the purpose of supporting the scientific visualization needs of PMARC 12. GVS is available separately.
It is available only for use by United States citizens.
The IBM PC version of PMARC 12 carries the NASA case number COS10081. The machine independent version carries the NASA case number ARC13362. PMARC 12 was originally released as part of the NASA COSMIC collection.

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