Cmarc is a inviscid fluid flow analysis program of the type
known as a low-order panel method. It is an enhanced version of
NASA's Pmarc-12, which is in turn a descendant of an early version
of Analytical Methods' VSAERO. Pmarc-12 and VSAERO took different
evolutionary paths, but their common ancestry is apparent in the
similarity between their input file formats and the results that
they produce. Low-order panel methods, in which the calculated coefficient
of pressure for each panel is applied uniformly over the entire
panel, have been shown to provide virtually the same level of accuracy
as higher-order methods, in which pressure gradients are calculated
within panels, so long as the meshing of the model is sufficiently
dense, particularly in areas of rapidly changing pressure coefficient.
On modern desktop and laptop computers, dense meshes of 5,000 or
more panels for a half-model can be analyzed in seconds.
the basic analysis is inviscid, a subsequent boundary-layer analysis
may be performed along individual streamlines or over the entire
surface. Provided that flow is attached and that large areas of
crossflow do not appear, the boundary layer analysis is quite accurate.
the frictional and lift-induced components of drag can be computed,
however, unless the user chooses to use Cmarc's nonlinear option,
which incorporates boundary-layer displacement in the iterated solution.
While an inviscid analysis is inherently unable to calculate pressure
or "form" drag, iterating over the boundary layer allows
Cmarc to predict pressure drag with good accuracy so long as large
areas of separated flow are not present..
and Pmarc-12 input files are mutually compatible. Cmarc's output
formats are a superset of Pmarc-12's; Cmarc adds several files whose
purpose is to communicate output data to Postmarc. Postmarc incorporates
a number of Cmarc procedures, particularly those related to the
boundary layer analysis, in order to permit interactive generation
of on- and off-body streamlines and of pressure and velocity maps
of the free stream. With Cmarc and Postmarc, it is not necessary
to re-run the entire analysis each time new streamlines or velocity
scans are desired.
program screen (below) allows the user to alter a number of parameters
and run conditions without editing the input file. In this it resembles
the "Analysis" screen in Digital Wind Tunnel (DWT). Batch processes
can be scheduled to occur at any future date and time, and batch
files can be saved and reused. Memory detection and management work
the same as in Digital Wing Tunnel.
which is written in ANSI C, can also be delivered to customers in
command-line form, either as a DOS executable or as UNIX-compatible
source code with a makefile. Source code is provided at AeroLogic's
discretion, and may be modified by the user, but not redistributed.