compflow 0.2.0

Compressible aerodynamics library.

compflow

This library contains functions to convert back and forth between Mach number and other non-dimensional compressible flow quantities.

Features

• Evaluation of ten non-dimensional flow quantities as explicit functions of Mach number;
• Iteration with Newton's method to invert the explicit relations and solve for Mach number;
• Creation and caching of lookup tables to speed up inversions;
• Fortran-accelerated, fully-vectorised in both directions.

Usage

compflow is available on the Python Package Index, so installation is as simple as,

$ python3 -m pip install compflow

We can then start doing some calculations,

>>> import compflow
>>> compflow.from_Ma(var='Po_P', Ma_in=0.3, ga=1.4)  # Explicit evaluation
1.0644302861529382
>>> compflow.to_Ma(var='Po_P', var_in=1.064, ga=1.4)  # Iterative solve
0.2990184500710573

The functions from_Ma and to_Ma are the primary interface to the library. They take a string argument indicating which quantity should be found from or converted to Mach number; see the docs for valid choices.

Numpy arrays are also accepted as inputs,

>>> import numpy
>>> Ma = numpy.array([0., 0.5, 1., 2.])
>>> compflow.from_Ma('Po_P', Ma, 1.4)
array([1.        , 1.18621264, 1.89292916, 7.82444907])

When solving for Mach number, it is assumed that we are on the subsonic branch of the curve unless a flag is specified. Where no solution is possible, for example if the flow would choke, nan is returned,

>>> capacity = [0.6, 2.]
>>> compflow.to_Ma('mcpTo_APo', capacity, 1.4)
array([0.28442265,        nan])
>>> compflow.to_Ma('mcpTo_APo', capacity, 1.4, supersonic=True)
array([2.27028708,        nan])

Lower level functions for each quantity are also available, but these are fussy about their inputs: some accept only Numpy arrays.

>>> compflow.Ma_from_Po_P(1.2,1.4)
0.5170711949922853
>>> compflow.A_Acrit_from_Ma(numpy.atleast_1d(0.3),1.4)
array([2.03506526])

Why compflow?

Like many libraries, compflow was written because the existing options did not meet the authors' needs.

• Super-fast because calculations are done in Fortran behind the scenes;
• Implements non-dimensional mass flow or capacity, which is commonly used for internal flow calculations;
• Simple, function-oriented interface;
• Supports inversions to solve for Mach number;
• Fully non-dimensional, no units-related nonsense.

TODO

• Comprehensive documentation.

James Brind December 2020