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qmil_doc.txt
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qmil_doc.txt
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QMIL User Guide Version 1.10
Mark Drela 4 Oct 05
General Description
===================
Motivation
----------
QMIL is a propeller/windmill design program, whose output
is in the format of the QPROP propeller file. Hence it is
ideally suited to be used in conjunction with QPROP,
although its output can be adapted for other uses
as needed.
Theoretical model
-----------------
QMIL and QPROP have identical theoretical formulations.
This is described in more detail in qprop_doc.txt, and
in the theory document qprop_theory.ps .
Their only difference is the variables which are treated
as knowns and unknowns:
knowns unknowns
----------- -----------
QMIL cl chords,angles
QPROP chords,angles cl
Input Files
===========
Fluid constants file qcon.def (optional)
--------------------
This optional file contains the fluid constants, in the following format:
1.225 ! rho (kg/m^3) density
1.78E-5 ! mu (kg/m-s) dynamic viscosity
340.0 ! a (m/s) speed of sound
If this file is absent, QPROP and QMIL will use the default constants
defined in file src/QDEF.INC . The current defaults correspond
to sea level air.
Design specification file
-------------------------
QMIL obtains its design inputs from a file with the following format,
given in SI units:
Template prop
2 ! Nblades
0.0000 6.2832 ! CL0 CL_a
-0.8000 1.2000 ! CLmin CLmax
0.01000 0.008 0.006 0.40 ! CD0 CD2u CD2l CLCD0
150000.0 -0.500 ! REref REexp
0.0 0.5 1.0 ! XIdes (r/R locations where design cl is specified)
0.6 0.5 0.4 ! CLdes (specified cl)
0.05 ! hub radius(m)
1.50 ! tip radius(m)
8.00 ! speed(m/s)
240.0 ! rpm
0.0 ! Thrust(N) ( 0 if power specified )
500.0 ! Power(W) ( 0 if thrust specified )
0 0.2 ! Ldes KQdes
30 ! Nout number of output stations (optional)
Lines 1-6 are identical to those of the QPROP input file.
See file qprop_doc.txt for a description. For a windmill,
"upside down" airfoils would typically be used. In this case...
* CL0 and CLCD0 are negated from their conventional definitions
* CLmin and CLmax actually are -CLmax and -CLmin
* CD2u and CD2l are swapped
For example, if a propeller airfoil which is defined by
0.2000 6.2832 ! CL0 CL_a
-0.8000 1.2000 ! CLmin CLmax
0.01000 0.008 0.006 0.40 ! CD0 CD2u CD2l CLCD0
is to be used upside-down on a windmill, it would be specified
as follows:
-0.2000 6.2832 ! CL0 CL_a
-1.2000 0.8000 ! CLmin CLmax
0.01000 0.006 0.008 -0.40 ! CD0 CD2u CD2l CLCD0
Lines 7-8 specify the cl distribution along the blade.
Any number of radial XIdes locations with CLdes values
can be given. These are interpolated via a spline to the
output radial stations. Two successive identical
XIdes values enable a slope break in the spline.
Lines 9-12 give the hub and tip radii, the freestream airspeed
(which can be zero), and the operating RPM.
Lines 13-14 specify the prescribed thrust OR the prescribed power.
Negative thrust or power are used for a windmill. Neither values
is used if the Ldes=2 option is chosen (below).
Line 15 indicates the type of design option to be used.
Ldes = 0 Minimum Induced Loss (usual prop design option)
Ldes = 1 Minimum Total Loss (not recommended -- very ill-behaved)
Ldes = 2 Maximum Total Power (only for windmills)
The second optional value on line 15 controls the optimality
condition on the power for the Ldes=2 case:
dPower/dSwirl ~ KQdes
KQdes = 0.0 gives the actual maximum power
KQdes = 0.0-1.0 reduces the max power by some factor
The intent is to "moderate" the optimality to get a more
practical windmill geometry. Significantly more practical
geometries can be obtained (e.g. 20% narrower chords) for
relatively minor power penalties (e.g. 5% or less).
Line 16 gives the number of output radii.
Program Execution
=================
QMIL is executed with the following command:
% qmil inputfile [ outputpropfile ]
The "inputfile" was described above. With only this argument,
the computed propeller results is printed to the screen.
If the second "outputpropfile" argument is given, the
propeller results are written to this outputpropfile.
This file can then be immediately used as an argument
to QPROP.