Input File
As Xoptfoil2 does not have a user interface, all settings and parameters for an optimization task are made via an input file.
When starting Xoptfoil2 the input file is read and checked for consistency. If an error is detected program execution will be stopped at this early stage.
If all parameters are consistent, the seed airfoil is loaded and pre-processed. After this the optimizer is ready to go and will start the iterations …
Table of contents
Format of the Input File
The parameters of the input file are grouped in sections called ‘namelists’ which start with &namelist_name and end with an / character. The format of the input file is also an indication of the language in which the program is written: Fortran.
&option_list
logical_option = .true. ! this is a remark
number_option = 1.0
string_option = 'bezier'
/
An option can either be
- logical with the values
.true.or.false. - numerical with a point as decimal separator
- a string enclosed in apostrophes like
'myString'
Remarks or comment are introduced by an exclamation mark. It is a good advice to use ‘remarks’ extensively in your input file to remember modifications made between several optimizations runs.
Minimum example
Only a few parameters are mandatory and most of the numerous Xoptfoil2 parameters are optional having a default value. Here is an example of a minimum input file for a valid optimization task
! Optimize cd while trying to preserve glide ratio of SD7003 at Reynolds 400,000
&optimization_options
airfoil_file = 'SD7003.dat' ! the seed airfoil
shape_functions = 'camb-thick' ! just optimize geometry parameters like camber
/
&operating_conditions
re_default = 400000 ! Reynolds number for all operating points
noppoint = 2 ! we define only 2 operating points
op_mode(1) = 'spec-cl' ! operating point based on cl-value
op_point(1) = 0.2 ! cl=0.2
optimization_type(1) = 'min-drag' ! minimize cd (drag) at this point
op_mode(2) = 'spec-cl' ! operating point based on cl-value
op_point(2) = 0.7 ! cl = 0.7
optimization_type(2) = 'target-glide' ! target is the glide ratio cl/cd
target_value(2) = -1.0 ! try to preserve the value of SD7003
/
Parameters as arguments
There are a few optimization parameters which can be provided as command line arguments. In this case the command line argument will overwrite the value in the input file.
-a <filename>overwrites<airfoil_file>of&optimization_options-r <number>overwrites<re_default>of&operating_conditions
Using command line arguments can be useful when a row of optimization tasks should be automized for example to build a series of airfoils for a single wing.
Quick Reference
Overview of all namelists with their parameters currently available. Only a short explanation is given for each parameter. See Input Reference for more details.
Copy & Paste single parameters or complete namelists from here into your input file
!
! Xoptfoil2 - Reference of input parameters
!
! Values shown are the default values of the parameters
!
&optimization_options ! main control of optimization
airfoil_file = '<mySeedAirfoil>' ! either '.dat', '.bez' or '.hicks' file
shape_functions = 'hicks-henne' ! either 'hicks-henne', 'bezier' or 'camb-thick'
cpu_threads = -1 ! no of cpu threads or -n less than available
show_details = .true. ! show details of actions and results
/
&hicks_henne_options ! options for shape_function 'hicks-henne'
nfunctions_top = 3 ! hicks-henne functions on top side
nfunctions_bot = 3 ! hicks-henne functions on bot side
initial_perturb = 0.1 ! max. perturb when creating initial designs
smooth_seed = .false. ! smooth (match bezier) of seed airfoil prior to optimization
/
&bezier_options ! options for shape_function 'bezier'
ncp_top = 5 ! no of bezier control points on top side
ncp_bot = 5 ! no of bezier control points on bot side
initial_perturb = 0.1 ! max. perturb when creating initial designs
/
&camb_thick_options ! options for shape_function 'camb_thick'
thickness = .true. ! optimize thickness
thickness_pos = .true. ! optimize max. thickness position
camber = .true. ! optimize camber
camber_pos = .true. ! optimize max. camber position
le_radius = .true. ! optimize leading edge radius
le_radius_blend = .true. ! optimize blending distance for le radius change
initial_perturb = 0.1d0 ! max. perturb when creating initial designs
/
&operating_conditions ! options to describe the optimization task
dynamic_weighting = .true. ! activate dynamic weighting during optimization
allow_improved_target = .true. ! allow result to be better than target value
re_default = 400000 ! use this Reynolds number for operating points
re_default_as_resqrtcl = .false. ! interpret re number as type 2 (Re*sqrt(cl))
mach_default = 0.0 ! use this Mach number for operating points
use_flap = .false. ! activate flap setting or optimization
x_flap = 0.75 ! chord position of flap
y_flap = 0.0 ! vertical hinge position
y_flap_spec = 'y/c' ! ... in chord unit or 'y/t' relative to height
flap_angle_default = 0.0 ! default flap angle for all op points
noppoint = 0 ! no of operating points
! --- repeat this per operating point ---------
op_mode(1) = 'spec_cl' ! op either 'spec_cl' or 'spec_al' based
op_point(1) = 0.0 ! value of either cl or alpha
optimization_type(1) = 'target-drag' ! 'min-drag', 'max-glide', 'min-sink',
! 'max-lift', 'max-xtr',
! 'target-drag', 'target-glide', 'target-moment',
target_value(1) = 0.0 ! target value if type = 'target-...'
weighting(1) = 1.0 ! weighting during optimization
reynolds(1) = ! individual re number of op (default: re_default)
mach(1) = ! individual mach number of op (default: mach_default)
ncrit_pt(1) = ! individual ncrit of op
flap_angle(1) = ! individual flap angle (default: flap_angle_default)
flap_optimize(1) = .false. ! optimize this flap angle
/
&geometry_targets ! geometry targets which should be achieved
ngeo_targets = 0 ! no of geometry targets
target_type(1) = '' ! either 'camber', 'thickness', 'match-foil'
target_value(1) = 0.0 ! target value to achieve
target_string(1) = 0.0 ! in case of 'match-foil' filename of airfoil
weighting(1) = 1.0 ! weighting of this target
preset_to_target(1) = .false. ! preset seed airfoil to this target
/
&curvature ! geometry curvature constraints for optimization
check_curvature = .true. ! check curvature during optimization
auto_curvature = .true. ! auto determine thresholds for curvature and bumps
max_curv_reverse_top = 0 ! max no of curvature reversals - top ("reflexed"?)
max_curv_reverse_bot = 0 ! max no of curvature reversals - bot ("rearloading"?)
curv_threshold = 0.1 ! threshold to detect reversals
max_te_curvature = 5.0 ! max curvature at trailing edge
max_le_curvature_diff = 5.0 ! Bezier: max curvature difference at leading edge
spike_threshold = 0.5 ! threshold to detect spikes aga bumps
max_spikes_top = 0 ! max no of curvature bumbs - top
max_spikes_bot = 0 ! max no of curvature bumbs - bot
/
&constraints ! geometry constraints for optimization
check_geometry = .true. ! check geometry against geometry constraints
min_te_angle = 2.d0 ! min trailing edge angle in degrees
symmetrical = .false. ! force airfoil to be symmetrical
min_thickness = ! min thickness (better use geometry targets)
max_thickness = ! max thickness (better use geometry targets)
min_camber = ! min camber (better use geometry targets)
max_camber = ! max camver (better use geometry targets)
/
&paneling_options ! options for re-paneling before optimization
npan = 160 ! no of panels of airfoil
npoint = 161 ! alternative: number of coordinate points
le_bunch = 0.86 ! panel bunch at leading edge - 0..1 (max)
te_bunch = 0.6 ! panel bunch at trailing edge - 0..1 (max)
/
&particle_swarm_options ! options for particle swarm optimization - PSO
pop = 30 ! swarm population - no of particles
min_radius = 0.001 ! design radius when optimization shall be finished
max_iterations = 500 ! max no of iterations
max_retries = 2 ! no of particle retries for geometry violations
max_speed = 0.1 ! max speed of a particle in solution space 0..1
init_attempts = 1000 ! no of tries to get initial, valid design
convergence_profile = 'exhaustive' ! either 'exhaustive' or 'quick' or 'quick_camb_thick'
/
&polar_generation ! options only for 'Worker'
polar_reynolds = 0 ! list of reynolds like 100000, 200000, 600000
polar_mach = 0 ! list of mach like 0.1, 0.2, 0.5
type_of_polar = 1 ! either Type 1 or Type 2 polar
auto_range = .false. ! best values for mode and range automatically set
op_mode = 'spec-al' ! range based on alpha or cl
op_point_range = -2, 10, 0.25 ! range start, end, delta
/
&xfoil_run_options
ncrit = 9 ! ncrit default value for op points
xtript = 1.0 ! forced transition point 0..1 - top
xtripb = 1.0 ! forced transition point 0..1 - bot
bl_maxit = 50 ! max no of xfoil iterations to converge
vaccel = 0.005 ! xfoil vaccel parameter
fix_unconverged = .true. ! auto retry when op point doesn't converge
reinitialize = .false. ! reinit xfoil boundary layer after each op point
/