DFDC 0.55 User Primer Jan 31 2005 Harold Youngren, Aerocraft, Inc. Mark Drela, MIT Aero & Astro History ======= DFDC is an analysis code for axisymmetric ducted rotor design and analysis. General Description =================== DFDC has a number of features intended for rapid duct and ducted rotor design and analysis. Axisymmetric components Centerbody Duct walls Rotor Stator Drag sources Input file Keyword-driven case input file Aerodynamic outputs Duct forces and moments Rotor forces Analysis capability Duct with actuator disk (specified loading) Duct with rotor blade (specified blade geometry) Specify rotor axial position Freestream velocity RPM Drive to specified thrust Effects of duct drag sources Rotor design capability Design blade chord to specified circulation Design blade twist for specified chord and circulation Blade pitch and twist changes Geometric redesign of duct walls XFOIL-like geometry modification (GDES) Aerodynamic redesign of duct walls to specified pressures Input Files =========== DFDC works with a single input file in plain text format. This file contains the duct case data, the duct geometry data, actuator disk or rotor blade data and drag source data. The sections of this file are separated by keywords and can be input in any order. The user provides files xxx.case which is typically created using any text editor. Sample files are provided for use as templates. These can be manually edited, although this is not really necessary since it is may be more convenient to edit the contents in DFDC and then write out the file again. Comments can be added to the input file using either a ! or # character to start the comment line. These lines are read but not used. The first part of the input file has a header that identifies the DFDC code and version number. This line is followed by a title line identifying the case (this is printed in plots and output print). A sample input file for DFDC looks like this: DFDC Version 0.50 FatDuct + CB test case OPER ! Vinf Vref RPM 0.0000 50.000 8000.0 ! Rho Vso Rmu Alt 1.2260 340.00 0.17800E-04 0.0000 ! XDwake Nwake 0.80000 20 ! Lwkrlx F ENDOPER AERO ! #sections 1 ! Xisection 0.0000 ! A0deg dCLdA CLmax CLmin 0.0000 6.2800 1.5000 -1.0000 ! dCLdAstall dCLstall Cmconst Mcrit 0.50000 0.20000 0.0000 0.70000 ! CDmin CLCDmin dCDdCL^2 0.12000E-01 0.10000 0.50000E-02 ! REref REexp 0.20000E+06 0.35000 ENDAERO ACTDISK ! Xdisk NRPdef 0.12000 11 ! #stations 10 0.50491E-01 10.000 0.61567E-01 10.000 0.72644E-01 10.000 0.83721E-01 10.000 0.94798E-01 10.000 0.10587 10.000 0.11695 10.000 0.12803 10.000 0.13911 10.000 0.15018 10.000 ENDACTDISK ROTOR ! Xdisk Nblds NRPdef 0.12000 5 11 ! #stations 10 ! r Chord Beta 0.50491E-01 0.59431E-01 72.604 0.61567E-01 0.55238E-01 62.306 0.72644E-01 0.51337E-01 54.568 0.83721E-01 0.47984E-01 48.599 0.94798E-01 0.45217E-01 43.869 0.10587 0.42988E-01 40.020 0.11695 0.41230E-01 36.810 0.12803 0.39884E-01 34.071 0.13911 0.38899E-01 31.680 0.15018 0.38242E-01 29.548 ENDROTOR DRAGOBJ ! #pts 3 ! x r CDA 0.40000E-01 0.60000E-01 0.40000E-01 0.40000E-01 0.80000E-01 0.35000E-01 0.40000E-01 0.12000E-00 0.30000E-01 ENDDRAGOBJ GEOM FatDuct + CB test case 0.306379 0.035928 0.296701 0.039168 0.285768 0.041795 0.274184 0.043576 0.262095 0.044564 0.248578 0.044839 0.232723 0.044847 0.216580 0.044866 0.200407 0.044882 0.184232 0.044898 0.168060 0.044913 0.151899 0.044930 0.135773 0.044950 0.120000 0.044952 0.109361 0.044999 0.099680 0.044922 0.090039 0.044561 0.080630 0.043916 0.071451 0.042966 0.062540 0.041690 0.053933 0.040075 0.045705 0.038107 0.037900 0.035771 0.030604 0.033068 0.023901 0.030001 0.017880 0.026585 0.012632 0.022848 0.008231 0.018825 0.004736 0.014551 0.002179 0.010047 0.000586 0.005293 0.000000 0.000000 999.0 999.0 0.304542 0.159526 0.296440 0.162842 0.285240 0.167270 0.273301 0.171796 0.261206 0.176188 0.249026 0.180416 0.236794 0.184470 0.224549 0.188335 0.212269 0.192017 0.200020 0.195490 0.187807 0.198746 0.175647 0.201771 0.163586 0.204547 0.151644 0.207051 0.139859 0.209267 0.128379 0.211153 0.117508 0.212618 0.106950 0.213649 0.096610 0.214255 0.086498 0.214421 0.076647 0.214136 0.067113 0.213390 0.057935 0.212174 0.049193 0.210487 0.040949 0.208332 0.033312 0.205736 0.026403 0.202735 0.020339 0.199393 0.015227 0.195790 0.011135 0.192004 0.008090 0.188086 0.006112 0.184067 0.005242 0.180005 0.005484 0.176154 0.006854 0.172546 0.009324 0.169289 0.012842 0.166404 0.017419 0.163862 0.023109 0.161648 0.029956 0.159771 0.037937 0.158256 0.046983 0.157103 0.057025 0.156294 0.067995 0.155792 0.079836 0.155546 0.092531 0.155498 0.106044 0.155585 0.120000 0.155721 0.134221 0.155902 0.148679 0.156177 0.163490 0.156523 0.178507 0.156897 0.193399 0.157258 0.208123 0.157586 0.222751 0.157864 0.237332 0.158088 0.251898 0.158254 0.266506 0.158365 0.281130 0.158423 0.294972 0.158441 0.304466 0.158439 ENDGEOM The file is divided into sections by keywords. Operating point section ======================= This section contains the flow condition and operating point data for the case. The first line contains the freestream velocity, reference velocity and RPM (used for actuator disk to estimate swirl effects, or a rotor for operating condition). The second line contains the fluid properties and/or the altitude (used to set atmosphere properties if they are otherwise set to 0.0). The next line contains the downstream vortex wake length to be used for the flow domain (in duct diameters, use 0.75 to 2 diameters for most cases). The number of points to use in the wake is set here (20 works well). The last input is a flag to set automatic wake realignment and regridding, normally not used as it slows the case convergence). OPER ! Vinf Vref RPM 0.0000 50.000 8000.0 ! Rho Vso Rmu Alt 1.2260 340.00 0.17800E-04 0.0000 ! XDwake Nwake 0.80000 20 ! Lwkrlx F ENDOPER Actuator disk section ======================= This section contains a specification for an actuator disk to model the duct rotor. The section starts with the ACTDISK keyword and ends with ENDACTDISK. The actuator disk is specified by an axial location for the disk (Xdisk) which must be located between the duct and centerbody leading and trailing edges. The number of points to use to represent the actuator disk loading (NRPdef) is also required (normallly 11-15 points is enough). Adding rotor/actuator disk analysis points slows the method as each rotor radial station emits a vortex wake (which has Nwake+ points on each). The rotor loading is specified by a set of radial stations with specified blade loading (B*GAMMA, or BGAM in the code) corresponding to bound circulation on the blade and (with OMEGA) to pressure loading and thrust. Note that the user can specify any number of radial stations that characterize the disk loading, these will be interpolated to the rotor analysis stations. Note that actuator disks are not defined along with rotors, use one or the other! ACTDISK ! Xdisk NRPdef 0.12000 11 ! #stations 10 0.50491E-01 10.000 0.61567E-01 10.000 . . 0.13911 10.000 0.15018 10.000 ENDACTDISK Rotor section ======================= This section contains a specification for the rotor blades in the ducted fan. The section starts with the ROTOR keyword and ends with ENDROTOR. The rotor is specified by an axial location for the rotor (Xdisk) which must be located between the duct and centerbody leading and trailing edges. The number of rotor blades (Nblds) is specified here. The number of points to use to represent the rotor blade elements (NRPdef) is also required (normallly 11-15 points is enough). Adding rotor/actuator disk analysis points slows the method as each rotor radial station emits a vortex wake (which has Nwake+ points on each). The rotor is specified by a set of radial stations with specified blade chord and blade angle. The blade angle is measured from the plane of rotor rotation (0 for flat pitch, 90deg for axial inflow direction). The radial station and chord are assumed to be dimensional in meters. Note that the user can specify any number of radial stations that characterize the rotor, these will be interpolated to the rotor analysis stations. Rotors, once defined, take precedence over actuator disks. Normally you don't use both. ROTOR ! Xdisk Nblds NRPdef 0.12000 5 11 ! #stations 10 ! r Chord Beta 0.50491E-01 0.59431E-01 72.604 0.61567E-01 0.55238E-01 62.306 0.72644E-01 0.51337E-01 54.568 0.83721E-01 0.47984E-01 48.599 0.94798E-01 0.45217E-01 43.869 0.10587 0.42988E-01 40.020 0.11695 0.41230E-01 36.810 0.12803 0.39884E-01 34.071 0.13911 0.38899E-01 31.680 0.15018 0.38242E-01 29.548 ENDROTOR Aero properties section ======================= This section starts with the AERO keyword and ends with ENDAERO. This section contains aerodynamic data that is used for each blade element in a rotor analysis or design. The data is used for a parametric model of the lifting and drag properties of an airfoil section (2D section). The details of the model are presented in the aero.f code sections but are derived from the XROTOR aero model for blade elements. Any number (one or more) aero "sections" are used, located on the blade by a XIsection coordinate (XI = r/R). If two or more aero "sections are specifed the aero properties for any blade element at XI=xi_i will be obtained by interpolation of aero properties of aero "sections" whose XIsection values bound the desired blade element radial station. If only one section is present its aero properties will be used for the whole blade from hub to tip. AERO ! #sections 1 ! Xisection 0.0000 ! A0deg dCLdA CLmax CLmin 0.0000 6.2800 1.5000 -1.0000 ! dCLdAstall dCLstall Cmconst Mcrit 0.50000 0.20000 0.0000 0.70000 ! CDmin CLCDmin dCDdCL^2 0.12000E-01 0.10000 0.50000E-02 ! REref REexp 0.20000E+06 0.35000 ENDAERO Drag object section =================== This section starts with the DRAGOBJ keyword and ends with ENDDRAGOBJ. This section contains a CDA (drag area) and X,Y (x,r in axisymmetric system) coordinates of the drag line. This is used to set up a line source that will represent the blockage and loss of the drag object on the flow field. DRAGOBJ ! #pts 3 ! x r CDA 0.40000E-01 0.60000E-01 0.40000E-01 0.40000E-01 0.80000E-01 0.35000E-01 0.40000E-01 0.12000E-00 0.30000E-01 ENDDRAGOBJ Geometry section ================ This section starts with the GEOM keyword and ends with ENDGEOM. The lines between these keywords are assumed to be an XFOIL-format multi-element airfoil coordinate file containing the centerbody and duct wall coordinates. The two sets of coordinates are separated by an extra line with 999. 999. The coordinates are in X,Y order as used in XFOIL, ordered from upper surface TE to LE to lower surface TE. CCW order is preferred but DFDC will reverse foils with CW input order automatically. Note that the centerbody is normally cut by the X axis but can be described as a symmetrical foil. In this case DFDC will cut the foil at the X axis to make a half-body shape. Coordinates for DFDC are currently assumed to be dimensional in meters for compatibility with the assumed MKS system used in the code. Options for other dimensional systems may be added to DFDC. Coordinate system ----------------- The geometry is described in the following Cartesian system: X axial downstream Y radial coordinate (also R sometimes) Input data is assumed to be defined in MKS, coordinates in meters!. Plotting Options ================ The top-level PLOP command produces the plot option menu, shown below with the default values. Most of these parameters must be changed before the first plot is made, otherwise they may not have the intended effect. ............................................... G raphics-enable flag T C olor PostScript output? F I ndividual PS file output? F A spect ratio of plot object 0.0000 S ize of plot object 9.00" P age dimensions 11.00 x 8.50" M argins from page edges 0.00", 0.00" F ont size (relative) 0.0170 W indow/screen size fraction 0.7000 O rientation of plot: Landscape B lowup input method: Keyboard Option, Value (or ) c> Normally, all hardcopy goes to the single multi-page plot.ps file. Toggling the Individual PS file flag to T will place successivehardcopy pages in an individual files, named plot000.ps plot001.ps plot002.ps etc. These may then be used to create mode animation, etc. The other parameters and options are mostly self-explanatory.