EP-704 ANSYS FLUENT Airfoil 2D Setup

EP-704 ANSYS FLUENT Airfoil 2D Setup

Date: <strong>June 17, 2015</strong> <h1><strong>1. </strong><strong>PURPOSE</strong><strong> / DESCRIPTION</strong></h1> <ul> <li>To set a standard procedure for airfoil simulation in ANSYS Fluent <ul> <li>This will be 2D simulation, which is the same as having two symmetry boundaries to the right and left of the airfoil.</li> <li>The setup will mostly follow the tutorial from SimCafe (<a href="https://goo.gl/OLIX5g">https://goo.gl/OLIX5g</a>)</li> </ul> </li> <li>The procedure follows the wind tunnel simulation that was run for the NX Drone</li> <li>Useful resources: <ul> <li>Full course videos on ANSYS website for Fluent.</li> <li>“Workshop 04: Airfoil” from ANSYS Fluent full course materials</li> <li>Airfoil Tools: <a href="http://airfoiltools.com/airfoil/details?airfoil=naca0015-il">http://airfoiltools.com/airfoil/details?airfoil=naca0015-il</a></li> <li>UIUC Airfoil Database: <a href="http://m-selig.ae.illinois.edu/ads/coord_database.html">http://m-selig.ae.illinois.edu/ads/coord_database.html</a></li> <li>How to import/plot points: <a href="http://pjotr.ru/ansys_dm_01/">http://pjotr.ru/ansys_dm_01/</a></li> <li>General Tips: <a href="http://www.computationalfluiddynamics.com.au/category/tips-and-tricks/">http://www.computationalfluiddynamics.com.au/category/tips-and-tricks/</a></li> <li>Air Properties Calculator: <a href="http://www.mhtl.uwaterloo.ca/old/onlinetools/airprop/airprop.html">http://www.mhtl.uwaterloo.ca/old/onlinetools/airprop/airprop.html</a></li> </ul> </li> <li>If you have no experience with ANSYS, it is recommended that you go through the ETP for Learning ANSYS.</li> </ul> <strong> </strong> <h1><strong>2. </strong><strong>Geometry &amp; Meshing PROCEDURE</strong><strong> (without explicit inflation layer definition)</strong></h1> NOTE: These instructions match the steps taken in SimCafe’s tutorial on airfoil ( <a href="https://goo.gl/OLIX5g">https://goo.gl/OLIX5g</a>) and the tutorial regarding importing points (<a href="http://pjotr.ru/ansys_dm_01/">http://pjotr.ru/ansys_dm_01/</a>) <ul> <li>Find online the coordinates for the desired airfoil. <ul> <li>You need to write the points into a .txt file with the following format<a href="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-00.png"><img class="aligncenter wp-image-324" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-00.png" alt="704-00" width="526" height="188" /></a></li> <li>Any lines beginning with #’s are simply comments and do not have to be included.</li> <li>The first number is the group number and the second is the order within the group. The remaining three numbers are the XYZ coordinates of each point. You only need 1 group, however, for this procedure.</li> </ul> </li> <li>Follow the first 5 steps in the tutorial about point importing. Because this is a 2D procedure, you will only have one surface (one group of points) to create. <ul> <li>Before creating the surface of the Make sure to zoom into the trailing edge and connect the open points after creating the curve from the points.</li> </ul> </li> <li>After successfully creating the surface of the airfoil, move on to the tutorial on SimCafe. <ul> <li>Set the velocity components to the desired velocity components depending on the desired angle of attack and Reynolds number.</li> <li>Save image captures of contours, plots, and graphics created throughout the tutorial.</li> </ul> </li> </ul> &nbsp; &nbsp; <!--nextpage--> <h1><strong>3. </strong><strong>Geometry &amp; Meshing PROCEDURE (with inflation layer definition)</strong></h1> NOTE: These instructions match the video on SimCafe’s webpage: <a href="https://goo.gl/A7aQHD">https://goo.gl/A7aQHD</a> <ul> <li>For this procedure it is recommended that you have a coordinate file with a trailing edge that you have to connect using a separate line, as in the tutorial <a href="http://pjotr.ru/ansys_dm_01/">http://pjotr.ru/ansys_dm_01/</a></li> <li>Use the same geometry made with the instructions from SimCafe but without the line projections. <ul> <li>The geometry should look similar to this:<img class="aligncenter wp-image-325" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-01.png" alt="704-01" width="404" height="433" /></li> </ul> </li> <li>Open Meshing and change the settings of <strong>Mesh</strong> to match the settings below (except for Statistics):</li> </ul> <img class="alignnone wp-image-327" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-03.png" alt="704-03" width="286" height="418" /><img class="alignnone wp-image-326" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-02.png" alt="704-02" width="288" height="474" /> <ul> <li>SETTINGS (especially Min Size) SHOULD BE ALTERED, TESTED, AND EXPERIMENTED WITH DEPENDING ON THE GEOMETRY.</li> <li>The statistics should be checked, as mentioned, each time the mesh generated.</li> <li>For 2D mesh, an orthogonal quality (OQ) above 0.4 is preferred, but using inflation will most likely result in lower OQ, which is acceptable.</li> </ul> <ul> <li>RCLK on Mesh &gt; Insert &gt; Sizing</li> </ul> <table> <tbody> <tr> <td rowspan="2" width="195">Scoping</td> <td width="315">Scoping Method</td> <td width="339">Geometry Selection</td> </tr> <tr> <td width="315">Geometry</td> <td width="339">Select the main edge of the airfoil. (excluding the trailing edge)</td> </tr> <tr> <td width="195">Definition</td> <td width="315">Type</td> <td width="339">Number of Divisions You can also use Element Size.</td> </tr> <tr> <td width="195"></td> <td width="315">Number of Divisions</td> <td width="339">900 Adjust number of divisions as needed.</td> </tr> <tr> <td width="195"></td> <td width="315">Behavior</td> <td width="339">Soft</td> </tr> <tr> <td width="195"></td> <td width="315">Bias Type</td> <td width="339">_____  ___  _  ___  _____ This is to have smaller sizing near the trailing edge in order to improve orthogonal quality. Adjust according to the geometry.</td> </tr> <tr> <td width="195"></td> <td width="315">Bias Option</td> <td width="339">Bias Factor</td> </tr> <tr> <td width="195"></td> <td width="315">Bias Factor</td> <td width="339">35 Adjust bias factor as needed.</td> </tr> </tbody> </table> <ul> <li>RCLK on Mesh &gt; Insert &gt; Sizing</li> </ul> <table> <tbody> <tr> <td rowspan="2" width="195">Scoping</td> <td width="315">Scoping Method</td> <td width="339">Geometry Selection</td> </tr> <tr> <td width="315">Geometry</td> <td width="339">Select the trailing edge of the airfoil.</td> </tr> <tr> <td width="195">Definition</td> <td width="315">Type</td> <td width="339">Number of Divisions Or you can use Element Size and use a size that is about half the height of the trailing edge.</td> </tr> <tr> <td width="195"></td> <td width="315">Number of Divisions</td> <td width="339">2</td> </tr> <tr> <td width="195"></td> <td width="315">Behavior</td> <td width="339">Hard</td> </tr> <tr> <td width="195"></td> <td width="315">Bias Type</td> <td width="339">No Bias</td> </tr> </tbody> </table> <ul> <li>RCLK on Mesh &gt; Insert &gt; Inflation</li> </ul> <table style="height: 694px" width="971"> <tbody> <tr> <td rowspan="2" width="195">Scoping</td> <td width="315">Scoping Method</td> <td width="339">Geometry Selection</td> </tr> <tr> <td width="315">Geometry</td> <td width="339">Select the main surface (do not select it as a body)</td> </tr> <tr> <td width="195">Definition</td> <td width="315">Boundary Scoping Method</td> <td width="339">Geometry Selection</td> </tr> <tr> <td width="195"></td> <td width="315">Boundary</td> <td width="339">Select the main edge (excluding the trailing edge) of the airfoil</td> </tr> <tr> <td width="195"></td> <td width="315">Inflation Option</td> <td width="339">First Layer Thickness Choose appropriate option depending on the situation.</td> </tr> <tr> <td width="195"></td> <td width="315">First Layer Height</td> <td width="339">.1 mm This was the desired first cell height calculated for an Re of 3000000. Calculate and use an appropriate height, or use another method.</td> </tr> <tr> <td width="195"></td> <td width="315">Maximum Layers</td> <td width="339">20</td> </tr> </tbody> </table> <ul> <li>(Optional) <ul> <li>RCLK on Coordinate Systems &gt; Insert &gt; Coordinate System</li> </ul> </li> </ul> <table> <tbody> <tr> <td width="135">Origin</td> <td width="315">Define By</td> <td width="339">Global Coordinates</td> </tr> <tr> <td width="135"></td> <td width="315">Origin X</td> <td width="339">1500 mm Select appropriate coordinates so that the sphere of influence is slightly to the right of the trailing edge.</td> </tr> <tr> <td width="135"></td> <td width="315">Origin Y</td> <td width="339">0</td> </tr> <tr> <td width="135"></td> <td width="315">Origin Z</td> <td width="339">0 &nbsp;</td> </tr> </tbody> </table> <ul> <li>Mesh &gt; Insert &gt; Body Sizing</li> </ul> <table> <tbody> <tr> <td rowspan="2" width="135">Scoping</td> <td width="315">Scoping Method</td> <td width="339">Geometry Selection</td> </tr> <tr> <td width="315">Geometry</td> <td width="339">Select the main body (do not select it as a surface)</td> </tr> <tr> <td width="135">Definition</td> <td width="315">Type</td> <td width="339">Sphere of Influence</td> </tr> <tr> <td width="135"></td> <td width="315">Sphere Center</td> <td width="339">Coordinate System Or select the coordinate system created in the step above.</td> </tr> <tr> <td width="135"></td> <td width="315">Sphere Radius</td> <td width="339">2000 mm This can be altered as needed.</td> </tr> <tr> <td width="135"></td> <td width="315">Element Size</td> <td width="339">40 mm This can be altered as needed. You can change this to do mesh independence study as well.</td> </tr> </tbody> </table> <ul> <li>Creating Named Selections <ul> <li>Select the edges that form the airfoil <ul> <li>RCLK on the graphics window &gt; Create Named Selections</li> <li>Name it “wing”</li> </ul> </li> <li>Do the same for the edges for the inlet and outlet as shown:<img class=" wp-image-328 aligncenter" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-04.png" alt="704-04" width="224" height="187" /></li> </ul> </li> </ul> <strong>Example of how it should look</strong>: <a href="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-05.png"><img class="wp-image-329 aligncenter" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-05.png" alt="704-05" width="467" height="398" /></a> &nbsp; &nbsp; <!--nextpage--> <h1><strong>4. </strong><strong>Setup &amp; Solution PROCEDURE</strong></h1> <strong>Setup</strong> <ul> <li>General <ul> <li>Click on Report Quality (Confirm that the values that appear are not close to the extremes that Fluent describes)</li> <li>Click on Check</li> </ul> </li> <li>Models <ul> <li>DCLK (double click) on Viscous <ul> <li>Model = k-omega (2 eqn)</li> <li>k-omega Model = SST</li> </ul> </li> <li>Materials <ul> <li>DCLK on air under Fluid <ul> <li>Use the default properties already there, or change the properties to match a desired temperature.</li> </ul> </li> <li>Cell Zone Conditions <ul> <li>Click on the cell zone (there should only be one).</li> <li>Confirm that Type is set to fluid.</li> </ul> </li> <li>Boundary Conditions (if names used are not the same, look for corresponding names) <ul> <li>DCLK on inlet</li> </ul> </li> </ul> </li> </ul> </li> </ul> <table> <tbody> <tr> <td rowspan="4" width="135">Momentum</td> <td width="315">Velocity Specification Method</td> <td width="339">Components</td> </tr> <tr> <td width="315">Reference Frame</td> <td width="339">Absolute</td> </tr> <tr> <td width="315">X-Velocity (m/s)</td> <td width="339">7.785564 The velocity will components will depend on the axes’ orientation and the angle of attack.</td> </tr> <tr> <td width="315">Y-Velocity (m/s)</td> <td width="339">0</td> </tr> </tbody> </table> <ul> <li>DCLK on outlet</li> </ul> <table> <tbody> <tr> <td width="135">Momentum</td> <td width="315">Gauge Pressure (pascal)</td> <td width="339">0</td> </tr> </tbody> </table> <ul> <li>DCLK on all walls to confirm they are Stationary, No-Slip Walls with 0 Thermal properties.</li> </ul> <ul> <li>Reference Values <ul> <li>By setting Compute from to inlet, Fluent will automatically set the appropriate values for density, viscosity, and temperature.</li> </ul> </li> </ul> <table> <tbody> <tr> <td width="195"></td> <td width="315">Compute from</td> <td width="339">outlet</td> </tr> <tr> <td rowspan="2" width="195">Reference Values</td> <td width="315">Area (m^2)</td> <td width="339">1 Use the appropriate planform area. (With chord length of 1m, it is recommended to keep the area at 1m^2)</td> </tr> <tr> <td width="315">Length (m)</td> <td width="339">1 Use the appropriate chord length of the airfoil.</td> </tr> </tbody> </table> &nbsp; <strong>Solution</strong> <ul> <li>Solution Methods</li> </ul> <table> <tbody> <tr> <td width="195">Pressure-Velocity Coupling</td> <td width="315">Scheme</td> <td width="339">COUPLED</td> </tr> <tr> <td rowspan="5" width="195">Spatial Discretization</td> <td width="315">Gradient</td> <td width="339">Least Squares Cell Based</td> </tr> <tr> <td width="315">Pressure</td> <td width="339">Second Order</td> </tr> <tr> <td width="315">Momentum</td> <td width="339">Second Order Upwind</td> </tr> <tr> <td width="315">Turbulent Kinetic Energy</td> <td width="339">Second Order Upwind</td> </tr> <tr> <td width="315">Specific Dissipation Rate</td> <td width="339">Second Order Upwind</td> </tr> </tbody> </table> <ul> <li>Refer to notes and course material to choose appropriate scheme and discretization methods.</li> </ul> <ul> <li>Solution Controls <ul> <li>These values should be changed case by case, but the defaults seem to be sufficient for the procedure-specific example.</li> </ul> </li> <li>Monitors <ul> <li>Click on Create under Residuals, Statistic and Force Monitors &gt; Drag…</li> </ul> </li> </ul> <table> <tbody> <tr> <td rowspan="2" width="135">Options</td> <td width="315">Print to Console</td> <td width="339">checked</td> </tr> <tr> <td width="315">Plot</td> <td width="339">checked</td> </tr> <tr> <td width="135">Force Vector</td> <td width="315">X</td> <td width="339">1 Force Vector should be determined depending on the angle of attack.</td> </tr> <tr> <td width="135"></td> <td width="315">Y</td> <td width="339">0</td> </tr> <tr> <td width="135"></td> <td width="315">Z</td> <td width="339">0</td> </tr> <tr> <td width="135"></td> <td width="315">Surfaces</td> <td width="339">wing Or choose surfaces that form the airfoil.</td> </tr> </tbody> </table> <ul> <li>Click on Create under Residuals, Statistic and Force Monitors &gt; Lift…</li> </ul> <table> <tbody> <tr> <td rowspan="2" width="135">Options</td> <td width="315">Print to Console</td> <td width="339">checked</td> </tr> <tr> <td width="315">Plot</td> <td width="339">checked</td> </tr> <tr> <td width="135">Force Vector</td> <td width="315">X</td> <td width="339">0 Force Vector should be determined depending on the angle of attack.</td> </tr> <tr> <td width="135"></td> <td width="315">Y</td> <td width="339">1</td> </tr> <tr> <td width="135"></td> <td width="315">Z</td> <td width="339">0</td> </tr> <tr> <td width="135"></td> <td width="315">Surfaces</td> <td width="339">wing Or choose surfaces that form the airfoil.</td> </tr> </tbody> </table> <ul> <li>Click on Create under Surface Monitors</li> </ul> <table> <tbody> <tr> <td width="135"></td> <td width="315">Report Type</td> <td width="339">Area-Weighted Averaged</td> </tr> <tr> <td rowspan="2" width="135">Options</td> <td width="315">Print to Console</td> <td width="339">checked</td> </tr> <tr> <td width="315">Plot</td> <td width="339">checked</td> </tr> <tr> <td rowspan="2" width="135"></td> <td rowspan="2" width="315">Field Variable</td> <td width="339">Pressure</td> </tr> <tr> <td width="339">Total Pressure</td> </tr> <tr> <td width="135"></td> <td width="315">Surfaces</td> <td width="339">wing Or choose surfaces that form the airfoil.</td> </tr> </tbody> </table> <ul> <li>The pressure plot will be used to see that values are stabilizing while solving.</li> <li>Note that Cd and Cl calculated while solving may not be true coefficients because the solver uses the Area input in the Reference section.</li> </ul> <ul> <li>Click on Convergence Manager… under Convergence Monitors <ul> <li>Set Stop Criterion and other parameters to check for convergence of the coefficients. These values are also should be decided according to the behavior of the problem.<img class="alignnone wp-image-330" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-06.png" alt="704-06" width="667" height="246" /></li> </ul> </li> <li>Solution Initialization <ul> <li>Click Initialize (while Hybrid Initialization is chosen)</li> <li>Choose Standard Initialization</li> </ul> </li> </ul> <table> <tbody> <tr> <td width="195"></td> <td width="315">Compute from</td> <td width="339">inlet</td> </tr> <tr> <td width="195"></td> <td width="315">Reference Frame</td> <td width="339">Absolute</td> </tr> <tr> <td rowspan="3" width="195">Initial Values</td> <td width="315">X Velocity (m/s)</td> <td width="339">7.785564 The velocity will components will depend on the axes’ orientation, the angle of attack, and desired Reynold’s number.</td> </tr> <tr> <td width="315">Y Velocity (m/s)</td> <td width="339">0</td> </tr> <tr> <td width="315">Z Velocity (m/s)</td> <td width="339">0</td> </tr> </tbody> </table> <ul> <li>Click Initialize</li> </ul> <ul> <li>Calculation Activities <ul> <li>Autosave Every (Iterations) = 50 (can be changed to 0 or another value if needed)</li> </ul> </li> <li>Run Calculation <ul> <li>Number of Iterations = 1000</li> <li>Click Check Case. There should be no recommendations that appear.</li> <li>File &gt; Save Project</li> <li>Click Calculate</li> <li>Click <a href="http://wiki.vairdo.com/wp-content/uploads/2015/11/703-05.png"><img class="alignnone size-full wp-image-279" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/703-05.png" alt="703-05" width="42" height="24" /></a> and choose an option to show all of the plots as the solver is solving. The window should show something similar to the screenshot below.<img class="alignnone wp-image-331" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-07.png" alt="704-07" width="639" height="304" /></li> <li>Check on the residuals to see that they decrease monotonically and the other plots to see that they reach a steady value. In general, residuals should be below 1e-4 to confirm convergence. However, the matter of convergence is problem-dependent, so the other values, such as drag coefficient, need to be monitored in addition to the residuals. Small oscillations in the variables may occur due to the characteristics of the flow, and so identifying convergence will be subject to individual judgment.</li> <li>If the solver is not converging it is a good idea to decrease the Courant number (you may or may not have this depending on the solver scheme) and relaxation factors bit by bit to help the solver converge.</li> <li>The example case took about 80 iterations to converge.</li> <li>File &gt; Save Project</li> </ul> </li> </ul> &nbsp; <strong>Results (and CFD-Post)</strong> <ul> <li>Plots &gt; DCLK on XY Plot</li> </ul> <table> <tbody> <tr> <td width="348"></td> <td width="229">Y Axis Function</td> <td width="257">Turbulence…</td> </tr> <tr> <td width="348"></td> <td width="229"></td> <td width="257">Wall Yplus</td> </tr> <tr> <td rowspan="3" width="348">Plot Direction</td> <td width="229">X</td> <td width="257">1</td> </tr> <tr> <td width="229">Y</td> <td width="257">0</td> </tr> <tr> <td width="229">Z</td> <td width="257">0</td> </tr> <tr> <td width="348"></td> <td width="229">X Axis Function</td> <td width="257">Direction Vector</td> </tr> <tr> <td width="348"></td> <td width="229">Surfaces</td> <td width="257">wing Or choose surfaces related to the subject.</td> </tr> </tbody> </table> <ul> <li>Click Plot and a plot like the one below should show. Yplus is a dimenionless value that shows how far the first grid point is from a wall and is important to consider when working with drag and turbulence. Since a significant majority of the Y+ values (especially the wings) are <strong>less than 11</strong>, it is considered satisfactory for accurate calculations that resolve the boundary layer. Same criterion can be applied to different cases. You can either screenshot this or use the camera button.<img class="alignnone wp-image-332" src="http://wiki.vairdo.com/wp-content/uploads/2015/11/704-08.png" alt="704-08" width="652" height="306" /></li> </ul> <ul> <li>Reports &gt; DCLK on Forces <ul> <li>Select wing (or corresponding zones) for Wall Zones and click Print.</li> <li>Change the direction vector appropriately and click Print</li> </ul> </li> <li>There are numerous analyses and graphics you can produce within Fluent. Search notes and researches for methods to obtain needed renderings and data.</li> <li>File &gt; Export &gt; Case &amp; Data… &gt; Save with appropriate name to represent this case. <ul> <li>This can be used to compare different cases later on.</li> </ul> </li> <li>Close ANSYS Fluent</li> </ul> &nbsp; <ul> <li>Double click on the Results cell to open CFD-Post <ul> <li>Use screenshot or to capture images.</li> <li>Switch to the Expressions tab and enter these expressions (Right click on Expressions &gt; New). Remember that expressions are case sensitive. (These expressions are for</li> </ul> </li> </ul> <table> <tbody> <tr> <td width="120">drag</td> <td width="669">force_y@wing Or use appropriate names for the subject</td> </tr> <tr> <td width="120">lift</td> <td width="669">force_x@wing</td> </tr> <tr> <td width="120">cop X</td> <td width="669">(areaInt_y(Pressure*X)@wing) /lift</td> </tr> <tr> <td width="120">cop Y</td> <td width="669">(areaInt_z(Pressure*Y)@wing) / drag</td> </tr> <tr> <td width="120">wing area</td> <td width="669">areaInt_y(if(Normal Y &gt; 0,1,0))@wing This is not exactly necessary as we know the area we assumed is 1m², so use appropriate values.</td> </tr> <tr> <td width="120">coef drag</td> <td width="669">drag*2/(massFlowAve(Density)@inlet *(massFlowAve(Velocity)@inlet)^2*wing area)</td> </tr> <tr> <td width="120">coef lift</td> <td width="669">lift*2/(massFlowAve(Density)@inlet*(massFlowAve(Velocity)@inlet)^2*wing area)</td> </tr> </tbody> </table> <ul> <li>There are many other functions in CFD-Post and should be researched and used according to needs.</li> </ul> &nbsp; <h1><strong>5. </strong><strong>Mesh Independence Study</strong></h1> <ul> <li>whether the solution depends on the mesh or not should be checked. These are the steps to take: <ul> <li>Make sure initial mesh converges.</li> <li>Refine the mesh (generally 1.5 times the initial size)</li> <li>Run solver again</li> <li>Compare results</li> <li>Repeat steps 1 to 4 until results become acceptably close.</li> </ul> </li> </ul> **It is recommended that you plot the results against the number of cells for each mesh to see where the change in solution is acceptably low.