December 4, 2019 at 11:05 amRay5049Subscriber
I am running a simulation of a NACA0012-Airfoil in a rectangular domain with polyhedral mesh from ANSYS Fluent. For this simulation I need to compare the lift and drag coefficient of the airfoil with the experimental result from XFoil Data (http://airfoiltools.com/polar/details?polar=xf-n0012-il-1000000). For example, by 4degree the lift coefficient is 0.06932798 and the drag coefficient is 0.012277595. The percentage error for these values are more than 60% from the experimental result (cl=0.4276 and cd=0.00728). I would assume the mesh is fine enough as the minimum orthogonal quality reaches 0.30014. The Reynolds number that i used to compare in this simulation is 1.000.000 and the velocity of the flow is 146.07m/s. The boundary conditions and solution methods that I used are as shown from the screenshots. Is there a possible way that i could make my solution closer with the experimental results at this point? Thank you for your help.
December 4, 2019 at 11:32 amRobAnsys Employee
I can't tell if you've used inflation: that will have a huge effect on lift & drag values. Also note that you're looking at coefficients: read the definitions for these in Fluent (in the documentation) and the paper.
There are several tutorials/YouTube videos on NACA airfoils so see how they've done it.
December 4, 2019 at 12:11 pmRay5049Subscriber
Thank you for the reply. I used prisms layer at the wing of airfoil with the following settings:
I followed the steps as from the YouTube videos on NACA airfoils https://www.youtube.com/watch?v=WCpUsh6otmc&list=PLEBoXla1uL0FH78AvyXfHirtnNuD-uJ1U&index=11&t=0s but still the result does not satisfy the experimental results.
December 4, 2019 at 1:24 pmRobAnsys Employee
What y+ value are you seeing? How do the definitions of coefficient compare?
December 4, 2019 at 2:07 pmRay5049Subscriber
the wall y+ value of the airfoil is between 10 and 130. Are the coeffcients from ANSYS fluent compared with the defined reference values? I have changed the area according to area of the airfoil (which is calculated through the surface integrals from results) and length with the chord length of the airfoil. The coefficents are defined from force reports as shown.
December 4, 2019 at 3:24 pmRobAnsys Employee
What does the manual/theory say about y+ values? How are the coefficients defined in the link?
As an aside: staff are not permitted to open/download files, so I've not read any of it.
December 4, 2019 at 4:38 pmRay5049Subscriber
the y+ value shown i supposed should be resolve using the strategy: resolving the viscous sublayer. Therefore, the SST k-w model is used for this simulation. The drag coefficent are defined as x=cos(degree) and y=sin(degree). As for the lift coefficient, x=-sin(degree) and y=cos(degree).
December 5, 2019 at 4:38 pmRobAnsys Employee
Ah, but check the exact definition in Fluent, and in the paper. Just because both are lift/drag coefficients doesn't mean they're calculated in the same way.
k-w is looking for y+ of around 1: this will also improve lift/drag force calculations. Does the experimental work have any force data?
December 7, 2019 at 10:01 amRay5049SubscriberWhere can i check the exact definition of these coefficients?
For the y+ value, should I remesh the entire geometry? The experimental work does not have any force data.
December 9, 2019 at 3:59 pmRobAnsys Employee
In Fluent, look in the User's Guide, in the experiment I have no idea.
Read the section on adaption. You'll need to change the setting using the TUI for poly elements
/mesh/adapt/set method (I think).
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