quick start manual xfoil

7/24/2019 Quick Start Manual XFOIL

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Quick Start Manual for XFOIL

Start XFOIL. The following screen will pop up:

Next load the airfoil of the practicum model (can be found on BB): NACA642A015 withthe load command:



You can check whether the right airfoil was loaded with the command gdes. Now theairfoil will be shown:

Turn back to the main menu with the <return> key and go to the analysis menu with the

oper command:

In any menu you can check the available option by entering the ? key. For example:



The first thing we will do is check how the Inviscid pressure distribution looks like by

prescribing the angle of attack with the alfa command. Select for example 0 deg angle ofattack.

The graphics window now shows the pressure distribution:



As you can see the upper and the lower Cp values are equal (symmetrical airfoil!).

Now try 2 deg angle of attack by alfa followed by 2. The result is now:

That was quick! We see that now there is a difference between the upper and lower side,

as expected.

Now that we know how this works we want to store a sequence of angles of attack (stillfor the inviscid case).

Use aseq and give the start, end and step values for alpha:



The result is:

You can also make a hard copy of the Cp-window using the command hard. The figure

is then written to a postscript file plot.ps which can be used by other programs:

You can write down the lift and drag coefficients versus alpha for the whole sequence butin fact you only need the values for alpha=0 and 1 some larger angle (f.e. 10 deg) since in

the inviscid case the relation is linear! Write down the value for later usage during

reporting.



Are you interested in how the pressure vectors look like in the inviscid case? Perform a

calculation for a certain angle of attack (f.e. 5 deg) and use the command cpv. Look whatcomes out. Did you expect that the suction at the nose of the airfoil would be that large? :

We now have characteristics for the inviscid flow case (no effects of viscosity) but in fact

we are interested in the viscous case!

For that reason we tell the program to perform viscous calculation with the visc command

and we enter the Reynolds number of the test (approx. 1 million based on the chord).Then we give an angle of attack of 0 deg:

The result is now:



And for 5 deg angle of attack:

Here the dashed lines are the inviscid results and the solid lines the viscous results. Do

you recognize the “Laminar Separation Bubble” at the upper and the lower side (seemanual).

Like before we want to have a sequence of angles of attack and store the results for laterusage. To enable storage we first have to run the pacc command and tell the program

where to store the data (polar5 for example):

quick start manual xfoil

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