After collecting pressure data from the twenty ports, we non-dimensionalized the data and plotted as function of percent chord length.
We split up the duties of calculating three different pressure coefficients. The analytical pressure for inviscid flow over an infinite wing (not plotted above) was found using potential flow theory.The experimental value (plotted in blue, above) was found by dividing our pressure values by the dynamic pressure of the tunnel. Finally, the numerical, inviscid solution (plotted in red, above) was found using XFoil.
We can note two major differences between the two pressure coefficients:
One of the values at x/c = 0.1 is consistently incorrect. The previous groups reported that there was bad port, and Dr. Doig corroborated that there may be an issue, but that we couldn’t do anything about it for the time being.
At higher angles of attack (passing 15°), our experimental upper surface values diverge from inviscid theory. This, along with the lift coefficient data that we later found, indicates flow separation around 15° angle of attack. Since XFoil doesn’t analyze the viscous effects that cause separation, its values don’t reflect the changes seen in the real world tests.