# Is it possible that as the Reynolds number increases, a laminar bubble increases in extension?

I'm studying the Benedek 10355 airfoil (Plot), which should be a profile used in air-controlled models. While I was carrying out a boundary layer analysis, I realized the particularity that I have placed in the title. By making an incompressible analysis at Re = 500,000 and alpha = 2 deg, the profile has a laminar bubble on the upper surface (H index which diverges from 2.5 to 4 and then falls to 1.4, negative friction coefficient and plateau of the pressure coefficient) and then it also looks like a bubble on the lower surface. In this last case, the H index starts from 2.5 reaches about 3.5 then drops to values ​​of 2.5, a sign that the boundary layer separates but there is no turbulent transition. The friction coefficient assumes slightly negative values. For Re = 1e6, alpha = 2 deg, the extension of the bubble on the upper surface decreases, while the bubble on the lower surface increases; H starts at 2.5 goes to 4 then drops back to 2.5 (so once again there is no transition on the belly). A Re = 8e6, no bubbles, either on the upper or on the lower surface. What is the cause of this abnormal behavior on the lower surface? It happens at every angle of attack, at every Reynolds. Thanks to those who will be able to help me!

• @leo95nf There is a pressure (better: suction) peak for both, but in the viscous case it is smoothed a bit by viscous effects. That the dotted line shows a sharp peak is not relevant, a suction peak is a minimum along the c$_p$ curve. – Peter Kämpf Nov 14 '20 at 20:26