The flow past the airfoil has less speed in the original direction and more orthogonal to it. Some of this orthogonal flow is concentrated in the wake, the part of air which formed the boundary layer when it was over the airfoil. In most conditions this boundary layer had a laminar-turbulent transition while flowing around the airfoil. Turbulence means that flow speeds orthogonal to the initial flow are amplified.
Some of the orthogonal speed increase is due to lift and affects a much greater amount of the air flowing off the airfoil. Lift means momentum transfer between airfoil and air, so the airflow behind a lift-creating airfoil is deflected away from the direction of this lift.
Some of the turbulence increases the noise radiating from the flow. In the end, noise is nothing more than pressure fluctuations and will slightly heat the material which absorbs it.
Eventually, all of this turbulence is damped down by itself, by flow guides and by the wind tunnel walls and is converted to heat.