Experimental Investigation of Turbulent Structures in a Two-Dimensional Momentumless Wake.

An experimental study was conducted to investigate the structures of a pure wake (no injection), a weak wake (some injection), a momentumless wake (injection adjusted to provide a thrust which exactly cancels the model's drag) and a weak jet (more injection than necessary to cancel the drag) by means of flow visualizations/hot-wire measurements in a wind tunnel. The weak wake/jet and momentumless wake were generated behind a two-dimensional airfoil model with mass injection through a slit along its rear end. The structures for the momentumless wake are neither wakelike nor jetlike, but instead burst out into the free stream at random intervals. Similarity of the turbulent intensities was observed. Turbulent quantities show that the momentumless wake decays downstream of the model very quickly and is analogous to isotropic turbulence.