INVESTIGATION OF A COMPOUND WALL JET IN THE VICINITY OF JET EXIT

Abstract

Wind tunnel tests are conducted to study the effect of upper surface blowing on aerodynamic characteristics. A wall jet is issued tangent to a flat plate that forms the upper surface of an airfoil at zero angle of attack. The leading edge of the airfoil is NACA 0015. The effect of chordwise blowing on the aerodynamic load is studied through investigation of the pressure distribution on the flat surface. The pressure coefficient shows two consecutive sharp peaks resulting in two adverse pressure gradients. Higher peaks are obtained for the higher jet/free stream velocity ratios. This feature indicates the complicated structure of the vortex flow in the transition region along the flat plate surface. In addition to the investigation of the aerodynamic load, the effect of upper surface blowing on the mean velocity, turbulence and Reynolds shear stress of the flow field is illustrated. It is found that the chordwise mean velocity profiles are similar in the free mixing region. As the jet/free stream velocity ratio becomes more than unity, jet blowing activates the mean upward lateral velocity which increases with increasing jet velocity. The inflection points of mean velocity profiles are accompanied by peaks of turbulence and Reynolds shear stress. Likewise, both normal and turbulent shear stress profiles exhibit the similarity episode.