VELOCITY FIELD BEHIND A PLATE INSTALLED IN THE INNER REGION OF A TURBULENT BOUNDARY LAYER

The authors have presented results of an experimental investigation into the velocity fi eld in a turbulent boundary layer behind a thin (0.00045 m) three-dimensional plate. The chord of the plate (streamwise length) was equal to 0.55δ (δ is the boundary-layer thickness), and its width, to 1.0δ. The plate was installed at a zero angle of attack at the center of a water channel at a distance of 0.09δ from the surface. Velocity-fi eld measurements have been performed by the Particle Image Velocimetry method at the Reynolds number Reh = 7750 calculated from the channel half-width and the velocity at the center of the channel. It has been shown that the average velocity increased in a logarithmic region of the boundary layer at a distance of its three thicknesses behind the plate. Longitudinal-velocity pulsations decreased in the buffer region of the boundary layer, but grew in the logarithmic region. Vertical pulsations only decreased to a distance of 0.8δ behind the plate, but downstream they were higher than in an unperturbed boundary layer. The high resolution of the velocity fi eld (50·10^–6 m) has made it possible to determine shear stresses on the wall from the velocity gradient in a laminar sublayer. Shear stresses on the surface behind the plate decreased in the interval where a growth in the average velocity in the logarithmic region was noted. Maximum reduction in the shear stresses occurred at a distance of 1.8δ and amounted to ~33%. The infl uence of edge effects was manifested in the less intense reduction on shear stresses in the shorter interval behind the plate.
   
Author:  V. L. Zhdanov I. G. Kukharchuk, and V. I. Terekhov
Keywords:  water channel, turbulent boundary layer, shear stresses, PIV
Page:  1233