An experimental investigation of the nonlinear disturbance development in boundary layer transition

An experimental investigation of the nonlinear disturbance development in boundary layer transition was conducted in a water channel. The initial laminar boundary layer developed over a flat plate without a pressure gradient. A disturbance was introduced by an oscillating wire, and its development was followed downstream with hot film anemometer measurements of the velocity components from the early nonlinear stage, u'r.m.s - .05 Uo to the early stages of the high shear layer breakdown. All three velocity components were measured in a three dimensional volume of grid points. Digital data analysis techniques were used to conditionally sample and ensemble average the velocity signals, in this way the entire instantaneous flow field could be reconstructed in terms of velocity vectors, vorticity contours and vorticity vectors at any desired instant in the cycle of the disturbance. This technique also allowed the velocity signals to be decomposed into their Fourier components to study the growth of the harmonics and the variations in the phase distributions.