Experimental study of boundary layer waves at large amplitudes

An attempt has been made to observe experimentally in a water tunnel the effects predicted by the two-dimensional theory of Tollmien waves, i.e., an expanding area of the neutral curve at increasing amplitudes and saturation at very large amplitudes. However, the experiment failed to produce two-dimensional Tollmien waves with amplitudes larger than 1%. Reasons which did not allow the reduction of the perturbations in the tunnel below a certain degree are examined. A new lighting is proposed for hydrogen bubbles used for flow visualization. Finally, amplification rate is analyzed as a function of the amplitude.