An experimental study of the wall-pressure field associated with a turbulent spot in a laminar boundary layer

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Abstract
Wall-pressure fluctuations were measured in the plane of symmetry and five off-axis positions in artificially generated turbulent spots in a laminar boundary layer. Ensemble averages of the wall-pressure signatures show that the spot's pressure signature is characterized by two positive-pressure peaks and a central negative-pressure region along the centre line which evolves into one negative- and one positive-pressure perturbation in the wing-tip region. In similarity co-ordinates, based on pressure-signature characteristics, the spatial growth of the pressure signature shows a small Reynolds-number dependence. Contours of the ensemble-averaged wall pressure measured relative to the laminar value show that a turbulent spot produces a leading-edge pressure excess followed by a pressure-defect region having its maximum values at the spot wing tips. The trailing edge of the pressure disturbance was found to consist of a spanwise region of pressure excess, also having its maximum value at the wing tips.