Conditioned hot-wire anemometer measurements and structural analysis of a turbulent spot in a laminar boundary layer

The downstream development of a turbulent spot generated by a tripping wire in a laminar boundary layer was investigated in wind tunnel tests. Spot shape, vertical and lateral growth, ensemble-averaged structure, and isovelocity contours look similar to those of earlier experiments. The correlation coefficient in a turbulent spot is in good agreement with that in a turbulent boundary layer. A quadrant analysis of the product of the fluctuation velocity components in both directions shows that the second and fourth quadrant are the main contributors; their average fractional contributions are 80% and 75% respectively, while the first and third quadrant give a contribution of -30% and -25% respectively. The second quadrant does not dominate the fourth in a spot in contrast with a turbulent boundary layer.