FIG. 1.

Schematic of air motions in speech sound production. Air flowing from the lungs from left to right is forced through constriction at the right, at velocity U_j(t). The airstream separates at some point downstream of the location of maximum constriction, forming a jet. The jet boundaries consist of vortical flow, which quickly breaks down into coherent vortical structures. These structures convect from left to right at the local flow speed, a fraction of U_j. As the vortices convect through the vocal tract, they induce unsteady forces on the vocal-tract walls. These forces produce sound. For wall features such as the “obstacle” shown here, where the shape changes rapidly, these forces, and hence the sound produced, are particularly intense.