Sonically‐Induced Microstreaming near a Plane Boundary. I. The Sonic Generator and Associated Acoustic Field

An experimental arrangement is described which permits controllable generation of small‐scale acoustic streaming, i.e., “microstreaming” near a plane boundary S. This arrangement, which consists essentially of a cylindrical bar oscillating longitudinally above the boundary S in question, has been used in studies of sonically‐produced effects at a fluid‐solid interface. The present paper deals with first‐order pressure and velocity fields in the thin layer of fluid between S and the vibrating face of the bar. Theoretical expressions are developed, based on a simple model in which incompressible flow is assumed. Experimental determination of the pressure field was accomplished by means of a special hydrophone arrangement described herein, which measures the pressure at points along the plane boundary. The first order theory agrees well with experiment, and is thus judged satisfactory as basis for a detailed treatment of the microstreaming flow, to be given in a subsequent paper. A byproduct of the work is a method for calibration of small hydrophones.