Journal of Sound and < ibration (2000) 235(2), 281}297 doi:10.1006/jsvi.2000.2920, available online at http://www.idealibrary.com on A NOVEL INVESTIGATION OF THE OSCILLATORY FIELD OVER A TRANSPIRING SURFACE JAMES T. BARRON Department of Mechanical Engineering, ¸AN Inc., ¸ee Park Center, 3141 Hood Street, Dallas, ¹X 75219, ;.S.A. E-mail: jbarron@lan-inc.com WILLIAM K. VAN MOORHEM Mechanical Engineering Department, ;niversity of ;tah, 2202 Merrill Engineering Building, Salt ¸ake City, ;¹ 84112, ;.S.A. E-mail: van@eng.utah.edu AND JOSEPH MAJDALANI Department of Mechanical and Industrial Engineering, Marquette ;niversity, 1515 = est =isconsin Avenue, Milwaukee, =I 53233, ;.S.A. E-mail: maji@mu.edu (Received 12 March 1999, and in ,nal form 11 February 2000) The #ow"eld character is investigated inside a long rectangular chamber in the presence of time-harmonic pressure waves. The chamber is designed with multiple interchangeable sections for the purpose of controlling the length and therefore the system's natural frequency. Pressure waves are induced externally at variable frequencies by means of a Scotch-yoke mechanism theoretically capable of imparting pure oscillatory motions. In characterizing the internal #ow"eld, velocity measurements are acquired inside a principal test section that can accommodate #at blocks of solid carbon dioxide (i.e., dry ice). As solid CO  sublimates, a #ow of gaseous carbon dioxide is generated at the bottom of the principal section and enters the chamber in the transverse direction. The resulting generalized Stokes layer formed above the transpiring surface exhibits several features associated with oscillatory #ows over impermeable surfaces, including an overshoot in the velocity amplitude in the vicinity of the transpiring wall known as Richardson's annular e!ect. Quantitative pressure and velocity measurements are in agreement with theoretical predictions obtained from recent models of the oscillatory "eld over transpiring surfaces. The acoustic Reynolds number based on the Stokes layer thickness increases linearly with increasing Scotch-yoke frequency except in the neighborhood of the system's natural frequency. Near resonance, a sharp non-linear increase in the acoustic Reynolds number is noted. Furthermore, both acoustic pressure and velocity amplitudes increase with the driving frequency in a manner that is consistent with current theories. Since the sublimation rate of dry ice can be expressed in a similar mathematical form to the regression rate at the burning surface of solid propellants, this experiment constitutes a cold #ow simulation of the internal #ow"eld in solid rocket motors.  2000 Academic Press 1. INTRODUCTION Going back through available literature, only few experimental investigations are found that address the nature of the oscillatory #ow"eld over a transpiring surface. This may be attributed to the inherent di$culty in designing and measuring #ow parameters in such 0022-460X/00/320281#17 $35.00/0  2000 Academic Press