James B. Mehl
Natl. Inst. of Standards and Technol., Thermophysics Div., Gaithersburg, MD 20899,
Phys. Dept., Univ. of Delaware, Newark, DE 19711-2570
Modified Greenspan viscometers are being studied with the objective of better understanding of inertial and dissipative duct-end effects for application to Greenspan viscometers. Greenspan viscometers are double Helmholtz resonators comprised of a circular duct coupling two concentric cylindrical chambers. Previous investigations [J. B. Mehl, J. Acoust. Soc. Am. 97, 3327 (1995)] of the acoustic fields and eigenfrequencies of viscometers with ducts terminating flush with the chamber ends have been extended to ducts which extend into the chambers a distance D. Numerically determined end effects are compared with analytic results for radiation from baffled and unbaffled open ducts. When D=0 the inertial end correction agrees well with the correction for a baffled open end; when D is greater than a few duct diameters it approaches the value for an unbaffled termination. In contrast, the resistance of the duct end (defined for the limiting case of a small viscous penetration length) is not sensitive to D. The numerical model permits easy investigation of the effects of rounding and chamfering corners. [Work supported by the Office of Naval Research.]