THE EFFECTS OF DISCONTINUOUS BOUNDARY CONDITIONS ON THE DIRECTIVITY OF SOUND FROM A PISTON

The radiation patterns of sound from a baffled, oscillating piston are studied via a numerical method. To investigate the effects of discontinuous boundary condition on the sound radiation from a piston, we introduce three piston models that have, respectively, definite characteristics at their own edges. Linearized Eulerʹs equations in Cartesian co-ordinates are solved by the dispersion relation preserving finite difference scheme. The numerical results are compared with the analytic results derived from the Kirchhoff–Helmholtz integral theorem. Through the comparison of numerical results of each boundary condition, we find that discontinuity at the edge of the piston as well as the Helmholtz number of the vibrating piston is an important factor in determining the sound radiation pattern of the piston. The validity of numerical simulation for discontinuity effects is confirmed by comparison of the numerical and analytic results.