A modified SIMPLEC method which can solve compressible flows at low Mach number is introduced and used to study thermoacoustic waves induced by a rapid change of temperature at a solid wall and alternating- direction flows generated by thermoacoustic effects in a ta- pered resonator. The results indicate that the algorithm adopted in this paper can be used for calculating com- pressible flows and thermoacoustic waves. It is found that the pressure and velocity in the resonator behave as stand- ing waves, and the tapered resonator can suppress high- frequency harmonic waves as observed in a cylindrical res- onator.