EFFECT OF THERMAL BOUNDARY CONDITIONS ON PROPAGATION OF SOUND WAVES IN A RAREFIED GAS

摘要

Existing studies on sound wave propagation in rarefied gases examine sound generation by actuated boundaries subjectrnto isothermal boundary conditions. We study the effect of replacing the isothermal conditions with heat-flux conditionsrn(which are easier to implement in practice) on the propagation of sound. Towards this end, we consider the responsernof a rarefied gas, confined in an adiabatic (thermally insulated) channel, to instantaneous (small-amplitude) motion ofrnits boundaries in the normal direction. The analytical problem is formulated and solved for an ideal monatomic gasrnat collisionless (highly rarefied) and continuum conditions, and the effect of heat-flux insulation is demonstrated throughrncomparisonwith counterpart results obtained for a gas confined between isothermalwalls. The results, found in quantitativernagreement with numericalMonte Carlo simulations, motivate further study on the effect of heat injection at the boundariesrnon propagation of sound waves in the gas. It is demonstrated that heat “injection” or “suction” may be applied to achievern‘acoustic cloaking’ of actuated boundaries, a much desired property in classical acoustics.