Nature of acoustic nonlinear radiation stress Rus Carlborg, Guillermo Acoustic Radiation Ultrasound Ultrasonic effects Sound pressure Reynolds stress modeling Velocimetry Viscosity When a fluid is insonified with ultrasound, a flow consequence of a net stress becomes observable, which has been described as acoustic streaming, quartz wind, acoustic radiation force or acoustic fountain. Following Sir James Lighthill's formulation of the Reynold's streaming, these phenomena have been attributed to a cumulative viscous effect. Instead, a new multiscale effect, whereby the constitutive elastic nonlinearity scales from the ultrasonic to the macroscopic time, is here proposed and formulated to explain its origin. This raises a new term in the Navier-Stokes equation, which ultimately stems from the anharmonicity of the atomic potential. In our experimental validation, this theory is consistent in water and for a range of ultrasonic configurations, whereas the formerly established viscous theory fails by an order of magnitude. This ultrasonic-fluid interaction, called nonlinear mechanical radiation since it is able to remotely exert a stress field, correctly explains a wide range of industrial and biomedical active ultrasonic uses including jet engines, acoustic tweezers, cyanobacteria propulsion mechanisms, nanofluidics or acoustic radiation force elastography. 2016-06-01T13:32:32Z 2016-06-01T13:32:32Z 2014 info:eu-repo/semantics/article Rus Carlborg, G. Nature of acoustic nonlinear radiation stress. Applied Physics Letters, 105(12): 121904 (2014). [http://hdl.handle.net/10481/41513] 0003-6951 1077-3118 http://hdl.handle.net/10481/41513 10.1063/1.4894827 eng info:eu-repo/semantics/openAccess American Institute of Physics (AIP)