In this paper we discuss two types of acoustic streaming, to which Lighthill (1978a,b, 1997) has made significant contributions, namely the “quartz wind” and Rayleigh streaming. Both are associated with flows that are dominated by their fluctuating components, and owe their origin to the action of Reynolds stresses. In the former, these stresses arise within the main body of the fluid when an ultrasonic beam propagates into it; in the latter they act in the Stokes shear-wave layer that forms at a solid boundary in a fluctuating flow. In spite of its acoustic origins, we show that streaming of the Rayleigh type is a phenomenon that occurs more widely than those origins suggest.
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