Air Jets

Referring again to Fig.B.8, the gas flow exiting the acoustic tube is shown as forming a jet. The jet ``carries its own pressure'' until it dissipates in some form, such as any combination of the following:

• heat (now allowing for ``friction'' in the flow),
• vortices (angular momentum),
• radiation (sound waves), or
• pressure recovery.

Pressure recovery refers to the conversion of flow kinetic energy back to pressure kinetic energy. In situations such as the one shown in Fig.B.8, the flow itself is driven by the pressure drop between the confined reservoir (pressure $p_m$ ) and the outside air (pressure $p_m - \rho u^2/2$ ). Therefore, any pressure recovery would erode the pressure drop and hence the flow velocity $u$ .

For a summary of more advanced aeroacoustics, including consideration of vortices, see [197]. In addition, basic textbooks on fluid mechanics are relevant [172].