Postprocessing Variables
Intensity
The flow of energy is expressed by the acoustic intensity I, which is formally defined by the time-averaged sound power per unit area (unit: W/m2). This quantity is available as a built-in postprocessing variable.
For a general fluid, including thermal and viscous losses (see Ref. 15 and Ref. 16 for details), the time-averaged intensity is given by
where the viscous stress tensors for the acoustic and background fields, τ and τ0 respectively, are given by (in index notation)
It is understood that all dependent variables in these equations are the complex amplitudes.
In the time domain, the equivalent quantity is the instantaneous intensity i given by
where the dependent variables now include the explicit time dependence. The instantaneous expression is not defined in the frequency domain since it would represent effects happening at the double frequency.
The intensity variables are defined for most Aeroacoustics physics where it makes sense. That is, the instantaneous quantities are defined in the time domain and the (time averaged) intensity variables are defined in the frequency domain. It is understood that the intensity vector is in general the time averaged quantity. For the Linearized Potential Flow interface, the variables are not defined in the time domain since it would require solving for an extra variable.
phys_id.I_mag
phys_id.Ii_mag
phys_id.I_mag
phys_id.Ii_mag
phys_id.I_mag
phys_id.Ii_mag