Acoustophoretic Radiation Force

Use the node to exert forces on small particles due to acoustic radiation. That is (nonlinear) momentum transfer from an acoustic harmonically oscillating field to a small particle. To be subjected to this force, particles must be in a region where the acoustic pressure or acoustic velocity is not spatially uniform. The radiation force models are valid in the Rayleigh limit, when particles are small compared to the wavelength. Options exist to include the effect of the thermal and viscous boundary layers (in both fluid and particle) on the radiation force. Note that the implemented models do not include so-called microstreaming effects. These effects tend to be important for systems where there are large density ratios between the particle and surrounding fluids.

In addition, the is only applied if the acoustic pressure or acoustic velocity has already been computed in a study type. This is because the magnitude of the acoustophoretic force depends on the frequency and complex pressure and velocity fields of the acoustic field.

Supported formulations:

This section determines how the equation for the acoustophoretic radiation force is defined. It also determines what inputs will be shown in subsequent sections.

Select an option from the list: (the default) or .

Select an option from the : (the default), , or . The loss model is the most detailed of the three but requires the most in-depth knowledge of the particle and fluid material properties.

Enter a value or expression for the following:

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u (SI unit: m/s). Similarly, this should be solved for in another physics interface such as the Pressure Acoustics, Frequency Domain interface.

Most of the required particle material properties are specified in the section for the Particle Properties node, with the exception of the following.

If is selected from the list, enter values or expressions for the:

If instead is selected, just enter the cp (SI unit: m/s, default 1445 m/s).

All of the inputs in this section are domain material properties that can either be taken or given a expression. The defaults given below are shown by first selecting .

For any , enter the:

If the is or , also enter the μ (SI unit: Pa·s, default 8.4 × 10-4 Pa·s).

If the is , also enter the:

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k (SI unit: W/(m·K), default 0.61 W/(m·K)). The thermal conductivity is always assumed to be a scalar for the purpose of computing the acoustophoretic radiation force.

Select the check box to smooth the radiation pressure using piecewise polynomial recovery. This can give a much more accurate representation of the radiation pressure because it uses information on adjacent mesh elements to reconstruct the field. If a coarse mesh is used to compute the field then this option can be especially useful.