Rotor–stator interaction

An important issue for the aeronautical industry is the reduction of aircraft noise.

The rotor–stator interaction is a predominant part of the noise emission.

Presented are an introduction to these interaction theories, whose applications are numerous.

For example, the conception of air-conditioning ventilators requires a full understanding of this interaction.

A rotor wake induces on the downstream stator blades a fluctuating vane loading, which is directly linked to the noise emission.

Nevertheless, this number V has a predominant role in the noise levels (

Back to the example : For m=1, with a Mach number M=0.3, the argument of the Bessel function is about 4.

If V=19, the minimum of mB-sV is 6, and the noise emission will be limited.

Remark : The case that is to be strictly avoided is when mB-sV can be nul, which causes the order of the Bessel function to be 0.

is a great step in the process of reducing the noise emission.

This will lead us to choose to minimize the Bessel functions for the most significant values of m. For example, if the source level for m=1 is very higher than for m=2, no consideration are taken for the Bessel functions of order 2B-sV.

The determination of the source levels is given by the Sears theory, which will not be explicated here.

All this study was made for a privileged direction : the axis of the rotor–stator.

All the results are acceptable when the noise reduction is ought to be in this direction.

In the case where the noise to reduce is perpendicular to the axis, the results are very different, as those figures shown : For B=13 and V=13, which is the worst case, the sound level is very high on the axis (for