Rotordynamics is a specialized branch of applied mechanics concerned with the behavior and diagnosis of axially symmetric rotating structures. Devices such as engines, motors, disk drives and turbines all develop characteristic inertia effects that can be analyzed to improve the design and decrease the possibility of failure. At higher rotational speeds, such as in a gas turbine engine, the inertia effects of the rotating parts must be consistently represented in order to accurately predict the rotor behavior.

An important part of the inertia effects is the gyroscopic moment introduced by the precession motion of the vibrating rotor as it spins. As spin velocity increases, the gyroscopic moment acting on the rotor becomes critically significant. Not accounting for these effects at the design level can lead to bearing and/or support structure damage. Accounting for bearing stiffness and support structure flexibility, and then understanding the resulting damping behavior is an important factor in enhancing the stability of a vibrating rotor.

The ANSYS 14 mechanical simulator offers a rich set of modeling features for gyroscopic effects and bearing support flexibility. By integrating these characteristic rotordynamic features into the standard FEA modal, harmonic and transient analysis procedures found in ANSYS one can analyze and determine the design integrity of rotating equipment.

Mistil e.V. is an anthroposophical organization according to Rudolf Steiner conducting research on new ways of cancer treatment. A central idea of the anthroposophical medicine deals with mixing carefully selected mistletoe extracts on disks rotating at supersonic speeds. Peer Technologies has sponsored the design of a 1-m carbon fiber wheel rotating at 10.000 rpm and beyond, essentially acting as a centrifugal compressor. Both the mechanical and computational fluid dynamics aspects of this design are very interesting.

UX-U10000

Fig. 1: 1-m Carbon Fiber Wheel rotating at 10.000 rpm. Axial Displacement [mm]

 

 

 

 


Carbon fiber wheels are amongst the lightest rotating structures featuring the highest elastic moduli at the same time. However, their stiffness behavior is highly orthotropic which may give rise to all sorts of mechanical deformations during spin-up.

CampbellDiagramm-Prestress

Fig. 2: Campbell Diagram showing Natural Frequencies under Prestress during Spin-up

 

 

 

 

ANSYS harmonic analysis will yield most spectacular insights into what natural frequencies of a rotating structure will develop as a function of angular speed and what their respective deformation characteristics will look like.

Rotor-Carbon-U10000-M20

Fig. 3: 1-m Carbon Fiber Wheel rotating at 10.000 rpm. 20th Natural Frequency (exaggerated)

 

 

 

 


Video 1: Video Animation of 1-m Carbon Fiber Wheel rotating at 10.000rpm