{"id":65810,"date":"2025-06-12T08:04:33","date_gmt":"2025-06-12T12:04:33","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/simcenter\/?p=65810"},"modified":"2026-03-26T06:47:04","modified_gmt":"2026-03-26T10:47:04","slug":"turbomachine-assemblies-and-the-challenges-of-designing-them-whats-new-in-simcenter-3d-for-rotor-dynamics-2506","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/simcenter\/turbomachine-assemblies-and-the-challenges-of-designing-them-whats-new-in-simcenter-3d-for-rotor-dynamics-2506\/","title":{"rendered":"Turbomachine assemblies and the challenges of designing them – What’s new"},"content":{"rendered":"\n

Turbomachines are made of assemblies of different bladed disks<\/h2>\n\n\n\n

In our previous blogs<\/a>, we introduced how to model large turbomachines made of assemblies of many bladed-disks. An interesting exploitation of the periodicity of the structure is to consider cyclic symmetry sectors, instead of the whole 3D structure. When the industrial application requires the machine to be made of different stages, each with a different number of sectors, special care is required when connecting those sectors to ensure a smooth junction between the two stages. <\/p>\n\n\n\n

When the periodic structure deviates from its regular axisymmetry shape like at the propellers with few blades, a simulation in a rotating frame can no longer be avoided, as we described in a previous blog, ‘Advances in response and cyclic symmetry of bladed rotor assemblies.’<\/a> We also explained that limitations on the non-rotating parts apply for such calculations: indeed, the non-rotating parts (stator and bearings) must be isotropic, which can be a rough assumption for industrial applications.

For such cases, the Simcenter nastran solver for Rotor Dynamics proposes a method of avoiding model limitations with the use of Coleman transformation. Indeed, with this method, bladed rotors assembled to an anisotropic<\/em> stator and bearings can be computed! \u00a0While this is a challenge to complete, it allows you to model the complexities and explore more possibilities when simulating and modeling rotating structures.<\/p>\n\n\n\n

For industrial applications like turbochargers, steam turbines, or jet engines, the assembly is made of multiple stages of bladed disks, and the assumption that the rotor has axisymmetry is not always true.  Therefore, Simcenter 3D<\/a> 2506 for Rotor Dynamics has expanded the use of the Coleman transformation to assemblies of multiple stages of cyclic symmetry rotors.<\/p>\n\n\n\n

<\/a><\/p>\n\n\n\n

 <\/p>\n\n\n\n

Coleman transformation for multiple stages of cyclic symmetry rotors<\/h2>\n\n\n\n

In our previous blog, ‘Advances in resonance and cyclic symmetry of bladed rotor assemblies<\/a>,’ we presented the Coleman transformation, as the solution to produce time invariant matrices in the fixed frame for cyclic symmetrical rotors as outlined by Kirchgassner 2016<\/a>. We then used Campbell diagrams and stability analysis for the calculation of the critical speeds at which resonance occurs. This method is equivalent to the Floquet method when the structure is strictly cyclic symmetrical outlined by Skjoldan 2009<\/a>.<\/p>\n\n\n\n

Simcenter 3D advanced capabilities for bladed rotors<\/h2>\n\n\n\n
\n

Simcenter 3D has taken a step further in the simulation of advanced bladed rotors applications, allowing an assembly to be computed satisfying the hypothesis of rotor dynamics calculations based on the axisymmetry or unsymmetry of the different parts of the system. It allows easy postprocessing including the production of Campbell diagrams and presents modes as output in a fixed reference frame for easy interpretation<\/p>\n<\/div>\n\n\n\n

\n
\"A\n\t\t\t\n\t\t\t\t\n\t\t\t<\/svg>\n\t\t<\/button><\/figure>\n\n\n\n
\"\"\n\t\t\t\n\t\t\t\t\n\t\t\t<\/svg>\n\t\t<\/button><\/figure>\n
Top right,  model preparation of different cyclic symmetry sectors connected at the junction; bottom right: the Campbell diagram output in fixed reference frame; left: complex mode; 57Hz at 600rpm, backward whirl.<\/em><\/figcaption><\/figure>\n\n\n\n

Complex modal analysis in 5 steps<\/h2>\n\n\n\n
\n
\n

Step one<\/h2>\n\n\n\n

In Simcenter 3D, prepare an associative model, where the different stages can be linked to the geometry.  It will allow any changes in the geometry to be communicated to the finite element model and adapted in such a way that only the simulation has to be computed again, to account for the changes. This method is called the master model concept, a video explaining this concept can be found here<\/a>.<\/p>\n\n\n\n

\"The<\/a><\/figure>\n<\/div>\n\n\n\n
\n

Step two<\/h2>\n\n\n\n

Prepare the finite element model of the cyclic symmetry sector of each stage, by identifying the sector as a portion of the structure that can be repeated about the rotor axis.  It can contain a single blade or multiple blades. <\/p>\n\n\n\n

\n

Step three<\/h2>\n\n\n\n

Assemble the different stages at the junction<\/p>\n\n\n\n

Identify each junction between two connected stages. The solver will take care of the continuity of results at this junction by automatically adding the higher order harmonics.<\/p>\n\n\n\n

\n

Step four<\/h2>\n\n\n\n

Prepare the simulation<\/p>\n\n\n\n

Set up a complex modal analysis in the rotating frame and activate the Coleman transformation.  The rotating parts modeled in cyclic symmetry will be calculated in multi blade coordinates for different cyclic waves (harmonic index).  The Coleman transformation will compute time-invariant matrices that will allow results to be output in a fixed reference frame.  The bearings and the stator can be anisotropic and are calculated in the fixed reference frame, allowing for the simulation of the whole assembly.<\/p>\n<\/div>\n\n\n\n

\n

Step five<\/h2>\n\n\n\n

Post-process results in Simcenter 3D<\/p>\n\n\n\n

The Campbell diagram shows the evolution of the eigenfrequencies with the rotation speed, highlighting the gyroscopic effects for the relevant modes.  The advantage of the Coleman transformation is the simultaneous consideration of multiple harmonic indices, which is usually not the case with simulations using cyclic symmetry.  Modes at 0-diameter, or 1-diameter are output in our example.<\/p>\n<\/div>\n<\/div><\/div>

<\/div>
<\/div>
<\/div><\/div>\n\n\n\n