Finite Element Analysis Capabilities – AxSTRESS

Introduction

An inefficient blade that does not break is always more performant than an aerodynamically efficient blade that snapped in half. This is why once the aero design of a 3D blade has been performed its structural characteristics should be investigated.

AxSTRESS is an express structural, modal and harmonic analysis solver using a Finite Elements Method with a customizable, automatic turbomachinery-specific mesh generation. AxSTRESS also performs Campbell and interference (SAFE) diagram calculations as well as hot-to-cold and cold-to-hot calculations to consider the effect of blade untwist under operation.

Pre-Processing

Data is read from the AxSTREAM® project database to define the blade geometry, aerodynamic loads and material properties as well as the rotation speed, number of blades, boundary conditions, etc. This allows for simplification of the pre-processing operations and prevents human errors.

Blade Attachments & Disk Design

AxSTRESS can be used to create blades with attachments and also blades as blisk. Different kinds of attachment templates for roots, shrouds, disks and lashing wires can be created and stored in the embedded attachment library and can be designed using interactive features.

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Once in the library, they can be scaled and moved to adapt to different blades within the same or different stress projects. Legacy or standard attachments can also be imported into the attachment library and modified.

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This allows significantly saving time when designing similar blade attachments. Additionally, AxSTRESS allows setting gap values between the blade root and the disk using a single click.

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Furthermore, automatic conservation of attachments when reloading blade geometry allows a significant reduction of both iteration time and human error (no need to rebuild the attachments). AxSTRESS automatically determines the contact surfaces and model contact interaction between blade and disk by merging all nodes on the surfaces in all directions.

 

Meshing

AxSTRESS uses an in-house turbomachinery-specific mesh generator (mapped hexahedral for airfoils and triangular for attachments) which improves the mesh quality in the fillets depending on the mesh density for more accuracy results in the stress concentration places.

For airfoils, AxSTRESS generates at mapped mesh for more accurate results. Fillets can be created between blades and attachments (root and shroud) as uniform or variable between the leading edge and the trailing edge of the blade to reduce stress concentrations.

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Analysis & Post-Processing

Additionally, for increased accuracy results of AxCFD computations can be used as aerodynamic loads for structural calculations and centrifugal, pressure and thermal loads can also be accounted for at design and off-design conditions.

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The different types of analyses which can be performed in AxSTRESS are presented below:

  • Static analysis: Allows calculating the values of stresses and displacements in the different directions.
  • Modal analysis: Includes the calculation of a given number of natural frequencies of the system and their mode shape with the option to simulate several blades that are assembled in the same package together while accounting for pre-stress effect.
  • Harmonic calculation: Used to calculate the response of the system under a steady-state sinusoidal loading at a given frequency.
  • “Hot-to-cold” and “cold-to-hot” calculations: Determines the system’s geometry transformation between its “hot” state (running conditions) and its “cold” state (after manufacturing) that result from the blade untwist during rotation in a moving flow.
  • Campbell and interference (SAFE) diagrams: Illustrate the interference between natural frequencies and common exciting forces to locate potential (Campbell) and actual (interference using nodal diameters) rotation speeds that could prevent the safe operation of a turbomachine. Range of rotation speeds, number of modes and orders can be inputted by the user for the analysis.
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Campbell diagram
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Interference diagram

Furthermore, AxSTRESS is equipped with excellent post-processing features including contours of displacement and stress in the direct directions as well as the option to extract stresses at custom-defined planes and sections.

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Once a blade and its attachments have been finalized their geometry can be export to CAD models to obtain manufacturing drawings.

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