Finite Element Analysis Capabilities – AxSTRESS

Introduction

An efficient blade that does not break is always preferable to a highly efficient blade that has snapped in half. This is why it is always important to investigate the structural characteristics of a blade once its aero design has been optimized.

AxSTRESS is a structural, modal and harmonic analysis solver that uses the Finite Element 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. All of this can be performed using unlimited cores and parallel processing.

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, and other key parameters. This simplifies the pre-processing operations and prevents human error from influencing the design and results.

Blade Attachments & Disk Design

AxSTRESS can be used to create blades with attachments, as well as blisks. Different 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.

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.

This significantly reduces times spent designing similar blade attachments. Additionally, AxSTRESS enables users to set gap values between the blade root and the disk with a single click.

By automatically storing blade attachments, there’s no need to rebuild any attachments which further reduces project time and minimizes the chances of human error. AxSTRESS automatically determines the contact surfaces and model contact interaction between the 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 accurate results in the stress concentration locations.

For airfoils, AxSTRESS generates a 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.

Analysis & Post-Processing

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

The different analyses which can be performed in AxSTRESS include:

• Static analysis: Calculates the values of stresses and displacements in different directions.
• Modal analysis: Includes the calculation of a given number of natural frequencies of the system and their mode shapes with the option to simulate several blades that are assembled in the same package together while accounting for pre-stress.
• Harmonic calculation: Calculates 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: Illustrates 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. The range of rotation speeds, number of modes and orders can be inputted by the user for the analysis.

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

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