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Simulation on demand for Luwa Air Engineering

Rotordynamic and strength assessment (FKM) using CADFEM ihf Toolbox

Simulation on demand for Luwa Air Engineering


Luwa Air Engineering AG is the leading supplier of industrial air engineering systems. The importance of energy saving in the Luwa product range is reflected by the newly developed Axial flow fan B600, to get the best aero- dynamic efficiency.
Axial Flow Fans for supply air and return air are main consumers of electrical power in spinning and weaving mills: In spinning this accounts to around 55% and in weaving it goes up to 75% of total consumed electrical power of the air conditioning and filtration plants.
The goal for the new generation of Luwa's Axial Flow Fan was a lower power consumption, higher fan capacity and lower noise level.
CADFEM was appointed to examine the structural integrity of the fan blades. In operation the blades shall not get into resonance while being subjected to centrifugal and aerodynamic loads.


To avoid resonance the rotordynamical behavior was studied by modal analysis including gyroscopic effects. The calculated eigenmodes were then judged by Campell- and SAFE-diagram to rule out interactions of rotation speed, disc nodal diameter and blade eigen- frequencies. Several geometry evolutions of the blade were evaluated to reach this target.
When the dynamic behavior was sufficient, the strength proof could be carried out. In the first load step bolt pretension was applied to simulate the assembly of the fan runner. In the second load step the rotational velocity and the aerodynamic pressures calculated with ANSYS CFX were applied.
The stresses calculated were evaluated using WB/FKM from the CADFEM ihf Toolbox. WB/FKM is an implementation of the FKM guideline “Analytical Strength Assessment” inside ANSYS Mechanical (Workbench) and offers an automated assessment of the static and fatigue utilization over the whole surface.

Customer Benefit

Luwa Air Engineering AG was able to improve the design by approx. 4% resulting in 1.2 MW less power consumption on all fans installed per year. The rotordynamic stability and structural integrity was reached without lengthy physical prototyping and testing cycles. In addition, Luwa was able to save the prototype and personnel cost for the five design iterations needed, amounting to more than 80’000 € saved. Through simulation resonance problems could be ruled out from the start and a deeper insight into the behavior could be gained as would have been possible by tests.



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