MIXED FLOW FAN IMPELLER

Fan Impeller Stress Analysis

Analysis Type: reverse engineering, stress analysis (FEA)
Objective: to evaluate the suitability of an existing design for a new high speed application
Sector: defence

Client Benefits: A rapid stress and deformation study provided additional resource at a busy time, and helped to minimise the test requirement. The detailed output provided valuable insight for the purpose of formulating potential design improvements.

Project Background: Established over 75 years ago, Ametek Airscrew is a recognised expert in the design and manufacture of fans, motors, generators, switches and sensors for the aerospace, defence and railway industries worldwide.

Airscrew had received a new enquiry to provide a fan design for a cooling application. The company’s highly experienced engineers were fairly certain that an existing design offered a potential solution, but it would need to operate at some 40% above the original design speed. With their substantial in-house analysis capability already operating at full capacity, additional resource was required in order to quickly evaluate the mechanical integrity of the impeller. Airscrew therefore engaged TriVista Engineering to carry out a stress study to run concurrently with their test programme.

Particular emphasis was placed on obtaining detailed insight into high stress and deformation areas with a view to deriving appropriate countermeasures where necessary.

Solution: In order to ensure that the modelled impeller was a faithful representation of the real casting, a reverse engineering approach was used. This comprised a measurement and digitising process, with additional solid modelling to complete the geometry definition.

The impeller was modelled as an assembly to include the central insert used for location on the fan shaft. The effects of temperature and centrifugal loads were modelled simultaneously. The analysis achieved the following:

  • The maximum safe rotational speed was determined and was used to guide the rig testing programme.
  • Regions of stress concentration and substantial deformation were identified, which enabled design change recommendations.

Once the FEA model had been established, a later programme of work was also able to make use of it. This provided a cost-effective means of evaluating possible future design changes.

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