QMT Features: January 2009
Full steam ahead
Contract measurement service saves OEM four and a half months in reverse engineering a steam turbine

NVision's Contract Service Division recently reverse engineered the complete core of a steam turbine for a major original equipment manufacturer (OEM) in only 6 weeks compared to the 6 months that the OEM had budgeted for the project using less sophisticated measurement methods.

"Measuring the critical blade geometry to high levels of accuracy made it possible for the turbine manufacturer to perform simulations that helped to redesign the blades and diaphragms to substantially improve the energy efficiency of the hundreds of existing turbines," said Steve Kersen, president of NVision.

Computational fluid dynamics (CFD) technology gives engineers the opportunity to understand how flow affects the performance of turbine blades and quickly and inexpensively evaluate alternative geometries by determining their impact on energy efficiency. In order to run CFD simulation it's essential to have a CAD model that accurately depicts the as-built turbine geometry.

Nearly all of the turbines that are prime candidates for design upgrades were designed without a CAD model so reverse engineering is an essential first step to improving the turbine blade design.

The turbine rotor in this application measures 11 feet in length and 6 feet in diameter and was not available as a CAD model. NVision contract service division technicians scanned all of the turbine components in only three weeks using the NVision HandHeld Non-contact Scanner and touch probe at the OEM's site and the MAXOS scanner in NVision's Wixom, Michigan facility.

The NVision MAXOS scanner  can measure complex geometry even if it has a shiny surface without the need for spraying and it is unaffected by the limitations of ball radius compensation from which traditional coordinate measuring machines suffer. The MAXOS is a widely used optical blade measurement system used by OEMs including Toshiba GE, Alstom, and Siemens in-house; NVision supplies the machines and also offers MAXOS contract services.

Next NVision technicians used NVision software to convert the point clouds to STL file format. The STL model was converted to a fully parametric CAD model which took another three weeks. NVision engineers edited the resulting CAD models by hand to correct machining inaccuracies in the as-built parts. The CAD models provided by NVision were used by the turbine manufacturer as the basis for CFD simulations that were used to design new blades and diaphragms that saved considerable amounts of energy by improving the efficiency of hundreds of existing turbines.

NVision Inc. has been the leader in non-contact 3D imaging and reverse engineering technologies since 1990 and it was in the mid-90s that it first started to work with companies on both sides of the Atlantic reverse engineering individual blades and vanes. A number of early movers in the field such as Alstom Power and Power Systems Manufacturing invested in NVision's HandHeld scanner as well as using NVision's own Contract Services Division. "Quickly obtaining a model of the original turbine geometry gives us a distinct advantage over our competitors," said Joe Hackett, metrology manager for Power Systems Manufacturing.

E-mail: sales@nvision3d.com


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