CFD analysis allowed one contract services provider of reverse engineering, inspection/gaging and rapid prototyping to reverse-engineer the complete core of a steam turbine for a major original equipment manufacturer. NVision's Contract Service Division was able to complete the project in six weeks, much less than the six months the OEM had budgeted for the project using less sophisticated measurement methods.
"Measuring 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," says Steve Kersen, NVision's president in Wixom, Mich.
Computational fluid dynamics (CFD) technology gives engineers the opportunity to understand how flow affects the performance of turbine blades and quickly evaluate alternative geometries by determining their impact on energy efficiency. According to NVision, in order to run CFD simulation, it is essential to have a CAD model that accurately depicts the as-built turbine geometry. Nearly all turbines that are prime candidates for design upgrades were designed without a CAD model, so reverse-engineering is seen by NVision as an essential first step to improving the turbine blade design.
The turbine rotor in the OEM application measures 11' long by 6' dia. and was not available as a CAD model. NVision technicians scanned all the turbine components in three weeks using their company's handheld noncontact scanner and touch probe at the OEM's site and the Maxos scanner in NVision's Wixom facility. The scanner can measure complex geometry - even if it has a shiny surface - without the need for spraying, and according to the company, it is unaffected by the limitations of ball-radius compensation from which traditional coordinate measuring machines often suffer.
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 turbine manufacturer used the CAD models as the basis for CFD simulations that were used to design new blades and diaphragms, which saved considerable amounts of energy by improving the efficiency of hundreds of existing turbines.
"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, in Jupiter, Fla., a user of NVision's scanner and Contract Services Division.