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ZF is one of the world’s leading providers of innovative wind power gear boxes. ZF’s advanced technology solutions contribute to the transformation of the global energy system with reliable, robust and efficient products and systems that conserve precious resources.
Harnessing the power of the wind is nothing new for humankind. The development of the sail for ships enabled travel and exploration around the globe. There is also the classic windmill, whether it be the large post mill style found across Europe or the multibladed wind pumps found across the Great Plains of the United States. These allowed humans to settle into different areas by using the energy of the wind and transforming it into useful work, such as pumping water or milling grains. While these technologies can still be used today, it is no longer the translation of wind energy into mechanical energy that is at the forefront of design, but the translation of wind energy into electrical energy.
Wind power is growing worldwide as one of the largest sources of renewable energy. To continue to meet this growing need, large numbers of wind turbines are being constructed both on land and at sea. A business unit of ZF Friedrichshafen,ZF Wind Power is a leader in the design, manufacture, supply, and servicing of wind turbine gearboxes. Since ZF Wind Power first entered the wind turbine market in 1979, its manufacturing plants have shipped more than 65,000 gearboxes powering more than 120,000 megawatts of installed wind energy capacity around the globe.
Wind gearboxes are a critical part of the turbine as they translate relatively slow-moving rotation from the large blades to a much higher rotational speed needed for the onboard electrical generator. These systems consist of multistage planetary and helical gear sets. A challenge faced in their design is that as the gearbox operates, a large amount of heat is generated at the bearings and gear mesh contacts. If the heat generation is not balanced with proper cooling and lubrication, the excess heat will cause issues such as overheating of the surface, resulting in failure mode scuffing. This will ultimately cause the failure of the machine, and a significant financial cost for repair or replacement, as well as the chance for more catastrophic damage in extreme cases.
During the design of the gearboxes, much engineering time is spent confirming that these systems have the appropriate flow rates and pressures. “Originally this process was accomplished using Microsoft Excel spreadsheets to calculate the expected flow rates based on the pressure drop of the individual parts of the gearbox flow paths,” says Jo Loenders, product management engineer, at ZF Wind Power. “However, this was a very complex and time-consuming process, as the distribution systems for the lubrication can involve hundreds or even thousands of small components that result in pressure losses.”
With this level of complexity, it was important to validate the mathematical models with a component-level test and then run an expensive verification of the combined systems. The result was a fairly inflexible solution that required a significant amount of engineering time both in the model construction and the requisite validation.
To address the complexity and increase engineering productivity, ZF Wind Power adopted Simcenter™ Flomaster™ software from Siemens Digital Industries Software, a system-level thermo-fluid simulation tool. The software offers built-in empirical data, a large library of components and sample systems to boost engineering efficiency. “The use of Simcenter Flomaster allows a significant streamlining of the development process,” says Loenders. “From the very beginning, creating the fluid model is easy and intuitive. Model construction is done by simply adding predefined components to the schematic and connecting them as designed. When it is necessary to make changes to the model it is as simple as replacing components, changing connections, or editing in the Simcenter Flomaster model, instead of updating input data or changing the coding in the Excel calculation sheet.”
Simcenter Flomaster also helps reduce the design time required to size distribution lines to achieve the required flow rates. In wind turbine gearboxes there is always more than one flow path that requires fluid flow. These paths are rarely naturally equal with regards to pressure drop, so it is necessary to implement restrictions in some lines to ensure the flow is balanced. In Simcenter Flomaster, the flow balancing functionality enables this to be done directly instead of through a time-consuming iterative design process. For each flow path, it is possible to simply set the desired flow rate in the part that needs to be sized (such as an orifice, pipe, or valve), and the software calculates the required size.
The use of Simcenter Flomaster also enabled simple and quick validation of the models since each component comes with validation data and results. “Unlike in-house programming, in which design changes require code changes and thus new validation, model updates in Simcenter Flomaster don’t require new validation,” says Loenders. “With the ability to determine flow rates and pressures anywhere in the model, the verification of the system against test data from flow measuring devices under realistic circumstances is easy.”
For ZF Wind Power, the use of Simcenter Flomaster leads to an efficient way of developing oil distribution networks for their wind turbine gearboxes. It enables reduction in design resources and validation effort, yielding a good return on investment.