Machine Design

CFD brings a better water turbine

Computational-fluid-dynamics software that works with an FEA program let consulting engineers cut the cost of designing a hydraulic turbine by 50%.

The water turbine uses helically shaped blades rotating at twice the velocity of the flow, and spinning the same direction regardless of flow direction. The turbine captures 35% of the water's energy, compared to 20% for conventional turbines. Anticipated costs for an open-river hydropower system should be $400 to $600/kW, lower than other systems. GCK Technology, San Antonio, is further developing the turbine.

A feature in the latest CosmosFloWorks includes a rotating frame of reference to simulate blade rotation. Results include forces generated by flow on the blades, and rotor torque. Analysis predictions closely matched experimental results.

Engineers at Sigma Designs Co., Springfield, N.J., used CosmosFloWorks CFD and FEAprogram CosmosWorks, both from SolidWorks Corp., Concord, Mass.,

"We created a single model, added boundary conditions to determine hydrodynamic forces, and distributed them across the blades," says Gerald Lynch, Sigma Design president.

The CFD software duplicated results of earlier physical measurements and provided more information than was available through experiments, including contour charts that show flow velocity, direction, pressure, and temperatures. "The software made it possible to optimize the turbine at about half the cost required by traditional methods," adds Lynch.

Traditional approaches would analyze the turbine using high-end and high-cost CFD and FEA software. An alternative was to put strain gages and encoders on the turbine, a time-consuming operation that would only have determined stress at a few points.

FloWorks, on the other hand, let engineers simulate blades turning and specify angular velocities using an Inlet-Swirl option. The software calculated fluid velocity and pressure values throughout the solution domain.

Turbine engineers then used the solid modeler to calculate moments of inertia for the structure, determine inertial loads, and add those forces to the hydrodynamic loads calculated in CFD to determine a total-load package for the FEA program. FEA revealed high stresses in a few areas and low stresses in others, so material could be redistributed to where it is needed — or eliminated. Load information also helped in specifying bearings.

TAGS: CAD Archive
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