Curved Surface of Pelton Bucket Based on Differential Geometry
A 3-D free curved surface of a Pelton bucket was discretized into the 51×51 = 2,601 nodes of boundary fitted grid (BFG) for the CFD. The non-orthogonal curvilinear local frames were introduced with the natural basis vector g for the respective nodes of BFG. The natural basis vector g and its partial derivatives ∂g/∂P at each node were computed based on the differential geometry. As a result, the strong effect of the singular shape of the cutout, especially of its end-wall, on the Pelton bucket was numerically clarified and managed by the differential geometry. After the whole curved surface was approximated by the 50×50 = 2,500 local flat panels tangent to each node, the local surface area ΔS and the Gaussian curvature κ in each panel were investigated to assess the quality of the BFG.
Unsteady separation of jet branch by cutout of rotating Pelton bucket
As a part of boundaries for a free curved surface of a Pelton bucket, the cutout is indispensable to secure the smooth entrance of the unsteady inflow of water jet into the rotating bucket. The cutout of the rotating bucket unsteadily separates a free jet into two branches in both space and time: the impinging branch landing on the relevant bucket surface, and the flow-off branch separated by the cutout toward the preceding bucket. In order to investigate the unsteady jet separation by the cutout three-dimensionally, a semicircular free jet was discretized into 641 nodes of boundary-fitted grids. The position P of impinging jet branch landing on the bucket surface was acquired with the relative velocity W and the water depth D at each node. The trailing edge surface of the flow-off jet branch was simultaneously computed unsteadily. The complicate unsteady interaction of the bucket cutout with the branched free jets was clarified visually with the 3D view of illustrations in order to research the unsteady hydraulic performance of Pelton turbines in space and time.
Observation of jet interference in 6-nozzle Pelton turbine
Jet interference in buckets and jet disturbance outside of buckets have been visually observed in a model runner for a 6-nozzle Pelton turbine. The visual observation has revealed that the jet from...