The guide vanes set the flow and give the water the rotation the runner needs. Their geometry is set in the Distributor tab.

Overview: Hydro Turbine design

The distributor is the control member of the turbine: its adjustable guide vanes set the flow and give the water its tangential component, which the runner turns into torque. The Distributor tab holds its whole geometry, and the runner diameter too, since the distributor outlet is the runner inlet.

Contents:

• Runner diameter D: the distributor outlet
• Guide vane axis circle
• b0: distributor guide vane height
• Guide vane profile: number, NACA profile and chord
• Distributor head losses: four Idel'cik terms

Runner diameter D: the distributor outlet

In this window, the distributor outlet diameter is the runner diameter. Three sources:

• ESHA: D = 84.5·(0.79 + 1.602·NQe)·√H / N, from the ESHA small hydropower guide;
• Kaplan statistics D1: D1 = 60·U1 / (π·N), with U1 = ξ1·√(2·g·Hn), ξ1 being read on the statistical curve for the current specific speed;
• Input.

D sets the axial velocity in the runner (flow divided by the swept ring) and, with the rpm, the blade tip speed.

Example

Dimensioned vertical cut in 3D: runner diameter, hub, height b0, axis circle and height H2.

Guide vane axis circle

This is the diameter of the circle on which the moving guide vanes pivot, in the optimum opening position. Default: 1.2 × D.

If it is too small, it puts the guide vanes inside the runner or chokes the passage: the throat velocity rises sharply, and the losses with it. Solver 2 can enlarge it by itself when the Euler opening cannot be reached.

Example

Top view with the guide vane passage and distributor outlet: the axis circle sets where the vanes sit around the runner.

b0: distributor guide vane height

b0 is the height of the passage under the guide vanes. Three sources: Input, Kaplan statistics b0 (ratio b0/D1 read on the similitude curve), or section equalization with the button of the control panel: b0·π·D = π·(D² − d²)/4.

A b0 that is too small accelerates the water in the distributor; too large, it slows it down before accelerating it again in the runner. Both cost head.

Example

Close-up of the distributor in dimensioned cut: the guide vane height b0 above the runner.

Guide vane profile: number, NACA profile and chord

• Number of guide vanes;
• Thickness (% of chord), camber and camber position: three sliders that build a four-digit NACA profile, whose name appears in the block title;
• Profile chord (mm): 1.1 times the side of the polygon formed by the guide vane axes on their circle. It therefore depends on the number of guide vanes and on the axis circle.

In the top view, the dotted lines show the natural path of the swirl: a well-cambered guide vane follows this path instead of striking it.

Example

The guide vanes in 3D: NACA profile, number of vanes and chord.

Distributor head losses: four Idel'cik terms

The distributor is counted as four losses, after Idel'cik, shown at the bottom of the tab:

1. inlet angle of attack: difference between the flow direction and that of the guide vanes;
2. passage contraction between guide vanes;
3. outlet expansion;
4. outlet bend: turning from radial flow to axial flow towards the runner;

then their total. This total enters the path losses, plotted in the Results tab. The deviation imposed by the guide vanes creates the swirl the runner recovers: its loss is therefore already counted in the net head Hn.

Example

The heads chart: the distributor loss among the path losses.

Going further

The Hydro Turbine design reference page presents the complete method and a worked case. The other help pages of the window:

• Control panel
• Layout
• Spiral casing
• Distributor
• Runner
• Draft tube
• Specific speed
• Statistics
• Views and piezometric graph
• Fabrication kit
• Results, method, errors