1. The other main type of energy-producing hydroturbine is the
A course in Turbomachinery…………………………………..….…Lecturer: Dr.Naseer Al-Janabi
Reaction Turbines
The other main type of energy-producing hydroturbine is the
reaction turbine, which consists of fixed guide vanes called stay vanes,
adjustable guide vanes called wicket gates, and rotating blades called
runner blades (Fig.4.4 below).
Fig. 4.4
A reaction turbine differs significantly from an impulse turbine; instead of
using water jets, a volute is filled with swirling water that drives the runner.
For hydroturbine applications, the axis is typically vertical. Top and side
views are shown, including the fixed stay vanes and adjustable wicket gates.

2. and the inner adjustable vanes (“wicket gates”).
A course in Turbomachinery…………………………………..….…Lecturer: Dr.Naseer Al-Janabi
Flow enters tangentially at high pressure, is turned toward the
runner by the stay vanes as it moves along the spiral casing or volute, and
then passes through the wicket gates with a large tangential velocity
component. Momentum is exchanged between the fluid and the runner as
the runner rotates, and there is a large pressure drop. Unlike the impulse
turbine, the water completely fills the casing of a reaction turbine. For this
reason, a reaction turbine generally produces more power than an impulse
turbine of the same diameter, net head, and volume flow rate.
There are two main types of reaction turbine—Francis and Kaplan.
The Francis turbine is somewhat similar in geometry to a centrifugal or
mixed flow pump, but with the flow in the opposite direction. Note,
however, that a typical pump running backward would not be a very
efficient turbine. The Francis turbine is named in honor of James B. Francis
(1815–1892), who developed the design in the 1840s.
Fig 4.5 Interior view of the 1.1-million hp (820-MW) turbine units on the Grand Coulee
Dam of the Columbia River, showing the spiral case, the outer fixed vanes (“stay ring”),
and the inner adjustable vanes (“wicket gates”).

3. In contrast, the Kaplan turbine is somewhat like an axial-flow fan
A course in Turbomachinery…………………………………..….…Lecturer: Dr.Naseer Al-Janabi
In contrast, the Kaplan turbine is somewhat like an axial-flow fan
running backward. If you have ever seen a window fan start spinning in the
wrong direction when wind blows hard into the window, you can visualize
the basic operating principle of a Kaplan turbine. The Kaplan turbine is
named in honor of its inventor, Viktor Kaplan (1876–1934).
Fig 4.6 The five-bladed propeller of a Kaplan turbine used at the
Warwick hydroelectric power station in USA. There are five runner
blades of outer diameter 12.7 ft (3.87 m). The turbine rotates at 100
rpm and produces 5.37 MW of power at a volume flow rate of 63.7
m3/s from a net head of 9.75 m.

4. P = w = pwQ(r2 Vt2 - r1 Vt1 ) = pQ(u2 V2 cosa2 - u1 V1 cosa1 ) 4.4
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Fig. 4.7 The distinguishing characteristics of the four subcategories of
reaction turbines: (a) Francis radial flow, (b) Francis mixed flow, (c)
Kaplan mixed flow, and (d) Kaplan axial flow.
Power P extracted by the runner:
P = w = pwQ(r2 Vt2 - r1 Vt1 ) = pQ(u2 V2 cosa2 - u1 V1 cosa1 )
where Vt2 and Vt1 are the absolute inlet and outlet circumferential velocity
components of the flow.

5. The Pitot probes are shown for illustrative purposes only.
A course in Turbomachinery…………………………………..….…Lecturer: Dr.Naseer Al-Janabi
Fig. 4.8 Inlet and outlet velocity diagrams for an idealized radial
flow reaction turbine runner.
Fig. 4.9 Typical setup and terminology for a hydroelectric plant that
utilizes a Francis turbine to generate electricity; drawing not to scale.
The Pitot probes are shown for illustrative purposes only.

6. The absolute inlet normal velocity Vn2 = V2 sin α2 is proportional to
A course in Turbomachinery…………………………………..….…Lecturer: Dr.Naseer Al-Janabi
The absolute inlet normal velocity Vn2 = V2 sin α2 is proportional to
the flow rate Q. If the flow rate changes and the runner speed u2 is constant,
the vanes must be adjusted to a new angle α2 so that w2 still follows the
blade surface. Thus adjustable inlet vanes are very important to avoid
shock loss.
EX: An idealized radial turbine is shown in Fig. below. The absolute flow
enters at 30° and leaves radially inward. The flow rate is 3.5 m3/s of water
at 20°C. The blade thickness is constant at 10 cm. Compute the theoretical
power developed at 100% efficiency.