J. Energy Power Sources Vol. 1, No. 2, 2014, pp. 72-78 Received: July 1, 2014, Published: August 30, 2014

Journal of Energy and Power Sources

www.ethanpublishing.com

Towards an Innovative Radial Flow Impulse Turbine and

a New Horizontal Archimedean Hydropower Screw

Bernhard Mayrhofer1, Alkistis Stergiopoulou2, Bernhard Pelikan1 and Efrossini Kalkani2

1. Department of Water, Atmosphere and Environment, University of Natural Resources and Life Sciences, Institute for Water

Management, Hydrology and Hydraulic Engineering, Vienna, 1190, Austria

2. Department of Water Resources and Environmental Engineering, National Technical University of Athens, School of Civil

Engineering, Athens, 15780, Greece

Corresponding author: Alkistis Stergiopoulou (alkisti_ster@yahoo.gr)

Abstract: The present paper explores the performance characteristics of two innovating hydropower systems, a radial flow impulse turbine and a new horizontal Archimedean screw system. Concerning the radial flow impulse turbine a functional description with a theoretical analysis of the turbine principle is given and the results of the first hydraulic measurements of a 7.5 kW prototype are shown. The analysis shows that the turbine efficiency is with 36.6 % low, in comparison to other turbines. In terms of the horizontal Archimedean screw the principle idea and a preliminary theoretical calculation of the screw are given. The preliminary theoretical calculation indicates an efficiency of 22 %. To verify the calculated efficiency a practical experiment arrangement is planned and described in this paper. Key words: Small hydropower, radial impulse turbines, Archimedean screw turbines, kinetic energy.

1. Introduction

All turbines convert hydraulic energy into rotational

mechanical energy, which is subsequently converted in

electric energy. There are three types of turbines, the

reaction, the impulse and the Archimedean screw

turbines, the difference being mainly the manner of

water head conversion. In the reaction turbines, the

fluid fills the blade passages, and the head change or

pressure drop occurs within the runner. An impulse

turbine first converts the water head through a nozzle

into a high-velocity jet, which then strikes the buckets

at one position as they pass by. The runner passages are

not fully filled, and the jet flow past the buckets is

essentially at constant pressure. Impulse turbines are

ideally suited for high head and relatively low power

[1].The third type of hydropower turbine concerns the

low and zero head Archimedean screw systems with

inclined and horizontal axis efficient and technically

feasible machines.

In the last centuries many turbines, which work on

the basis of the three types, have been invented. This

doesn’t mean that there can’t be new inventions in this

field. The paper presents experimental research of an

IRFIT (Innovative Radial Flow Impulse Turbine) and

preliminary research efforts for a HAAHT (Horizontal

Axis Archimedean Hydropower Turbines) harnessing

the kinetic energy of rivers, currents and open channels

works.

2. Functional Description of the IRFIT

Fig. 1 shows a schematical picture of the researched

IRFIT and of its 8-bladed rotor [2]. The supplied water,

which is under pressure, comes from the bottom and

flows through a reduction to the jet nozzle. The jet

nozzle converts the energy of the water stream into

kinetic energy and deflects the water into the radial

direction. The water jet passes centrifugally the rotor,

Towards an Innovative Radial Flow Impulse Turbine and a New Horizontal Archimedean Hydropower Screw

73

where rotor blades deflect the water. The deflection

leads to a momentum, which moves the rotor and

causes a torque. The energy from the rotor is led by a

shaft to the generator. The rotor and the shaft are fixed

with a bearing. This bearing absorbs all the forces and

contains the sealing, which prevents flow out of the

housing. After having passed the rotor the housing

collects the water and brings it back to the river channel.

It also contains the mounting of the turbine.

The housing is not completely filled with water, so

that the rotor is surrounded by air, which results in

lower friction losses and ensures atmospheric pressure

conditions. This also allows air to enter the rotor

through an air gap which is the most important

characteristic of the turbine, as explained later. Due to

the air there is no force locked connection between

upstream and downstream water, which results in head

losses.

Fig. 2 shows the cylinders used for the flow rate

regulation of the radial impulse turbine. With these

cylinders it is possible to lift and lower the rotor. This

leads to a change of the jet nozzle gap, which is among

Fig. 1 Turbine description.

Fig. 2 IRFIT regulation.

other factors responsible for the flow rate. After the air

gap the jet nozzle is necessary, because all the available

potential energy should be converted into kinetic

energy. The air also ensures that there is almost no

retroactivity from the rotor to the jet nozzle. In the rotor

channel the air should reduce the friction losses,

because of the resulting higher hydraulic diameter and

is necessary for the flow rate regulation.

For this turbine a high relative output velocity is

important. The air allows a maximum speed of the

water jet because it reduces the water filled

cross-section area, so that theoretically by a lower flow

rate more air is in the channel, the water filled

cross-section area decrease and according to the

equation of continuity the velocity of the water jet

remains constant. The ambient air pressure around and

inside the rotor, the radial jet inlet flow and the loading

principle differentiate the researched turbine from

other types, such as Francis as well as Pelton turbines.

3. A First Theoretical Analysis of IRFIT

With the theoretical analyses the maximum

efficiency of the researched turbine should be

determined. This research is based on an ideal turbine

without losses. This ideal turbine has an endless

number of rotor blades with a thickness of zero. The

water jet enters the rotor inlet normal to the

circumferential direction and leaves the rotor outlet

tangential against the circumferential direction. No air

in the rotor is considered. By using this assumption and

the law of conservation of energy, the ideal turbine

efficiency ηideal can be determined, as Eq. (1) shows:

ηideal=1- P2

P1=1- m·c2

2

2

m·c12

2

=1- c22

c12 (1)

P1 and P2 represent the input and output power of the

water jet, the mass flow and c1 and c2 the input and

output velocity of the water jet [3-4]. The input velocity

is a function of the head H and the gravitational

acceleration g, as written in Eq. (2):

c1= 2·g·H (2)

The output velocity can be calculated with the relative

74

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circumferenti

Both veloc

(4)-(5), wher

rotation speed

Fig. 3 il

depending on

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maximal effi

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low heads a

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[5-6]. Howev

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4. IRFIT M

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etical maximum

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c2=cities w2 and u

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s the rotor ra

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nd a New

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Towards an Innovative Radial Flow Impulse Turbine and a New Horizontal Archimedean Hydropower Screw

76

Fig. 9 The horizontal screw rotor could change

horizontally direction (Δθ = 100°).

Fig. 10 Rotation possibilities of the horizontal screw.

Fig. 11 Artistic photorealistic view of a series of horizontal screw rotors in the natural channel of Euripus Strait.

Fig. 12 Views of the new 3-bladed horizontal axis Archimedean screw turbine.

depth 1 m). According to the second possibility the

horizontal screw rotor could be rotated horizontally (θ1,

θ2, θ3…) with the help of the “right guide”, which

could also be rotated.

An artistic photorealistic view of a series of

horizontal screw rotors in the natural channel of

Euripus Strait, Greece, is given below in Fig. 11.

Some views of the new 3-bladed horizontal axis

Archimedean screw turbine, before installing in the

experimental channel of the Laboratory are given in

Fig. 12.

6. Preliminary HAAHT Theoretical Efforts

To illustrate a quite simple basic theory of horizontal

screw machine based on the drag principle, the

classical undershot waterwheel with flat blades is

considered as a good example to simulate a horizontal

screw waterwheel. Consider the screw waterwheel,

having an effective radius R, a blade area Ab and an

angular velocity ω rotating in a stream flow of velocity

Vc (see Fig. 13).

The force exerted on the flat blade, simulating one

screw blade, is given by Eq. (6):

Fd=0.5·ρ·Ab·Cd· Vr2 (6)

where ρ represent the fluid density, Cd is the blade

coefficient of drag and Vr is the difference (Vc - Vb)

Towards an Innovative Radial Flow Impulse Turbine and a New Horizontal Archimedean Hydropower Screw

77

Fig.13 Screw waterwheel rotating in stream flow of velocity Vc = V.

between stream flow velocity Vc and blade velocity Vb

= ω * R. The relative velocity Vr decreases as ω/R

approaches V c and the force Fd decreases toward zero.

The power produced by the blade can be calculated

with Eq. (7) PT=Fd·Vb (7)

and combining the previous relations gives the power: PT= 0.5·ρ·Ab·Cd·ω·R· Vc-Vb

2

= 0.5·ρ·Ab·Cd·ω·R· 1-λ2·Vc

3 (8)

where λ is the tip-speed ratio. By using Eq. (9)

Cp=Cd·λ· 1-λ2 (9)

the power equation reduces to

PT=0.5·ρ·Ab·Cp·Vc3 (10)

The derived function for Cp gives a value of zero for

λ = 0 and λ = 1 and a maximum value of 0.148 for λ =

1/3. However, based on the total projected area of the

screw waterwheel, the maximum power coefficient is

about 0.06. The power for constant-speed operation is

proportional to (Cp/λ3) but as the stream velocity

increases the power continues to increase. Τhe flow

and the geometrical data are Vc = 1.76 m/s, Αb = blade

wet area = Lb * (Ro - Ri) = 1 m * 0.05 m = 0.05 m2, Lb =

length of the blade, Ro and Ri are the outlet and the inlet

radius of the blade.

The theoretical power of the input current in the

open channel could be:

Pth=0.5·ρ·Ab·Cd·Vc3=136.29 W (11)

The power produced by the horizontal screw wheel is PT=ω·T=2·π·n·T (12)

where ω is the angular velocity of the runner, T is the

torque acting on the turbine shaft, and N is the

rotational speed of the runner. The hydraulic efficiency

of the screw turbine is defined as the ratio between the

mechanical power developed by the turbine to the

available theoretical water power, as Eq. (13) shows:

ηhyd=Pt

Pth=0.22 (13)

For the above preliminary HAAHTcalculations, the

following characteristic values are used: Fd = 51.62 N,

ω = 7.882 r/s, T = Fd * R = 3.8175 Nm, Vb = Vc/3 =

0.5866 m/s.

7. Conclusions and Further Researches

This paper has explored the performance

characteristics of two very promising hydropower

systems, an innovative radial flow impulse turbine and

a new horizontal Archimedean hydropower screw

system.

The functional description of the radial flow impulse

turbine shows the innovative concept of the researched

turbine. Theoretically the turbine is similar to the

Segner Wheel, although the design and operating

principle show considerable differences. The

measurement results have shown that the efficiency of

the investigated prototype reaches only 36.6 %. The

measured data indicates that at higher pressures and

flow rates an increased efficiency can be obtained.

Without the maximum efficiency it is hard to analyses

the turbine performance, so that further measurements

with more operation points are necessary. Due to

optimizations, for example of the jet nozzle, the rotor,

the air gap and so on, the efficiency could be increased.

Therefore more measurements of different prototypes,

mathematic calculations or simulation are needed.

The preliminary theoretical calculation of the

horizontal Archimedean screw indicates an efficiency of

22 %. To verify this efficiency practical measurements

on the described experiment arrangement are necessary.

With these measurements also the optimal operation

condition for a high efficiency can be determined and

general advices for the use of horizontal Archimedean

screws can be given.

References

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Towards an Innovative Radial Flow Impulse Turbine and a New Horizontal Archimedean Hydropower Screw

78

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