Numerical Modeling of Effects of Geometrical Parameters on Amount of Torque Produced by a Floating Water Turbine in a Rectangular Open Channel

Document Type : Research Article


Manager of Mechanical Department / Iranian Research Organization for Science and Technology


In this research work, the maximized transmitted torque due to the impulse from flowing water in an open channel has been studied for five types of cylindrical turbines to find the best water turbine in terms of maximum produced electrical energy. For this purpose, using numerical finite volume method, a set of turbine and blades, consisting of a 3-dimensional cylindrical water turbine of equal diameter and length (1m), with five different blade configurations, has been simulated in a 10 m long and 3 m wide rectangular open channel with no inclination, subjected to a water flow of 2 m/s velocity. Considering the weight of various elements, the set of turbine and blades has been designed so that it remains floating in the channel at various immersion depths. Furthermore, with change in flow depth, the immersion depth remains constant. Considering the magnitude of the flowing water impulse in the channel, the corresponding torque transmitted from the water to the blades of the five types of turbines was determined and the maximum torque value was obtained.

In the present research, five types of blades, attached to a hollow cylindrical turbine of 1 m length and 1 m diameter, have been used. The turbine floats on water at a particular depth in an open channel. The water speed in the open channel determines the torque due to the impulse from the flowing water. Considering the various blades, the resultant torque has been studied numerically using two-phase flow finite volume method. The material for the construction of the cylindrical turbine and the blades is dense polyethylene having a density of with 950 kg/m3. Moreover, the fluids considered in the finite volume numerical computations are water with a density of 998 kg/m3, and air with a density of 1 kg/m3 at a constant temperature of 20° Celsius. The hollow turbine cylinder has a volume of 0.78 m3 and is filled with air. The three-dimensional flow channel, in which the turbine is placed, is a rectangular concrete channel of 10 m length and 3 m width, through which water flow at a depth of 35 cm. To avoid the effect of surrounding walls on the transfer of the flow impulse to the turbine, width of the channel has been considered slightly oversized. The roughness values for the bottom surface of the concrete channel and the turbine walls and the blade set is 1 mm and 0.01 mm, respectively. The depth of the channel is constant at 1 m, which is equivalent to the average depth of most city open channels.

Results and Discussion
The difference between type 1 and type 2 turbines is in the blade’s angle along the turbine rotational axis. As a result, the produced torque by type 1 turbine is more than that of type 2. On one hand, increase in contact area between the blades and the flowing water in the channel results in higher torques. On the other hand, the angular shape of the increases the slip between the flow and the blades, which reduces the conversion of kinetic energy into static energy. Ultimately, the result of the above two phenomena in type 2 turbine is a reduction in the produced torque to about 15 N/m. In type 3 turbine, an increase in the produced torque was achieved through the increase in the number and shape of the turbine blades. Hence, the implementation of the aforementioned changes relative to type 2 turbine resulted in an increase in the produced torque to about 56 N/m. Therefore, increase in the number of blades and change in the blade shape in this type of turbine compensated for the effects of blade angle elongation in type 2 turbine. Furthermore, in type 4 turbine, the internal diameter of the blades was reduced, while the number of blades was increased, blades distribution angle was changed from 45° to a straight configuration, and the contact area also decreased. Consequently, the amount of flow slip along the blades also decreased. Specifically, the result of all the above mentioned changes in type 4 turbine was to reduce the produced torque to about 14 N/m compared to type 3 turbine. Therefore, the combined effect of reduction in the contact area and reduced internal diameter of the turbine blades is more dominant than the combined effect of increased number of blades and reduced flow slip on the blades. In type 5 turbine, number of blades was reduced by 10 and the blades internal diameter was tripled relative to type 4 turbine, which resulted in a significant increase in the produced torque. Therefore, type 5 turbine, as a floating turbine, may be recommended for production of electric energy in open channels.

Considering the results of the calculations, type 5 turbine with 21 semicircular shape blades, 11 cm in external diameter and 10.5 cm internal diameter, has a higher capacity to produce more torque compared to other types of turbine studied. The factors affecting the final produced torque include the contact area between the blades and the flowing water in the channel, the length of the blades along the turbine axis, the extent of slip of flow when facing the turbine blades, and the number of blades. The produced torque by type 5 turbine is 458.96 N/m, which is the highest among the turbine types studied in this research.


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  • Receive Date: 13 July 2020
  • Revise Date: 13 September 2020
  • Accept Date: 23 September 2020
  • First Publish Date: 23 September 2020