"A water turbine constructed on the water turbulence or whirlpool principle is capable of utilizing very small sources even for untapped water, and it is highly suitable for the closed circuit production of electrical energy. The non-monotonic distribution of the radial velocity component is important for the onset of the driving force of the angular instability. This instability and the existence of the radial fluid motion give rise to the angular volume force. The strong gradient of entropy in the boundary layer of the inner rotating conical cylinder is a dominant source of vorticity." - © 2012 Elsevier Ltd -
Hydro-energy is currently the biggest commodity of renewable energy. The process of hydrokinetic energy conversion normally implies utilization of kinetic energy contained in rivers, ocean currents, tidal streams, or man-made waterways for generation of electricity. At the same time, however, the traditional hydro-energy in many places around the world is considered to be exhausted, at least in respect of the potential of the bigger energy resources. The accessibility of power energy at relatively low prices pushed to the background its actual externalities. It should be noted, however, that interest in the traditional renewable resource of water is permanent, long-term and not liable to surges of short term interest.
In recent years we have tended to encounter some new approach towards energy production, and this is usually found in an effort to use smaller amounts of renewable resources, in various marginal sources of water potential (waste-water treatment plant, small streams and creeks, low-speed low-volume ocean currents). From this viewpoint we focused on a very small rolling liquid turbine, which could bring about a certain benefit from these non-traditional hydrokinetic sources. It has already been verified in practice that it is technically feasible to sufficiently convert very small water potentials (read low flow capacity and hydraulic gradient) to an effective output. It can deal with both the case of renewable energy, for example of a mountain stream, and the case of hydropower, and which has been until now thwarted as a nonutilized potential in various systems of the production process or within the framework of the operation of higher buildings, etc. One of the biggest energy consumers in modern society are the so called statistically average households.
Fig 1. Initial position of the rotor and deviated position of the rotor in motion. This shape of rotor is usual for contemporary turbines in praxis but on the other hand for theoretical analysis conical shape is more suitable.
Description of the bladeless turbine
The rotor and the stator create in a quiescent state a symmetrical coaxial diffuser as shown in Figs. 1 and 2. However, this state is unstable and as a consequence of the instability of the flow through the gap between the rotor and the stator it changes to an asymmetrical one. The shape of the rotor and stator can be variable i.e. it might be improved or optimized. In practice the most common rotors are hemispheres as in Fig. 1, but what really matters is the diffusion angle of the gap between the rotor and the stator.
One tip of the rotor’s shaft is fixed, so that the rotor can roll along the inner side of the confuser. When the fluid flows along the rotor, then due to the flow field instability, the fluid starts to rotate and vorticity is generated. The direct consequence of the vorticity generation is the onset of velocity circulation and the force interaction between the fluid and the rotor. This fluid structure interaction results in the rotation of the shaft on which the rotor is placed.
Fig 2. Simplified scheme of the turbine. Fluid flows between the inner cone and the outer cylinder.
In practice more complicated shapes of the rotor and stator have been developed but this figure shows the most important feature of the turbine, the diverging non-symmetrical gap crucial for the appearance of volume forces responsible for the rotation.
In principle it does not matter if it is hanging or supported. The rotor with the shaft then performs a precession movement and rotates (circulates) around its direct axis. The amount of rotation depends on the ratio between the inner and outer radii. When this ratio is close to one, i.e. when the gap between the cylinder is small, the number of precessions needed for one rotation of the rotor around its axis increases as the width of the gap decreases. The number of precessions can be simply changed by changing the width of the gap. In the case of a conical stator this can be done by changing the vertical position of the rotor.
The first embodiment of rolling turbines used a rotor hanging from the entry part of an outlet nozzle. The diameter of the rotor for example can be just several centimeters or millimeters. Water flow rates can change usually from single liters to tens of liters per second.
The advantage of such turbine lies especially in its simplicity, environmental safety and ability to operate in ultra low sources of water. The turbine design allows easy adjustments as might be required by specific applications.
3D printing has been used in order to promptly incorporate the design changes necessary for turbine performance optimization under a variety of operational conditions.
Vortex SETUR turbines of different sizes have been extensively tested since 2008.