GB2508814A

GB2508814A - Concentric turbine arrangement

Info

Publication number: GB2508814A
Application number: GB1221869.9A
Authority: GB
Inventors: Hugh Malcolm Ian Bell
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-12-05
Filing date: 2012-12-05
Publication date: 2014-06-18
Anticipated expiration: 2032-12-05
Also published as: GB2508814B

Abstract

A turbine assembly has several turbine sections 1, 2, 3, 4 rotating concentrically at different diameters, each capable of rotating at a different rate. Each turbine section 1, 2, 3, 4 can be arranged to output power to a single drive shaft 10 via gearing to match the different turbine speeds. This arrangement uses relatively short blades 1, 2, 3, 4 which enables the tip speed of the turbine blades to be optimised to reduce drag and consequently increase efficiency. The driveshafts and gearing may be fitted with a low drag cover 12, and attachment points 14 for a generator may be provided. This arrangement avoids the use of long turbine blades that comprise of continuous structural form from the axis of rotation to their tip.

Description

MODULAR HIGH EFFICIENCY RENEWABLE ENERGY TURBINE

Description

Existing tidal turbines are almost exclusively using hydrofoil blades with fixed physical form, and where the profile of the blade changes from the hub to the tip of each blade.

Extensive work has been done in the design of wind turbine blades and this has been adopted by those designing marine renewable energy devices.

However, there are a number of major differences in the medium driving a wind turbine and that driving a water turbine. This is perhaps considered obvious until you examine the behaviour of the two mediums, namely air and water.

Air is of much lower density that water and the wind exhibits wide variations in velocity through gusting. Wind turbines have very large diameter rotors typically 30+ metres where marine turbines are currently only 11 metres. although larger ones are planned.

It is well understood that as diameter increases so does the tip speed for the same number of rotations in a fixed time.

As the tip speed of the rotating blades increases, so does the drag resisting rotation on each section of a typical blade from the centre of rotation progressively to its tip.

As the blade is one continuous structure, each point on it moves at a different speed from the centre of rotation to the tip, and profile presented to the direction of flow changes to try and give the best performance in terms of drag and efficiency. The direction of flow and a drag component is introduced opposing the rotation of the blade. This is proportional to the speed of rotation. The blade sees' the current from an angle to the direction of flow. A wind turbine blade is complex in design and expensive to construct as it needs to possess minimal inertia in order to respond quickly to changes in wind velocity.

It is essential to understand wind if you are designing a wind turbine, but the (-) is equally true about a water turbine.

Marine currents change in magnitude and direction slowly and in a predictable manner. The invention uses these factors to produce a design of turbine that does not require a one piece blade with a changing hydrodynamic profile to the same degree along the entire blade length.

Instead of a continuously changing profile along what is a single structural member, this invention uses a number of turbines each operating within the envelope of the other, but each free to operate at a different number of revolutions per unit of time.

Figure 1 shows in section one embodiment of the invention which depicts for illustration only four sets of turbines to operate and rotate independently of each

I

Instead of a continuously changing profile along what is a single structural member, this invention uses a number of turbines sections each operating within the envelope of the other, but with the ability for each to operate at a different number of revolutions per unit of time depending upon the desired speed of the blades.

It is preferable that each turbine has its blades mounted on the extremities of spokes a distance from the hub to avoid as much interference from the effects of -neighbouring turbines sections If the blade sections are rotating at the same velocity and being turned by the same current acting in the same direction, then their profiles can all be the same. They can be optimised in terms of hydrodynarnic efficiency and the tip speed can be controlled be the design of the number of revolutions per unit of time.

This removes the requirement vested within one piece turbine blades to increase the speed of the furthest point of the blade from the axis of rotation, namely the tip speed to derive an overall efficiency of the blade. The higher the tip speed, the higher the drag and the loss of efficiency in converting the kinetic energy in the flow of the medium into mechanical and subsequently electrical power. The drag is greatest at the point of greatest diameter and this creates a mechanical disadvantage because it is furthest from the centre of rotation.

In theory, the diameter of the larger turbine wheel in this invention is principafly governed by the design of the spokes which have to resist the torque imposed by the blades mounted on their extremities. In marine turbine applications, inertia and weight are not as important as in wind turbines because current velocities build very slowly and predictably.

An advantage of large diameter marine turbine wheels is that much more energy can be garnered because of the increase in swept area of the turbine and deeper water energy reserved may be harvest.

The cost of producing the turbine blades is reduced as they can all be the similar, easily handled and of modular construction.

If each blade in each turbine section moves through the water at the same speed, each turbine section will have a different number of revolutions per unit of time although both tip speed and revolutions per unit of time can be designed to give the most efficient combinations.

The output of each turbine wheel assembly can be combined through a gearbox or in another manner to give a common output shaft before being used to drive a generator directly or indirectly.

The following shows one manifestation of the invention for illustrative purposes, and to allow a unit to be built. The drawings do not show support structures or bearings for clarity, but these can easily be designed by engineers skilled in the art. Gears are shown but they could be configured in a number of ways, and other types of drive employed including belts.chains. toothed drives and hydraulics for example.

Figure 1 shows one turbine section of the turbine envisaged which could comprise one or more such sections.

The current 1 impinges on turbine blades 2 attached to spokes 3. The number of turbine blades attached to each spoke may be one or more, and the number of spokes may also be one or more. The spokes radiate from a drive shaft 4 and are attached to it to form the shape of a wheel. Figure 1 is shown in section. The current 1 acting on the turbine blades 2 cooses it to rotate with the spokes 3 to about the axis of a central shaft 5. The drive shaft 4 also rotates as it is attached to the spokes and turns gear 6. which in turn drives gear 7. Gear 7 is attached to a lay shaft 8 which drives gear 9. Gear 9 drives gear 10 which is attached to the central shaft 5.

The central shaft in turn provides power to a generator or other device.

The turbine blades 2 may have different physical profiles and/or be inclined at different angles of attack to the direction of the current. The term angle of attack is to be used by definition in known works on the theory of hydrodynamics. In Figure 1 the spokes 3 pass preferably through the turbine blades 2 to allow uninterrupted flow of the medium.

Figure 2 shows four (1, 2.3 & 4) turbine sections as depicted in Figure 1 assembled to produce a composite turbine. Each turbine section is of a different size and diameter and arranged so that the flow of the medium impinges upon an array of blades from the periphery of the largest diameter turbine section to the smallest, preferably without interference.

Each of the turbine sections may be so geared so that they all contribute to a common output shaFt 10, using ratios and in gear configurations that correspond with the most efficient use of the bladesafter consideration of blade tip velocity drag and other known factors.

Figure 2 shows how each of the turbine sections drive shafts (5,6,7and 8) respectively of turbine sections (1.2.3and 4) respectively rotate about and are desirably supported by each other all rotating about a common axis 9.

Any number of turbine sections and blades on these sections may be used as dictated by the design criteria in the quest for efficiency.

A 1gearbox' section is shown at 11 and preferably a suitable low drag hydrodynamic cover 12 fitted.

The gearbox is preferably mounted to an electrical generator encased in a housing 13 by suitable location and attachment points 14, depicted for illustration purposes.

The blades may be fitted with guidance devices to control the flow of the driving medium and structural members designed to aide rotation and or reduce turbulence. If,