GB2476801A

GB2476801A - Surface features for increasing the efficiency of wind turbine Flettner rotors.

Info

Publication number: GB2476801A
Application number: GB1000199A
Authority: GB
Inventors: Stephen Martin Redcliffe
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-01-08
Filing date: 2010-01-08
Publication date: 2011-07-13
Also published as: GB201000199D0

Abstract

A Flettner rotor uses surface protrusions or depressions to increase the turbulent flow around the rotor, thus reducing the area of separation behind the rotor and increasing the amount of time the airflow is attached to the surface of the rotor enabling the maximum acceleration and deceleration of the airflow around the cylinder. The features may be protrusions, dimples 5 or blind holes 6, surface scratches 7, circumferential 8 or longitudinal 4 grooves or ridges or square, triangular, rectangular or hexagonal uniform surface patterns.

Description

Method to Increase the Efficiency of Flettner Rotors.

This invention relates to a method for increasing the efficiency of Flettner rotors for their use in wind turbines.

Wind turbines are used to convert the energy available from the wind into electrical energy; they use blades of an aerofoil cross section to produce lift forces which turn a generator.

However, the high rotational speeds needed with a bladed wind turbine lead to a noise disturbance making bladed wind turbines controversial when mounted on or near residential buildings. Also horizontally mounted wind turbines experience a loss in efficiency because of wind turbulence caused by surrounding structures and trees. To overcome these problems Flettner rotors could be used which rotate along their vertical axis, this causes a localised reduction in wind speed on one side of the rotor and a localised increase in wind speed on the other, these changes in wind speed results in a reduction in pressure on one side of the rotor and an increase on the other, creating lift, this is called the Magnus effect', However Flettner rotors suffer from reduced performance due to the flow around them being laminar, this leads to the airflow around the rotor separating from the surface of the rotor very early creating a lot of drag behind the rotor known as pressure drag due to separation.

The present invention proposes the use of surface projections or depressions to create a turbulent airflow around the Flettner rotor, thus delaying separation of the airflow from the surface of the rotor and reducing the region of separation behind the rotor. The turbulent flow has more energy than the laminar flow and thus, the flow stays attached longer. The increased length of time that the airflow is attached to the surface of the Flettner rotor also has the advantage of increasing the acceleration and deceleration imparted to the airflow by the rotation of the cylinder.

The invention will now be described solely by way of example and with reference to the accompanying drawings, in which: Figure 1 Shows a plan view of the laminar flow around a Flettner rotor with no surface projections or depressions Figure 2 Shows a plan view of the turbulent flow around a Flettner rotor with surface projections or depressions Figure 3 Shows the preferred method of increasing the turbulent flow in a Flettner rotor.

Figure 4 Shows an alternative surface design in the form of dimples.

Figure 5 Shows an alternative surface design in the form of blind holes.

Figure 6 Shows an alternative surface design in the form of a series of surface scratches.

Figure 7 Shows an alternative surface design in the form of a series of ridges or grooves, which run around the circumference of the Flettner rotor.

Figure 8 Shows an alternative surface design in the form of a pattern of shapes such as triangles, squares, diamonds, rectangles or hexagons that protrude from or extend into the surface of the Flettner rotor.

n figure 1, the airflow (1,) around a Flettner rotor (2) with a smooth surface is shown. The air flow separates from the surface of the rotor very early thus creating a large area of separation behind the rotor (3), which in turn creates a large amount of pressure drag.

n Figure 2, the airflow (1) around a Flettner rotor (2) with surface projections or depressions is shown, these projections or depressions create a turbulent flow around the rotor which means the airflow does not separate from the surface of the rotor until much later, thus reducing the size of the area of separation behind the rotor (3). This has the added advantage of increasing the length of time that the airflow is attached to the surface of the Flettner rotor so that the amount of acceleration and deceleration imparted to the airflow by the rotation of the cylinder increases, this increases the lift force produced by Flettner rotor.

In figure 3 the preferred method of increasing the turbulent flow in a Flettner rotor, this consists of a series of ridges or grooves (4) which run along the length of the Flettner rotor (2) In figure 4 an alternative surface design id shown in the form of dimples (5), which protrude from the surface of the Flettner rotor.

In Figure 5 an alternative surface design is shown in the form of blind holes (6), which extend into the surface of the of the Flettner rotor.

In figure 6 an alternative surface design is shown in the form of a series of surface scratches (7), which has the effect of roughening up the surface of the Flettner rotor.

In figure 7 an alternative surface design is shown in the form of a series of ridges or grooves (8), which run around the circumference of the Flettner rotor.

In figure 8 an alternative surface design is shown in the form a uniform pattern of shapes such as triangles, squares, diamonds, rectangles or hexagons that protrude from or extend into the surface of the Flettner rotor (9). CIams