Vertical axis wind machines

Vertical axis wind machines : 

Vertical axis wind machines Various types of rotors developed use drag forces to turn the rotors of different shapes. These are having high starting torques But relatively low tip speed ratios. These include panemones use plates, cups----drag devices Savonius-S shaped ----lift force( drag type) The cup anemometer is a drag based device. Whose rotational speed Is nearly equal to wind speed having low TSR’s .the savonius type works On the same principle but adopted to produce shaft power.

Slide 2: 

There are variety of panamones. these are drag devices, in which one side of the rotor carries blades While the other side produces reduced drag by shielding or furling the blades. Less efficient because low TSRs. Although a few are available commecially cross flow or Darrieus wind turbines. The greatest advantage being independent of wind direction. These devices are less attention because of low power coefficient even at high tip speed ratios. These are very difficult to control in the strong winds. But the generator and transmission are on the ground rather than at the top of a tall tower

Slide 3: 

Distinct advantages of vertical axis than the Horizontal axis machines. Do not need the Yawing equipment to turn the rotor into the wind Require less structural support because heavy components can be located at ground level Since the blades do not turn end over end, the rotor is not subjected to continuous cyclic gravity loads The only disadvantage is less far known about them.

Slide 4: 

THE SAVONIUS ROTOR: Was invented by S J Savonius in the year 1920 Requires low velocity winds for operation It consists of 2 half cylinders facing opposite directions in such a way as to have almost An S-shaped cross section. Irrespective of the wind direction the rotor rotates such as to make the convex sides of the buckets head into the wind.the force of the is greater is greater on the cupped face then on the rounded face. The wind curving around the back side of the cupped face exerts a force less as compared to the top of it. It helps in rotation. The ratio of the height to the overall diameter can be less than 3 to 1. The power coefficient is low, but might be possible be improved by changes in the design, Number, arrangement of the vanes.

Slide 5: 

Characteristics of Savonius rotor are: Self starting Low speed Low efficiency. Advantages of savonius rotor are: It eliminates expensive system. Low ct in speed(8km/hour), for effective operation Less dependent on the storage of supplementary fuels Cost is low, simple structure, yaw and pitch controls are not needed. Ground level mounting, low overall weight. Disadvantages are : Too solid,not useful for a very tall installation because of long drive shaft problems. Having so much metal surface compared with the amount of wind intercepted leading to excessive weights.

Slide 6: 

Areas of concern: The savonius type has moderately good efficiency. Satisfactory starting torques(use with positive displacement pumps) The rotor area required is higher than any other systems Used for Pumping , Small agricultural machines, Bird scarers, Grinders etc. Also can be used with Darrieus rotors for starting purpose.

Slide 7: 

THE DARRIEUS TYPE MACHINES(high velocity wind) Invented by G J M Darrieus in 1925. Already use in Canada. In India, at BHEL,NAL Bangalore research and development are in progress. By use of efficient airfoil, effective interception of large area of wind with a small blade area is advantageous. And it supports its blades in a way that minimizes bending stresses in normal operation. It has 2 or 3 tin curved blades with airfoil cross section and constant chord length. The force in the blade due to rotation is pure tension.this provides a stifness to help withstand the wind forces experienced. Darrieus type rotors are of low solidity,low starting torque,high TSRs. Various rotor configurations are Ф-Darrieus,Δ-Darrieus,Y-Darrieus, -Darrieus etc.

Slide 8: 

Characteristics of darrieus rotor: Note self starting High speed High efficiency Potentially low capital cost. Vertical shaft Support structure Aerofoil blades

Slide 9: 

The concept of this rotor principle is based on the principle by which a Bermulda-rigged sailing ship can sail across the wind at speeds greater than that of wing. Lift causes turning action stronger than the drag force. Modern rotors are not self starting under Steady wind conditions. The Darrieus turbine is usually shaped like an egg beater in profile, with blades curved in a form that minimizes the bending stresses caused by centrifugal forces- the so called Troposkien effect.

Slide 10: 

Advantages: The rotor blades can accept wind from any direction or compass. It can be operated closely to the ground Easier access and serviceability Airfoel rotor fabrication costs are expected tobe reduced over conventional rotor blade costs The absense of pitch control requirements may yield additional cost saving The tip speed ratio and power coefficient are considerably better

Slide 11: 

Disadvantages: It requires external mechanical aid for start up. Rotor power output efficiency of a darries system is somewhat lower than that of a conventional horizontal rotor 3. It may also experience a lower velocity wind 4. Greater vibratory stresses are encountered. 5. Since no yaw control special high torque breaking system must be incorporated. Other types of vertical axis machines are magnus effect rotors.