1. INTRODUCTION
Wind energy systems have been utilized for centuries as a source of energy for mankind. At present， wind power is growing at a rate in excess of 35% per annum，which is predicted to continue at this rate at least until 2020. Modern wind turbines are categorized as Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines(VAWT)， which are currently being utilized for diversified remote applications. Mostof wind turbines install today are HAWT， largely due to significant investments made by many countries over the last decades that have overshadowed progress in VAWT technology. Recently there is a resurgence of interests on different types of renewable energy technologies， including HAWT， because of growing environmental concerns and the demand for more enhanced energy security. The report outlines the current utilization scenario and the future prospects of these environmentally benign energy converters in remote far-flung areas.
The involute spiral shaped turbine is an innovative wind turbine design; small，silent， and affordable. This design mimics a shellfish， the Nautilidae. Main characteristics of this innovative design wind turbine are high efficiency (~39%)， low start-up wind speed(1m/s)， providing for the highest yield (W/m 2 )， silent operation， insensitive to turbulence， low maintenance， and an organic appearance. All together making this involute spiral shaped wind turbine is able to generate about 2 times more energy than standard conventional wind turbines (3 blades) of the same diameter.
The aim of this project is to design and implement a ‘horizontal-axis spiral-shaped wind turbine’ system that has the ability to operate in both high and low wind speed conditions. Unlike the traditional rotating blade (spinning propeller) wind turbine， our design is spiral-shaped wind turbine incorporates 3 involute spiral sails in a configuration that utilizes the maximum mass momentum of the wind to spin the sails horizontally on a rotor shaft. The conceptual design also entails the usage of spiral shaped blades and with continuing effective research into the functioning of sails in varying wind speeds and other factors， an efficient shape and size will be determined for a suitable turbine blade for the project.
2. PERFORMANCE TEST
2.1 Instrument and Process
After all the parts were ready and assembled， we started to fabricate the HAWT generator with involute spiral sails， in our school campus. With the help of the tools from our school’s design and technology workshop， the assembly work had been finished within a couple of weeks. Finally， a prototype of ‘magnetically-levitated horizontal-axis spiral- shaped wind turbine’ generator is made. Thereafter， we may start to process a series of diversion test with some instrument，(e.g. strong blower， anemometer， power meter) on a spaced ground at a still place where no other wind disturbance. The stability of the spiral shaped turbine blades rotation is good and satisfied. For getting more details of technical data of the performance of the HAWT generator， e.g. wind power input (correspondence with the wind speed)， generator (electrical) output power， maximum allowed angular speed (ω， rpm) for turbine disc， maximum torque， rpm etc…. These data can be get through a ‘blower test’， from which a ‘snail shape’ blower can provide a strong laminate flow of air current that can make the wind turbine rotate in high speed. The blower can generate a high wind speed up to around 10 m/s with a distance of 1.5 meter blowing from the HAWT for getting such data.
The main advantage of testing with a strong fan rather than testing in a wind tunnel is the relative ease of access. You can just put blower on the same level of the wind turbine disc with a favorable distance and start the machine. The turbine disc starts to rotate and therefore electricity is generated - simple. The required data： the electric current (I)， the voltage (V) and the electrical power output (Pout) can be seen from a Power meter and recorded down manually. A hand held Anemometer(AZ Instrument 8918) can check out the wind speed immediately while we put it into the air current right in front of the turbine. This testing method is simple and easy to carry out， and the accuracy of the result is acceptable too.
After making several ‘blowing test’ and each last for around 10 minutes， we have noted down the data of 40 test points which enough for generating a clear picture (graph) of the HAWT’s performance. All the results， including voltage (V)， current (I)， wind power input (P in )， rotation speed (ù).， electrical power output (P out ) and the efficiency (î)， have been plotted on a graph with illustration.
2.2 Results and Discussion
(A)Wind power input can be got by multiplying the figures of; air-density (ρ = 1.225 kg/m 3 )， effective area (A = 0.03m 2 ) of turbine vane and the wind speed (v) with the energy formula (P in = 1/2.ρAv 3 ).
(B)Electrical power output (from the axial flux generator) can be measured by means of a power meter， from which also can display the three other figures; voltage (V) and current (I) and Energy (E) via a formula (P out =VI) and (E = Pout.t = V I.t) where the power output can be calculated’
(C) Efficiency (î) of the VAWT can be obtained from the ratio of electric power output versus wind power input;(î = P out / P in ).
(D) Linear speed (v) of the turbine disc can be got by multiplying angular speed (ù) to 2ðr/60;(v = ù.2ðr / 60).
If we change the unit to kilometer per hour， a factor of 3.6 have to multiply too.
The maximum wind speed， which generates from the blower from a distance of 1 meter， can be reached up to 10.16 m/s (~40 km/hr).
The maximum efficiency (î = P out / P in ) can be reached up to 11% at the wind speed of around 10 m/s. It can be increased by increasing the power output of the axial flux generator through adding more copper coils on the base unit. Because there are only 12 copper coils on the base and it can add 12 more copper coils to fulfill the room space. In this way， the power output can be double and then the efficiency can be double too.
Furthermore， we can contract the diameter of the copper coils， making smaller size copper coils for putting more pieces on the base unit. Then the power output can be further increased and correspondent efficiency will be increase too.
Another way to increase the performance; as for increasing the quantity of the magnetic field line (B)， using disc type permanent magnet as the diameter is same as the coils， which can increase the induced electromotive force， then electrical power output will increase too.
Narrowing the entrance of the wind blowing to the HAWT generator for making a venturi(wind tunnel) effect， it can increase wind speed. The wind power will be increased in a cubic grade too. - Further to increase the performance， a ‘relay switch’ for activating the DC generator can be installed， which for increasing the power output and retarding the rotational speed (ù) of the turbine disc in the mean times while the wind speed exceeds a critical value (25 m/s or 90 km/hr).
3. CONCLUSIONS
Overall， the magnetically-levitated horizontal-axis involute spiral-shaped wind turbine was a success. The rotor that was designed to harness enough air to rotate at low and high wind speeds while keeping the center of mass closer to the base yielding stability. The wind turbine levitated properly using permanent magnets which allowed for a smooth rotation with negligible friction. At moderate wind speeds， the power output of the generator satisfied the specifications needed to supply the LED load. The SEPIC circuit operated efficiently and to the specifications that were slated at the beginning of the circuit design. Lastly， the stainless-steel plate that was used for the sails of the wind turbine was so rigid. Due to the fact it was as strong as we had hoped， there was no sag in sail about the shaft where the majority of the weight and force was located. If this heavy duty material is used in future design， it would allow for more precision in magnet placement.
After testing the project as an overall system， we found that it functioned properly but there are many things that can be improved upon. The axial generator itself had some design flaws， which we feel had limited the amount of power it could output. Another set- back was due to the overall structure and complexity of the horizontal axis wind turbine， to scale it up to a size where it could provide the amount of power to satisfy a commercial/ industrial park or feed into the grid would not be practical. The size of the rotor would have to be immense and would cost too much to make. Aside from the cost， the area that it would consume and the aesthetics of the product would not be desired by this type of consumer.
In terms of large scale power production， horizontal axis wind turbines are good for these applications because they do not take up as much space and are positioned high up where they can obtain higher wind speeds to provide an optimum power output. The home for the magnetically levitated horizontal axis involute spiral-shaped wind turbine would be in residential areas. Here it can be mounted to a roof and be very efficient and practical. A home owner would be able to extract free clean energy thus experiencing a reduction in their utility cost and also contribute to the “Green Energy” awareness that is increasingly gaining popularity.
专家评语
该项目设计既有创新的思路，也有科学的理论推导，研究内容较为全面，工作量大，独立性强，在螺旋形车叶的设计、磁悬浮底座技术方面具有很强的创新性。该研究团队成员分工明确、责任到位，问辩过程表达清晰，展现出了较高的科学素质。
