Reinventing the Wind Turbine
The Archimedes spiral wind turbine is a type of horizontal axis wind turbine HAWTs but unlike traditional HAWT that uses lift force generated by air pushed down by an Aerodynamic shape ( Airfoil), This turbine uses drag force to harness the energy from the wind. It consists of 3 blades three-dimensional conical shape. One of the key features of this turbine is that can start rotating at low wind speed as demonstrated in this video of the field test (Low Wind Speed)
The study goal is to investigate the aerodynamic characteristics of an Archimedes spiral wind turbine for urban usage. This is done by carrying numerical and experimental studies. The turbine is designed to produce energy by both lift and drag forces on the blade but it mainly depends on the drag force.
The experimental study was to measure instantaneous velocity fields near the field of the blade using a 2D PIV method ( Particle Image Velocimetry). The turbine model was scaled down by 1/10 to acquire detailed flow field information.
The numerical study was to predict the mean velocity profiles using steady and unsteady state CFD simulation. Ansys CFX, CFD study used to conduct both steady and unsteady state analysis, the turbulence model was SST ( Shear Stress Transport).
Three wind speeds are used as operating conditions to run both numerical and experimental tests. Inlet wind velocity are 3.5m/s, 4m/s, and 4.5m/s; rotating velocities are 300rpm,
400rpm and 500rpm, respectively.
Thes results of the Unsteady CFD simulation compared with the results obtained from the PIV measurements. Several notes are listed down as follows:
- The higher velocities are obtained at the inner outermost of the rotor and this is due to the nature of local acceleration around the corner of the blunt-body.
- There was a recirculation zone with lower speeds between each blade’s spiral sectors.
- The flow was much slower at the center than at the edge. This suggests the stronger flow near the tips of blades would be very beneficial as the flow drives the blade with a longer moment arm.
- PIV measurements revealed the presence of dominant vortical structures downstream the hub and near the blade tip.
- The analysis of near rotor wake shows that the blade is a major source of disturbances and unsteady aerodynamic effects.
- The maximum power coefficient Cp obtained is equal to 0.25 and it was near a tip speed ratio of 2.5.
The study presented that Archemdies spiral wind turbine has a fruitful potential for implementation and usage in an urban environment like near buildings where it can operate at low wind speed and wind direction change.
- Due to the PIV experiment, the preferable information of the blade flow under different wind velocities of attack is obtained, which would be very helpful to improve the performance and the design method of the Archimedes spiral wind turbine.
- The experimental results showed a good agreement with the results of the Unsteady CFD simulation.