Report KD 658 has been added to the menu KD-reports. The tittle of this report is: “Calculations executed for an alternative rotor of the VIRYA-4.2 windmill (lambda design = 6.5, Gö 711 airfoil) used for 24 V battery charging”. The advantage of the alternative VIRYA-4.2 rotor is that it has a higher starting torque coefficient than the original rotor which has a design tip speed ratio of 8. The starting wind speed is therefore lower. The Pel-V curve is better at low wind speeds but worse at high wind speeds. So the alternative rotor is especially meant for regions with low wind speeds.
A new chapter 6 has been added to report KD 656. In this chapter it is investigated how the rotor and the characteristics change if the 0.5 m long connecting strip which connects both blades is changed by a 0.75 m long connecting strip. It appears that the same blades can be used but that now the connecting strip has to be twisted 4 degrees in stead of 5 degrees. With this bigger rotor, the windmill is called the VIRYA-3.17. The Pel-V curve of the VIRYA-3.17 is better than the one of the VIRYA-2.92.
Report KD 656 has been added to the menu KD-reports. The title of this report is: “Calculations executed for the 2-bladed rotor of the VIRYA-2.92 windmill (lambda design = 6, stainless steel tapered blades) driving the VIRYA-2.68 PM-generator for 24 V battery charging”.
Wind tunnel measurements of a similar rotor with tapered blades made out of a cylinder have already been performed in 1978. The measurements for a stainless steel rotor with a diameter of 1.8 m and with blades with a sheet thickness of 2 mm are given in report KD 616. This report has inspired me to design a bigger rotor using 3 mm stainless steel sheet for the blades and stainless steel strip size 150 * 6 mm for the connecting strip.
A new chapter 7 has been added to report KD 598 about the VIRYA-0.65 floating water turbine. In this chapter it is investigated if the matching in between rotor and generator can be improved by taking a simple 2-bladed rotor with a slightly smaller rotor diameter of 0.625 m in stead of 0.65 m and a design tip speed ratio of 3.5 in stead of 3. The matching of this VIRYA-0.625 for 26 V battery charging and star rectification of the original 230/400 V winding is better than for the VIRYA-0.65. The better matching results in reduction of the cut-in water speed from 0.7 m/s to 0.6 m/s. The starting water speed is increased from 0.37 m/s up to 0.5 m/s but, as it is still lower than the cut-in water speed of 0.6 m/s, this is no problem. The maximum power at V = 2 m/s is 160 W, so the same as for the VIRYA-0.65. The negative effect of the slightly smaller rotor diameter is compensated by the better matching.