Проблема использования энергии ветра. Ч. 4 : Теория и аэродинамический расчет ветряных двигателей

— 69 The relation between the number of moduli and the number of relative moduli г « 2 _ (45) When the valves of jx are small expression (45) can be put in the simp ­ lified form + 1 -f 1 ^ 2(1 —e) • In chapter III are deduced the expressions for the torque developed by the windmill M = R ^ ^ ^ ^ ' (50) the power, and the efficiency. Chapter IV deals with the losses in windmills. These losses are divided Into tip losses which are due to the induced drag of blades, the profile losses, the losses resulting from the twisting of the stream, and the losses due to the failure to utilize the whole disc area of the windmill. Given good aerodynamical shape of the blades, the most important of the losses are the tip losses, the magnitude of which is, approxiinately, inversely proportional to the number of blades and the number of the moduli, and directly proportional to p = e (expression 71). This relation was confirmed by an expe ­ rimental comparison of t he power ou t pu t of two-bladed a nd four-bladed wind­ mills (Fig. 13 and 14). In chapter V is discussed t h e law of aerodynamical similarity of windmills. In chapter VI is given the calculation of a four-bladed windmill a s an examp l e illustrating the application of t he theory (Table II). Chap t e r VII deals with the calculation of the characteristic curve of a windmill. As an examp l e is given t h e calculation of the characteristic curve of the • four-bladed windmill shown in Fig. 24.. The calculations are made for five blade sections at different radii (Table III). For the independent variable is chosen the angle of incidence, hence all other quantities are easily cdculated. For each of the blade section chosen is plotted the curve of torque ДУИ ==/(.^ (Fig. 17), after which is graphically found the torque for the whole blade (Fig. 18). In Fig. 19 is shown the torque curve of the windmill (the upper curve with circles). By lowering this curve by an amount corresponding to the tip loosen there is obtained the final curve (the lower curve with circles). The. curve dotted line with points is the experimental curve. A t the end of the volume are given experimental characteristic curves for typical windmills. There are also given graphs of C^, н- for a series of aerofoil shapes of the „Espero" type. List of Notations. • a —Ang l e of incidence in degrees. b —Wi d t h of blade in meters; also the barometric pressure in mm . of mercury. p —An g l e of t h e relative velocity W with the plane of rotation of t he windmill,