Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . the symbols in these equations (including 2g = 773 inches)are in inch units. If tj is the minimum thickness of the disk, then equation (38)can be written w(yl2 _ V2) t=V 2gS 1 (39) where Vj is the peripheral velocity at the radius correspondingto tj and V is the velocity corresponding to t as before. If the disk is not made of uniform strength throughout, thenVj is the velocity where the portion designed for uniform strengthbegins. Equations (38) and (39) are ge
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . the symbols in these equations (including 2g = 773 inches)are in inch units. If tj is the minimum thickness of the disk, then equation (38)can be written w(yl2 _ V2) t=V 2gS 1 (39) where Vj is the peripheral velocity at the radius correspondingto tj and V is the velocity corresponding to t as before. If the disk is not made of uniform strength throughout, thenVj is the velocity where the portion designed for uniform strengthbegins. Equations (38) and (39) are generally used by the designers of impulse turbines, and forthe conditions of average prac-tice they are sufficiently accu-rate. Design of the Rim. Anenlarged section or rim is usu-ally required at the circumfer-ence of a disk for the attachment of the blades. Stresses in thissection require careful consideration. In Fig. 211, tx is the smallest thickness of the disk where itjoins the rim (at the radius rj and t* is the thickness and b2 the * The change from linear to angular velocity was made to make Fig. 211. Section of a Turbine Wheel. STRESSES IN RINGS, DRUMS, AND DISKS 417 breadth of the rim of which the center of gravity is at the radiusr2.* Blades attached to the rim produce by the centrifugal forcedue to their weight the stress S2 in pounds per square this there is exerted on the section of the rim the stressdue to the centrifugal force of its own weight and also the radialstress (Sr) in the disk exerted over the thickness tr The expan-sion due to these forces acting on the rim must, for equilibrium,be equal to the expansion of the section of the disk where it joinsthe rim. The sum of the radial forces Fr acting on the rim perinch of length may be stated then as wV 2bt tFr = S2t2 + ^Ll^J _„ Srti> (4o) in which w is the weight of a cubic inch of the material of therim, V2 is the velocity at the radius r2 in inches per second. Radial e
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