Design and Stress Analysis of Extraterrestrial ... - The Black Vault

• C a is the axial velocity of the working medium in m/s. We
can assume C = 140-170 m/s.
The working part of the blades is designed according to the
velocity triangles known from
gas-dynamics analysis.
With short blades (I = 10-20 mm) it is expedient to use active
turbines. The longer blades are a becter design according to the
principle of reactive turbines since higher efficiency can thus be
obtained.
The chord of the blade b and the pitch t are matched with the
length of the blade. As blade length increases I/b the axial
dimensions of the turbine stage decrease; however, the stresses
from bending and vibrations also increase. First-stage blades
operating under more difficult conditions are usually shorter
(1/b = 1.5-2.5) than last-stage blades.
By cascade solidity we mean the ratio b/t. To reduce weight
an attempt is made to increase the cascade solidity by decreasing
the pitch. Minimum blade pitch is usually determined by the spacing
of the blade shafts on tha crown 'of the disk.
b/t in the root lies within 2-2.2.
The maximum value of
blade.
The chord most frequently is constant along the length of the
An increase in the chord b toward the periphery increases the
efficiency of the turbines; however, the vibrational reliability of
A the blade foil is reduced. Decreasing the thickness of the profile
sections of a blade improves the gas-dynamic qualities and reduces
the weight of the rotor wheel; however, stresses in the blades grow.
Usually blades are made with a variable cross-sectional area;
for long and highly loaded blades the ratio of the avea F(r 0 ) of
the root to the area F(R) of the end is F(r 0 )/F(R) = 4-6, and for
*a short and less loaded blades (ir 0 )/F(R) = 2-3.
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