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

ME-
(3.15a)
The bend of-blades from centrifugal forces
Under the effect of centrifugal forces blades bend when the
centers of gravity of separate sections along the length of the blade
do not coincide with tbe Or axis which passes through the center of
gravity of the root section.
Let us examine the bending of a blade under the effect of gas
forces Px and Py in the field of centrifugal forces (Fig. 3.20).
Let us assume that the axis of the centers of gravity of the unbent
blade coincides with the Or axis.
Under the effect of forces P
and Py the blade will bend. Acting on the bent blade will be
the centrifugal force creating mc. wnts MxC and MyC, which attempts
to turn the axis of the blade to a neutral position.
Thus, the action of the centrifugal forces makes the total bend
of the blade less than it would be under the action of gas forces
only (see the dashed line of bend on Fig. 3.20). The bending stresses
of the blade will be less. These are used for unloading blades from
extremely large bending stresses by gas-dynamic forces. It is
possible to so design a blade that in the framing cr near it low
or even zero bending moment will appear.
There are two design methods for reducing bending stresses in
blades or, as they say, two methods of "unloading" the blade.
In the first case, a blade with a rectilinear axis passing
through the cross-sectional centers of gravity is installed in
framing with an inclination so that the axis is to the side of the
action of the gas-dynamic bending forces (relativ, to the axis
passing through the center of gravity of the root section of the
blade). Such a method is technologically convenient L•nd rrequently
used for unloading short turbine blades.
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