An OEM or a research interview is designed to test the ability of the candidate to solve a problem by applying physics driven thinking skills. Unless the interviews are for people who would develop mechanical methods/mathematical models for high-end research interviews mostly check fundamentals, application and thinking skills.
Analysis: What is the difference between a plane disc and a bladed disc?
For a bladed disc, the rim must support the blade load hence the radial stress is non-zero. Hence the following is the distribution of radial stress
Observation: Gravity could act axially and when the blade is horizontal it could cause bending. Nature of bending changes from left to right position casing fatigue. Of course axial load variation may not be significant. However quantification is important
However the gravity can affect the stress stiffening effect, by varying axial load
As the blade rotates angle with the vertical of the left blade decreases and that of the right blade increases by ωt
Gravity is a variable load
The variation if significant not only causes fatigue but could change the natural frequency by varying stress stiffening effect
The blade’s centrifugal load determines rim loading for the wheel. Further, the blade height decides the flow annulus which is decided from fluid mechanics considerations. In our calculations blade height may be varied but the annulus area must be kept constant
System-level understanding helps!
Blade height can be larger or smaller but the annulus area must be kept constant. Now let us quantify!
Where r is the CG, distance of blade from the axis of rotation.