7/30/2019 Vibration Analysis of Low Pressure Stages of Large Steam Turbines With ANSYS

1/2

Vibration Analysis of Low Pressure Stages of Large Steam Turbines with ANSYSL. Moroz, L. G. Romanenko SoftInWay, Inc., Burlington, MA 01803

High cycle fatigue (HCF) plays a significant role in a bulk of turbine blade failures. Duringoperation, periodic fluctuations in the steam force occur at frequencies corresponding to the

operating speed and harmonics and cause vibration of the bladed disks. Digital prototyping and

optimization become the most practical and economical means for turbine stages design and foridentification and solving HCF-caused failures associated with resonant conditions. During

fabrication, 2-3% variation of blades thickness is considered acceptable. Such fluctuations can

lead to deviation of the blades vibration from expected values within the range of 5%. Moredrastic difference of blades dynamic properties during turbine operation could occur as a result

of blades erosion. Significant amount of research efforts went into developing strategies of

grouping blades such that minimize adversary effect of blade variations. These techniques are

illustrated with analysis of gas turbine working wheel with 34 buckets. Mistuning was modeledby blade material density variation. It was presumed that a half of the blades ware 5% heavier

than another half. This leads to 2.5% difference in natural frequencies. Two simplest blading

methods were considered: blades of the same type were arranged in either 4 interlaced sectors, or

in 8 sectors.

One of the most important design parameters for Straight Bladed Vertical Axis Wind

Turbine is selection of blade material. Its blades must be produced at moderate cost for the

resulting energy to be competitive in price and the blade should last during the predicted lifetime

(usually between 20 to 30 years). At present, Aluminum blades fabricated by extrusion and

bending are the most common type of vertical axis wind turbine materials. The major problem

with Aluminum alloy for wind turbine application is its poor fatigue properties and its allowable

stress levels in dynamic application decrease quite markedly at increasing numbers of cyclic

stress applications. Under this backdrop, an attempt has been made in our project to investigate

alternative materials as straight bladed vertical axis wind turbine blade material.

In our project, required properties of the Straight Bladed Vertical Axis Wind Turbine

Blade Materials are first identified. Then available prospective materials are shortlisted and

assessed. Subsequently, comparisons are made between the available materials based on their

mechanical properties and costs. Finally, comparisons have been made between the design

features of a straight bladed vertical axis wind turbine with Aluminum and the alternative

material blades using one of the prospective airfoils. The results of the design analyses

demonstrate the superiority of the alternative blade material over conventionally used

Aluminum. Structural and modal analyses have been conducted using advanced finite element

methods.

7/30/2019 Vibration Analysis of Low Pressure Stages of Large Steam Turbines With ANSYS

2/2