Optimization Of Ventilation Holes In An Aeronautic Turbine Hole.

Abstract

Ventilation of turbine blades is used in aeronautic jet engines to increase the gas
temperature inside the turbine, without incrementing the blades temperature beyond certain
limits and thus preserving their expected lifetime. Ventilation is achieved by taking cold air
from the compressor and passing it through holes in a rotating disc previous to the turbine. The
shape of the hole plays a major role in the air flow and in the stress distribution of the disc.
Numerical optimization techniques were used to solve this problem. These methods provide a
computational tool for design and a systematic approach to take design decisions that previously
relied more on experiments and intuition. Classical optimization algorithms usually minimize
an objective function under certain design constraints, by varying the design variables within
prescribed bounds. The optimization algorithms use information computed by other analysis
software to recalculate the design variables at each iteration.
The objective of the present study is the optimization of the shape of the ventilation hole in
order to maximize the cross section area of the air channel and to minimize the equivalent stress
in the surroundings of the hole. In order to perform the optimization, a parametric model of the
disc was created. Several alternatives for defining the optimization problem were evaluated, and
a final mechanical design was proposed that takes full account of the three-dimensional features
of the problem.
The analysis was performed using the software Samcef. BOSS/Quattro was the optimization
module, while the mechanical analysis was made using Mecano and Asef modules (nonlinear
and linear modules, respectively) to carry out the coupled thermo- mechanical analysis.