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A Framework for the Optimal and Robust Tolerance Design of Compressor Blades Under Functional Uncertainties”

Mirhosseini, Darya | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55290 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Khodaygan, Saeed
  7. Abstract:
  8. Improving the performance of compressors plays a key role in saving energy in industries. The presence of aleatory and epistemic uncertainties, such as dimensional, geometrical and environmental uncertainties, causes the tolerances that are within the allowed ranges in normal assembly conditions to violate the assembly requirements in operational conditions and cause a drop in compressor efficiency. In order to reach the dimensional and geometrical tolerances of the components of a compressor, especially in the design of the rotor and stator blades, that guarantees the optimal and stable performance while not increasi the production costs, there is a need for an optimal and robust tolerance design.The main goal of this research is to achieve a framework for the optimal and robust design of dimensional and geometrical tolerances of compressor parts. The tolerance design of rotor blades is performed as the case study. Achieving this goal requires two stages of design; The first stage is optimal and robust design of parameters’ nominal values. This includes optimizing rotors functional characteristics in real conditions while minimizing functional changes. To achieve this purpose, the designed rotor under operational and environmental uncertainties is investigated and its performance characteristics including efficiency and pressure ratio are calculated and their instability and changes are modeled with the help of their probability distribution. Then, the design parameters are determined more accurately by applying two phases of robust optimization, first by Taguchi method and in the second phase by probabilistic method. As a result of this stage of optimal and robust nominal design, in the presence of manufacturing and environmental uncertainties, efficiency and pressure ratio have been optimized and robust. In this way, the rotor efficiency has improved by increasing the average value of 2.82% and reducing the standard deviation value from 0.79 to 0.34, and the pressure ratio has been associated with an increase of 0.005 in the average value and a decrease of 0.0216 in the standard deviation value.The second stage, tolerance design is done using Taguchi method. Allocation of optimal dimensional and geometrical tolerances of the rotor blade requires compliance with functional and assembly requirements, under the lowest production costs possible. Therefore, having two conflicting goals (reducing the tolerance interval to improve performance while increasing it to reduce the production cost), tolerance-cost optimization has been carried out. For this purpose, the production cost functions of each level of tolerance of the parameters have been determined. By determining the orthogonal arrays by Taguchi method, the optimal selection for design parameters’ tolerances has been made. As a result, while maintaining the performance characteristics close to the optimal and robust values, the manufacturing cost has been reduced by 3% compared to the traditional methods of tolerance design
  9. Keywords:
  10. Robust Design ; Tolerance ; Uncertainty ; Axial Compressor ; Uncertainty-Base Multidisciplinary Design Optimization ; Compressor Blade

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