Multi-Disciplinary Design Optimisation of the Cooled Squealer Tip for High Pressure Turbines

Stefano Caloni,Vassili Toropov,Shahrokh Shahpar

doi:10.3390/aerospace5040116

Abstract

The turbine tip geometry can significantly alter the performance of the turbine stage; its design represents a challenge for a variety of reasons. Multiple disciplines are involved in its design and their requirements limit the creativity of the designer. Multi-Disciplinary Design Optimisation (MDO) offers the capability to improve the performance whilst satisfying all the design constraints. This paper presents a novel design of a turbine tip achieved via MDO techniques. A fully parametrised Computer-Aided Design (CAD) model of the turbine rotor is used to create the squealer geometry and to control the location of the cooling and dust holes. A Conjugate Heat Transfer Computational Fluid Dynamics (CFD) analysis is performed for evaluating the aerothermal performance of the component and the temperature the turbine operates at. A Finite Element (FE) analysis is then performed to find the stress level that the turbine has to withstand. A bi-objective optimisation reduces simultaneously the aerodynamic loss and the stress level. The Multipoint Approximation Method (MAM) recently enhanced for multi-objective problems is chosen to solve this optimisation problem. The paper presents its logic in detail. The novel geometry offers a significant improvement in the aerodynamic performance whilst reducing the maximum stress. The flow associated with the new geometry is analysed in detail to understand the source of the improvement.

Highlights

In a high pressure turbine, a third of the loss can be associated with the leakage flow at the tip.A classic design with a shroud above the tip can help in reducing this loss acting effectively as a seal [1,2]; this configuration has become less feasible in recent large civil aircraft engines.the common trend in more efficient engines is to increase the total temperature at the inlet of the turbine
This work shows the benefit of using automatic optimisation for a practical design of a high pressure turbine rotor tip that is driven by multiple disciplines
The optimiser has been applied for improving the rotor tip of the high pressure turbine

Summary

Introduction

In a high pressure turbine, a third of the loss can be associated with the leakage flow at the tip.A classic design with a shroud above the tip can help in reducing this loss acting effectively as a seal [1,2]; this configuration has become less feasible in recent large civil aircraft engines.the common trend in more efficient engines is to increase the total temperature at the inlet of the turbine. In a high pressure turbine, a third of the loss can be associated with the leakage flow at the tip. A classic design with a shroud above the tip can help in reducing this loss acting effectively as a seal [1,2]; this configuration has become less feasible in recent large civil aircraft engines. The common trend in more efficient engines is to increase the total temperature at the inlet of the turbine. This implies that more coolant is required for protecting the shroud and, as the rotor speed increases, it becomes harder to withstand the centrifugal forces. All major gas turbine engine producers are moving towards a shroudless configuration. It remains important to control the temperature of the tip for the shroudless configuration [4]

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Conclusion