Heterogeneous Optimization Strategies for Carved and Squealer-Like Turbine Blade Tips

Abstract

Superior rotor tip geometries possess the potential to simultaneously mitigate aerodynamic losses and severe thermal loads onto the rotor overtip region. However, classical design strategies are usually constrained to a specific type of geometry, narrowing the spread of shape topologies considered during the design phase. The current paper presents two novel multi-objective optimization methodologies that enable the exploration of a broad range of distinct tip configurations for unshrouded rotor blades. The first methodology is a shape optimization process that creates a fully carved blade tip shape defined through a Bezier surface controlled by 40 parameters. Combined with a differential evolution (DE) optimization strategy, this approach is applied to a rotor blade for two tip gap sizes: 0.85% (tight) and 1.38% (design) of the blade span. The second methodology is based on a topology optimization process that targets the creation of arbitrary tip shapes comprising one or multiple rims with a fixed height. The tip section of the blade has been divided into more than 200 separate zones, where each zone can be either part of an upstanding rim or part of the cavity floor. This methodology was tested with a level-set approach in combination with a DE optimizer and coupled to an optimization routine based on genetic algorithms (GAs). The current study was carried out on a modern high-pressure turbine operating at engine-like Reynolds and high subsonic outlet Mach numbers. A fully hexahedral unstructured mesh was used to discretize the fluid domain. The aerothermal performance of each tip profile was evaluated accurately through Reynolds-averaged Navier–Stokes (RANS) simulations adopting the shear-stress transport (SST) turbulence model. Multi-objective optimizations were set for both design strategies that target higher aerodynamic rotor efficiencies and simultaneous minimization of the heat load. This paper illustrates a wide variety of profiles obtained throughout the optimization and compares the performance of the different strategies. The research shows the potential of such novel methodologies to reach new unexplored types of blade tip designs with enhanced aerothermal performances.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part II — Tip Flow Analysis and Loss Mechanisms

“…Blade IN01D adopts a conventional single-squealer geometry, typically employed in real industrial turbines. The tip geometries AC06D and AC07T were obtained via a numerical optimization procedure elaborated in [23]. The objectives of the optimization were to increase the rotor efficiency while limiting the thermal loads on the blade tip.…”

Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

“…The rotor disk was divided into seven sectors, each presenting 6-7 blades of equal tip geometry to ensure flow periodicity and all sharing the same baseline blade profile. The alternative blade tip designs were obtained from a previous optimization effort [20,21]. The paper presents the aerodynamic performance of two optimized profiles, a squealer-like rimmed geometry (AC06D) and a contoured tip (AC07T), in comparison to a baseline conventional squealer tip (IN01D) ( Figure 1c).…”

Variable Blade Tip Geometry Inserts for Combined Aerothermal Measurements for Bladed Disk Rotors

“…Cylindrical pin fins and strips along the leakage direction were even found to increase heat transfer coefficients by up to 20% in some cases. The potential of new tip geometries was also shown by (De Maesschalck et al, 2016) with extensive CFD simulations.…”