Liquid Crystal Thermography in Gas Turbine Heat Transfer: A Review on Measurement Techniques and Recent Investigations

Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to design hot gas path components that can meet the modern-day engine performance and emission goals. LCT provides valuable information on the local surface temperature, which is used in different experimental methods to arrive at the local h and η. The detailed nature of h and η through LCT sets it apart from conventional thermocouple-based measurements and provides valuable insights into cooling designers for concept development and its further iterations. This article presents a comprehensive review of the state-of-the-art experimental methods employing LCT, where a critical analysis is presented for each, as well as some recent investigations (2016–present) where LCT was used. The goal of this article is to familiarize researchers with the evolving nature of LCT given the advancements in instrumentation and computing capabilities, and its relevance in turbine heat transfer problems in current times.

Experimental and Analytical Analysis of Aero-Derivative Micro Gas Turbine Heat Transfer and Performance

Small-scale gas turbines offer a light weight alternative to engine generators. Despite the many benefits of a micro gas turbine, its efficiency cannot match that of its competitors. This discrepancy is mostly due to Reynolds number losses in turbomachinery but also partly due to internal heat transfer problems, which degrade the performance below what is adiabatically expected. In general, a good understanding about the heat transfer inside the machine is of paramount importance, and innovative engineering solutions are required to improve overall performance. Overall, one of the less exploited areas in the public literature is the effect of the generator cooling approach. Small jet engines can be used as a simple and affordable foundation to produce portable aero derivative micro gas turbines for demonstrating the specific challenges they face but also to study different flow configurations. This study presents combined analytical and experimental analysis of a portable aero derivative micro gas turbine with three main objectives. The first objective is to evaluate the contributions of different heat leakage losses on the overall performance. The second objective is to compare the influence of different generator cooling approaches. And the third objective is to evaluate the effect of different technical modifications. As a result, suggestions are given about the most suitable machine layouts and the importance of several design choices.

Advanced Cooling in Gas Turbines 2016 Max Jakob Memorial Award Paper

Gas turbines have been extensively used for aircraft engine propulsion, land-based power generation, and industrial applications. Power output and thermal efficiency of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Currently, advanced gas turbines operate at turbine RIT around 1700 °C far higher than the yielding point of the blade material temperature about 1200 °C. Therefore, turbine rotor blades need to be cooled by 3–5% of high-pressure compressor air around 700 °C. To design an efficient turbine blade cooling system, it is critical to have a thorough understanding of gas turbine heat transfer characteristics within complex three-dimensional (3D) unsteady high-turbulence flow conditions. Moreover, recent research trend focuses on aircraft gas turbines that operate at even higher RIT up to 2000 °C with a limited amount of cooling air, and land-based power generation gas turbines (including 300–400 MW combined cycles with 60% efficiency) burn alternative syngas fuels with higher heat load to turbine components. It is important to understand gas turbine heat transfer problems with efficient cooling strategies under new harsh working environments. Advanced cooling technology and durable thermal barrier coatings (TBCs) play most critical roles for development of new-generation high-efficiency gas turbines with near-zero emissions for safe and long-life operation. This paper reviews basic gas turbine heat transfer issues with advanced cooling technologies and documents important relevant papers for future research references.

Build Direction Effects on Additively Manufactured Channels

With the advance of direct metal laser sintering (DMLS), also generically referred to as additive manufacturing (AM), novel geometric features of internal channels for gas turbine cooling can be achieved beyond those features using traditional manufacturing techniques. There are many variables, however, in the DMLS process that affect the final quality of the part. Of most interest to gas turbine heat transfer designers are the roughness levels and tolerance levels that can be held for the internal channels. This study investigates the effect of DMLS build direction and channel shape on the pressure loss and heat transfer measurements of small-scale channels. Results indicate that differences in pressure loss occur between the test cases with differing channel shapes and build directions, while little change is measured in heat transfer performance.

Build Direction Effects on Additively Manufactured Channels

With the advances of Direct Metal Laser Sintering (DMLS), also generically referred to as additive manufacturing, novel geometric features of internal channels for gas turbine cooling can be achieved beyond those features using traditional manufacturing techniques. There are many variables, however, in the DMLS process that affect the final quality of the part. Of most interest to gas turbine heat transfer designers are the roughness levels and tolerance levels that can be held for the internal channels. This study investigates the effect of DMLS build direction and channel shape on the pressure loss and heat transfer measurements of small scale channels. Results indicate that differences in pressure loss occur between the test cases with differing channel shapes and build directions, while little change is measured in heat transfer performance.

On Computational Heat Transfer in Industrial Applications

Industrial energy systems involve many components where fluid flow, heat and mass transfer are the important transport processes. For design and development as well as investigation of innovative ideas, computational methods are of vital importance. Since the early pioneering works (by, e.g., the Spalding group) in the 1960s and 1970s, the development has been tremendous and nowadays CFD (computational fluid dynamics) is an established methodology. During the same time period computer capacities in addition have been brought extensively forward. Although still many topics need further development, applications to industrial problems are constantly increasing. In this paper examples of computational heat transfer, fluid flow and related transport phenmena applied to plate heat exchangers (PHEs), gas turbine heat transfer, and fuel cells are highlighted.

Fundamental Gas Turbine Heat Transfer

Gas turbines are used for aircraft propulsion and land-based power generation or industrial applications. Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Current advanced gas turbine engines operate at turbine RIT (1700 °C) far higher than the melting point of the blade material (1000 °C); therefore, turbine blades are cooled by compressor discharge air (700 °C). To design an efficient cooling system, it is a great need to increase the understanding of gas turbine heat transfer behaviors within complex 3D high-turbulence unsteady engine-flow environments. Moreover, recent research focuses on aircraft gas turbines operating at even higher RIT with limited cooling air and land-based gas turbines burn coal-gasified fuels with a higher heat load. It is important to understand and solve gas turbine heat transfer problems under new harsh working environments. The advanced cooling technology and durable thermal barrier coatings play critical roles for the development of advanced gas turbines with near zero emissions for safe and long-life operation. This paper reviews fundamental gas turbine heat transfer research topics and documents important relevant papers for future research.