Turbine Cooling Systems Design: Past, Present and Future

Abstract

Over a half a century ago, the power and performance of the first gas turbine engines were constrained by material limits on operating temperature. In these machines, the combustor exit temperature could not exceed the capability of the materials used to construct the turbine. Eventually, cooling was introduced into turbine components to enable turbine power and efficiency to be increased. That revolutionary step enabled gas turbines to become competitive with other heat engines for business, particularly in the rapidly expanding aviation and electrical power generation sectors. Although the first cooled turbine components may be considered crude by present standards, the underlying foundation of internal convection cooling remains the backbone for cooled turbine components today. Since its introduction, many improvements and additions to the fundamental basis of turbine component cooling have been developed. The introduction of film cooling is a prominent example. With this past research and development, turbine cooling system designs have progressed to the point where they represent the norm, rather than the exception in today’s gas turbines. Further, the confidence and robustness of these systems has been elevated to the point where the working fluid temperatures can exceed the maximum temperature of the structural materials by wide margins. In this paper, from an engineering perspective, we explore some of the significant accomplishments that have led to the current state-of-the-art in turbine cooling systems design. These systems employ a delicate balance of structural material capabilities with advanced internal and film cooling and the use of thermal barrier coatings to satisfy the goals and objectives of specific applications. At the same time, it is widely recognized that the use of cooling flows in the turbine results in parasitic losses that reduce performance. To that end, we also consider some of the specific challenges that face cooling system designers to reduce cooling flows today. Based on the research and development that has been performed to date, we consider the current status of cooling technology relative to a theoretical peak. Finally, we explore some of the hurdles that must be overcome to effectively raise the bar and realize future advancement of the state-of-the-art. The goal is to measure and separate new technologies that are merely different from those that are superior to past designs. Clearly, the identification of risk and risk reduction will play an important role in the development of future turbine cooling systems.