REVIEW OF HEAT TRANSFER AUGMENTATION FOR COOLING OF TURBINE BLADE TIP BY GEOMETRICAL MODIFICATIONS TO THE SURFACES OF BLADE

In today's industrial scenario, Gas Turbine is one of the most important components of auxiliary power plant system. In order maximize the overall performance and efficiency of all modern turbines, which theoretically operate according to Brayton cycle, they are operated at a very high temperature. These temperatures are so high that, which may fall in the region of turbine blade material melting point temperatures. Due to such high temperatures there is a possibility that the turbine blades may get damaged due to produced thermal stresses and presents a possible threat to the turbine system as well as the operators. Hence to ensure safe and reliable working of the turbines an effective and reliable cooling system is necessary.Currently available methods for cooling of the turbine blades include film cooling with impingement cooling for the leading edge, rib turbulated cooling using serpentine passages for the middle portion of the blade and pin fin cooling for the trailing edge of the turbine blades. The cooling mechanism for turbine blades must include cooling for all possible regions which are exposed to hot gas flow. The turbine blade tip is one of the critical regions which are severely exposed to hot gas flow occurring due to the leakage of gases from the clearance gap between the turbine tip and the shroud. Hence the tip of the turbine blade must be cooled effectively to prevent thermal expansion of the turbine blade tip due to heating. This cooling will eventually help to avoid rubbing of blades to the shroud which may cause their wear. In this paper, we will be presenting the review of various efforts made by various authors towards the cooling of the turbine blade tip. The paper includes both, experimental methods developed as well as numerical efforts reported. Various experimental setups developed for turbine blade tip cooling includes the pioneer work of R. S. Bunker It has been noted that most of the authors had attempted this kind of problems experimentally only. They have found that the heat transfer can be improved by adding various types of protrusions on the flat plate surface. These added surface essentially help to produce vortex kind of structure and eventually increases the turbulence level near the tip surface. However it is also fact that to carry out the experimentations for various conditions is very costly due to the need of the today's sophisticated measuring devices required to understand and visualize the heat transfer phenomena. On the other hand numerical simulations will provide the detailed visualization and analysis of the heat transfer and flow characteristics for cooling of turbine blade tip. However producing the accurate and reliable results using available CFD software ANSYS-Fluent also need to be reviewedAn attempt here is to explore and present most of the recentcontributions presented by various authors. These reviews will help and provide the detailed guidelines for planned numerical and experimental investigations required for the cooling of turbine blade tip, which help to provide the feasible and practically usable solution for cooling turbine tip.