Mukesh Prakash Mishra*, A K Sahani, Sunil Chandel and R K Mishra Enhancement of Full Coverage Film Cooling Effectiveness with Mixed Injection Holes https://doi.org/10.1515/tjj-2018-0025 Received July 12, 2018; accepted August 01, 2018 Abstract: In the present work numerical study of full coverage film cooling on an adiabatic flat plate is carried out. Cooling performance of three configurations of cylindrical holes is studied with downstream injection, upstream injection and mixed injection. In mixed injec- tion configuration one column of holes inject in down- stream direction and the holes in the adjacent column inject in the upstream direction. Numerical simulations are carried out at different velocity ratios and circumfer- entially averaged value of adiabatic film cooling effec- tiveness is estimated. Simulation results indicate that the mixed injection configuration has better and more uni- form cooling, throughout the perforated plate, than with downstream injection. The difference is greater with increase in the velocity ratio. Configuration with upstream injection gives better cooling than mixed injec- tion at front few rows of cooling holes but it shows poorer performance with downstream injection in the down- stream rows of cooling holes. The obtained results from this study can be an invaluable input for highly loaded combustion chambers. Keywords: effusion cooling, film cooling, cooling effec- tiveness, downstream injection, upstream injection PACS ® (2010). 81.20.Ka Introduction The performance of gas turbine engines mainly depends on the Compressor Pressure Ratio (CPR) and Turbine Inlet Temperature (TIT), i. e. the maximum pressure and tem- perature in the thermodynamic cycle [1, 2]. High thrust requirements of the modern aircrafts necessitate the engines to operate at extreme conditions of pressure and temperature and the mean turbine inlet temperature approaches 1850 K in engines meant for combat applica- tion. Considering the allowable temperature traverse at the combustor exit, the combustor and turbine compo- nents experience extremely high local temperatures caus- ing erosion that restricts the life of hot end parts of the engine [3, 4]. Though many high temperature materials and high temperature coatings including thermal barrier coatings (TBCs) have been developed, these materials and coatings alone are not yet capable of withstanding this high temperature [5, 6]. In order to enable the com- ponents to survive in the high temperature environment they are heavily cooled by various cooling techniques. The cooling can be internal; such as impingement cool- ing, pin-fins, rib turbulators or external, such as film cooling. In film cooling technique the cool air is injected through small holes which form a protective cold layer on the walls of the hot components. This cold layer sepa- rates the wall from the hot combustion products [7–9]. Generally, cylindrical and shaped holes are used in film cooling. Cylindrical holes have uniform circular cross section throughout their length. On the other hand shaped holes have uniform circular cross section up to a certain length of hole-inlet called throat and after the throat these are shaped as a diffuser with expansion in the circumferential as well as in the flow direction [10]. Kidney vortex and jet penetration are common two main disadvantages for cylindrical film cooling holes at high blowing ratios that limits its film cooling effectiveness. An expanded exit of shaped holes reduces kidney vor- tices and jet penetration by reducing the jet momentum and thus counteracts the disadvantages of cylindrical holes and improves film cooling performance [11]. Shaped holes also demonstrate better cooling in circum- ferential direction. Although shaped holes result improved cooling performance than that with cylindrical holes, due to their complex shape they are very difficult and expensive to manufacture. Cylindrical holes, on the other hand, are simple in structure and easy to manufac- ture. Cylindrical holes with compound angle of injection provide improved film cooling effectiveness compared with cylindrical holes with downstream injection [12]. *Corresponding author: Mukesh Prakash Mishra, Instruments Research and Development Establishment, Raipur Road, Dehradun 248008, India, E-mail: akashrolee@gmail.com A K Sahani, Instruments Research and Development Establishment, Raipur Road, Dehradun 248008, India Sunil Chandel, Department of Mechanical Engineering, Defence Institute of Advanced Technology, Girinagar, Pune 411025, India R K Mishra, Centre for Military Airworthiness & Certification, Bangalore 560037, India Int J Turbo Jet Eng 2018; aop Brought to you by | University Paris-Sud Authenticated Download Date | 11/28/18 3:59 AM