Heat and Mass Transfer Research Journal (HMTRJ)

Research Article

Airfoil deposition and mist injection for enhancing film cooling effectiveness in gas turbine blades

Muhammad Awais, Saydus Salehin and Md. Hamidur Rahman

Department of Mechanical and chemical Engineering, Islamic University of Technology (IUT), Board Bazar, Gazipur-1704, Dhaka, Bangladesh.

Submitted: February 1, 2020; Accepted: April 15, 2020

Abstract

Gas turbines components such as vanes (nozzles), blades, and combustor liners are exposed to predominantly higher temperature while in operation. To sustain better performance of such components various critical conventional cooling techniques, e.g. air-film cooling, impingement jet cooling, inclusions of tabulators are employed. In this numerical study a novel technique has been employed with air/stream film cooling. The symmetric airfoil as deposition is used on 2D-flat plate surface to further improve the cooling performance of conventional air-film cooling techniques. Furthermore, water droplets are injected (mist injection) in cooling jet to concede the augmentation of local and average centerline film cooling effectiveness in downstream regions. This prediction of two-phase flow (continuous and discrete) is investigated by utilizing discrete phase model (DPM). The comprehensive investigation on variation of various ratios of density, mass flux, momentum flux and velocity and their influences on cooling effectiveness is also performed. Results demonstrated the significant enhancement of low temperature regions in downstream due to the inclusion of airfoil deposition and hence higher cooling effectiveness was achieved. Moreover, substantial increment in cooling effectiveness was achieved with a small amount of mist injection (2% mist) into the coolant jet. The evaporation of mist in downstream regions increased lower temperature regions and enhanced the cooling performance. Lastly, it was concluded that higher density ratio (DR=2.74) and moderate blowing ratio (BR=3.01) with the insertion of airfoil deposition and mist injection yield 13.6% higher average centerline film cooling effectiveness ( η̅ ) than conventional film cooling technique without the presence of mist injection and airfoil deposition.

Keywords

Gas turbine Film cooling; Numerical; Mist; Airfoil.

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