Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film-Cooling

[+] Author and Article Information
Zachary T. Stratton

School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907, USA

Tom I-P. Shih

School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907, USA

1Corresponding author.

ASME doi:10.1115/1.4041218 History: Received August 09, 2018; Revised August 16, 2018


Large eddy simulations (LES) were performed to investigate film cooling of a flat plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated - one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair. At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.

Copyright (c) 2018 by ASME
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