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Fluids 2016, 1(4), 39; doi:10.3390/fluids1040039

The Formation of Counter-Rotating Vortex Pair and the Nature of Liftoff-Reattachment in Film-Cooling Flow

1
Department of Mechanical and Industrial Engineering, Concordia University, Montreal, QC H3G 2W1, Canada
2
Mechanical Engineering Department, Texas A&M University at Qatar 228C Texas A&M Engineering Building, P.O. Box 23874 Doha, Qatar
*
Authors to whom correspondence should be addressed.
Academic Editor: Mehrdad Massoudi
Received: 4 May 2016 / Revised: 3 November 2016 / Accepted: 15 November 2016 / Published: 2 December 2016
(This article belongs to the Special Issue Computational Fluid Dynamics)
View Full-Text   |   Download PDF [8078 KB, uploaded 7 December 2016]   |  

Abstract

Traditionally, the formation of the Counter-Rotating Vortex Pair (CRVP) has been attributed to three main sources: the jet-mainstream shear layer where the jet meets with the mainstream flow right outside the pipe, the in-tube boundary layer developing along the pipe wall, and the in-tube vortices associated with the tube inlet vorticity; whereas the liftoff-reattachment phenomenon occurring in the main flow along the plate right downstream of the jet has been associated with the jet flow trajectory. The jet-mainstream shear layer has also been demonstrated to be the dominant source of CRVP formation, whereby the shear layer disintegrates into vortex rings that deform as the jet convects downstream, becoming a pair of CRVPs flowing within the jet and eventually turning into the main flow direction. These traditional findings are assessed qualitatively and quantitatively for film-cooling flow in gas turbines by simulating numerically the flow and evaluating the extent to which the traditional flow phenomena are taking place particularly for CRVP and for flow liftoff-reattachment. To this end, three flow simulation cases are used; they are referred to as 1—the baseline case; 2—the free-slip in-tube wall case (FSIT); and 3—the unsteady flow case. The baseline case is a typical film-cooling case. The FSIT case is used to assess the in-tube boundary layer. Cases 1 and 2 are simulated using the Reynolds-averaged Navier-Stokes equations (RANS), whereas Case 3 solves a Detached Eddy Simulation (DES) model. It is concluded that decreasing the strength of the CRVP, which is the case for e.g., shaped holes, provides high cooling performance, and the liftoff-reattachment phenomenon was thus found to be strongly influenced by the entrainment caused by the CRVP, rather than the jet flow trajectory. These interpretations of the flow physics that are more relevant to gas turbine cooling flow are new and provide a physics-based guideline for designing new film-cooling schemes. View Full-Text
Keywords: counter-rotating vortex pair; source; CRVP formation; liftoff; reattachment counter-rotating vortex pair; source; CRVP formation; liftoff; reattachment
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Li, H.M.; Ghaly, W.; Hassan, I. The Formation of Counter-Rotating Vortex Pair and the Nature of Liftoff-Reattachment in Film-Cooling Flow. Fluids 2016, 1, 39.

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