UFR 4-18 Description
Flow and heat transfer in a pin-fin array
Confined Flows
Underlying Flow Regime 4-18
Description
Here some information about the objectives for investigating the flow in a pin-fin array and an overview about the works relevant to this flow are given.
Introduction
The present case consists in the flow through a wall bounded pin matrix in a staggered arrangement with a heated bottom wall. In addition to its interest for the complex underlying physics, this case is close to several industrial configurations for internal cooling of gas-turbine blades, electronic devices and can be also found in the nuclear field.
The pin fins accelerate the flow in the reduced passages and produce wake regions behind the pins caracterized by strong vortex shedding. This leads to high turbulence levels which enhance heat transfer. The presence of endwalls leads to the apparition of horseshoe vortices which alse enhances heat transfer.
Finally, the available heat transfer measurements by Ames et al. (2004, 2005, 2006, 2007), which will be used all along this UFR, are rare and valuable for CFD validation. The present case can be qualified as a semi-industrial test-case as it has a complex physics but its geomhetry in enough simple to allow deep and precise analysis.
Review of UFR studies and choice of test case
Here some information about the objectives for investigating the flow in a pin-fin array and an overview about the works relevant to this flow are given.
Relevent studies
The present configuration has been studied in the framework of the 15th ERCOFTAC-SIG15/IAHR Workshop on Refined Turbulence Modelling which took place in 2011 at EDF Chatou, France. The computations which will be shown have been partly published by Benhamadouche et al. (2012) and should be published soon in a journal paper.
Experimental investigations
Several experiment exist in the literature around the use of pin fin arrays to increase the turbulence levels which leads to enhance heat transfer. One recalls here the experiments and computations which are directly related to the present configuration. The reader can refer to the two following articles to have additional references: Lawson et al. (2011) and Rao et al. (2012).
Ames et al. (2004, 2005, 2006, 2007) from University of North Dakota published several articles around the present test-case. Almost all the data which will be used to confront CFD computations are from this team except the correlations for pressure drop coefficients (Jacob (1938), Metzger et al. (1982)) and averaged Nusselt numbers (Metzger et al. (1982), Van Fossen (1982)). Three Reynolds numbers based on the gap velocity and the diameter of the pins have been tested, Re=3000, Re=10000 and Re=30000. Only the configuration in which the bottom wall is heated is studied (a configuration with heated pins existe).
Numerical investigations
This configuration has already been studied numerically by Delibra et al. (2008, 2009, 2010) using Unsteady Reynolds Average Navier Stokes (URANS) with the ζ-f model (Hanjalic et al. (2004)) and a hybrid RANS/LES for the two highest Reynolds numbers. They also performed a LES but it seemed to be under-resolved. They concluded that the URANS approach presented several discrepancies, among them, its inability to reproduce the unsteadiness of the flow around the first three arrays of the matrix. They also suggested that the small structures unresolved by URANS need to be predicted. This brought them to conduct hybrid RANS/LES (LES using a dynamic Smagorinsky model with RANS wall-treatment based on the ζ-f model). They found that hybrid RANS/LES gave more acceptable accuracy than URANS in particular for capturing the large convective structures. Note that the computational domain of the URANS and hybrid RANS/LES approaches consisted of 8 by 2 and 8 by 1 pins, respectively, and that the wall temperature and not the heat flux was fixed.
Ames and Dvorak (2006a) also conducted RANS computations with the Realizable and RNG k-ε. They concluded that their approach was underpredicting heat transfer and pressure drop. This discrepancy was attributed to the fact that unsteadiness was not possible to predict(no vortex shedding).
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