Geometry effect on flow fluctuation and heat transfer in unsteady forced convection over backward and forward facing steps

This study presents a direct numerical simulation of the geometry effect on fluid flow and heat transfer characteristics in the transitional flow over backward and forward facing steps. A computer program of FORTRAN code is used to solve the governing equations according to finite volume method. The effects of the bottom wall length and the step height are investigated. With the increase of bottom wall length, a fundamental frequency of flow fluctuation appears at Lb = 10 h and then disappears at Lb = 14 h. This fundamental fluctuating frequency decreases with the increase of step height. The fact that the heat transfer performance is better in the reattachment region at Lb = 12 h and S = h indicates that the periodic flow fluctuation with a larger fluctuating velocity has positive effects on heat transfer enhancement. The results of the relationship between flow fluctuation and heat transfer enhancement are significant for certain practical applications of energy conversion.

[1]  Y. Nagano,et al.  Investigation of turbulent boundary layer over forward-facing step via direct numerical simulation , 2010 .

[2]  S. A. Gandjalikhan Nassab,et al.  Turbulent Forced Convection Over A Single Inclined Forward Step In A Duct: Part I – Flow Field , 2008 .

[3]  J. Tihon,et al.  The transitional backward-facing step flow in a water channel with variable expansion geometry , 2012 .

[4]  B. Armaly,et al.  Experimental and theoretical investigation of backward-facing step flow , 1983, Journal of Fluid Mechanics.

[5]  Bassem F. Armaly,et al.  Three-dimensional convective flow adjacent to backward-facing step: effects of step height , 2002 .

[6]  G. N. Xi,et al.  Effect of the vortical structure on heat transfer in the transitional flow over a backward-facing step , 2017 .

[7]  B. Mikic,et al.  Numerical investigation of incompressible flow in grooved channels. Part 1. Stability and self-sustained oscillations , 1986, Journal of Fluid Mechanics.

[8]  Anthony T. Patera,et al.  Numerical investigation of incompressible flow in grooved channels. Part 2. Resonance and oscillatory heat-transfer enhancement , 1986, Journal of Fluid Mechanics.

[9]  K. Mushatet.  SIMULATION OF TURBULENT FLOW AND HEAT TRANSFER OVER A BACKWARD-FACING STEP WITH RIBS TURBULATORS , 2011 .

[10]  Masoud Mirzaei,et al.  Experimental study of separation bubble control behind a backward-facing step using plasma actuators , 2015 .

[11]  S. Sarvari,et al.  Turbulent forced convection flow adjacent to inclined forward step in a duct , 2009 .

[12]  John Sheridan,et al.  An experimental investigation of the recirculation zone formed downstream of a forward facing step , 2010 .

[13]  J. F. Largeau,et al.  Wall pressure fluctuations and topology in separated flows over a forward-facing step , 2006 .

[14]  Numerical investigation of entropy generation in laminar forced convection flow over inclined backward and forward facing steps in a duct under bleeding condition , 2014 .

[15]  R. Henderson,et al.  Three-dimensional instability in flow over a backward-facing step , 2000, Journal of Fluid Mechanics.

[16]  Jae Min Hyun,et al.  Forced convection heat transfer from two heated blocks in pulsating channel flow , 1998 .

[17]  T. Sheu,et al.  Eddy structures in a transitional backward-facing step flow , 2007, Journal of Fluid Mechanics.

[18]  Paul Fischer,et al.  Direct simulation of turbulent heat transfer in swept flow over a wire in a channel , 2011 .

[19]  Goodarz Ahmadi,et al.  Thermal performance of nanofluid in ducts with double forward-facing steps , 2015 .

[20]  F. Durst,et al.  Backward-Facing Step Flows for Various Expansion Ratios at Low and Moderate Reynolds Numbers , 2004 .

[21]  J. Khodadadi,et al.  Computational Study of Turbulent Forced Convection Flow in a Square Cavity with Ventilation Ports , 2011 .

[22]  Hussein A. Mohammed,et al.  Experimental and numerical study of nanofluid flow and heat transfer over microscale backward-facing step , 2014 .

[23]  Hsuan-Tsung Hsieh,et al.  Turbulent separated convection flow adjacent to backward-facing step—effects of step height , 2006 .

[24]  P. Mello,et al.  Heat transfer and pressure drop correlations for finned plate ceramic heat exchangers , 2015 .

[25]  D. Spalding,et al.  A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows , 1972 .

[26]  H. Kahalerras,et al.  Mixed convection in a channel provided with heated porous blocks of various shapes , 2010 .