## THERMAL SCIENCE

International Scientific Journal

### SIMULATION OF TURBULENT FLOW AND HEAT TRANSFER OVER A BACKWARD FACING STEP WITH RIBS TURBULATORS

**ABSTRACT**

Simulation is presented for a backward facing step flow and heat transfer inside a channel with ribs turbulators. The problem was investigated for Reynolds numbers up to 32000. The effect of a step height, the number of ribs and the rib thickness on the flow and thermal field were investigated. The computed results are presented as streamlines counters, velocity vectors and graphs of Nusselt number and turbulent kinetic energy variation. A control volume method employing a staggered grid techniques was imposed to discretize the governing continuity, full Navier Stockes and energy equations. A computer program using a SIMPLE algorithm was developed to handle the considered problem. The effect of turbulence was modeled by using a k-є model with its wall function formulas. The obtained results show that the strength and size of the re-circulation zones behind the step are increased with the increase of contraction ratio(i.e. with the increase of a step height). The size of recirculation regions and the reattachment length after the ribs are decreased with increasing of the contraction ratio. Also the results show that the Reynolds number and contraction ratio have a significant effect on the variation of turbulent kinetic energy and Nusselt number.

**KEYWORDS**

PAPER SUBMITTED: 2009-09-26

PAPER REVISED: 2010-05-04

PAPER ACCEPTED: 2010-06-06

**THERMAL SCIENCE** YEAR

**2011**, VOLUME

**15**, ISSUE

**1**, PAGES [245 - 255]

- Lio, T., Hwang, J., Developing Heat Transfer and Friction in a Ribbed Rectangular Duct with Flow Separation at Inlet, ASME J. Heat Transfer, 114(1992), pp.546-573.
- Wang, B., Zhang, H.Q, Wang, X.L, Large Eddy Simulation of Particle Response to Turbulence Along its Trajectory in a Backward-Facing Step Turbulent Flow, Int. J. Heat and Mass Transfer, 49(2006), pp. 415-420.
- Nie, J.H., Armaly, B.F., Three Dimensional Convective Flow Adjacent to a Backward Facing Step-Effects of Step Height, Int. J. Heat Mass Transfer, 45(2002), pp.2431-2438.
- Thangam, S., Knight, D., Effect of Step Height on the Separated Flow Past a Backward Facing Step, Phys. Fluids, 3(1989), pp.604-606,.
- Chen, Y.T., Nie, J.H, Hseih, H.T, Sun, L.J., Three Dimensional Convective Flow Adjacent to Inclined Backward Facing Step, Int. J. Heat and Mass Transfer, 49(2006), pp. 4795-4803.
- KE Feng, Liu Ying-Zheng, Chen Han-Ping, Simultaneous Flow Visualization and Wall Pressure Measurement of The Turbulent Separated and Reattachment Flow Over a Backward Facing Step, Journal of Hydrodynamics, 119(2007), pp.108-187.
- Han, J.C, Heat Transfer and Friction Characteristics in Rectangular Channels with Rib Turbulators, ASME Journal of Heat Transfer, 110 (1988), pp. 91-98.
- Rau, G., Cakan, M., Moeller, D. and Arts, T. ,The Effect of Periodic Ribs on the Local Aerodynamics and Heat Transfer Performance of a Straight Cooling Channel, ASME Journal of Turbo machinery, 120(1988), pp. 368-375.
- Webb, R.L, Eckert, E.R.G., and Goldsten, R.J., Heat transfer and Friction in Tubes with Repeated Rib Roughness, International Journal of Heat and Mass, 14(1984), pp. 601-617.
- Lio, T.M, Hwang, G.G. and Chen, S.H., Simulation and Measurements of Enhanced Turbulent Heat Transfer in Channels with Periodic Ribs on One Principal Wall", International Journal of Heat Mass Transfer, 36(1997), pp. 507-507.
- Han, J.C. and Park, J.S., Developing Heat Transfer Through Rectangular Channels with Rib Turbulators, International Journal of Heat mass Transfer, 31(1988), pp. 183-194.
- Tsai, W.B, Lin, W.W, Chieng, C.C., Computation of Enhanced Turbulent Heat Transfer in a Channel With Periodic Ribs, Int. J. Numerical Methods for Heat and Fluid Flow, 36(1997), pp.507-517.
- Lacovides, H., Jackson, D.C., Kelemenis, G., Launder, B.E, Yaun, Y.M., Flow and Heat Transfer in a Rotating U-Bend with 45 Ribs, Int. J. Heat and Fluid Flow, 22(2001), pp. 308-314.
- Jones, W.P., Lunder, B.E., The Prediction of Laminarization with a Two Equation Model of Turbulence", J. Heat and Mass Transfer, 1972.
- Versteege, H.K., Malalasekera, W., An Introduction of Computational Fluid Dynamics, Hemisophere Publishing Corporation, United States of America, 1995.