Investigations on the Effect of Backward-Facing and Forward-Facing Steps on Turbulent Mixed-Convection Flow Over a Flat Plate

The effects of backward-facing and forward-facing steps on a turbulent buoyancy-dominated mixed-convection flow over a flat plate are examined experimentally. Air velocity and temperature distributions and their turbulent fluctuations are measured simultaneously by using a two-component laser-Doppler velocimeter and a cold wire anemometer, respectively. The experiment was carried out for a step (backward-facing/forward-facing) height of 22 mm, a temperature difference, ΔT, of 30°C between the heated walls and the free-stream air (corresponding to a local Grashof number Gr xi = 6.45 × 1010), and a free-stream velocity of 0.48 m/s. It was found that the introduction of backward- and forward-facing steps increases the turbulence intensity of the velocity and temperature fluctuations downstream of the step. The present results also reveal that the maximum local Nusselt number occurs in the vicinity of the reattachment zone, and it is approximately twice for the case of the backward-facing step and three times for the case of the forward-facing step than that of the flat plate value at similar flow and thermal conditions.

[1]  Toshihiro Tsuji,et al.  Turbulence measurements in a natural convection boundary layer along a vertical flat plate , 1988 .

[2]  Terrence W. Simon,et al.  Evaluation of local wall temperature, heat flux, and convective heat transfer coefficient from the near-wall temperature profile , 1995 .

[3]  T. Tsuji,et al.  Effects of freestream on turbulent combined-convection boundary layer along a vertical heated plate , 2001 .

[4]  Robert J. Moffat,et al.  Describing the Uncertainties in Experimental Results , 1988 .

[5]  B. Armaly,et al.  Measurements of laminar mixed convection flow over a horizontal forward-facing step , 1993 .

[6]  B. Armaly,et al.  EFFECTS OF FREE-STREAM VELOCITY ON TURBULENT NATURAL-CONVECTION FLOW ALONG A VERTICAL PLATE , 2000 .

[7]  John K. Eaton,et al.  Combined Heat Transfer and Fluid Dynamic Measurements Downstream of a Backward-Facing Step , 1985 .

[8]  B. Armaly,et al.  Measurements in Buoyancy-Assisting Separated Flow Behind a Vertical Backward-Facing Step , 1993 .

[9]  Ken-ichi Abe,et al.  A new turbulence model for predicting fluid flow and heat transfer in separating and reattaching flows—I. Flow field calculations , 1995 .

[10]  T. Inagaki.  HEAT TRANSFER AND FLUID FLOW OF TURBULENT NATURAL CONVECTION ALONG A VERTICAL FLAT PLATE WITH A BACKWARD-FACING STEP , 1994 .

[11]  H. I. Abu-Mulaweh, T. S. Chen, B. F. Armaly.  EFFECTS OF FREE-STREAM VELOCITY ON TURBULENT NATURAL-CONVECTION FLOW ALONG A VERTICAL PLATE , 2000 .

[12]  Hosni I. Abu-Mulaweh,et al.  Turbulent mixed convection flow over a backward-facing step , 2001 .

[13]  Hosni I. Abu-Mulaweh,et al.  Turbulent mixed convection flow over a backward-facing step - the effect of the step heights , 2002 .

[14]  B. Armaly,et al.  Measurements and Predictions of Laminar Mixed Convection Flow Adjacent to a Vertical Surface , 1985 .

[15]  B. Armaly,et al.  Turbulent natural convection flow over a backward-facing step , 1999 .