Abstract
Velocity, turbulent intensity, static pressure and temperature measurements over the flat plate and blocked surfaces were investigated in a low speed wind tunnel in the presence of free stream velocity and block height. The experiments were carried out for free stream velocities of 5, 7 and 10 m/s encompassing the transitional region and for block heights of 10, 15 and 20 mm forming the different flow samples. A constant-temperature anemometer, a micro-manometer and copper-constant thermocouples were used for measurements of velocity and turbulent intensity, static pressure and temperature, respectively. The results showed that the flow separations and reattachments occurred on the blocked surfaces which enhanced the average heat transfer up to 1.54, 1.71 and 1.84 fold of the flat plate value at 5 m/s for the rising block height, 1.49, 1.68 and 1.80 at 7 m/s, and 1.44, 1.63 and 1.78 at 10 m/s, respectively.
Similar content being viewed by others
Abbreviations
- Cp :
-
Pressure coefficient, dimensionless
- h:
-
Convective heat transfer coefficient, W/m2K
- h:
-
Block height, mm
- H:
-
Shape factor, dimensionless
- H:
-
Channel height, mm
- K:
-
Thermal conductivity, W/mK
- Nu:
-
Nusselt number, dimensionless
- P:
-
Pressure, Pa
- Pr :
-
Prandtl number, dimensionless
- q:
-
Heat flux, W/m2
- Re x :
-
Streamwise distance Reynolds number, dimensionless
- Re θ :
-
Momentum thickness Reynolds number, dimensionless
- Re H :
-
Channel height Reynolds number, dimensionless
- s:
-
Block spacing, mm
- Tu:
-
Turbulence level, %
- T:
-
Temperature, °C
- u:
-
Streamwise velocity, m/s
- urms :
-
Root mean square velocity, m/s
- U:
-
Mean free stream velocity, m/s
- w:
-
Block width, mm
- W:
-
Channel width, mm
- x:
-
Streamwise directions, mm
- xl :
-
Unheated starting length, mm
- XF :
-
Length of the recirculation region of downstream surface of the first block, mm
- XR :
-
Reattachment length of the recirculation region of upstream surface of the last block, mm
- XT :
-
Length of the recirculation region of top face of the first block, mm
- y:
-
Pitch wise directions, mm
- γ:
-
Intermittency factor, dimensionless
- δ:
-
Boundary layer thickness, mm
- θ:
-
Momentum thickness, mm
- ρ:
-
Density, kg/m3
- o:
-
Flow-off
- f:
-
Flow-on
- in:
-
Inlet
- L:
-
Laminar
- T:
-
Turbulent
- 0:
-
Free stream
- w:
-
Wall
- f:
-
Flat
References
Liou TM, Wu YY, Chang Y (1993) LDV measurements of periodic fully developed main and flows in a channel with rib-disturbed walls. ASME J Fluids Eng 115:109–114
Bilen K, Yapici S (2002) Heat transfer from a surface fitted with rectangular blocks at different orientation angle. Heat Mass Transf 38:649–655
Lee CK, Abdel-Moneim SA (2001) Computational analysis of heat transfer in turbulent flow past a horizontal surface with two-dimensional ribs. Int Commun Heat Mass Transf 28:161–170
Wang L, Sunden B (2007) Experimental investigation of local heat transfer in a square duct with various-shaped ribs. Heat Mass Transf 43:759–766
Igarashi T, Takasaki H (1992) Fluid flow around three rectangular blocks in a flat-plate laminar boundary layer. Exp Heat Transf 5:17–31
Grigoriadis DGE, Kassinos SC (2009) Lagrangian particle dispersion in turbulent flow over a wall mounted obstacle. Int J Heat Fluid Flow 30:462–470
Tropea CD, Gackstatter R (1985) The flow over two-dimensional surface-mounted obstacles at low Reynolds numbers. ASME J Fluids Eng 107:489–494
Wahidi R, Chakrouni W, Al-Fahed S (2005) The behavior of the skin-friction coefficient of a turbulent boundary layer flow over a flat plate with differently configured transverse square grooves. Exp Therm Fluid Sci 30:141–152
Hsieh KJ, Lien FS (2005) Conjugate turbulent forced convection in a channel with an array of ribs. Int J Numer Methods Heat Fluid Flow 15:462–482
Tsia WB, Lin WW, Cheng CC (2000) Computation of enhanced turbulent heat transfer in a channel with periodic ribs. Int J Numer Methods Heat Fluid Flow 10:47–66
Alves TA, Altemani CAC (2010) Thermal design of a protruding heater in laminar channel flow. In: Proceedings of 14th international heat transfer conference, Washington, DC 14:1–10. DOI: http://doi.org/10.1115/IHTC14-22906
Chen YM, Wang KC (1998) Experimental study on the forced convective flow in a channel with heated blocks in tandem. Exp Therm Fluid Sci 16:286–298
Kim SH, Anand NK (1994) Turbulent heat transfer between a series of parallel plates with surface-mounted discrete heat sources. ASME J Heat Transf 116:577–587
Braun H, Neumann H, Mitra NK (1999) Experimental and numerical investigation of turbulent heat transfer in a channel with periodically arranged rib roughness elements. Exp Therm Fluid Sci 19:67–76
Yuan ZX (2000) Numerical study of periodically turbulent flow and heat transfer in a channel with transverse fin arrays. Int J Numer Methods Heat Fluid Flow 10:842–861
Anderson AM (1997) A comparison of computational and experimental results for flow and heat transfer from an array of heated blocks. ASME J Electron Packag 119:32–39
Perng S-W, Wu H-W (2008) Numerical investigation of mixed convective heat transfer for unsteady turbulent flow over heated blocks in a horizontal channel. Int J Therm Sci 47:620–632
Beig SA, Mirzakhalili E, Kowsari F (2011) Investigation of optimal position of a vortex generator in a blocked channel for heat transfer enhancement of electronic chips. Int J Heat Mass Transf 54:4317–4324
Ryu DN, Choi DH, Patel VC (2007) Analysis of turbulent flow in channels roughened by two-dimensional ribs and three-dimensional blocks Part I: resistance. Int J Heat Fluid Flow 28:1098–1111
Herman C, Kang E (2001) Comparative evaluation of three heat transfer enhancement strategies in a grooved channel. Heat Mass Transf 37:563–575
Kline SJ, McClintock FA (1953) Describing uncertainties in single sample experiments. Mech Eng 75:3–8
Atli V (1988) Subsonic flow over a two dimensional obstacle immersed in a turbulent boundary layer on a flat surface. J Wind Eng Ind Aerodyn 31:225–239
Umur H, Ozalp AA (2006) Fluid flow and heat transfer in transitional boundary layers: effects of surface curvature and free stream velocity. Heat Mass Transf 43:7–15
Sinha SN, Gupta AK, Oberai MM (1981) Laminar separating flow over backsteps and cavities Part I: backsteps. AIAA J 19:1527–1530
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Yemenici, O., Firatoglu, Z.A. Transitional boundary layer flow and heat transfer over blocked surfaces with influence of free stream velocity and block height. Heat Mass Transfer 49, 1637–1646 (2013). https://doi.org/10.1007/s00231-013-1208-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00231-013-1208-x