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International Journal of Fluid Mechanics Research
ESCI SJR: 0.206 SNIP: 0.446 CiteScore™: 0.5

ISSN Print: 2152-5102
ISSN Online: 2152-5110

International Journal of Fluid Mechanics Research

DOI: 10.1615/InterJFluidMechRes.v25.i1-3.180
pages 212-219

Rough-Wall Heat Transfer in Tbrbulent Boundary Layers

M. H. Hosni
Department of Mechanical Engineering, Kansas State University, Manhattan, USA
H. W. Coleman
Mechanical Engineering Department, University of Alabama in Huntsville, Huntsville, USA
Robert P. Taylor
Mechanical Engineering Department, Mississippi State University, Mississippi State, MS, USA 39762

ABSTRACT

Measurements for heat transfer in the rough wall turbulent boundary layers are presented. This paper summarizes the previous experimental results for six test surfaces five rough and one smooth. Three of the rough surfaces are smooth plates roughened with hemispherical elements uniformly distributed 2, 4, and 10 base diameters apart. The remaining two rough surfaces are smooth plates roughened with truncated, right circular cones uniformly distributed 2 and 4 base diameters apart. Both of the roughness geometries hemispheres and truncated cones have a 1.27 mm base diameter and a roughness height of 0.635 mm. The Stanton number data are for zero pressure gradient incompressible turbulent boundary layer air flow for several freestream velocities ranging from 6 to 66 m/s which cover the aerodynamically smooth transitionally rough and fully rough flow regimes. These data are compared with previously published results from another similar test facility using a rough surface comprised of spheres of a single size (1.27 mm diameter) packed in the most dense array. It is shown that data for a given rough surface viewed in Stanton number versus enthalpy thickness coordinates do not collapse to a single curve in the fully rough regime as had been postulated based on observations of a single set of rough wall data. The heat transfer data also show that for a given surface Stanton number data in Rex, coordinates approach an asymptotic curve as freestream velocity is increased, becoming a function of Rex, alone (as in the case for smooth wall turbulent flows). However, there is a different asymptotic St-Rex curve for each rough surface, with Stanton number at a given Rex, increasing with decreasing roughness spacing, that is as the surface becomes "rougher". The data also show a measurable difference in Stanton numbers due to roughness elements shape effects.


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