Numerical investigation on turbulence statistics and heat transfer of a circular jet impinging on a roughened flat plate

A detailed numerical study of a three-dimensional impinging jet on a roughened isothermal surface is investigated from flow physics vantage point under the influence of different parameters. The effects of Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer are studied. Additionally, the relations between average heat transfer coefficient and flow physics including flow vortices, wall shear stress and turbulence intensity with thermodynamic non-equilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of a rib to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three radial locations (R/D) =1, 1.5 and 2 and at each location its height (i.e. width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study employed a jet angle (a) of 90°, jet-to-target distance ( H/D=6) and Re ranges from 10,000 to 50,000. The results show that the average heat transfer coefficient can be significantly affected by changing the geometry and dimensions of the roughness element. An enhancement of 29.6% in the average heat transfer coefficient was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. Furthermore, the numerical data was correlated by an empirical equation to obtain average heat transfer coefficient as a function of Re, R/D and e/D.