Numerical Study of Laminar and Turbulent Flow in a Structured Rough Nondimensional Channel using Les-wale Model

Abstract

Present study is conducted to understand the fluid flow behavior and effect of various changes in geometric parameters on flow properties in 2-D mini-channel. To analyze the

flow numerically turbulent model Large Eddy Simulation (LES) is employed. The objec- tive of this analysis is to find the changes in friction factor, pressure variation and eddies

formation with respect to changes in Reynolds number for roughness spacing (s) of 4.5h,

10h and 20h by keeping the amplitude (h) and width (b) constant. For the analysis rect- angular and hemispherical roughness cavity shape is introduces. Each channel is analyzed

for three Reynolds number 1500, 2000, 3000 such that the analysis can cover laminar and turbulent region. Analysis also include understanding the effect of secondary flow which is responsible for the change in magnitude of the turbulence and Eddies. At spacing 4.5h

turbulence increases for both the shape of the cavity at same Reynolds number but hemi- spherical cavity produces higher eddies in comparison to rectangular cavity. Therefore

friction factor is higher in case of hemispherical cavity than rectangular cavity. Friction factor increase by almost 20% in case of hemispherical cavity in comparison to rectangular cavity. An attempt is also made to understand the flow transition in a channel by using FFT (Fast Fourier Transform) and Phase Portrait. Phase plot for Reynolds number 3000 shows that the flow is chaotic in nature for both rectangular and hemispherical roughness.