Experimental Determination of Transition to Turbulence in a Rectangular Channel With Eddy Promoters

Abstract

We report on laminar-to-turbulent transition in a rectangular channel in the presence of periodically placed cylindrical eddy promoters. Transition is identified through the analysis of power spectral density (PSD) of velocity fluctuations. Placement of the eddy promoters in the channel, depending on the geometric configuration, can significantly reduce the value of Reynolds number at transition. The critical Reynolds number (based on the average velocity and the channel height) ranges from 1500 (for an unobstructed channel) to about 400 (for the most unstable configuration we have deployed). For all the configurations tested, demarcation of transition can be correlated with the expression: Reτ ≡ τw,αv/ρ H / 2 / ν = 44 ̃ 51, where τ w,αv is the spatially averaged value of mean wall shear stress and H is the channel height.