Laminar–Turbulent Transition in Yield-Stress Fluids in Channel and Pipe Flow: Experimental and DNS Study

We perform direct numerical simulations (DNS) to investigate the transition from laminar to turbulent flow in a pressure-driven pipe flow of a Herschel–Bulkley fluid, characterized by yield stress (τ_Y ), consistency index (K), and power-law index (n). The simulations span generalized Reynolds numbers from Re_G = 378 to 4488 and resolve the full transition dynamics by solving the Cauchy momentum equation with Herschel-Bulkley constitutive relation. Turbulence intensity, plotted as a function of the generalized Reynolds number (Re_G), shows earlier onset near the walls (r/R = ±0.75) compared to the centerline, with a sharp, uniform drop during relaminarization. DNS results align closely with experimental observations for 0.1% Carbopol, underscoring the influence of shear-thinning rheology on transitional flow behavior. We further conduct DNS of pipe flow with high yield-stress fluids to explore the onset and evolution of transition. We also present an experimental investigation of laminar–turbulent transition in channel flow of a yield-stress shear-thinning fluid using Particle Image Velocimetry (PIV), along with DNS study. The test section is a 3.6-meter-long acrylic channel designed for fully developed flow, and the working fluid is an aqueous Carbopol (∼ 0.1%) exhibiting Herschel–Bulkley rheology. PIV measurements capture velocity fields, turbulence intensity, and asymmetries across the channel to identify transition thresholds and plug breakdown dynamics.