Detecting turbulent patterns in particulate pipe flow by streak-angle visualization

Abstract

Detecting the transition from laminar to turbulent flow in particulate pipe systems remains a complex issue in fluid dynamics, often requiring sophisticated and costly experimental apparatus. This research presents an innovative streak visualization method designed to offer a simple and robust approach to identify transitional turbulent patterns in particulate pipe flows with neutrally buoyant particles. The technique employs a laser arrangement and a low-cost camera setup to capture particle-generated streaks within the fluid, enabling the capture of the temporal evolution of flow patterns. The novelty of the method lies in identifying laminar and turbulent flow patterns from the statistical properties of streak-angle distributions. Validation of the proposed method was conducted through comparison with established techniques like particle image velocimetry (PIV) and pressure drop measurements, confirming its accuracy and reliability. Experiments demonstrate the streak visualization method’s capacity to differentiate between laminar, transitional, and turbulent flow regimes by analysing the standard deviation of streak angles. The method is applicable across a wide range of particle concentrations, as long as the statistical distributions of laminar and turbulent patterns differ, making it versatile where other methods may face limitations. Furthermore, this technique enables us to identify a critical Reynolds number using the Kullback–Leibler divergence built on the statistical distribution of streak angles, which is consistent with previous studies. This streak visualization method offers potential for analysing particulate pipe flows in both laboratory environments and specific industrial scenarios, especially when the fluid is transparent and particles are either naturally occurring or added as tracers.