Turbulence characteristic evolution in jets interacting with viscoplastic fluids

Abstract

We experimentally study the dynamics of a horizontal jet of a Newtonian fluid injected into a viscoplastic ambient fluid (Carbopol gel) to simulate jet cleaning in plug and abandonment operations of oil and gas wells. The jet flow is analyzed using high-speed imaging, planar laser induced fluorescence, and time-resolved tomographic particle image velocimetry techniques to capture concentration and velocity fields with high spatial and temporal resolution. By varying the Reynolds and Bingham numbers, we analyze three recently identified flow regimes, i.e., mixing, mushroom, and fingering, focusing on their mixing index, velocity fields, fluctuation intensity, half-radius, vorticity, Reynolds stresses, probability density functions, and statistical moments (skewness and kurtosis). In the mixing regime, velocity and vorticity symmetry, axisymmetric mixing, and dominant axial Reynolds stresses align with Newtonian empirical correlations. The mushroom regime shows slight asymmetry, reduced mixing from turbulence suppression by yield stress, and moderate turbulence, while the fingering regime features pronounced asymmetry, erratic fluctuations, and suppressed velocity due to viscoplastic resistance. Self-similarity analysis of velocity, concentration, and Reynolds stress profiles confirms strong scaling in the mixing regime, partial scaling in the mushroom regime, and deviations in the fingering regime, where viscoplastic effects disrupt jet structure and turbulence.