Experimental investigation on the effects of surfactant on a turbulent boundary layer flow Roi Gurka1, Alex Liberzon2, Gad Hetsroni3 (original) (raw)
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Experimental investigation on the effects of surfactant on a turbulent boundary layer flow
We investigated the influence of low concentration, bio-degradable surfactant solution in a turbulent boundary layer in a flume, by using Particle Image Velocimetry (PIV). The flow was measured in the spanwise-streamwise plane (x-z). The results present a comparison between water and surfactant solution flow at the same flow rate, as characterized by the Reynolds stress, turbulent energy production and auto-correlation functions. The results shown here complement the previously reported effects related to the decorrelation between the streamwise and the spanwise velocity components and following strong suppression of the turbulent kinetic energy production. In the present investigation we extend the existing results related to the Reynolds stresses and the turbulent kinetic energy production term in the streamwise-spanwise plane of a turbulent boundary layer in a flume. In addition, proper orthogonal decomposition (POD) was applied to the fields of out-of-plane vorticity component and the comparison between the linear combinations of the first three POD modes is shown for the water and surfactant solution flows.
International Journal of Heat and Fluid Flow, 2002
The turbulent frictional drag of water can be reduced dramatically by adding small amounts of drag-reducing materials, such as polymers or surfactants. As a percentage drag reduction of 80% can easily be achieved, this technique is thought to be the most practical method of reducing turbulent frictional drag. In this work, a double pulse particle image velocimetry (PIV) system was used to clarify the spatial velocity distribution of surfactant solution flow in a two-dimensional channel. A type of cationic surfactant cetyltrimethyl ammonium chloride (C 16 H 33 N(CH 3 ) 3 Cl) mixed with the same weight of counter-ion material NaSal (HOC 6 H 4 COONa) was used as a drag-reducing additive to water at a mass concentration of 40 ppm. Instantaneous velocity distribution taken by PIV was examined to clarify the effect of surfactant. It was found that the instantaneous velocity distribution taken in water flow exhibits penetration from the low-speed fluid region into the high-speed region, which is one of the important events of turbulence energy production and turbulent mixing. Although this structure is commonly observed in water flow, it was not found in drag-reducing flow under the same Reynolds number. The strong vorticity fluctuation near the wall also disappeared and the integral length scale in streamwise direction of turbulent fluctuation had a smaller value in surfactant solution flow. Ó
Effect of Surfactants on Free-Surface Turbulent Flows
Journal of Fluid …, 2004
In two earlier papers, we studied the statistical and mechanistic structure of the tur-bulent boundary layer under a stress-free (clean) free surface. Findings there, such as the presence of inner and outer surface layers, are very much the direct result of the absence of shear stresses at ...
Experimental Investigation on Effects of Surface Roughness Geometry Affecting to Flow Resistance
ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011
We investigated the influence of low concentration, bio-degradable surfactant solution in a turbulent boundary layer in a flume, by using Particle Image Velocimetry (PIV). The flow was measured in the spanwise-streamwise plane (x-z). The results present a comparison between water and surfactant solution flow at the same flow rate, as characterized by the Reynolds stress, turbulent energy production and auto-correlation functions. The results shown here complement the previously reported effects related to the decorrelation between the streamwise and the spanwise velocity components and following strong suppression of the turbulent kinetic energy production. In the present investigation we extend the existing results related to the Reynolds stresses and the turbulent kinetic energy production term in the streamwise-spanwise plane of a turbulent boundary layer in a flume. In addition, proper orthogonal decomposition (POD) was applied to the fields of out-of-plane vorticity component and the comparison between the linear combinations of the first three POD modes is shown for the water and surfactant solution flows.
Drag Reduction by Surfactant in Closed Turbulent Flow
HAL (Le Centre pour la Communication Scientifique Directe), 2010
Many surfactants and polymers are considered as excellent drag reducing agents. This phenomenon induces a significant head loss reduction compared to the pure solvent. In this study an aqueous solution of CTAC/NaSal (CetylTrimethyl Ammonium Chloride and Sodium Salicylate) is used in turbulent pipe flow system. Drag reduction experiments were carried out for different experimental conditions using pressure drop measurements. At the same time the spatial velocity distribution was measured and analysed using particle image velocimetry (PIV).
Effect of surfactant-laden droplets on turbulent flow topology
Physical Review Fluids, 2020
In this work we investigate flow topology modifications produced by a swarm of large surfactant-laden droplets released in a turbulent channel flow. Droplets have the same density and viscosity of the carrier fluid, so only surface tension effects are considered. We run one single-phase flow simulation at Re τ = ρu τ h/μ = 300 and ten droplet-laden simulations at the same Re τ with a constant volume fraction 5.4%. For each simulation, we vary the Weber number We (ratio between inertial and surface tension forces) and the elasticity number β s (parameter that quantifies the surface tension reduction). We use direct numerical simulations of turbulence coupled with a phase-field method to investigate the role of capillary forces (normal to the interface) and Marangoni forces (tangential to the interface) on turbulence (inside and outside the droplets). As expected, due to the low volume fraction of droplets, we observe minor modifications in the macroscopic flow statistics. However, we observe major modifications of the vorticity at the interface and important changes in the local flow topology. We highlight the role of Marangoni forces in promoting an elongational type of flow in the dispersed phase and at the interface. We provide detailed statistical quantification of these local changes as a function of the Weber number and elasticity number, which may be useful for simplified models.
The decay of grid turbulence in polymer and surfactant solutions
Physics of Fluids, 1999
The decay of turbulence behind a towed grid is studied in polymer and surfactant solutions with the use of particle image velocimetry. Unlike in water, the turbulent energy components show marked anisotropy, and decay more slowly. These differences are stronger for initial periods of time, but persist through the entire period of decay. The major difference between the polymer and surfactant solutions is that the small scales are more strongly damped in the former.
Engineering reports, 2020
Particle image velocimetry (PIV) measurement technique provides an excellent opportunity for investigating instantaneous spatial structures which are not always possible with point measurements techniques like laser Doppler velocimetry. In this review, it was shown that PIV technique provides an effective means of visualizing important structures of Newtonian and drag-reducing fluid flows. Such structures include large-scale-events that constitute an important portion of the Reynolds stress tensor; shear layers of drag-reducing flows, which have been suggested to constitute the mechanism of drag reduction (DR); and near wall vortices/low speed streaks which constitute the mechanism of turbulence production. PIV investigations of turbulence statistics in Newtonian and drag-reducing fluid flows were reviewed with the view of providing explanation to DR by additives. Results of turbulence statistics, for Newtonian fluid flow, showed that streamwise velocity fluctuations and turbulence intensity had peak values close to the wall, in a region of high mean velocity gradient, while radial fluctuating velocity and Reynolds stress tensor had peaks further from the wall and at approximately the same detachment from the wall. In single-and two-phase flows in horizontal channels, the velocity profile of polymer solution, in the turbulent regime, show asymmetric behavior. This review highlighted important interfacial characteristics in gas-liquid flows such as S-shaped velocity profile as well as the turbulences statistics in each phase and across the interface region. Drag-reducing agents (DRAs)-imposed changes on turbulence statistics and flow structures were also examined. PIV studies of drag-reducing flows showed that DRAs act to dampen wall-normal-, streamwise fluctuating velocity, and Reynolds stress tensor. The reduction in Reynolds stress tensor is higher than the reduction of both wall-normal and streamwise velocity fluctuations and this discrepancy has been associated with the decorrelation of the component of fluctuating velocity. Furthermore, the addition of DRA produces a shift of the peak of wall-normal velocity fluctuations further from the wall due to increased buffer layer thickness. DRAs do not only act to reduce drag but also to modify the flow structure. The major influence of DRAs on flow structures is seen in the This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.