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Numerical Simulation of Flow and Heat Transfer
Modeling and Simulation of Turbulent Drag Reduction Flow by Surfactant
Modeling and simulation of turbulent drag reduction is performed by adding a surfactant to clarify the resistance-reducing mechanism. Simultaneously, heat transfer analysis is performed to investigate the flow and heat transfer characteristics in detail.
Content of research
The significant drag reduction in turbulent channels due to the addition of a small amount of long-chain polymers or surfactants that form rod micelles in water, is known as Toms effect. A model that simulates polymers with small dumbbell-shaped elements was constructed, and direct numerical simulation (DNS) of turbulent flow in a two-dimensional channel was performed using this model to reproduce Toms effect. It was shown that the discrete element has two mechanisms: one is a resistance reduction mechanism due to the longitudinal vortex damping, and the other is a resistance increasing mechanism due to the additional stress near the wall. Furthermore, by adding the effect of cutting the element to which a strong force is applied, we were able to reproduce the feature that drag reduction occurs in a specific Reynolds number range.
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The friction coefficient vs Reynolds number
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It can be seen that turbulence element near the wall is attenuated by adding drag reducing elements (the figure shows velocity vectors on the cross section perpendicular to the flow and colors represent the pressure).
Potential for social implementation
- ・Reduction of flow resistance in pipes
- ・Turbulent boundary layer resistance source
- ・Heat transfer promotion
Appealing points to industry and local governments
This model can clarify the mechanism of turbulent drag reduction by surfactants and predict flow and heat transfer. The model can be used to reduce the running cost of district heating and cooling systems by reducing the flow resistance.
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