Slip Length Of Flow Research Articles

Influence of incompressible surfactant on drag in flow along an array of gas-filled grooves

Surfactants can have a detrimental effect on the drag reduction in shear flow over superhydrophobic surfaces in the Cassie state. Assuming an incompressible, inviscid surfactant phase at the gas-liquid interfaces, we study liquid flow over an array of narrow gas-filled grooves embedded in an otherwise planar surface, with the gas-liquid interface protruding above or below the plane. A recirculating flow develops at the gas-liquid interfaces, such that the slip length for flow over such surfaces is much smaller than at corresponding surfactant-free interfaces.

Modified smoothed particle hydrodynamics approach for modelling dynamic contact angle hysteresis

Dynamic wetting plays an important role in the physics of multiphase flow, and has a significant influence on many industrial and geotechnical applications. In this work, a modified smoothed particle hydrodynamics (SPH) model is employed to simulate surface tension, contact angle and dynamic wetting effects at meso-scale. The wetting and dewetting phenomena are simulated in a capillary tube, where the liquid particles are raised or withdrawn by a shifting substrate. The SPH model is modified by introducing a newly developed viscous force formulation at the liquid–solid interface to reproduce the rate-dependent behaviour of the moving contact line. Dynamic contact angle simulations with the interfacial viscous force are conducted to verify the effectiveness and accuracy of this new formulation. In addition, the influence of interfacial viscous forces with different magnitude on the contact angle dynamics is examined by empirical power-law correlations; the derived constants suggest that the dynamic contact angle changes monotonically with the interfacial viscous force. The simulation results are consistent with experimental observations and theoretical predictions, implying that the interfacial viscous force can be associated with the slip length of flow and the microscopic surface roughness. This work demonstrates that the modified SPH model can successfully account for the rate-dependent effects of a moving contact line, and can be used for realistic multiphase flow simulations under dynamic conditions.

Effects of Channel Scale on Slip Length of Flow in Micro/Nanochannels

The concept of slip length, related to surface velocity and shear rate, is often used to analyze the slip surface property for flow in micro- or nanochannels. In this study, a hybrid scheme that couples molecular dynamics simulation (used near the solid boundary to include the surface effect) and a continuum solution (to study the fluid mechanics) is validated and used for the study of slip length behavior in the Couette flow problem. By varying the height of the channel across multiple length scales, we investigate the effect of channel scale on surface slip length. In addition, by changing the velocity of the moving-solid wall, the influence of shear rate on the slip length is studied. The results show that within a certain range of the channel heights, the slip length is size dependent. This upper bound of the channel height can vary with the shear rate. Under different magnitudes of moving velocities and channel heights, a relative slip length can be introduced, which changes with channel height following a logarithmic function, with the coefficients of the function being the properties of the fluid and wall materials.