Influence Of Lift Force Research Articles

Influence of lift forces on particle capture on a functionalized surface

Numerous situations involve the capture of particles onto a functionalized surface in a laminar flow, such as classical biomedical assays, lab on a chip devices or even biological research protocols. Being able to control this capture is thus an important issue that we address in this paper. We focus on a simple and widely used geometry, the straight microfluidic channel, in which particles undergo two weak effects: diffusion towards the functionalized surface and lift forces expelling them away from it. We show that the competition between these two weak mechanisms yields strongly different capture behavior whose occurrence depends on the value of a new lifto-diffusive dimensionless number $${\mathcal {N}}_{\text {LD}}$$ . We show that tuning the flow rate and the channel dimension to get proper values of this number allow to trigger, via a pure hydrodynamic effect, the capture or non-capture of particles on surfaces. For example, we show that, under certain conditions, doubling the flow rate reduces the capture rate by four orders of magnitude. Additionally, we provide the particle distribution in the liquid along the channel, resulting from this competition, for different $${\mathcal {N}}_{\text {LD}}$$ values. We believe that this work opens new perspectives for analysis and biotechnology applications. More precisely, the proposed model should extend to any transverse force that can be written in the form of a potential energy.

Influence of forces on vehicle’s instability in floodwaters

Abstract Flood hazards to vehicle have become more frequent and noticeable in the recent years. Therefore, this paper aims at estimating the forces observed on a partially submerged vehicle in floodwater, namely frictional, buoyancy, lift and drag forces. An understanding of the relevant forces involved is necessary to attempt to characterize the instability thresholds of vehicles in floodwater flows. With that regards, a model vehicle with the scale ratio of 1:24 was used and a series of flume experiments were conducted. While determining the vertical pushing force, the influence of lift force was found insignificant due to sub-critical state of the flow. Moreover, the critical water depth at which the up-thrust force governed was observed when the water depth exceeded 0.042 m. Below critical depth, the vehicle stability governed unless the drag force imposed by the flowing water was lower than the frictional force between the tires and floodplain surface.

Fast reactor: an experimental study of thermohydraulic processes in different operating regimes

Results of integrated water model studies of temperature fields and a flow pattern of a nonisothermal primary coolant in the elements of the fast neutron reactor (hereinafter, fast reactor) primary circuit with primary sodium in different regimes, such as forced circulation (FC), transition to the reactor cooldown and emergency cooldown with natural coolant convection, are presented. It is shown that, under the influence of lift forces on the nonisothermal coolant flow in the upper chamber at the periphery of its bottom region over the side shields, a stable cold coolant isothermal zone is formed, whose dimensions increase with increase of total water flowrate. An essential and stable coolant temperature stratification is detected in the peripheral area of the upper (hot) chamber over the side shields, in the pressure and cold side chambers, in the elevator baffle, in the cooling system of the reactor vessel, and in the outlet of intermediate and autonomous heat exchangers in different operating regimes. Large gradients and temperature fluctuations are registered at the interface of stratified and recycling formations. In all of the studied cooldown versions, the coolant outlet temperature at the core fuel assembly is decreased and the coolant temperature in the peripheral zone of the upper chamber is increased compared to the FC. High performance of a passive emergency cooldown system of a fast reactor (BN-1200) with submersible autonomous heat exchangers (AHE) is confirmed. Thus, in a normal operation regime, even in case of malfunction of three submersible AHEs, the temperature of the equipment inside the reactor remains within acceptable limits and decay heat removal from the reactor does not exceed safe operation limits. The obtained results can be used both for computer code verification and for approximate estimate of the reactor plant parameters on the similarity criteria basis.

Influence of Lift Force on the Settling Velocities of Rotating Particles in Two-Dimensional Shear Flow

AbstractWe derive a simple theoretical model for estimating the change in the magnitude of the particle slip velocity and the deflection in the trajectory of a particle induced by the lift force acting on a freely rotating particle settling under gravity in a shear flow. The lift force on the particle in small, intermediate, and large particle Reynolds number, is studied. We have found that the magnitude of the slip velocity is always reduced by the lift force, implying reduced particle settling velocities. The reduction in the slip velocity and the angle of deflection are the greatest when the shear is the greatest and the particle Reynolds number is the smallest. However, these effects decrease as the particle Reynolds number becomes larger. The derived equations are applied to evaluate the effect of the lift force on particle transport within turbidity currents, on the entrainment of small particles embedded in the lower boundary of a shear flow, and on sediment-laden open-channel flow.

Flow Near Self-Excited and Forced Vibrating Circular Cylinders

Many studies of flow-bluff body interactions have been undertaken because of the practical need to know the fluid forces acting on a body immersed in a flowing stream. Experiments were performed to investigate the interaction process between the vibrating cylinder and the wake flow for free-stream Reynolds numbers between 550 and 900 in the irregular range. Two circular cylinders of equal diameter were used for experimentation—one was tuned to self-excite under the influence of lift forces and another was a rigid cylinder mounted in a shaker and forced to vibrate sinusoidally perpendicular to the mean flow direction under conditions that duplicated the Reynolds number, Strouhal number, motion amplitude, and relative frequency of the tuned cylinder. Experimental results for the two means of vibration and the mechanics of the wake formation are discussed in terms of the fluid dynamical parameters that influence the vibrations. One finds the wake formation process to be similar for both cylinders under the same conditions of flow, and the amplitude and distribution of near wake velocity fluctuations also to be the same. A phase shift of ninety deg is observed between eighty and one hundred and ten percent of the peak self-excited resonance condition, with the phase angle between the velocity fluctuation and cylinder motion signals being equal for both means of excitation. The critical relative frequency that corresponds to peak resonant conditions is less than unity. The independent parameters that govern the vibrations are not the same for the two means of excitation, and the bounds for the forced and self-excited motions are discussed in terms of the present results and those reported in the literature.