Influence of Particle Mass Fraction over the Turbulent Behaviour of an Incompressible Particle-Laden Flow

The presence of spherical solid particles immersed in an incompressible turbulent flow was numerically investigated from the perspective of the particle mass fraction (PMF or ϕm), a measure of the particle-to-fluid mass ratio. Although a number of different changes have been reported to be obtained by the presence of solid particles in incompressible turbulent flows, the present study reports the findings of varying ϕm in the the turbulent behaviour of the flow, including aspects such as: turbulent statistics, skin-friction coefficient, and the general dynamics of a particle-laden flow. For this purpose, a particle-laden turbulent channel flow transporting solid particles at three different friction Reynolds numbers, namely Reτ=180, 365, and 950, with a fixed particle volume fraction of ϕv=10−3, was employed as conceptual flow model and simulated using large eddy simulations. The value adopted for ϕv allowed the use of a two-way coupling approach between the particles and the flow or carrier phase. Three different values of ϕm were explored in this work ϕm≈1,2.96, and 12.4. Assessment of the effect of ϕm was performed by examining changes of mean velocity profiles, velocity fluctuation profiles, and a number of other relevant turbulence statistics. Our results show that attenuation of turbulence activity of the carrier phase is attained, and that such attenuation increases with ϕm at fixed Reynolds numbers and ϕv. For the smallest Reynolds number case considered, flows carrying particles with higher ϕm exhibited lower energy requirements to sustain constant fluid mass flow rate conditions. By examining the flow velocity field, as well as instantaneous velocity components contours, it is shown that the attenuation acts even on the largest scales of the flow dynamics, and not only at the smaller levels. These findings reinforce the concept of a selective stabilising effect induced by the solid particles, particularly enhanced by high values of ϕm, which could eventually be exploited for improvement of energetic efficiency of piping or equivalent particles transport systems.

Computational method for simultaneous inertial measuring of fluid mass flow rate and density

This work represents the decision of the problem of nonstationary one-dimensioned flow of fluid in a straight pipeline. It shows the method to generate non-stationary flow regime based on utilizing additional pipeline in which mechanical oscillations of fluid are being excited. Pressure difference along the length of oscillating fluid appears to be a measure for the density of the fluid and for its mass flow rate. The possibility of creating a new instrument for measuring the density and mass flow rate of a fluid based on results obtained is shown.

Numerical study of the sound generated by two tandem arranged wings in forward flight

The sound generated by two tandem arranged flexible wings in forward flight is numerically studied by using an immersed boundary method, at a Reynolds number of 100 and Mach number of 0.1. Three distinct cases are studied, encompassing a single wing and two tandem wings flapping in phase and out of phase. The sound generation of flapping wings is systematically studied by varying the wing flexibility (represented by the frequency ratio [Formula: see text]), structure-to-fluid mass ratio ([Formula: see text]), the phase difference (φ), and the gap ([Formula: see text]) between the two flapping wings. The results show that there is a direct correlation between the wing flexibility and sound generation for all cases considered. Specifically, for wings of low mass ratios ([Formula: see text]), an increase in flexibility resulted in a decrease in sound generation. For wings of high mass ratios ([Formula: see text]), an increase in flexibility resulted in higher sound output. The introduction of a second wing flapping in-phase resulted in an increase in aerodynamic features and sound generation, while the introduction of a second wing flapping out-of-phase experiences a decrease in sound output when compared to the in-phase case. In both cases, the effect of the wing flexibility on the sound production is similar to that of the single wing. An increase in flexibility is also found to have an impact on the plane of maximum sound pressure. For example, increasing flexibility resulted in a rotation of the plane of maximum sound pressure counter-clockwise relative to those at lower frequency ratios. Flexible wings with a structure-to-fluid mass ratio of unity and medium flexibility (i.e. [Formula: see text] and [Formula: see text]) are found to generate lower sound with high aerodynamic performance conserved.

Locomotion of a self-propulsive pitching plate in a quiescent viscous fluid

The locomotion of a flexible plate pitching in a quiescent viscous fluid is numerically studied by using the lattice Boltzmann method (LBM) for the fluid and a finite element method (FEM) for the plate, with an immersed boundary (IB) method for the fluid–structure interaction (FSI). In the simulation, the leading edge of the plate undergoes a prescribed pitching motion, and the entire plate moves freely due to the fluid–plate interaction. The effects of the pitching amplitude, bending rigidity, plate-to-fluid mass ratio and Reynolds number on the propulsive performance of the flexible plate are examined in a range of parameters. The numerical results show that a certain flexibility can remarkably improve the propulsive speed and efficiency. The optimal parameters for the pitching plate are obtained, i.e. [Formula: see text] ([Formula: see text] is a non-dimensional frequency, with [Formula: see text] means rigid plate and larger [Formula: see text] means more flexible) and 20° ≤ α0 ≤ 25° ( α0 is the pitching amplitude). The comparisons of three plate-to-fluid mass ratios (1.0, 2.5 and 5.0) show that the mass of the plate decreases the propulsive speed, but contrarily increases the efficiency. The results obtained in the present study provide an insight into the understanding of the performance of self-propulsive plate in pitching motion and can further guide the engineering design of micro aerial vehicles.