Momentum and heat transfer characteristics of a rotating elliptical cylinder in vortex shedding flow of power-law fluids

In this paper, a multiple-relaxation-time lattice Boltzmann method (MRT LBM) is used to simulate the steady fluid flow through and around a rotating porous circular cylinder in uniform flow. This study aims at investigating the effect of Darcy number (10-6{less than or equal to}Da{less than or equal to}1×0-2), velocity ratio (0{less than or equal to}VR{less than or equal to}2), and Reynolds number (Re=20 and 40) on the Magnus lift as well as on the flow pattern and pressure coefficient inside and around the rotating porous cylinder. The results reveal that besides the enveloping and detached wakes reported in the literature for rotating solid cylinders, a new type of wake called confined wake in this study is observed in this study within the rotating porous cylinders at high Darcy numbers and velocity ratios of less than one. It is seen that the Magnus lift increases almost linearly with the velocity ratio for Da{less than or equal to}10-3, however, through curve-fitting, the rate of increase is shown to decrease with Darcy number in a non-linear manner. For Darcy numbers higher than 10-3, the Magnus lift varies non-linearly with both velocity ratio and Darcy number in such a way that, interestingly, for Re=40 and very high Darcy numbers of 7.5×10-3 and 10-2 the Magnus lift becomes negative showing a behavior called the inverse Magnus effect.

On the Magnus effect of a rotating porous circular cylinder in uniform flow: A lattice Boltzmann study

Imani

Mozafari-Shamsi

2023

Lift characteristics of an airfoil at low Reynolds numbers for Newtonian and shear-thinning Carreau fluids

Raj,

Roy

2023

In the present study, we have numerically investigated Carreau and Newtonian fluid flow over a stationary National Advisory Committee for Aeronautics 0012 airfoil using a sharp interface immersed boundary method. We have explained the mean lift behavior and stall phenomena by identifying different vortex formation patterns over the airfoil surface for different angles of attack. We found that not all but some shear-thinning fluids avoid stall altogether at high angles of attack. It is observed that the lift behavior is strongly related to the frequency of vortex departure from the suction surface. We have correlated fluctuating energies with mean lift characteristics, which is one of the novelties of our work. We have also used time-averaged vorticity transport rate analysis to explain the effect of non-linear viscosity distribution in the departure of vortices at high angles of attack. It is observed that the apparent viscosity dominates the transport of vorticity, and the effect of shear straining is negligible at high angles of attack.

An insight into the wake evolution of power-law flow past three tandem circular cylinders

Zhu,

Xie,

et al. 2024

This paper reports the wake flow evolution of power-law flow past three tandem cylinders with identical diameter and spacing at a low incoming Reynolds number of Re = 80. The flow characteristics of power-law fluid with variable power-law index n are examined at spacing ratios of L/D = 3, 5, and 8 (where L is the spacing between the centers of two adjacent cylinders and D is the cylinder diameter). Three combined wake interference regimes are identified, including the overshoot-overshoot, overshoot-alternate reattachment, and alternate reattachment-quasi-co-shedding regimes, which are distinctly illustrated from the dynamic mode decomposition results. The quasi-co-shedding regime mainly occurs between the middle and downstream cylinders (denoted as C2 and C3, respectively) when L/D = 5 and L/D = 8. The switching of wake regime contributes to the sudden changes of hydrodynamic coefficients of the cylinders. Nevertheless, due to the shadowing effect, the drags of C2 and C3 remain to smaller than that of the upstream cylinder (denoted as C1).