Narrow Results

An explicit Taylor series expansion and least square-based lattice Boltzmann method (TLLBM) is used to simulate the two-dimensional unsteady viscous incompressible flows. TLLBM is based on the well-known Taylor series expansion and the least square optimization. It has no limitation on mesh structure and lattice model. Its marching in time is accurate. Therefore, it is very suitable for simulation of time dependent problems. Numerical experiments are performed for simulation of flows past a rotational circular cylinder. Good agreement is achieved between the present results and available data in the literature.

Demonstration of heat release phenomenon by employing the numerical approach is the main purpose of current research. Water as PCM was combined by particles and homogeneous mixture was assumed. Various shapes of powder with different concentrations were employed. The unsteady energy equation involving nanomaterial properties and freezing source term has been analyzed and for finding the solution, the Galerkin technique was employed. The adaptive grid generates greater number of elements in solid front region. Implicit formulations for unsteady terms were implemented and automatic time step was employed in software. Solid front changes with alteration of shapes of nanopowder and its fraction. With fraction augmentation, freezing finishes in lower time. The needed time diminishes by about 10.29% and 13.78%, respectively. Changing the shape of particles to the biggest level makes the period decline by less than 4.8% and 8.4%. A greater fraction of nanomaterial leads to a higher effect on the shape of nanomaterial.

An experimental investigation of the stability in roll of a square section missile at high incidence was conducted in FL-23 wind tunnel. Dynamic motions were obtained on a square section missile that is free to rotate about its longitudinal axis. Different dynamic rolling motions were observed depending on the incidence of the model sting. These dynamic regimes include damped oscillations, quasi-limit-cycle wing-rock motion, and constant rolling. A coupling numerical method was established by solving the fluid dynamics equations and the rigid-body dynamics equations synchronously in order to predict the onset and the development of uncommented motions and then explore the unsteady movement characteristics of the aircraft. The study indicates that the aircraft loss stability at high incidence is caused by the asymmetric vertex on the level fin tip liftoff and attach alternately. The computation results are in line with the experiment results.

Unsteady pulsatile flow of blood through a porous-saturated, tapered and overlapping stenotic artery in the presence of magnetic field is examined theoretically and computationally. The power law constitutive model is employed to simulate hameo-rheological characteristics. The governing equation is derived assuming the flow to be unsteady, laminar, uni-directional and one-dimensional (1D). A robust, finite difference method is employed for the solution of the governing equation, subject to appropriate boundary conditions. Based on this solution, an extensive quantitative analysis is performed to analyze the effects of blood rheology, body acceleration, magnetohydrodynamic parameter, permeability parameter and arterial geometrical parameters of stenosis on various quantities of interest such as axial velocity, flow rate, resistance impedance and wall shear stress. The computations demonstrate that velocity, flow rate and shear stress increase while resistance to flow decreases with greater permeability parameter. Additionally, the effects of magnetic field are observed to be converse to those of permeability i.e., flow is decelerated and resistance is increased, demonstrating the powerful utility of exploiting magnetic fields in hemodynamic flow control (e.g., intra-corporeal surgical procedures). Furthermore, the size of trapped bolus of fluid is also found to be reduced for large values of the permeability parameter indicating that progressively more porous media circumvent bolus growth.

Numerical investigations of non-Newtonian blood flow are carried out through an asymmetric arterial constriction (stenosis) obtained from casting of mildly stenosed artery [Back et al. [1984] Effect of mild atherosclerosis on flow resistance in a coronary artery casting by man, J. Biomech. Eng., Trans. ASME106, 48]. The Marker and Cell method, for governing equations of motion for the flow in primitive variables formulations is developed in a staggered grid to discretize the momentum equations representing the non-Newtonian viscous incompressible flow characterized by the generalized Power-law model in cylindrical coordinates system under axial symmetric conditions so that the problem effectively becomes two-dimensional. The modified pressure equation has been solved by Successive-Over-Relaxation method and the pressure–velocity correction formulae have been derived. Satisfactory level of convergence namely, the mass conservation of the order of 0.5 × 10^-12 and consequently the steady-state criteria have been achieved. The separation points, reattachment points, pressure drop, and the wall shear stress distribution resulting from the present simulation agree well with the available numerical and experimental results. Secondary separation has also been predicted at higher Reynolds numbers. Further, in-depth study of the flow patterns reveals that shear-thickening model of generalized Power-law fluid experiences excess pressure drop more than that of shear-thinning model as in the case of flow past through cosine and smooth-shaped constrictions than irregular ones. The efficiency of the numerical code is illustrated by applying it to a test problem in order to validate the applicability of the technique as well as the simulation under consideration.

The unsteady flow over a continuously shrinking sheet with wall mass suction in a nanofluid is numerically studied. The governing boundary layer equations are transformed into a set of nonlinear ordinary differential equations by using similarity transformation. The resulting similarity equations are then solved by the shooting method for three types of nanofluid: copper-water, alumina-water and titania-water to investigate the effect of nanoparticle volume fraction parameter ɸ to the flow in nanofluid. The skin friction coefficient and velocity profiles are presented and results show that dual solutions exist for a certain range of unsteadiness parameter A. It is also found that the nanoparticle volume fraction parameter ɸ and types of nanofluid play an important role to significantly determine the flow behaviour.