Gravity Modulation Research Articles

Unsteady mixed convection flow of Casson fluid past an inclined stretching sheet in the presence of nanoparticles

The influence of nanoparticles on the unsteady mixed convection flow of Casson fluid past an inclined stretching sheet is investigated in this paper. The effect of gravity modulation on the flow is also considered. Carboxymethyl cellulose solution (CMC) is chosen as the base fluid and copper as nanoparticles. The basic governing nonlinear partial differential equations are transformed using appropriate similarity transformation and solved numerically using an implicit finite difference scheme by means of the Keller-box method. The effect of nanoparticles volume fraction together with the effect of inclination angle and Casson parameter on the enhancement of heat transfer of Casson nanofluid is discussed in details. The velocity and temperature profiles as well as the skin friction coefficient and the Nusselt number are presented and analyzed.

Analytical study of weakly nonlinear mass transfer in rotating fluid layer under time-periodic concentration/gravity modulation

The article deals with a weakly nonlinear stability analysis in rotating fluid subjected to time-periodic concentration/gravity modulation. Navier–Stoke’s momentum equation with Coriolis term has been used to describe the flow. The system is considered rotating about z-axis with uniform angular velocity. We consider three types of imposed time-periodic boundary concentration (ITBC). The effect of time dependent sinusoidal gravitational acceleration i.e. imposed time-periodic gravity modulation (ITGM) is also studied in this problem. In the case of ITBC, the concentration gradient between the plates of the fluid layer consists of a steady part and a time-dependent periodic part. The concentration of both plates is modulated in this case. In the problem involving ITGM, the gravity field has two parts: a constant part and an externally imposed time-periodic part. The Ginzburg–Landau amplitude equation is obtained by using power series expansion in terms of the amplitude of modulation, which is assumed to be small. The individual effects of concentration and gravity modulation on mass transports have been investigated in terms of Sherwood number. Further, the effects of various parameters on mass transports have been analyzed and depicted graphically. It is found that the effect of increasing Taylor number is decreases the value of Sherwood number. Effect of Schmidt number and various parameters occurring in the system on mass transfer is also discussed. Further, it is found that the mass transport can be controlled by suitably adjusting the frequency and amplitude of the modulation.

Effect of gravity modulation on mixed convection flow of second grade fluid with different shapes of nanoparticles

The problem of unsteady mixed convection flow of second grade fluid over an inclined stretching plate under the influence of different shapes of nanoparticles is studied in this paper. The influence of gravity modulation is also considered. Carboxymethyl cellulose solution (CMC) is chosen as the non-Newtonian base fluid. Based on Tiwari-Das nanofluid model, the governing partial differential equations are transformed into a system of ordinary differential equations and solved numerically using an implicit finite difference scheme. The effect of different shapes and volume fraction of solid nanoparticles on the enhancement of convective heat transfer of second grade nanofluid associated with the effect amplitude of modulation, frequency of oscillation, and material parameter is discussed in details. The results indicated that, the needle-shaped nanoparticles give the highest enhancement on the heat transfer of second grade nanofluid compared to sphere and disk-shaped nanoparticles.

Throughflow and G-jitter effects on chaotic convection in an anisotropic porous medium

Abstract The present article is to investigate the effect of various parameters on chaotic convection in an anisotropic porous medium under gravity modulation. For this, the problem is reduced into Lorenz system (non-autonomous) by employing truncated Galerkin expansion method. It is found that the system shows either chaotic or periodic nature for suitable values of scaled Rayleigh number. The influence of amplitude of modulation is to advance the chaotic nature in the system while that of frequency of modulation has tendency to delay the chaotic behaviour. The effects of Peclet number and anisotropic parameters on the chaotic system are also studied and found these are delay the chaotic nature. The phase portrait and time domain diagrams of the Lorenz system for suitable parametric values has been used to analysed the system. Finally, we conclude that the system has either chaotic or periodic solution depending upon the values of the parameters.

Floquet Instability of Gravity-Modulated Salt Fingering in a Porous Medium

Fingering convection in a horizontal doubly stratified fluid-saturated porous medium is examined under the influence of modulating gravitational field. The Brinkman model of momentum transfer is considered, and the Boussinesq approximation is assumed for natural convection. Floquet theory is employed to determine the onset condition within the framework of linear theory. Continued fractions that can handle arbitrary modulational parameters has been used to predict the dynamic instability regions at the marginal state and critical instability boundaries. Certain combinations of solutal Rayleigh and Schmidt numbers give rise to the occurrence of doubly unstable regions. An increase in the modulation amplitude always encourages instability. The competition between synchronous and subharmonic instability modes is observed for a certain range of values of the parameters. Solutal convection is found to introduce closed disconnected instability loops at the marginal state. It is seen that gravity modulation effe...

Gravity-gradient suppression in spaceborne atomic tests of the equivalence principle

The gravity gradient is one of the most serious systematic effects in atomic tests of the equivalence principle (EP). While differential acceleration measurements performed with different atomic species under free fall test the validity of the EP, minute displacements between the test masses in a gravity gradient produce a false EP-violating signal that limits the precision of the test. We show that gravity inversion and modulation using a gimbal mount can suppress the systematics due to gravity gradients caused by both moving and stationary parts of the instrument as well as the environment, strongly reducing the need to overlap two species.

Frequency Response and Heat Transfer of Thermal Convection Generated by Nanofluids under Microgravity Envionments with Gravity Modulation

Three-dimensional numerical analysis was performed to clarify the frequency response and heat transfer characteristics of the nanofluid to the gravity modulation under the microgravity environment. Gravity modulation was modeled as a sinusoidal oscillation of gravity. The frequency response of the nanofluid is good at low gravity modulation frequencies, so a heat transfer rate becomes high when the gravity modulation maximizes. Also, the heat transfer rate becomes maximum when the volume fraction of nanofluid is low. On the contrary, since the frequency response is poor at high gravity modulation frequencies, the time variations of the heat transfer rate are not observed. Therefore, the heat transfer rate is constant, and always the maximum at the low volume fraction. In the low frequency range, the time averaged heat transfer rate increases as the average temperature of nanofluid increases, and then the oscillation amplitude of heat transfer rate becomes large as the diameter of nanoparticle increases.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Gravity modulation effect on the onset of thermal buoyancy convection in a horizontal layer of the Oldroyd fluid

The effect of gravity modulation on the onset of convection in a horizontal layer of viscoelastic Oldroyd fluid heated from below is considered. The analytical solution of the problem has been obtained for the case of stress-free boundaries and rectangular modulation. It has been shown that depending on the parameter values, the modulation can produce either stabilizing or destabilizing effects. The deformation retardation always exerts a stabilizing effect, which is most pronounced in the shortwave range. The numerical results obtained by the solution of full nonlinear problems agree well with the results of linear stability analysis.

Free Convection Heat and Mass Transfer Flow for Magnetohydrodynamic Chemically Reacting and Radiating Elastico-Viscous Fluid Past a Vertical Permeable Plate with Gravity Modulation

An analysis of a two-dimensional unsteady magnetohydrodynamic free convective heat and mass transfer flow of an electrically conducting, optically thin, incompressible, and radiating elastico-viscous fluid (characterised by Walters’ liquid $${B}'$$ ) past a vertical permeable infinite plate embedded in a uniform porous medium with gravity modulation is considered. It is assumed that there exists a homogeneous first-order chemical reaction. Analytical solutions for velocity, temperature and concentration field have been derived. The effects of gravity modulation, radiation, and chemical reaction on velocity profile and shear stress for both Newtonian and elastico-viscous fluid have been studied and presented graphically. It was observed that velocity distribution increases with an increase in gravity modulation parameter and radiation parameter for both Newtonian and elastico-viscous fluid, where as it shows reverse effects in the case of magnetic field parameter and viscoelastic parameter. It is seen that viscous drag on the plate is reduced under the effect of chemical reaction parameter, where as it shows reverse effect in the case of gravity modulation parameter and radiation parameter.

Weakly Nonlinear Oscillatory Convection in an Electrically Conduction Fluid Layer Under Gravity Modulation

The time dependant and constant gravity field is investigated on electrically conducting fluid layer using weakly nonlinear stability analysis. The small amplitude perturbation is imposed on physical quantities like fluid velocity, energy and magnetic flux for simplifying nonlinear model. An amplitude equation is derived from solvability condition for the oscillatory mode of convection. Using this amplitude heat transfer is measured in terms of the Nusselt number. Also the effect of various system parameters are discussed on heat transfer. The effect of Prandtl number, magnetic Prandtl number and amplitude of modulation is to enhance the heat transfer. While the Chandrasekhar number, modulation frequency is to reduce the heat transfer. Further, it is found that, heat transfer is more for oscillatory mode than the stationary mode. Finally it is also found that, gravity modulation can be effectively used in either enhancing or diminishing the heat transfer.

Study of heat and mass transport in Couple-Stress liquid under G-jitter effect

Abstract In the present paper, we deal with the effect of G-jitter (time periodic gravity modulation) on the stability of double diffusive convection in couple stress liquid by method of non-linear analysis. The infinitesimal disturbances are expanded in terms of power series of amplitude of modulation. Couple stress term has been employed in momentum equation. For the stationary convection, the Ginzburg–Landau equation has been used to investigate the effect of modulation on heat and mass transfer. The effect of Prandtl number, couple stress parameter, Lewis number and solute Rayleigh number has also been investigated.

Effects of Gravity Modulation and Internal Heat Generation on the onset of Rayleigh-Benard convection in a Micropolar Fluid

The effect of gravity modulation (time periodic body force or g-jitter) on the onset of Rayleigh-Bénard convection in a micropolar fluid with internal heat generation is investigated by making a linear stability analysis. The stability of a horizontal layer of fluid heated from below is examined by assuming time periodic body force in the presence of internal heat source. A regular perturbation method is used to arrive at an expression to compute the critical Rayleigh number for small amplitude of modulation and dimensionless internal heat source. The Venezian approach is adopted to obtain the eigen value of the problem. The results obtained during the analysis have been presented graphically.

Thermal Convection in a Nanofluid Saturated Porous Medium with Internal Heating and Gravity Modulation

Thermal Convection in a Nanofluid Saturated Porous Medium with Internal Heating and Gravity Modulation

Throughflow and Gravity Modulation Effects on Heat Transport in a Porous Medium

Throughflow and Gravity Modulation Effects on Heat Transport in a Porous Medium

3D numerical simulation of the evolutionary process of aeolian downsized crescent-shaped dunes

Abstract A dune constitutive model was coupled with a large eddy simulation (LES) with the Smagorinsky subgrid-scale (SGS) model to accurately describe the evolutionary process of dunes from the macroscopic perspective of morphological dynamics. A 3D numerical simulation of the evolution of aeolian downsized crescent-shaped dunes was then performed. The evolution of the 3D structure of Gaussian-shaped dunes was simulated under the influence of gravity modulation, which was the same with the vertical oscillation of the sand bed to adjust the threshold of sand grain liftoff in wind tunnel experiments under the same wind speed. The influence of gravity modulation intensity on the characteristic scale parameter of the dune was discussed. Results indicated that the crescent shape of the dune was reproduced with the action of gravity during regulation of the saturation of wind-sand flow at specific times. The crescent shape was not dynamically maintained as time passed, and the dunes dwindled until they reached final decomposition because of wind erosion. The height of the dunes decreased over time, and the height–time curve converged as the intensity of modulation increased linearly. The results qualitatively agreed with those obtained from wind tunnel experiments.

Nonlinear throughflow and internal heating effects on vibrating porous medium

The effect of vertical throughflow and internal heating effects on fluid saturated porous medium under gravity modulation is investigated. The amplitude of modulation is considered to be very small and the disturbances are expanded in terms of power series of amplitude of convection. A weakly nonlinear stability analysis is proposed to study stationary convection. The Nusselt number is obtained numerically to present the results of heat transfer while using Ginzburg–Landau equation. The vertical throughflow has dual effect either to destabilize or to stabilize the system for downward or upward directions. The effect of internal heat source (Ri>0) enhances or sink (Ri<0) diminishes heat transfer in the system. The amplitude and frequency of modulation have the effects of increasing or diminishing heat transport. For linear model Venezian approach suggested that throughflow and internal heating have both destabilizing and stabilizing effects for suitable ranges of Ω. Further, the study establishes that heat transport can be controlled effectively by a mechanism that is external to the system throughflow and gravity modulation.

Effect of Gravity Modulation on the Onset of Rayleigh-Bénard Convection in a Weak Electrically Conducting Couple Stress Fluid with Saturated Porous Layer

The effect of time-periodic body force (TBF, also called gravity modulation) of small amplitude in a weak electrically conducting couple stress fluid with saturated porous layer is investigated by using a linear stability analysis. A regular perturbation method is used to arrive at an expression for the correction Rayleigh number. The Venezian approach is adopted in arriving at the critical Rayleigh and wave number for small amplitudes of TBF. The effect of roles of Couple stress parameter, Hartmann number, Darcy number, Porous parameter and Prandtl number on the onset of convection is studied. It is found that TBF leads to delay in convection. Also the results suggest that instead of taking electrically non-conducting fluid it is better to consider electrically conducting fluid with weak electrical conductivity as this ensures a stable environment in the presence of a magnetic field. The system is most stable with respect to TBF.

微小重力場の重力変調によって発生するナノ流体の熱対流に関する数値解析

微小重力場の重力変調によって発生するナノ流体の熱対流に関する数値解析

微小重力環境におけるナノ流体による熱対流に及ぼす重力変調の影響

微小重力環境におけるナノ流体による熱対流に及ぼす重力変調の影響