Dimensional Unsteady Flow Research Articles

Effects of Chemical Reaction on Unsteady MHD Free Convective Flows past a Vertical Porous Plate Embedded in a Porous Medium with Variable Suction

In the present analysis we study two dimensional unsteady MHD free convection laminar heat and mass transfer flows past a vertical porous plate embedded in a porous medium with variable suction in the presence of chemical reaction and soret effects. Perturbation technique is applied to transform the non linear coupled governing partial differential equations in dimensionless form into a system of ordinary differential equations. The equations are solved analytically and the solutions for velocity, temperature and concentration fields are obtained. The effects of various parameters on velocity, temperature and concentration fields are presented graphically.

Speeding up soft pneumatic actuators through pressure and flow dynamics modeling and optimization

Soft pneumatic actuators (SPAs) possess the potential to be used in various scenarios due to the softness of their compositional materials to generate various modes of motion. The actuation frequency of SPAs is commonly in the range of 0-4 Hz, limiting their applications only to normal-speed tasks. To reveal the key affecting factors to the actuation speed and further optimize an SPA’s response speed for more dynamic applications, a predictive model of the whole pneumatic supply system (PSS) that takes the pressure and flow dynamics into consideration is needed. In this work, we introduce a comprehensive pressure and flow dynamic model of high-speed PSSs and SPAs. Here, the PSS is regarded as a compressed air source and a volume-fixed reservoir that are connected by a tube. The pressure and flow dynamic is modeled by correcting the adiabatic model to account for real heat exchange, and considering the assumptions of steady state of the gas flow through an orifice and the one dimensional unsteady gas flow in the tube. After calibration and validation with experiment results, we investigated the key affecting factors of PSSs on the attainable frequency of the SPA, which provides the design guidelines for the high-speed PSSs. Results show that the PSS with pure helium is dramatically faster than that with air. Finally, we present a demonstration of a helium-PSS actuated fiber-reinforced, bending SPA that achieves high frequency of up to 39 Hz in its blocked force.

Non stationary channel flow of a Herschel-Bulkley fluid

In this paper we study the one dimensional unsteady Poiseuille flow of an Herschel-Bulkley fluid driven by a prescribed pressure gradient. We formulate the mathematical problem that turns out to be a degenerate parabolic free boundary problem for the stress field. For such a problem we prove existence and uniqueness of a classical solution having a regular free boundary.

Two dimensional unsteady flow past a square cylinder: Influence of proximal plane wall and power-law index

A numerical analysis using Ansys Fluent has been done to investigate the flow physics involved in both Newtonian and Power-law (shear-thinning) fluid flow over a square cylinder, placed near a wall with altered gap-to-side (G/a) ratios (where G represents the gap between the cylinder and the plane wall and a represents side of the square cylinder). At a constant Reynolds number, Re = 150, numerical calculations for unsteady, incompressible Navier-Stroke (N-S) equation with varying viscosity is carried out by using second-order upwind momentum and least square cell based pressure solver. It is found that for small G/a ratio shear-thinning fluid exhibits vortex shedding which was absent for Newtonian fluid. G/a ratio and power-law index have a strong influence on the coefficient of lift and coefficient of drag (CL and CD respectively). With the increase in gap-ratio, CD decreases and CL increases at a constant value of power-law (n) index. Also, CL increases and CD reduces with a decrease in n at a constant value of G/a. Detailed observation of instantaneous and mean vorticity and streamlines, coefficient of lift and drag, mean pressure distribution over the cylinder and the plane wall and recirculation length have been presented.

Two dimensional unsteady stagnation point flow of Casson hybrid nanofluid over a permeable flat surface and heat transfer analysis with radiation

The inclined magnetohydrodynamic (MHD) unsteady flow and heat transfer of Casson hybrid nanofluid (HNF) due to porous stretching sheet is investigated. In the present paper we analyze the Casson fluid unsteady flow over permeable flat plate in the presence of inclined magnetic field and heat transfer of fluid with the effect of thermal radiation. The conservation of mass, conservation of momentum and thermal equations are non-dimensional into the system of nonlinear ODEs by taking the suitable similarity transformation. An exact analytical solution is obtained for velocity. The energy equation in the presence of inclined magnetic field and radiation is a differential equation with variable coefficients, which is transformed to an incomplete gamma function using a new variable and using the Rosseland approximation for the radiation. The governing differential equations are solved analytically and the effects of various parameters on velocity profiles, skin friction coefficient, temperature profile and wall heat transfer are presented graphically. There is an enhancement in heat transfer and pressure drop by usage of HNF. The variations in velocity and temperature profiles with respect to different various pertinent physical parameters. An increase of the mass transpiration (suction) parameter intensity increases the skin friction, which consequently improves the heat transfer enhancement and reduces the HNF temperature. Furthermore, the skin friction coefficient increases due to mass suction and MHD in the stretching sheet, whereas the rate of heat transfer decays. The results have possible technological applications in liquid-based systems involving stretchable materials.

Exact and Numerical Solution Using Lie Group Analysis for the Cylindrical Shock Waves in a Self-Gravitating Ideal Gas with Axial Magnetic Field

In this paper, we seek the exact and numerical solutions using Lie group analysis for one dimensional unsteady adiabatic flow in a self-gravitating ideal gas behind a cylindrical shock wave with axial magnetic field. With the help of Lie group analysis, the one-dimensional optimal system of sub-algebra is obtained for the system of equations of motion. With the help of optimal classes of infinitesimal generators, we constructed the similarity variable and transformation of the flow variables, which convert the system of partial differential equations into system of ordinary differential equations. In three particular cases, we have derived a general framework to solve the fundamental equations and exact feasible solutions are obtained. In two cases, the similarity solutions with exponential law and power law shock path are discussed. The similarity solution is obtained using numerical method in the case of power law shock path. It is obtained that the increase in the values of magnetic field strength and adiabatic index have the decaying effect on the shock wave. Also, increase in the strength of shock wave is witnessed with the rise in the gravitation parameter value. The effects of variation of magnetic field strength, adiabatic exponent and gravitational parameter on the flow variables are analyzed graphically.

Analysis of Turbulence on Cylinder with Additional Fairing with Free Surface

In this study, two dimensional unsteady flows of cylinder and cylinder with additional fairing close to a free surface were numerically investigated. The governing momentum equations were solved by using the Semi Implicit Method for Pressure Linked Equations(SIMPLE). The Volume of Fluid(VOF) method applied to simulate a free surface. Non- uniform grid structures were used in the simulation with denser grids near the cylinder. Under the conditions of Reynolds number 150624, 271123, 210874 and 331373, the cylinders were simulated with different depths of invasion. It was shown that the flow characteristics were influenced by submergence depth and Reynolds numbers. When the cylinder close to the free surface, the drag coefficient, lift coefficient and Strouhal numbers will increase due to the effect of free liquid surface on vortex shedding. With additional fairing, can effectively reduce the influence of the free surface on the drag coefficient. Fairing will reduce lift coefficient at high Reynolds numbers, but increase lift coefficient when Reynolds numbers are small. Fairing can effectively reduce Strouhal numbers, thus can well suppress the vortex induced vibration

Numerical Analysis of Unsteady Laminar Flow past a Pentagonal Obstacle

The current article dispenses the numerical investigation of a two dimensional unsteady laminar flow of incompressible fluid passing a regular pentagonal obstacle in an open rectangular channel. The centre of attention of this work is the comparison of drag coefficients estimated for two distinct cases based on the orientation of face and corner of an obstacle against the flow direction. The numerical results shows that the corner – oriented obstacle bring about 42% larger value of drag coefficient at Re = 500 than face – oriented obstacle. The substantial growth in the expanse of vortex behind obstacle (presented as a function of fluid inertia 25 < Re < 500) is analyzed through the contours and streamline patterns of velocity field. The two eddies in the downstream become entirely unsymmetrical at Re = 500 for both the cases, whereas; the flow separation phenomena occurs a bit earlier in the face – oriented case at Re = 250. Two dimensional Pressure – Based – Segregated solver is employed to model the governing equations written in velocity and pressure fields. The numerical simulations of unsteady flow are presented for 50 seconds time frame with time step 0.01 by using one of the best available commercial based Computational Fluid Dynamics (CFD) software, ANSYS 15.0.

Atangana-Baleanu and Caputo-Fabrizio Analysis of Fractional Derivatives on MHD Flow past a Moving Vertical Plate with Variable Viscosity and Thermal Conductivity in a Porous Medium

In this paper, a numerical investigation is presented for non-integer order derivatives with Atangana-Baleanu (AB) and Caputo-Fabrizio (CF) fractional derivatives for the variable viscosity and thermal conductivity over a moving vertical plate in a porous medium two dimensional free convection unsteady MHD flow. The effects of radiation have also been considered. The governing partial differential equations along with the boundary conditions are changed to ordinary form by similarity transformations. Hence physical parameters show up in the equations and interpretations on these parameters can be achieved suitably.By using ordinary finite difference scheme the equations are discritized and developed in fractional form. These discritized equations are numerically solved by the approach based on Gauss-seidel iteration scheme. Some numerical strategies are used to find the values of AB and CF approaches on time by developing programming code in MATLAB. The effects of all the physical parameters involved in the problem on velocity, temperature and concentration distribution are compared graphically as well as in tabular form. The effects of each parameter are found to be prominent. We have observed a significant variation of values under different parameters using AB and CF approaches on velocity, temperature and concentration distribution with respect to time.

Overland Flow Characteristics Using Kinematic Wave Formulation.(Dept.C)

The characteristics of overland flow resulting from a uniform rainfall intensity on an impervious sloping plane are investigated. The characteristic solution of the one dimensional unsteady nonuniform flow equations with the kinematic wave approximation applied to the momentum equation is used. The influence of the different overland flow parameters on the synthesized hydrograph, the peak runoff discharge, and the time taken to reach equilibrium is studied for the case of turbulent flow. The overland flow parameters include the slope and the length of the plane, the surface resistance, and the uniform rainfall intensity. A dimensionless peak runoff hydrograph is determined and compared with both Izzard's experimental dimensionless hydrograph and the dimensionless hydrograph determined by the finite difference solution of the full dynamic form of the momentum equation.

A Study of Two Dimensional Unsteady MHD Free Convection Flow over a Vertical Plate in the Presence of Radiation

This paper compacts with an exact analysis of radiative effects on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over a vertical plate. The non-dimensional continuity, momentum, and energy equations are solved using appropriate transformation. The dimensionless momentum and energy equations are solved numerically through an explicit finite difference method. The stability and convergence analysis also discussed. Finally, outcomes of the parameters on velocity and temperature profiles are displayed graphically and qualitatively.

Flow structure around two tandem square cylinders close to a free surface

In this study, two dimensional unsteady flow between and in the downstream region of two tandem cylinders close to a free surface was numerically investigated. The governing momentum equations were solved by using the Semi Implicit Method for Pressure Linked Equations (SIMPLE). To simulate a free surface, the Volume of Fluid (VOF) method was used. Central differences and Quadratic Upwind Interpolation (QUICK) methods were applied to discretize the viscous and convective terms respectively. Non-uniform grid structures were used in the simulation with denser grids near the free surface, bottom plate, and in the vicinity of the cylinders. The working fluid was water (Fr = 0.3). The degree of submergence of the cylinders (G) ranged from 0.25D to 5.5D, the distance between the cylinders (L) ranged from 1.5D to 4.0D, and the channel depths (H) were 16D, 8D and 4D. The simulations were performed for the Reynolds numbers of 180, 250 and 400. It was shown that the flow characteristics were influenced by the submergence depth, the distance between the cylinders and the depth of the channel as well as by the Reynolds numbers. As the distance to the free surface increased, the vortices in the downstream region were formed at longer distances. As the flow depth decreased, the flow parameters on the cylinders (CDmean, CLmax, and St) increased due to the influence of the boundary layer that was formed on the bottom wall. When the distance between the cylinders was increased (L/D = 4), the cylinders had higher CDmean and CLmax values as the vortex was formed between the cylinders. Increases were observed in all flow parameters as the Re number increased.

Long term sediment transport simulation of the Danube, Sava, and Tisa rivers

The aim of this paper is to evaluate a newly developed one dimensional unsteady flow, sediment transport and bed evolution model for a looped river network through a long term simulation of a real-life scenario. The model was assessed by verifying it for the Danube, Tisa, and Sava rivers in Serbia for a five year time interval. The total length of the modeled domain was 741.94 km from which 486.48 km is the length of the modeled Danube River reach, 132.50 km the modeled section of the Sava and 122.96 km the length of the modeled Tisa River reach. The simulated domain included smaller tributaries such as the Kolubara, Mlava, Nera, Pek, Porecka, Tamis, and Great Morava rivers. Due to the size of the domain that was included in the model, the work also includes extensive research regarding the available measurements, issues with measurement errors, and suggestions on overcoming incomplete measurements by developing different types of correlations. The attained results were analyzed by comparing the simulation results with measured water levels, discharges, and suspended sediment concentrations. The implemented evaluation of the results confirmed the developed model's reliability.

Building HEC-RAS model to detect the areas of Water Cycle Interruption in river stream and their sections

The purpose of this paper is to build a simulation model by using HEC-RAS software to simulate the reality of water movement in the main river of Basra City (South of Iraq) which is known as Siraji-Khoura River. The main objective of the simulation is to detect areas where the water cycle is interrupted in some stations of the river stream, as this river has become an outlet for the disposal of sewage, leading to pollution and causing weakness in some sections of the river & obstructing the water cycle that takes place between this river and Shatt al – Arab river. A field survey data of the river and its banks were adopted to derive the grades, longitudinal and cross sections of the river, these data included three-dimensional coordinates observed by precise GPS device. Depending on the river’s derived sections and elevation of water, a one dimensional unsteady flow model was constructed by HEC-RAS software to simulate the behavior of water flow during the tide periods. The results of simulation illustrated the weak areas that cause obstruction in the water flow within the river stream. It also determines the solid waste accumulation areas and stations where bed level rises from the water levels, causing the water cycle to break down in some parts of the river. Thus, an integrated database for the rivers of the study area was obtained, in order to the correct design decisions that are in the interest of these rivers.

Impulsively Started Horizontal Riga Plate Embedded in Unsteady Casson Fluid Flow with Rotation

This article is based on the impulsively started horizontal Riga plate in two dimensional unsteady Casson fluid flows with rotation. The plate starts abruptly from the rest relative to the rotating fluids moving with uniform acceleration in its plane. Numerical solutions are acquired by using explicit finite difference method and estimated results have been gained for various values of the Rotational parameter, modified Hartmann number, Prandtl number, Radiative parameter, Eckert number, Heat source parameter, Schmidt number, and the Soret number. Both the Compaq visual FORTRAN 6.6a and MATLAB R2015a tools have been used to find the numerical solutions and the graphical presentation. The Skin friction, Nusselt number and Sherwood number have been computed and the effects of some pertinent parameters on various distributions are discussed briefly and presented graphically.

A Study of Two Dimensional Unsteady MHD Free Convection Flow over a Vertical Plate

In this paper, unsteady free convection heat transfer flow over a vertical plate in the presence of a magnetic field is discussed in detail. The dimensionless partial differential equations of continuity, momentum along energy are analyzed with suitable transformations. For numerical calculation, an implicit finite difference method is applied to solve a set of nonlinear dimensionless partial differential equations. Dimensionless velocity and temperature profile are also investigated due to the effects of assumed parameters in the concerned problem. An explicit finite difference technique is used to compute velocity and temperature profiles. The stability conditions are also examined.

Entropy optimized MHD 3D nanomaterial of non-Newtonian fluid: A combined approach to good absorber of solar energy and intensification of heat transport

BackgroundThe present work provides important insights regarding three dimensional unsteady magnetohydrodynamic flow and entropy generation of micropolar Casson Cross nanofluid subject to nonlinear thermal radiation and chemical reaction. The Buongiorno's nanofluid model featured with Brownian movement and thermophoresis is considered. Realistic aspects namely convective boundary condition, viscous dissipation and joule heating are introduced. The present problem is modeled by momentum, temperature, microrotation and nanoparticles concentration equations. MethodThe non-dimensional highly nonlinear differential equations are solved numerically via shooting iteration technique together with 4th order Runge-Kutta integration scheme. ResultsThe current study imparts a reasonable, pragmatic and realistic approach to a good absorber of solar energy. In addition, strong and visionary profiles of velocity, microrotation, temperature, nanoparticles concentration, entropy generation rate and Bejan number for concern nanofluids are presented. Besides, intensive physical interpretation of the involved thermophycal parameters has been well-addressed. ConclusionsThe present investigation shows that strengthening of Weissenberg number uplifts the axial as well transverse fluid velocities while that of Hartmann number turns out to be a reverse trend. Furthermore, heat and mass transfer rates exhibit ascending and descending trends for intensified Brownian motion and thermophoresis respectively. Improved thermal boundary layer due to the upgrading temperature ratio parameter is another outcome of the current analysis.

Unsteady Three-Dimensional MHD Nanofluid Flow Over a Stretching Sheet with Variable Wall Thickness and Slip Effects

The stretching sheets with variable thickness may occur in engineering applications more frequently than a flat sheet. Due to its various applications, in the present analysis we considered a three dimensional unsteady MHD nanofluid flow over a stretching sheet with a variable wall thickness in a porous medium. The effects of radiation, viscous dissipation and slip boundary conditions are considered. Buongiorno’s model is incorporated to study the combined effects of thermophoresis and Brownian motion. The dimensionless governing equations are solved by using MATLAB bvp4c package. The impact of various important flow parameters is presented and analysed through graphs and tables. It is interesting to note that all the three boundary layer thicknesses are diminished by slip parameters. Further, the unsteady parameter decreases the hydromagnetic boundary layer thickness.

Mathematical analysis of bio-convective micropolar nanofluid

Abstract The present investigation concentrates on three dimensional unsteady forced bio-convection flow of a viscous fluid. An incompressible flow of a micropolar nanofluid encloses micro-organisms past an exponentially stretching sheet with magnetic field is analyzed. By employing convenient transformation the partial differential equations are converted into the ordinary differential equations which are non-linear. By using shooting method to solved these equations numerically. The influence of the determining parameters on the velocity, temperature, micro-rotation, nanoparticle volume fraction, microorganism are incorporated. The skin friction, heat transfer rate, and the microorganism rate are analyzed. The results depicts that the value of the wall shear stress and Nusselt number are declined while an enhancement take place in the microorganism number. The slip parameters increases the velocity, thermal energy, and microorganism number consequentially. The present investigation are important in improving achievement of microbial fuel cells.

Investigation of the BulbT conical diffuser flow dynamics with TR-PIV and pressure measurements

The three dimensional unsteady swirling flow inside the draft tube of a bulb turbine is investigated using time-resolved stereoscopic particle image velocimetry. The measurement plane located inside the conical diffuser, together with synchronous pressure measurements from thirteen sensors distributed across the draft tube, allow to link the draft tube flow dynamics to a known efficiency drop of the turbine. This paper presents the experimental setup and the first observations based on statistical analyses and instantaneous snapshots of the velocity field. After the efficiency drop, the intermittency and skewness of the draft tube pressure recovery are found to be reflected onto the velocity fields. Spectral analysis reveals the presence of a coherent and non-axisymmetric structure that rotates at the same frequency as the runner, but in the opposite direction.