Unsteady Poiseuille Flow Research Articles

Analytical Solutions to the Unsteady Poiseuille Flow of a Second Grade Fluid with Slip Boundary Conditions.

This paper deals with an initial-boundary value problem modeling the unidirectional pressure-driven flow of a second grade fluid in a plane channel with impermeable solid walls. On the channel walls, Navier-type slip boundary conditions are stated. Our aim is to investigate the well-posedness of this problem and obtain its analytical solution under weak regularity requirements on a function describing the velocity distribution at initial time. In order to overcome difficulties related to finding classical solutions, we propose the concept of a generalized solution that is defined as the limit of a uniformly convergent sequence of classical solutions with vanishing perturbations in the initial data. We prove the unique solvability of the problem under consideration in the class of generalized solutions. The main ingredients of our proof are a generalized Abel criterion for uniform convergence of function series and the use of an orthonormal basis consisting of eigenfunctions of the related Sturm-Liouville problem. As a result, explicit expressions for the flow velocity and the pressure in the channel are established. The constructed analytical solutions favor a better understanding of the qualitative features of time-dependent flows of polymer fluids and can be applied to the verification of relevant numerical, asymptotic, and approximate analytical methods.

A Finite Difference Method for Solving Unsteady Fractional Oldroyd-B Viscoelastic Flow Based on Caputo Derivative

In this paper, the effect of a fractional constitutive model on the rheological properties of fluids and its application in numerical simulation are investigated, which is important to characterize the rheological properties of fluids and physical characteristics of materials more accurately. Based on this consideration, numerical simulation and analytical study of unsteady fractional Oldroyd-B viscoelastic flow are carried out. In order to improve the degree of accuracy, the mixed partial derivative including the fractional derivative in the differential equation is converted effectively by integrating by parts instead of by direct discretization. Then, the stability, convergence, and unique solvability of the difference scheme are verified. The validity of the finite difference method is tested by making comparisons with analytical solutions for two kinds of fractional Oldroyd-B viscoelastic flow. Numerical results obtained using the finite difference method are in good agreement with analytical solutions obtained via the variable separation method. Viscoelastic characteristics of the unsteady Poiseuille flow are similar to the second-order fluid or integer-order Oldroyd-B fluid when the parameter is close to 0 or to 1. Oscillation characteristics of fractional viscoelastic oscillatory flow are similar to those of the classical viscoelastic fluid under the same condition. Compared with the previous research, the present work studies the rheological properties of fluids with the finite difference method, and the application of fractional constitutive models in describing the rheological properties of fluids is developed. Meanwhile, more cases reflecting the fractional-order characteristics are given. The present method can accurately capture the flow characteristics of unsteady fractional Oldroyd-B viscoelastic fluid and is applicable for the generalized fractional fluid.

Numerical study of unsteady pipe flow of an elastoviscoplastic fluid

In this paper we investigate, numerically, unsteady Poiseuille flow of an elastoviscoplastic fluid. The material is described by the rheological model by Putz and Burghelea (2009). The model can describe an elastic solid regime for low stresses, a solid–fluid phase of stresses in the vicinity of the yield stress and a fully fluid regime for large stresses. We impose a time dependent pressure ramp with the form of a triangular function to drive the flow. We compare average velocity across the pipe as a function of pressure drop for different slip laws. We find that the solid–fluid transition is correlated to the slip-law used in the computations but the boundary conditions do not affect neither the deformation-rates nor stress at the bulk and the wall. • Unsteady pipe flow. • Elastoviscoplasticity. • Slip law.

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.

One Dimensional Model for Droplet Ejection Process in Inkjet Devices

In recent years, physics-based computer models have been increasingly applied to design the drop-on-demand (DOD) inkjet devices. The initial design stage for these devices often requires a fast turnaround time of computer models, because it usually involves a massive screening of a large number of design parameters. Thus, in the present study, a 1D model is developed to achieve the fast prediction of droplet ejection process from DOD devices, including the droplet breakup and coalescence. A popular 1D slender-jet method (Egger, 1994) is adopted in this study. The fluid dynamics in the nozzle region is described by a 2D axisymmetric unsteady Poiseuille flow model. Droplet formation and nozzle fluid dynamics are coupled, and hence solved together, to simulate the inkjet droplet ejection. The arbitrary Lagrangian–Eulerian method is employed to solve the governing equations. Numerical methods have been proposed to handle the breakup and coalescence of droplets. The proposed methods are implemented in an in-house developed MATLAB code. A series of validation examples have been carried out to evaluate the accuracy and the robustness of the proposed 1D model. Finally, a case study of the inkjet droplet ejection with different Ohnesorge number (Oh) is presented to demonstrate the capability of the proposed 1D model for DOD inkjet process. Our study has shown that 1D model can significantly reduce the computational time (usually less than one minute) yet with acceptable accuracy, which makes it very useful to explore the large parameter space of inkjet devices in a short amount of time.

Extraction of macroscopic and microscopic adjoint concepts using a lattice Boltzmann method and discrete adjoint approach.

In the present research, we tried to improve the performance of the lattice Boltzmann (LB) -based adjoint approach by utilizing the mesoscopic inherent of the LB method. In this regard, two macroscopic discrete adjoint (MADA) and microscopic discrete adjoint (MIDA) approaches are used to answer the following two challenging questions. Is it possible to extend the concept of the macroscopic and microscopic variables of the flow field to the corresponding adjoint ones? Further, similar to the conservative laws in the LB method, is it possible to find the comparable conservation equations in the adjoint approach? If so, then a definite framework, similar to that used in the flow solution by the LB method, can be employed in the flow sensitivity analysis by the MIDA approach. This achievement can decrease the implementation cost and coding efforts of the MIDA method in complicated sensitivity analysis problems. First, the MADA and MIDA equations are extracted based on the LB method using the duality viewpoint. Meanwhile, using an elementary case, inverse design of a two-dimensional unsteady Poiseuille flow in a periodic channel with constant body forces, the procedure of analytical evaluation of the adjoint variables is described. The numerical results show that similar correlations between the distribution functions can be seen between the corresponding adjoint ones. Besides, the results are promising, emphasizing the flow field adjoint variables can be evaluated via the adjoint distribution functions. Finally, the adjoint conservative laws are introduced.

Flow of a binary mixture of fluids in a semicircular duct

The purpose of this work is to examine the flow of a binary mixture including chemically inert incompressible Newtonian fluids in a duct of semicircular cross-section. Such a flow model has great significance not only of its own theoretical interest, but also for application to various engineering processes. The governing equations have been solved analytically using the finite Fourier sine and Hankel transforms for the following four problems: (1) steady Couette flow in a semicircular duct, (2) unsteady Couette flow in a semicircular duct, (3) steady Poiseuille flow in a semicircular duct, (4) unsteady Poiseuille flow in a semicircular duct. The previous solutions corresponding to pure Newtonian fluid appear as the special cases of the present analysis. Key words: Binary mixture, Newtonian fluid, Couette flow, Poiseuille flow, Fourier sine transform, Hankel transform.

Analysis on fractional Oldroyd-B viscoelastic Poiseuille flow by numerical inversion of Laplace transforms

In this paper the unsteady Poiseuille flow of fractional Oldroyd-B viscoelastics fluid between two parallel plates is studied, which sheds light on the investigation on fractional differential equations. Stehfest algorithm for numerical inversion of Laplace transform is used for obtaining the numerical solutions, and its validity is verified by comparing the results with approximate analytic solutions. Then the laminar Poiseuille flow of fractional Oldroyd-B viscoelastic fluid is investigated by the Stehfest algorithm. Phenomena of velocity and stress overshootings are found, which are proved to be dependent on the order of fractional derivative. Simultaneously, compared with the integer constitutive equations, the fractional constitutive equations have wider scope of application. This conclusion was drawn based on the obvious fact that the integer constitutive equations are only special cases of the fractional constitutive equations.

Unsteady viscous flows and Stokes's first problem

Unsteady viscous flows and Stokes's first problem are examined. Three problems are considered: unsteady Couette flow, unsteady Poiseuille flow, and unsteady boundary layer flow. The relationship between these three fundamental unsteady flows and Stokes' first problem is illustrated. Scaling principles are used to deduce the short time and long time characteristics of these three problems. Asymptotic analysis is used to obtain exact short and long time characteristics and to show the relationship of each problem to Stokes's first problem for short times. Finally, compact robust models are developed for all values of time using the Churchill–Usagi asymptotic correlation method to combine the short and long time characteristics.

On the unsteady Poiseuille flow in a pipe

We show that in an unsteady Poiseuille flow of a Navier–Stokes fluid in an infinite straight pipe of constant cross-section, σ, the flow rate, F(t), and the axial pressure drop, q(t), are related, at each time t, by a linear Volterra integral equation of the second type, where the kernel depends only upon t and σ. One significant consequence of this result is that it allows us to prove that the inverse parabolic problem of finding a Poiseuille flow corresponding to a given F(t) is equivalent to the resolution of the classical initial-boundary value problem for the heat equation.

Nonlinear damped wave equation arising in viscoelastic fluid flows

We consider the nonlinear damped wave equation arising in unsteady Poiseuille flow of shear thinning Maxwell fluid. We show the global existence of the smooth solution to the corresponding nonlinear system. We also give some numerical examples.

Orthogonal cubic spline collocation method for the nonlinear parabolic equation arising in non-Newtonian fluid flow

Using the orthogonal cubic spline collocation method, solution for the nonlinear parabolic equation arising in magneto-hydrodynamic unsteady Poiseuille flow of the generalized Newtonian fluid (Carreau rheological model) is obtained. Also, using the Lyapunov functional, a bound for the maximum norm of the semi-discrete solution is derived. Moreover, optimal error estimates are established for the semi-discrete solution. Numerical results thus obtained are presented graphically and the salient features of the solution are discussed, for various values of the parameters. The results obtained reveal many interesting behaviors that warrant further study on the parabolic equations related to non-Newtonian fluid phenomena. Furthermore the analysis can be used to study the mathematical models that involve the flow of viscous fluids with shear rate-dependent properties: For example, models dealing with polymer processing, tribology and lubrication, and food processing.

Unsteady flows of a binary mixture of incompressible Newtonian fluids in an annulus

This paper is concerned with applying the mixture theory of two chemically inert incompressible Newtonian fluids to some simple unsteady flows in the annular region between two infinitely long coaxial cylinders. The equations governing the motion of the binary mixture under discussion are reduced to a system of coupled partial differential equations. With the help of finite Hankel transforms, the exact solutions of these equations are obtained in series form for the following three problems: (i) unsteady axial Couette flow in an annulus, (ii) unsteady Poiseuille flow in an annulus, (iii) unsteady circular Couette flow in an annulus.

On some unsteady flows of a non-Newtonian fluid

Some properties of unsteady unidirectional flows of a fluid of second grade are considered for flows impulsively started from rest by the motion of a boundary or two boundaries or by sudden application of a pressure gradient. Flows considered are: unsteady flow over a plane wall, unsteady Couette flow, flow between two parallel plates suddenly set in motion with the same speed, flow due to one rigid boundary moved suddenly and one being free, unsteady Poiseuille flow and unsteady generalized Couette flow. The results obtained are compared with those of the exact solutions of the Navier–Stokes equations. It is found that the stress at time zero on the stationary boundary for the flows generated by impulsive motion of a boundary or two boundaries is finite for a fluid of second grade and infinite for a Newtonian fluid. Furthermore, it is shown that for unsteady Poiseuille flow the stress at time zero on the boundary is zero for a Newtonian fluid, but it is not zero for a fluid of second grade.

Flow of a binary mixture of incompressible Newtonian fluids in a rectangular channel

The problems concerning some simple steady and unsteady flows of a mixture composed of two incompressible Newtonian fluids in an infinitely long channel of rectangular cross-section are examined. By means of finite Fourier sine transforms, the exact solutions of the field equations are obtained for the following four problems: (i) steady Couette flow in a rectangular channel, (ii) unsteady Couette flow in a rectangular channel, (iii) steady Poiseuille flow in a rectangular channel, (iv) unsteady Poiseuille flow in a rectangular channel.

Exact solutions of flow problems of an Oldroyd-B fluid

Exact analytical solutions of the following six problems of flow of an Oldroyd-B fluid between two boundaries are obtained: (i) unsteady Couette flow, (ii) unsteady flow for rigid and free boundaries, (iii) flow between two parallel plates suddenly set in motion with same speed, (iv) unsteady Poiseuille flow, (v) unsteady generalized Couette flow and (vi) unsteady generalized Couette flow for rigid and free boundaries. The viscoelasticity of the fluid increases the order of the differential equation. It is shown that the solutions exist for all values of non-Newtonian parameters. The solutions for the second grade, Maxwell and Newtonian fluids can be obtained from those for fluids of Oldroyd-B fluid as the limiting cases.