Transient Laminar Flow Research Articles

Unified Approach for Damping Rate of Transient Laminar Flow: Experiments, Computational Fluid Dynamics, and One-Dimensional, and Global Models

Abstract Pipe networks exhibit complex geometries and are equipped with electromechanical devices capable of generating hydraulic transients. Most of these devices are remotely controlled and managed through an integrated system that prioritizes network demands. This implies that potential hazardous pressure peaks, that may occur during each operation, may need to be taken into account. Consequently, when multiple operations take place in a short time interval, transient pressure waves, generated in different parts of the network and traveling back and forward, overlap and can be larger than the design maximum pressure. To address this concern, it is essential to evaluate the pressure-damping rate of critical maneuvers and to identify a “safe” time interval between maneuvers to prevent the risk of inappropriate pressure waves overlapping. With the aim of analyzing the damping rate of closure maneuvers, both numerical and laboratory experiments have been executed for a laminar flow in a reservoir-pipe-valve system. In this context, a three-dimensional computational fluid dynamics, a one-dimensional and global model, the latter based on a sinusoidal function, have been used. Guidelines are then presented for identifying the safe time interval between maneuvers.

Effect of Viscous Energy Dissipation on Transient Laminar Free Convective Flow of a Dusty Viscous Fluid through a Porous Medium

Effect of Viscous Energy Dissipation on Transient Laminar Free Convective Flow of a Dusty Viscous Fluid through a Porous Medium

Using internal sinusoidal fins and phase change material for performance enhancement of thermal energy storage systems: Heat transfer and entropy generation analyses

In comparison to sensible energy storage, LHTES (Latent Heat Thermal Energy Storage) offers large storage energy densities per unit mass/volume at nearly constant temperatures. This study is carried out to assess thermo-hydraulic performance of the simultaneous utilization of sinusoidal internal fins and PCM (Phase Change Material) in LHTES systems. For this, a validated numerical framework is developed using Ansys-Fluent software. The RT82 is considered as working substance in a transient laminar flow. The geometrical parameters of fins, (including length, height, and thickness) are evaluated by defining 15 different geometries to look for the most optimal case in terms of faster PCM melting. Furthermore, the impact of fins’ material (copper and gold) is also involved in the investigations. A comprehensive sensitivity analysis is conducted to completely investigate different heat transfer and thermodynamic characteristics. The results illustrated that in case 4 (with H/L = 0.125 and thickness of 3 mm), the highest growth of normalized liquid fraction compared to normalized heat transfer coefficient is achieved which results in Dhl number of about 0.55. Also, the second-law analysis revealed that the lowest entropy is generated in this case. So that, 62% increment of liquid fraction and 59.5% reduction of entropy generation is observed in case 4 compared to a case with simple straight fins.

4-dimensional local radial basis function interpolation of large, uniformly spaced datasets

Background and ObjectiveLarge, uniformly spaced, complex and time varying datasets derived from high resolution medical image velocimetry can provide a wealth of information regarding small-scale transient physiological flow phenomena and pulsation of anatomical boundaries. However, there remains a need for interpolation techniques to effectively reconstruct a fully 4-dimensional functional relationship from this data. This paper presents a preliminary evaluation of a 4-dimensional local radial basis function (RBF) algorithm as a means of addressing this problem for laminar flows. MethodsA 4D interpolation algorithm is proposed based on a Local Hermitian Interpolation (LHI) using a combination of multi-quadric RBF with a partition of unity scheme. The domain is divided into uniform sub-systems with size restricted to immediately neighbouring points. The validity of the algorithm is first established on a known 4D analytical dataset and a CFD based laminar flow phantom. Application is then demonstrated through characterisation of a large 4D laminar flow dataset obtained from magnetic resonance imaging (MRI) measurements of cerebrospinal fluid velocities in the brain. ResultsPerformance of the algorithm is compared to that of a quad-linear interpolation, demonstrating favourable improvement in accuracy. The technique is shown to be robust, computationally efficient and capable of refined interpolation in Euclidean space and time. Application to MR velocimetry data is shown to produce promising results for the 4D reconstruction of the transient flow field and movement of the fluid boundaries at spatial and temporal locations intermediate to the original data. ConclusionThis study has demonstrated feasibility of an accurate, stable and efficient 4-dimensional local RBF interpolation method for large, transient laminar flow velocimetry datasets. The proposed approach does not suffer from ill-conditioning or high computational cost due to domain decomposition into local stencils where the RBF is only ever applied to a limited number of points. This work offers a potential tool to assist medical diagnoses and drug delivery through better understanding of physiological flow fields such as cerebrospinal fluid. Further work will evaluate the technique on a wider range of flow fields and against CFD simulation.

Womersley's solution for the measurement of volume flow rates in transient laminar flow tubes

The characterization of transient flows within the Reynolds number range of Re = 10–100 and the Womersley number range α = 0.8–10 is required for the ongoing development of green monopropellant thrusters. However, at the ml/min scale flow rates of interest, these measurements are outside the capabilities of current commercial flow meters. It is proposed here that transient flows under the required dynamic conditions can be characterized via Womersley's solution for transient flow in a rigid tube. This solution method requires only the measured transient pressure gradient within a controlled laminar flow section and can be accomplished using existing commercial pressure measurement hardware. Experiments were performed where flow similarity was maintained with the ultimate thruster characterization application, but the radius of the flow passage was increased so that flows could be simultaneously characterized by both the proposed solution method and a commercial ultrasonic flow meter. It was shown that across the range of interest, applying Womersley's solution to a measured pressure gradient was an effective method of transient flow characterization. Additionally, it was shown that non-periodic flows can be characterized except for the initial flow startup transient with solution convergence times approximating the analytical solution to starting flow in a pipe. While these results were expected due to an experimental design matching the assumptions required for Womersley's analytic solution, this work demonstrates that this method is practically feasible as novel instrumentation enabling previously unobtainable measurements.

Reducing Pumping Power Consumption by Pulsed Operation?

Abstract A computational study, based on exact solutions for transient laminar flow in pipes and on an empirical correlation for transition to turbulence in the presence of temporal acceleration, shows that, provided certain conditions are met, pumping an incompressible fluid at a prescribed flow rate by a series of consecutive pressure gradient pulses may require less mechanical power consumption than pumping the same flow rate under steady-state turbulent flow conditions. The reason is that, in the former case, the fluid is pumped under conditions of accelerated laminar flow, for which the onset of turbulence occurs at Reynolds numbers much larger than the steady-state critical value of ∼2,100. The conclusions of this study rest crucially on the exact criterion for transition to turbulence in accelerated laminar flow, for which, unfortunately, existing experimental results exhibit a large scatter and general consensus is still lacking. Also, this study adopts a simplified description of the problem, and further model refinements, design efforts, and supporting experimental tests will have to be performed before the hypothesis that pulsed pumping can provide energetic advantages can be demonstrated in “real-world” situations.

Heat transfer enhancement in a nanofluid saturated porous medium with cross diffusion and nonequilibrium: A regression approach

The work has been made to analyze the influence of local thermal nonequilibrium through a stretching surface in a laminar transient flow of nanofluid with the inclusion of cross diffusion. Brownian motion and thermophoresis are taken into account for the modeling of nanofluid. To describe the departure from thermal equilibrium, three temperature model has been assumed. The governing transport equations are transformed using similarity analysis and they are evaluated by Runge–Kutta–Fehlberg with shooting technique. The present results are compared with the previously published reports and they met agreement. The obtained numeric values of the boundary layer flow characteristics such as velocity, thermal, and mass transfer among the phases are illustrated graphically for different combinations of the interphase parameters. In addition, the regression study on heat and mass transfer with prominent parameters has been made to provide a highly accurate rendition and can be accessibly used in engineering problems.

Transient sensitivity analysis and topology optimization of particle suspended in transient laminar fluid

This study develops a new topology optimization scheme using coupled forward and coupled sensitivity analyses to manipulate and control time-varying particle trajectories in transient laminar flow, that is transient fluid–particle assemblies. It is an important scientific and engineering subject to manipulate or control the trajectories of particles by the drag force in steady-state or transient fluids. The drag force varies with the material properties of fluid, and the velocity differences between fluid and particles cause the particles to move. Despite some research regarding the shape and topological optimization frameworks for particles in steady-state flow, the optimization of transient particle motion in transient laminar flow is still a difficult subject. Thus, this study presents a new topology optimization scheme that considers the transient motion of particles in transient laminar flow. Owing to the time variation in the direction and magnitude of the fluid, the optimization of particle motion requires a new development of the transient sensitivity analysis. For efficient optimization, a two-scale time integration scheme for the fluid and particle was developed. The developed coupled analysis and optimization framework were applied to determine optimal layouts for transient fluids and particles. Several optimization problems were formulated and solved to validate the present scheme.

Transient Free Convective Flow of CNT Water Nanofluid with Heat Transfer from a Moving Cylinder

Background: In this paper, transient two-dimensional laminar boundary layer viscous incompressible free convective flow of water based nanofluid with carbon nanotubes (CNTs) past a moving vertical cylinder with variable surface temperature is studied numerically in the presence of thermal radiation and heat generation. Methods: The prevailing partial differential equations which model the flow with initial and boundary conditions are solved by implicit finite difference method of Crank Nicolson type, which is unconditionally stable and convergent. Results: Influence of Grashof number (Gr), nanoparticle volume fraction (φ), heat generation parameter (Q), temperature exponent (m), radiation parameter (N) and time (t) on velocity and temperature profiles are sketched graphically and elaborated comprehensively. Conclusion: Analysis of Nusselt number and Skin friction coefficient is also discussed numerically for both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

Influence of slip condition on transient laminar flow over an infinite vertical plate with ramped temperature in the presence of chemical reaction and thermal radiation

AbstractAn analysis was made using the numerical approach of a transient laminar slip flow over an infinite vertical plate with ramped and constant temperatures in which chemical reaction is involved and thermal radiation had to be considered. Slip conditions have caused much concern because of their broad applicability in industry and chemical engineering. By following the finite element technique, the equation of momentum together with the equations of energy and species was numerically solved. The expressions for skin friction, Nusselt number, and Sherwood number are also derived. The variations in fluid velocity, fluid temperature, and species concentration are displayed graphically whereas numerical values of skin friction, Nusselt number, and Sherwood number are presented in tabular form for various values of the pertinent flow parameters. The findings indicate that the radiation has a noticeable impact to a minor intensity of R and is more apparent in the constant condition than in the ramped condition. Radiation and buoyancy effects produce a strong flow near the plate, which is accelerated by slip. Finally, it is shown logically and mathematically that when two buoyancies are opposite and equal in magnitude with equal solutal and thermal diffusions, the flow should be taken as stationary flow in the absence of radiation and the presence/absence of slip.

Theoretical and experimental investigations of transient flow in oil-hydraulic small-diameter pipe system

This paper investigates unsteady flow phenomena in a new oil-hydraulic small-diameter pipeline apparatus at the Wrocław University of Science and Technology, Poland. The steel pipe section lengths can be either 2 or 7 m, and the internal pipe diameter 4 mm (micro-hydraulic system). Transient event was triggered by a rapid closure of a downstream end bi-directional poppet valve. Pressures and velocities were investigated at the pipe end points. The main objective was to investigate effects of valve action on pressure magnitudes and timing in a number of transient laminar flow situations. In the method of characteristics numerical simulations a quasi-steady and a novel computationally effective Urbanowicz’s convolution-based unsteady friction models were used, as well as a quadratic bi-directional poppet valve function boundary condition. Comparisons between measured and calculated results clearly show that the valve closure path and the unsteady friction control the effects of unsteadiness on attenuation, shape and timing of pressure pulses in a small-diameter pipeline system; however, the unsteady friction is less important for the cases characterized by a relatively large fluid hammer number.

Investigating the Effect of Valve Shape on Anti-Lock Braking System Plunger Pump Performance Using Fluid-Structure Interaction Simulation

An anti-lock braking system (ABS) is an anti-skid braking system commonly used as a safety feature in vehicles. The hydraulic control unit for the ABS of a vehicle includes a plunger pump between the wheel and master cylinder. This paper presents numerical investigations of the effect of valve shapes on the performance improvement provided by a plunger pump, focusing on two different valve shapes, ball-type and hat-type. Transient laminar flow analyses of plunger pumps with ball and hat-type inlet valves are performed under motor speeds from 1000 to 5000 rpm using the fluid-structure interaction (FSI) and user-defined function (UDF) techniques. An experimental verification of the simulation results for the plunger pump with a ball-type valve was conducted using the standard pump test of the Mando Corporation, South Korea. A comparison of the simulation and experimental results suggests that these are in good agreement. The simulation results indicate that the hat-type valve outperforms the ball-type valve due to a shorter delay in the closing time at the end of the suction cycle. These findings suggest that valve shape has a considerable impact on the performance improvement provided by a plunger pump, providing crucial insights into the future design of high-efficiency pumps.

Simulations of unsteady flows with adsorption equilibrium in dynamic axial compression column

Simulated moving bed chromatography process, which is a multicolumn chromatography process, has been used in various industrial applications. Dynamic axial compression columns are key elements in simulated moving beds, and their flow characteristics are worth exploring using state-of-the-art numerical methodologies. In this study, new fluid distributors for the dynamic axial compression column were designed and fabricated based on mass conservation in fluid mechanics and the computer-aided design in the preliminary stage. Computational fluid dynamics was employed to resolve the flow field, and the numerical chromatograms were validated by laboratory experiments. For the computational fluid dynamics–based simulation of flow in the dynamic axial compression, the transient laminar flow fields were described by the momentum and species transport equations with Darcy’s law to model the porous zone in the packed bed. In addition, reverse engineering processes were applied to obtain the unknown physical parameters, such as viscous resistance and adsorption equilibrium coefficients. Moreover, including the adsorption equilibrium equation in the fundamental governing equations made the simulated results agree with the experimental data in chromatograms, providing a more feasible result for practical applications.

Physics-informed deep learning for incompressible laminar flows

Physics-informed deep learning has drawn tremendous interest in recent years to solve computational physics problems, whose basic concept is to embed physical laws to constrain/inform neural networks, with the need of less data for training a reliable model. This can be achieved by incorporating the residual of physics equations into the loss function. Through minimizing the loss function, the network could approximate the solution. In this paper, we propose a mixed-variable scheme of physics-informed neural network (PINN) for fluid dynamics and apply it to simulate steady and transient laminar flows at low Reynolds numbers. A parametric study indicates that the mixed-variable scheme can improve the PINN trainability and the solution accuracy. The predicted velocity and pressure fields by the proposed PINN approach are also compared with the reference numerical solutions. Simulation results demonstrate great potential of the proposed PINN for fluid flow simulation with a high accuracy.

Lapping flow and starting plume on an evenly heated horizontal plate

Transient laminar flows on an evenly heated horizontal plate are a common phenomenon in nature and industry. In this study, a lapping flow and a starting plume on a horizontal plate suddenly heated with a uniform heat flux are investigated using a scaling analysis, and the dynamics and heat transfer are analyzed. It is demonstrated that the starting plume has three possible scenarios and four regimes, including an unsteady viscous conduction regime, an unsteady inertial conduction regime, a steady inertial conduction regime and a steady viscous conduction regime. In addition, the obtained scaling laws are validated by numerical results calculated for Rayleigh numbers of 2 × 103 ≤ Ra ≤ 6 × 105.

CFD based investigations on the effects of blockage shapes on transient mixed convective nanofluid flow over a backward facing step

The separation and reattachment flow occurs in a backward-facing step (BFS) is available in various industrial applications such as gas turbine engines, combustors, aircraft, buildings and many other devices of heat transfer. It represents the pillar key of determining the flow structure and significantly affecting the heat transfer mechanism. This work studies numerically the effects of four various types of blockage shapes on transient laminar mixed convective nanofluid flow over a horizontal BFS placed in a duct. Nanoparticles of SiO2 with ethylene glycol as a base fluid at 2% of volume fraction and 20 nm of nanoparticle diameter are considered to examine the effect of different blockage shape on the thermal and flow fields at different time scales. The downstream of the step is kept at a constant heat flux of 500 W/m2, while other walls and sides of the duct are considered thermally insulated. The Reynolds number used in this study is in the range of 50–200. The relevant governing equations (continuity, momentum and energy) along with the boundary conditions are solved with the aid of finite volume method (FVM). The results reveal that after dimensionless time of τ = 5 the trend of nanofluid flow and recirculation area near the step and behind the blockage shape does not change significantly and this time is selected as a quasi-steady state time and the point of comparison. The velocity distributions for front facing triangular blockage decreased and this blockage shape has the highest value of skin friction coefficient beyond Re = 150. The results indicate that the front facing triangular blockage has the highest value of average Nusselt number and performance evaluation index while the trapezoidal blockage has the lowest value

Transient Dean flow in a channel with suction/injection: A semi-analytical approach

The mathematical model responsible for fully developed laminar transient flow formation between the gaps of two stationary concentric porous tubes due to the imposition of azimuthal pressure gradient (Dean flow) is solved semi-analytically. The tubes walls are porous so that a radial flow can be superimposed. The solution of the momentum and continuity equations are obtained semi-analytically by using the combination of Laplace transform technique and a Laplace inversion method called Riemann sum approximation method. The solutions for skin friction at [Formula: see text] (outer surface of the inner porous tube) and [Formula: see text] (inner surface of the outer porous tube) are presented. The impact of suction/injection parameter and the ratio of the radii of the tubes are examined for the velocity profile and skin friction. Results show that the velocity profile decreases with increase in suction/injection parameter for various values of time, [Formula: see text] and at large value of time, ([Formula: see text]), the velocity and the skin friction attain a steady state.

An explicit meshless point collocation method for electrically driven magnetohydrodynamics (MHD) flow

In this paper, we develop a meshless collocation scheme for the numerical solution of magnetohydrodynamics (MHD) flow equations. We consider the transient laminar flow of an incompressible, viscous and electrically conducting fluid in a rectangular duct. The flow is driven by the current produced by electrodes placed on the walls of the duct. The method combines a meshless collocation scheme with the newly developed Discretization Corrected Particle Strength Exchange (DC PSE) interpolation method. To highlight the applicability of the method, we discretize the spatial domain by using uniformly (Cartesian) and irregularly distributed nodes. The proposed solution method can handle high Hartmann (Ha) numbers and captures the boundary layers formed in such cases, without the presence of unwanted oscillations, by employing a local mesh refinement procedure close to the boundaries. The use of local refinement reduces the computational cost. We apply an explicit time integration scheme and we compute the critical time step that ensures stability through the Gershgorin theorem. Finally, we present numerical results obtained using different orientation of the applied magnetic field.

Transient Dean flow in an annulus: a semi-analytical approach

The mathematical model of a fully developed laminar transient flow formation between the gaps of two horizontally stationary concentric tubes forming concentric annulus due to the impact of sudden application of azimuthal pressure gradient is analysed. Analytical and numerical solutions of the momentum equations are obtained by the aid of two-step process. The first step is by solving the governing partial differential equation analytically by using Laplace transform technique in the Laplace domain. Using Riemann–sum approximation of Laplace inversion, the velocity and skin friction are then inverted to time domain. Expressions for steady-state velocity and skin friction are obtained for the validations of the method employed. In the course of numerical computations, it is observed that increase in dimensionless time leads to increase in velocity as well as skin friction at the surfaces of tubes. It is also found that at large values of dimensionless time , the velocity and skin friction reach steady state.

On an analytic solution for general unsteady/transient turbulent pipe flow and starting turbulent flow

Abstract The literature already offers analytic solutions for steady-state laminar (Hagen–Poiseuille), transient laminar (Szymanski) and steady-state turbulent (Pai) incompressible pipe flows. However, no reference could be found for the most general case that encompasses all of them: the unsteady turbulent incompressible pipe flow. This study presents a General Analytic Solution (GAS) for the Reynolds–averaged Navier–Stokes equations corresponding to unsteady turbulent incompressible circular pipe flow, which is composed of the transient response of the initial mean velocity field to external interactions, the unsteady response to time-dependent pressure gradient, and the unsteady component due to the turbulence’s Reynolds stress. The particular cases of laminar, turbulent, steady-state and transient incompressible pipe flows emanate directly from such solution. A general method is proposed to obtain an analytical solution for any particular pipe flow problem for which some relevant function could be provided. That general method is exemplified in a test case, a much simplified version of the starting flow initiated in a circular pipe, after suddenly applying a constant pressure gradient. The time evolution for such starting flow, with a growing stage and a shrinking stage, is presented graphically and discussed.