Duct Flow Research Articles

Viscous Dissipation and Fluid Axial Heat Conduction Effect on the Heat Transfer to a Laminar Non-Newtonian Fluid Flow in Cylindrical Annular Duct with an Axially Moving Core

Viscous Dissipation and Fluid Axial Heat Conduction Effect on the Heat Transfer to a Laminar Non-Newtonian Fluid Flow in Cylindrical Annular Duct with an Axially Moving Core

Electromagnetic energy harvesting via flow-induced vibration of flexible diaphragm in the presence of square cylinders at varied incidence angles: An experimental investigation

This study designs an electromagnetic energy harvester that uses a magnet in translation within a coil to harness energy from flow-induced vibrations when wall confinement affects a change in the wake formation behind a bluff body. An attached permanent magnet surrounded by a coil is attached to a flow channel with a flexible diaphragm, and a square cylinder acts as the bluff body that generates a vortex-induced street, thereby oscillating the diaphragm and generating electrical energy. The main novelty presented in the current investigation is developing a quick and efficient way of capturing fluid energy for practical applications, at the cost of augmented mechatronical complexity. Fluid flow and electromagnetic induction convert flow energy into electrical energy, and the influences of the Reynolds number (Re = 3000, 4000, and 5000) and the position of square cylinders (X*=X/D) on the dynamic characteristics are considered. As a result of different incidence angles (α) and spacing between two identical square cylinders (L*=L/D), Reynolds number and incidence angles have significant effects on the harvesting of energy. Additionally, based on experimental data, an output voltage of 0.04 V can be generated when the excitation pressure oscillates at about 20 Hz. Whether a single square or two identical squares are arranged, the 45-degree incidence angle is the most suitable arrangement for power conversion, and L*=4 can produce maximum energy for all configurations. Finally, the experimental results provide deeper insight into the physics behind the relationship between square spacing, rotation angle, and energy harvesting. Regarding hydroelastic energy extraction, tandem diamond configurations have substantial advantages over square ones. With high amplitudes and high frequencies, tandem diamond cylinders can generate mechanical power even beyond typical circular cross-sections. Furthermore, complementary numerical simulations are presented to provide a solid foundation for the reasoning behind the variation in extracted energy as well as complement the experiment results. By conducting numerical simulations, it is found that changing the incidence angle can significantly alter the flow patterns, which is attributable to the sequential formation of a primary vortex from the lee of the bluff body.

Формування динамічних моделей газотурбінних двигунів для використання в системах автоматичного керування та контролю

The subject of the study is the process of forming a mathematical model (MM) of an aviation gas turbine engine, which provides the calculation of parameters of the work process in stable and transient operating modes for use in the evaluation of dynamic characteristics, in the analysis and synthesis of automatic engine and aircraft control systems, as part of aviation simulators, and in on-board control and diagnostics algorithms. The goal is to substantiate the structure and methodology of MM formation, intended for use in real and accelerated time scale systems. Task: formulation of requirements for MM, substantiation of the interaction between static and dynamic submodels, substantiation of the composition of arguments and the way of considering the influence of external conditions, as well as the position of the elements of the mechanization of the gas flow duct. For this, the methods of the theory of airjet engines are used. The following results were obtained: the requirements for MM of aircraft gas turbine engines designed to solve the problems of engine and aircraft control were formulated, and the structural forms of MM were substantiated, which ensure high accuracy of modeling with minimal complexity and the possibility of real-time implementation. The scientific and practical novelty of the obtained results is as follows: the requirements for dynamic MM of aircraft engines have been summarized, the problems of structural implementation and combination of static and dynamic submodels, the rational selection of their input parameters and considering the influence of external conditions on static and dynamic characteristics have been analyzed, the software implementation of MM in in the Matlab Simulink environment of a two-shaft turbofan engine and compared the simulation results obtained using the developed simplified MM and the original nonlinear thermo-gas-dynamic model based on the solution of the joint operation equations of components. It is shown that in the working range of modes, the MM error does not exceed 5%, the dynamic errors of the rotor rotation frequencies are less than 4%, the compressor pressure and gas temperature are less than 7%, or the thrust is less than 10%. Errors in estimating the duration of acceleration and deceleration of the engine are within 0.2...0.6 s.

Large eddy simulation of supersonic flow in ducts with complex cross-sections

Large Eddy Simulation (LES) has been employed for the investigation of supersonic flow characteristics in five ducts with varying cross-sectional geometries. The numerical results reveal that flow channel configurations exert a considerable influence on the mainstream flow and the near-wall flow behavior. In contrast to straight ducts, square-to-circular and rectangular-to-circular ducts exhibit thicker boundary layers and a greater presence of vortex structures. Given the same inlet area, rectangular-to-circular ducts lead to higher flow drag force and total pressure loss than square-to-circular ducts. Characterized by the substantial flow separation and shock waves, the “S-shaped duct shows significant vertically-asymmetric characteristics.

Large-scale parallel topology optimization of three-dimensional incompressible fluid flows in a level set, anisotropic mesh adaptation framework

This papers considers the topology optimization of duct flows governed by the three-dimensional steady state Navier–Stokes equations, using anisotropic mesh adaptation to achieve a high-fidelity description of all fluid–solid interfaces. The numerical framework combines an immersed volume method solving stabilized, linear equal-order finite element formulations cast in the Variational Multiscale (VMS) framework, and level set representations of the interface, used as a posteriori anisotropic error estimator to minimize the interpolation error under the constraint of a prescribed number of nodes in the mesh. Both the resolution and remeshing steps are performed in a massively parallel framework allowing for the optimization of large-scale systems. In particular, an original parallelization strategy is used for mesh adaptation, that combines local remeshing performed sequentially and independently on each subdomain with blocked interfaces, and constrained repartitioning to optimally move the interfaces between subdomains in an optimal way, both iterated until a satisfying mesh and partition are obtained. The proposed approach reduces the computational burden related to the call of the finite element solver, compared to classical optimization schemes working on uniform grids with similar mesh refinement. For a given number of nodes, it improves the accuracy in the geometric description of all layouts. Finally, it has the potential to alleviates the end user from most of the post-processing step aiming at extracting the final layout, due to ability of anisotropic adapted meshes to generate intrinsically smooth designs. Numerical results are provided for several three-dimensional problems of power dissipation minimization involving several dozen million state degrees of freedom, for which the optimal designs agree well with reference results from the literature, while providing superior accuracy over prior studies solved on isotropic meshes (in the sense that the flow is better resolved, especially in the near-wall regions, and the layouts are more smooth). The potential of the method for engineering problems of practical interest is eventually exposed by optimizing the distributor section conveying the cold fluid within the plates of a plate fin heat exchanger.

Stratified inclined duct: direct numerical simulations

The stratified inclined duct (SID) experiment consists of a zero-net-volume exchange flow in a long tilted rectangular duct, which allows the study of realistic stratified shear flows with sustained internal forcing. We present the first three-dimensional direct numerical simulations (DNS) of SID to explore the transitions between increasingly turbulent flow regimes first described by Meyer & Linden (J. Fluid Mech., vol. 753, 2014, pp. 242–253). We develop a numerical set-up that faithfully reproduces the experiments and sustains the flow for arbitrarily long times at minimal computational cost. We recover the four qualitative flow regimes found experimentally in the same regions of parameter space: laminar flow, waves, intermittent turbulence and fully developed turbulence. We find good qualitative and quantitative agreement between DNS and experiments and highlight the added value of DNS to complement experimental diagnostics and increase our understanding of the transition to turbulence, both temporally (laminar/turbulent cycles) and parametrically (as the tilt angle of the duct and the Reynolds number are increased). These results demonstrate that numerical studies of SID – and deeper integration between simulations and experiments – have the potential to lead to a better understanding of stratified turbulence.

Investigation of solar Photovoltaic cell utilizing hybrid nanofluid confined jet and helical fins for improving electrical efficiency in existence of thermoelectric module

One of the choices for improving the productivity of a PVT solar unit is selecting a more effective cooling unit. To reach the better configuration of cooling technique, the circular tube has been equipped with helical fins in current study. Also, the confined jet has been considered in the bottom of the PVT system. The existence of a thermoelectric layer under the Tedlar layer makes the electrical performance increase. The testing fluid consists of the mixture of water and ND-Co3O4. The regime of flow in both duct and heat sink is laminar and the properties of testing fluid were predicted according to homogeneous mixture. The validation step showed that present code has good accuracy with published experimental data. Among various scrutinized configurations of fins, the best performance obtained for the case with four fins and nine revolutions. Although such configuration makes the overall efficiency to increase about 9.12%, it should be evaluated in view of pressure drop with calculating performance evaluation coefficient (PEC). The value of PEC of best case is about 5.4 which means that it is logical to use such configuration. Combining the jet with the best configuration of cooling duct makes the temperature uniformity and overall performance to increase about 62.38% and 10.58%.

Magnetoconvection in a horizontal duct flow — A parametric study

Mixed convection flows in a horizontal duct with a heated bottom wall and a magnetic field imposed in the horizontal transverse direction are analyzed numerically using the two-dimensional approximation valid in the limit of strong magnetic field effect. A parametric study is carried out to understand the effect of the Reynolds, Hartmann, and Grashof numbers on the flow. The focus is on the convection instability of the quasi-two-dimensional states that occur under strong magnetic fields. The range of existence of such states is established. Linear stability analysis and simulations of nonlinear regimes demonstrate that high-amplitude low-frequency magnetoconvective fluctuations are generated by the instability in a broad range of parameters and that their strength is not diminished as the magnetic field becomes stronger. Good agreement with experimental data is found.

Hepatic Bile Formation: Developing a New Paradigm.

In 1959, Ivar Sperber contrasted bile formation with that of urine and proposed that water flow into the canalicular conduit is in response to an osmotic, not a hydrostatic, gradient. Early attempts to support the hypothesis using a bile acid, sodium taurocholate, and the hormone secretin to stimulate bile flow led to conflicting data and a moratorium on attempts to further develop the initial proposal. However, current data amplify the initial proposal and indicate both paracellular and transcellular water flow into hepatic ductules and the canalicular conduit in response to an osmotic gradient. Also, the need to further modify the initial proposal became apparent with the recognition that bile acid aggregates (micelles), which form in the canalicular conduit, generate lecithin-cholesterol vesicles that contain water unrelated to an osmotic gradient. As part of this development is the recent introduction of the fluorescent localization after photobleaching technique for direct determination of hepatic duct flow and clarification of the role of biomarkers such as mannitol and polyethylene glycol 900. With the new paradigm, these biomarkers may prove useful for quantifying paracellular and transcellular water flow, respectively. SIGNIFICANCE STATEMENT: It is essential to identify and characterize all the sites for water flow during hepatic bile formation to obtain more precision in evaluating the causes and possible therapeutic approaches to cholestatic syndromes. Updating the Sperber proposal provides a new paradigm that addresses the advances in knowledge that have occurred.

An open-source anisotropic k−ε−v2−f model for turbulent viscoelastic duct flows

A novel open-source anisotropic k−ε−v2−f model is presented for turbulent viscoelastic duct flow with dilute polymeric solutions described by the finitely extensible nonlinear elastic-Peterlin constitutive model. The turbulence model for channel and square duct flow of Newtonian fluids is adapted to incorporate the polymeric terms within the governing equations. All the required non-linear terms are validated with simple closure models and are assessed a priori against independent direct numerical simulation data in fully developed channel flow. The NLTij term, which accounts for the interaction between fluctuating components of the conformation tensor and the velocity gradient tensor, is modeled with the mean flow direction, ti, and wall-normal, ni, present in the Newtonian model, based on the streamwise alignment of mean polymer stretch. The implicit polymer effects on pressure–strain are assessed with a simple ad hoc closure accounting for the reduced near-wall production of turbulent kinetic energy. The same closure is also adapted for the spanwise Reynolds stress predictions of polymer-enhanced secondary flow. The model performs well in channel flow and captures low, intermediate, and high drag reduction features for a wide range of rheological parameters. The capabilities are extended for square ducts (or any regular polygon) due to the symmetric modeling of the closure models, which can predict the mean streamwise and secondary flow features associated with second normal Reynolds stress differences. Accessible codes and models are crucial for the advancement and improvement of turbulent viscoelastic models, and an OpenFOAM C++ code package is developed and freely available on GitHub (https://github.com/MikeMcDermott-Code/v2f).

Numerical Study of Flow and Particle Deposition in a Block Duct

The primary of this study is to evaluate the characteristics of airflow organization and particle deposition in blocked ducts with various subgrid models. Five popular sublattice models are chosen to conduct this and the LES method is utilized to simulate the flow field and particle deposition properties of the duct. The results demonstrate that the features of the flow field varied amongst the different sub-grid models. The Smagorinsky and WALE models provide comparable findings, with only one pair of separated vortices in the leeward region. With small separated vortices and a small vortex structure near the wall in the leeward region, the WALES model, the WALES-Omega model, and the KET model are more informative. Simultaneously, a large number of particle groups with particle sizes ranging from 1nm to 50μm were selected for particle phase analysis. It was discovered that the deposition velocity of ultrafine particles below 1μm steadily reduced as particle size grew, whereas the deposition velocity of particles larger than 1μm rose as particle size increased.

Calibration of Miniature Mass Flow Plug for Metering and Control of Intake Duct Flows

The results of experimental calibration of 63mm mass flow plug are presented here. An orifice meter was used as a reference along with total pressure rake to calculate mass flow through the intake duct. The calibration was carried out without intake and fore-body at pressurized condition including atmospheric as well as with intake and fore-body at atmospheric condition only. The results showed that the choked area obtained from orifice plate and total pressure rake data is linear. The calibration data obtained from rake data was higher than that of orifice data, which may be due to highly distorted flow at the dump region. The discharge coefficient is comparable to previously carried out calibration of bigger size of 94 mm mass flow plug.

Design and Numerical Simulation of the Performance of Acoustic Plenum Chamber of a Marine Gas Turbine Air Supply System

In the present work, an approach to obtain a design method for the size of the plenum chamber cross-section of a marine gas turbine air supply system has been investigated. Flow in ducts makes noise which is very high in the turbine inlet part because of the large amount of flow. Therefore, this phenomenon should be considered in the design process. A suitable approach to design the duct is proposed (considering acoustic and aerodynamic performance at the same time). In this method, an air supply channel system of the marine gas turbine has been categorized into three sections according to the requirements of the aerodynamic and acoustic; inlet, plenum chamber, and outlet channels with circular cross-sections. The geometrical dimensions of inlet and outlet channels have been determined using the plane waves theory about a channel, in which the effects of flow is ignored. Space limitations of battleships at the dominant frequency have been considered. Then, the optimized size of the mid-channel section, in terms of both aerodynamic and acoustic requirements, using numerical methods and regarding the effects of flow has been calculated. Various 3D turbulent flows inside the plenum chamber have been considered, in which large eddy simulation turbulence model is utilized. Ffowcs, Williams and Hawkings models are used for the sound propagation process based on the Lighthill integral equation. The validity of the simulation has been checked by comparing results (sound pressure level) with experimental data obtained from a chamber. The comparison revealed the acceptable errors for a variety of frequencies. The results disclosed that the performance of channel system aerodynamic decreased when the fraction of plenum chamber cross-section to inlet/outlet channel cross-section increased. With an increase in the cross-section size at first Acoustic performance is improved and then worsen. Six different cases of marine gas turbine air supply system configurations have been presented, in which the limitation of the battleship space is considered. Examining and comparing the acoustic performance of different cases of the air supply channel system, it was found that the amount of sound pressure level, around the air supply channel system, and the high-pressure sound area can move along the air supply channel system. Additionally, deviations from plane waves considering the effects of flow have been inspected in all cases. The reason for this deviation is the effects of the airflow through the channel system and quadrupole sources in the production of sound in the channel system, which causes higher modes.

Fully Developed Laminar Flow of Heat Transfer Non-Newtonian Flow in Ducts with Arbitrary Cross-Sectional Shape

The pressure drop and heat transfer properties of a laminar flow with circular, square, and triangular cross sections and a constant heat flux boundary condition are given by a numerical solution. A 3D Navier-Stokes incompressible flow and energy equation serves as the foundation for the numerical model. Results are tabulated and given visually for the velocity field, Poiseuille number, and Nusselt number product for various power-law indices (0.5 n 1.0). One of the analyzed ducts causes a greater heat transfer intensification along with a significant pressure loss. A different type of duct allows for a better balance between pressure loss and heat transfer. In order to verify the accuracy of the numerical codes created in the current study, critical comparisons with earlier findings in the literature are also carried out.

ISO-FLUCS: symmetrization of optofluidic manipulations in quasi-isothermal micro-environments

Recently, it has been demonstrated that thermoviscous flows can be used for a range of fine micromanipulations, such as moving the cytoplasm of cells and developing embryos, intracellular rheology, and femtonewton-range force measurements. These flows, also known as focused-light-induced cytoplasmic streaming (FLUCS), are induced by mid-infrared laser scanning of a temperature spot through the sample. However, localized laser scanning can inflict temperature perturbations of several Kelvins on the sample, potentially eliciting unspecific biological responses. In this study, we demonstrate how exploiting symmetry relations during laser scanning effectively disentangles laser heating and flow induction. We introduce flow-neutral scan sequences that use dynamic photothermal stimuli and spatiotemporal symmetry relations of scanning bridging up to three distinct time scales. We leverage further insights from a recently published analytical model of flow fields to present quasi-homogenous temperature distributions that leave flow lines and their local and directed character largely invariant. We present practical, intuitive solutions through predesigned sets of scan lines with near isothermal distributions and demonstrate that they are sufficient to generate and control flows in Caenorhabditis elegans embryos on a magnitude well in excess of endogenous flow velocities. Our results enable the separation of two previously tightly linked classes of physical stimuli, introduce a new, even less invasive standard for performing FLUCS perturbations, and pave the way for new unexplored avenues in the fields of soft matter and biomedicine.Graphical

Adjoint shape sensitivities of blood flows considering non‐Newtonian properties

AbstractThis article discusses the derivation and numerical implementation of an adjoint system, to the primal Navier–Stokes equations, for the computation of shape sensitivities of ducted blood flows considering non‐Newtonian fluid properties. The ever‐growing advancements in blood flow simulations are, naturally, accompanied by an increased interest in the optimization of related medical devices. In the majority of the computational studies, the Newtonian assumption is used to describe the rheology of blood. While this assumption has been shown to satisfactorily capture the flow when it is governed by high shear rates, it falls short at low shear rates. A rich variety of viscosity models has been proposed to tackle this shortcoming. In this article we show how such models can be incorporated into an adjoint system targeting to produce the shape sensitivity which can be used by a gradient‐based optimization method for the minimization of an objective functional. A general formulation of the adjoint equations is proposed, in which contributions of the non‐Newtonian properties explicitly occur. The numerical implementation is discussed and the validity of the method is assessed by means of numerical experiments of steady blood flows in a 2D stenosed duct, where results are compared against second‐order finite‐difference (FD) studies. The proposed methodology is then applied to CAD‐free, gradient‐based shape optimizations of an idealized 3D arterial bypass‐graft operating at three relevant Reynolds numbers. It is observed that the impact of the adjoint viscosity treatment is amplified in low shear‐rate flow regimes while fades for higher shear‐rates, analogous to its primal counterpart.

DRBEM solution of singularly perturbed coupled MHD flow equations

In this study, the numerical solution of singularly perturbed magnetohydrodynamic (MHD) flow in a square duct with no-slip, and insulated or perfectly conducting walls is investigated by using the Dual Reciprocity Boundary Element Method (DRBEM). The steady, laminar and fully-developed MHD flow of an incompressible, viscous, and electrically conducting fluid in a long channel of square cross-section (duct) is driven by a pressure gradient. The governing MHD flow equations are convection–diffusion type and coupled in terms of the velocity V(x,y) and induced magnetic field B(x,y). When the intensity of horizontally applied external magnetic field is high, the Hartmann number (Ha) which is the coefficient of convection terms becomes large, that is, the coupled MHD flow equations become convection dominated. In other words, the coefficient of the diffusion terms is very small giving singularly perturbed MHD duct flow which exhibits thin boundary layers. The numerical scheme uses Shishkin mesh which depends on the number of points on one side and Ha. Numerical results obtained by DRBEM reveal that the well-known characteristics of the MHD flow problem are found as Ha increases and it is possible to obtain V(x,y) and B(x,y) for large values of Hartmann number up to Ha=1000.

Thermal streak spacing in fully developed duct flow with different Reynolds and Prandtl numbers

The present study investigates the behaviour of thermal streaks on a heated foil which is cooled with turbulent flow in a square duct channel. Real-time infrared thermography is used to visualize and measure the spacing between the thermal streaks. A stainless-steel foil with a thickness of 25 microns is cooled by water. The experiments were performed in a range of Reynolds numbers from 5000 to 20000 and Prandtl numbers from 3 to 7. The mean temperature, root-mean-square of temperature and autocorrelation function have been calculated and used to measure the average thermal streak spacing and power spectra in the spanwise and streamwise directions. The root mean square temperature was 0.3 °C to 0.5 °C which corresponds to roughly 10% of the mean temperature difference between foil and water. The uncertainty in mean temperature difference and root mean square temperature was around 5% and 10%, respectively. The measured thermal streak spacing was 100 wall unit to 180 wall unit under the present experimental range. The uncertainty in measured thermal streak spacing was around 2.5%. The effects of Reynolds number, Prandtl number and heat flux on the thermal streak spacing and also on the statistics of the temperature field have been presented and discussed in this paper. A new correlation has been proposed to predict the dimensionless thermal streak spacing. The error in the prediction is estimated within ± 15 %.

A study of the effect of curvature and pressure gradient on aerodynamics performance and turbulence structure of S-shaped compressor transition duct

ABSTRACT The overall performance of the high-pressure compressor in a turbofan engine entirely depends on the flow supplied by the upstream transition duct. A robust and efficient design of the transition duct conveys a highly uniform flow with minimum pressure loss. The present study aimed to determine the effect of adverse pressure gradient and curvature on the flow of the compressor duct. The results suggest that the outer wall curvature causes a significant decrease in from +0.19 to −0.6, and as a result, 75% length of the outer wall is suspended in the favourable pressure gradient. On the contrary, it increases from −0.54 to +0.14 along the inner wall. It implies that most of the inner wall lies in the adverse pressure gradient; consequently, the turbulence structure, mean flow behaviour, and Reynolds stresses are considerably modified. The presence of a strong adverse pressure gradient significantly enhances turbulence quantities along the inner wall. Additionally, the boundary layer parameters grow relatively thicker along the inner wall than on the outer wall. As a result, a considerable increase in the shape parameter (H = 2.12) is obtained.

Simulation of latent heat thermal storage evaluation utilizing NEPCM for new ventilation system for building

In present attempt, MWCNT nano-powders were loaded inside paraffin (SP24E) to boost the rate of phase changing to liquid. The melting process needs heat and warm air flow supplies such heat. The air flow duct was combined with different circular cylinders which filled with paraffin. The flow inside air zone is laminar and gravity effect has been neglected. With changing the diameter of cylinder, four various arrangements have been generated and simulation of melting process have been presented via ANSYS FLUENT. Loading MWCNT can decrease the time of melting about 3.86% and the related percentage for the case with lower DR decreases about 1.11%. Reducing diameter ratio from 0.16 to 0.08 makes the completion time to reduce about 38.77%. The quickest charging occurs at φ = 0.04, DR = 0.08 in which melting completed after 247.75 min.