Vortex Size Research Articles

Conjugate Heat Transfer Analysis of Flat Plate Subjected to Impingement and Film Cooling

Abstract: The present computational study involves a flat plate subjected to combined effect of jet impingement and film cooling. A conjugate heat transfer model in conjunction with k-ω SST turbulence model is employed to study the turbulence effects. The effect of Reynolds number varying from 389 to 2140 on static temperature, Nusselt number and film cooling effectiveness has be discussed for the blowing ratios of 0.6, 0.8, 1.0. The variation in the size of vortices formed on the impinging surface with Reynolds number is studied. It has been observed that the local Nusselt number shows a rising trend with the increase in Reynolds number, while the static temperatures follow the downfall in its values. As a result, an enhancement in the effectiveness is observed, which is credited to the capabilities of combined impingement and film cooling. At Reynolds number of 972, the coolant jet is found to be attached to the surface, for this condition the heat transfer phenomena for blowing ratios of 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 2.4, 2.6 are studied to understand the flow distribution on the plate surface. Keywords: Jet impingement, film cooling, effectiveness, conjugate heat transfer

Study of Flow and Heat Transfer for the Supercritical Hydrogen in Spallation-Type Cylindrical Neutron Moderator

Pipe height in cylindrical neutron moderator is an important factor to flow pattern, temperature distribution and even the neutron characters. In this paper, the steady-state thermal analysis of cold neutron moderator is carrying out with different heights, conjugated heat transfer method and one-way coupled with a neutron transfer software. The different pipe heights, which is the jet-to-surface distances (H/D = 0.5~6), were compared using a 2D moderator model. The results show that vortex size and velocity gradient from container wall to vortex center vary with H/D, the center of recirculation zone nearly remain constant, and heat transfer effect is weakened on the target bottom surface. With H/D increasing, the velocity at bottom target surface is progressively decreased, and cooling effect is poor, leading to the rise in temperature. The optimal range cooling performance is (H/D) = 0.5~1 at Re = 1.7 × 105, and the enhancement of beam power further strengthens the thermal deposition difference between container and liquid hydrogen. The results can be applied to moderator component design and optimization in the future spallation neutron source.

Aerodynamics-assisted, efficient and scalable kirigami fog collectors

To address the global water shortage crisis, one of the promising solutions is to collect freshwater from the environmental resources such as fog. However, the efficiency of conventional fog collectors remains low due to the viscous drag of fog-laden wind deflected around the collecting surface. Here, we show that the three-dimensional and centimetric kirigami structures can control the wind flow, forming quasi-stable counter-rotating vortices. The vortices regulate the trajectories of incoming fog clusters and eject extensive droplets to the substrate. As the characteristic structural length is increased to the size of vortices, we greatly reduce the dependence of fog collection on the structural delicacy. Together with gravity-directed gathering by the folds, the kirigami fog collector yields a collection efficiency of 16.1% at a low wind speed of 0.8 m/s and is robust against surface characteristics. The collection efficiency is maintained even on a 1 m2 collector in an outdoor setting.

Electroconvective Instability in Water Electrolysis: An Evaluation of Electroconvective Patterns and Their Onset Features

In electrochemical systems, an understanding of the underlying transport processes is required to aid in their better design. This includes knowledge of possible near-electrode convective mixing that can enhance measured currents. Here, for a binary acidic electrolyte in contact with a platinum electrode, we provide evidence of electroconvective instability during electrocatalytic proton reduction. The current-voltage characteristics indicate that electroconvection, visualized with a fluorescent dye, drives current densities larger than the diffusion transport limit. The onset and transition times of the instability do not follow the expected inverse-square dependence on the current density, but, above a bulk-reaction-limited current density are delayed by the water dissociation reaction. The dominant size of the electroconvective patterns is also measured and found to vary as the diffusion length scale, confirming previous predictions on the size of electroconvective vortices.

Internal structure of localized quantized vortex tangles

In this study, we numerically investigate the internal structure of localized quantum turbulence in superfluid $^4$He at zero temperature with the expectation of self-similarity in the real space. In our previous study, we collected the statistics of vortex rings emitted from a localized vortex tangle. As a result, the power law between the minimum size of detectable vortex rings and the emission frequency is obtained, which suggests that the vortex tangle has self-similarity in the real space [Nakagawa $et$ $al.$, Phys. Rev. B $\boldsymbol{101}$, 184515 (2020)]. In this work, we study the fractal dimension and vortex length distribution of localized vortex tangles, which can show their self-similar structure. We generate statistically steady and localized vortex tangles by injecting vortex rings with a fixed size. We used two types of injection methods that produce anisotropic or isotropic tangles. The injected vortex rings develop into a localized vortex tangle consisting of vortex rings of various sizes through reconnections (fusions and splitting of vortices). The fractal dimension is an increasing function of the vortex line density and becomes saturated to a value of approximately 1.8, as the density increases sufficiently. The behavior of the fractal dimension was independent of the anisotropy of the vortex tangles. The vortex length distribution indicates the number of vortex rings of each size that are distributed in a tangle. The distribution of the anisotropic vortex tangle shows the power law in the range above the injected vortex size, although the distribution of the isotropic vortex does not.

Numerical Simulation and Linearized Theory of Vortex Waves in a Viscoelastic, Polymeric Fluid

In a high viscosity, polymeric fluid initially at rest, the release of elastic energy produces vorticity in the form of coherent motions (vortex rings). Such behavior may enhance mixing in the low Reynolds number flows encountered in microfluidic applications. In this work, we develop a theory for such flows by linearizing the governing equations of motion. The linear theory predicts that when elastic energy is released in a symmetric manner, a wave of vorticity is produced with two distinct periods of wave motion: (1) a period of wave expansion and growth extending over a transition time scale, followed by (2) a period of wave translation and viscous decay. The vortex wave speeds are predicted to be proportional to the square root of the initial fluid tension, and the fluid tension itself scales as the viscosity. Besides verifying the predictions of the linearized theory, numerical solutions of the equations of motion for the velocity field, obtained using a pseudo-spectral method, show that the flow is composed of right- and left-traveling columnar vortex pairs, called vortex waves for short. Wave speeds obtained from the numerical simulations are within 1.5% of those from the linear theory when the assumption of linearity holds. Vortex waves are found to decay on a time scale of the order of the vortex size divided by the solution viscosity, in reasonable agreement with the analytical solution of the linearized model for damped vortex waves. When the viscoelastic fluid is governed by a nonlinear spring model, as represented by the Peterlin function, wave speeds are found to be larger than the predictions of the linear theory for small polymer extension lengths.

Space-Charge breakdown phenomenon and spatio-temporal ion concentration and fluid flow patterns in overlimiting current electrodialysis

Overlimiting current regimes are of practical interest for electrodialysis with ion-exchange membranes (IEMs) operating at current densities significantly higher than the limiting current density. Such high ion currents across the membranes allows reducing the investments into expensive IEMs and stacks. Electroconvection (EC) is the major contributor to the overlimiting current and concepts to utilize EC are highly desired. Most of the known theoretical works describing EC in electrodialysis channels are performed when only a single cation exchange membrane is considered. The presence of a neighboring anion-exchange membrane has not been considered so far.We report the results of direct numerical simulations of ion and water transport involving EC in an electrodialysis channel formed by a cation- and an anion-exchange membrane. A 2D “basic” model involving the Nernst-Planck-Poisson-Navier-Stokes equations is introduced. Details of spatio-temporal changes in the distribution of concentrations and space charge patterns as well as the interactions of EC vortices are analyzed.The presence of the anion-exchange membrane in the transition to a close-to-chaotic regime at high potential difference is examined. For the first time, we discover the phenomenon of space-charge breakdown where the space charges of opposite sign formed at the two membranes are short-circuited throughout the desalination channel. The details of the mechanism of this phenomenon are analyzed using the 2D model and a simplified 1D model. Simulations show that the space-charge breakdown leads to a decrease in the size and number of EC vortices in the region of breakdown, which results in a reduction of the local current density. This phenomenon, apparently, determines the upper limit of the possible increase in the mass transfer rate by electroconvection.

Effects of diffuse and collimated beam radiation on a symmetrical cooling case of natural convection

In any scenario of heat transfer in fluid medium, all modes, i.e., conduction, convection and radiation are present. Further, the radiation heat transfer may be diffuse (propagation of energy in all directions) or collimated (energy propagates in single direction). The qualitative and quantitative analysis of radiation heat transfer are required in order to understand its effects on the fluid flow and also on heat transfer. In the present work, the effects of diffuse and collimated radiation on the symmetrical cooling case of natural convection in a two-dimensional cavity heated from the bottom have been investigated, numerically. The cavity is convectively heated from the bottom, while both vertical walls of the cavity are isothermal. The top wall is adiabatic and all walls are opaque for radiation heat transfer. For the collimated case, a small semitransparent window has been created on the left wall and collimated irradiation of value 1000 W/m2 at an azimuthal angle 135°is applied on this semitransparent window. The study has been performed in two stages, first, the effect of diffuse radiation on the natural convection has been observed and then, in the second stage, a collimated beam is passed through the semitransparent window. The results reveal that the diffuse radiation has little effect on the dynamics of two rolls inside the cavity, however, collimated beam irradiation changes the dynamics of two rolls significantly and also the heat transfer characteristics. This further changes with the optical thickness of the fluid. The left vortex is bigger than the right vortex for collimated beam in transparent fluid, whereas, a reverse trend is seen for the collimated beam for the non-zero optical thickness of the fluid. The size of the left vortex increases with the increase of optical thickness of the fluid. The heat transfer reversal happens at the zone of a collimated beam incident on the bottom wall for transparent medium, whereas, this does not happen for participating medium. Further, this study helps in understanding the heat transfer in a room, fluid flow in shallow water lakes affecting aquatic life etc., due to solar radiation.

Vortex-induced Vibration and Control of Split Three-Box Girder Bridges

The vortex-induced vibration (VIV) performance and aerodynamic mechanism of VIV control of a split three-box girder bridge were investigated numerically by Computational Fluid Dynamics (CFD). Large-scale section model wind tunnel tests show that the integrated countermeasure combined by 30% ventilation ratio grids and new scheme for maintenance tracks can effectively restrain vertical and torsional VIVs. The reliability of numerical method is verified by comparing static three-component coefficients and Strouhal numbers obtained from CFD and wind tunnel tests. The flow structure and changes of aerodynamic forces were analyzed via delayed detached-eddy simulation (DDES). For the original section, large-scale vortices form with shedding behind the safety barrier of the upstream box and behind the maintenance tracks, as well above the downstream highway box, introducing periodic pulsating lifts and moments that result in severe VIVs. The grids can effectively reduce the size of vortices in the gaps, prevent the flow from fluctuating and reduce the pressure difference between upper and lower surfaces. The torsional VIVs at non-negative attack angles are not controlled because the grids cannot interfere with the vortices behind the maintenance tracks. The new scheme for maintenance tracks, which has grid-like effects, can eliminate the torsional VIVs at non-negative attack angles by preventing the vortices behind maintenance tracks from impacting downstream boxes. The aerodynamic force components are analyzed to find that box 1 mainly contributes the mean values and box 3 mainly contributes the fluctuating values. The integrated countermeasure can reduce the mean and RMS values of aerodynamic forces to varying degrees. The streamlines and RMS pressure contours indicate that the integrated countermeasure effectively reduced the wake height and vortices motion range, which is conducive to VIV control. This work lays a solid foundation for an in-depth understanding of the aerodynamic characteristics and optimization mechanism of split three-box girder bridges.

Numerical investigation on splitter plate jet assisted mixing in supersonic flow

Efficient mixing is of great importance for engineering applications of hypersonic propulsion systems. With supersonic air flowing through the interior of combustor in milliseconds, rapid mixing of airstream and fuel becomes one of the great challenges, and it is imperative to employ mixing enhancement strategies to improve the system performance. In present work the splitter plate jet assisted mixing (SPJAM) strategy is proposed and direct numerical simulations are conducted to reveal enhanced-mixing mechanisms. Both instantaneous fine structures and turbulent intensity distributions are obtained to analyze the flow dynamical behaviors. Mixing layer thickness growth rate and structure topology properties affected by SPJAM are researched as well. The results indicate that the introduction of SPJAM can significantly promote mixing by means of the newly found T-shaped structures and its dynamics. The interaction of T-shaped structure and inherent Kelvin-Helmholtz vortex leads to the breakdown of flow structures, which can obviously increase the interface of upper and lower streams. Turbulent intensity analysis suggests that with the effect of SPJAM, the region where turbulent activity exists is notably extended, and the peak values of the fluctuations are much larger. The evolution of transversely-integrated turbulent kinetic energy (IK) indicates that rapid increase of IK appear in the near field of the flow. Spatial correlation analysis results indicate that vortex size is notably increased with the introduction of SPJAM, especially for that with the strategy set at the front of the splitter plate. Through exploration of the enhanced-mixing mechanisms, present preliminary work indicates that the proposed strategy is a good candidate for efficient mixing, and in the future more detailed work including three-dimensional simulations concerning the strategy optimization should be conducted.

Effect of inlet temperature on flow behavior and performance characteristics of supercritical carbon dioxide compressor

Centrifugal compressors have been widely applied in supercritical carbon dioxide (SCO2) Brayton cycle because of its compactness and low power consumption. However, the dramatic change in supercritical carbon dioxide near the critical point (304.13 K, 7.38 MPa) under different inlet temperatures brings challenges to compressor operation, especially with asymmetric boundary conditions. In this study, full annular calculations of a centrifugal compressor with a volute are conducted by imposing different inlet total temperatures. The sensitivity of the performance characteristics of each component to the inlet temperature was obtained. Two-phase region, dominant flow structure in the impeller, and downstream flow field structure distortion caused by inlet temperatures were revealed. The results showed that when the inlet condition was close to the critical point of supercritical carbon dioxide, the size of the two-phase region in the impeller increased and its circumferential nonuniformity was intensified. At 309 K, the two-phase region caused an enthalpy rise fluctuation at the blade tip and a difference in enthalpy at the blade outlet. Moreover, with the decrease in inlet temperature, the size and range of the counterclockwise vortex gradually increased, leading to the transportation of low-momentum fluid from the pressure side to the suction side of the blade. In addition, the wake at the impeller outlet was accumulated and the impeller discharge flow deteriorated, resulting in local flow separation in the vaneless diffuser.

Heat vortices of ballistic and hydrodynamic phonon transport in two-dimensional materials

Heat conduction in solid materials may behave like fluid dynamics when normal (N) scattering dominates phonon transport. In this hydrodynamic regime, the heat vortices have been predicted with frequency-independent relaxation time. So can this phenomena appear in other regimes? And what are the differences? In order to answer these questions, in this work, the heat vortices in two-dimensional materials are investigated based on the frequency-dependent phonon Boltzmann transport equation (BTE) under the Callaway model. We find that apart from the hydrodynamic regime, the heat vortices can appear in the ballistic and other transition regimes, which is a wider window of heat vortices compared to previous study (Fig. 1). The differences of heat vortices in the ballistic and hydrodynamic regime are investigated. In ribbon structure, the vortices sizes increase with system length in the ballistic regime but are confined by the system width in the hydrodynamic regime. In porous structures, the critical values of τR (or τN) about when the heat vortices disappear (or when the vortices size starts to become smaller) are found.

Influence of Boundary Layer Skew on the Tip Leakage Vortex of an Axial Compressor Stator

Abstract For an axial compressor stator with tip gap, the boundary layer (BL) in the hub endwall region has a significant influence on the development and progression of the tip leakage vortex. Herein, the so-called BL skew, which develops through relative motion of the hub, is of particular interest. Therefore, experimental and numerical investigations of a single axial compressor stator row with varying tip gap height (tip gap height/chord length =2.0%|5.4%|6.7%) have been conducted. Comparing cases with rotating or stationary hub endwall segments upstream of the examined vanes allowed to determine the effect of the skewed and un-skewed inflow BL. The steady-state flow fields up- and downstream of the stator row were measured using five-hole pressure probes. For validation and to improve the understanding of the existing flow phenomena, 3D-Reynolds-averaged Navier–Stokes (RANS) CFD simulations using a commercial flow solver were carried out. Furthermore, analog cases with no tip gap were examined and considered in the comparisons to extend the knowledge on this BL characteristic. The results show that the BL skew has a major influence on the trajectory and size of the tip leakage vortex for the cases with tip clearance. The effect of reduction of the produced losses decreases with increasing tip gap height.

Aerodynamic and Mechanic Analyses of An Asymmetrically Scalloped Radial Turbine

In order to reduce the aerodynamic efficiency loss of deeply scalloped radial turbines, asymmetrically scalloping of turbines’ backdisc has been invented for a number of years. However, the mechanism how this works and its mechanical implication have not been reported in the open literature. In this paper, taking the symmetrically scalloped turbine of a turbocharger for marine generator application as the baseline, two asymmetrically scalloped turbines were developed from it: one with scalloping bias to the pressure side, and the other to the suction side of the blades. Mechanic and aerodynamic analyses of these three turbines were carried out using ANSYS Workbench. The results indicate that the asymmetrically scalloped turbine with scalloping bias to the pressure side can reduce the backdisc-heat shield cavity leakage flow going into the blade suction surface through the scalloped backdisc, due to the influence of the high pressure near the pressure surface of the blade, thus decrease the size of vortices the leakage flow generated near the suction surface inside the blade passages and associated mixing loss. Compared to the symmetrically scalloped turbine, it increases the maximum principal stress by 0.39% and 5.2% at blade fillet and backdisc respectively, but the aerodynamic efficiency of the turbine is increased by 0.78% point at a turbine U/C value of 0.43, and the smaller the value of the U/C is, the greater the efficiency advantage will be. By contrast, the turbine with suction side bias scalloping shows the poorest aerodynamic performance, due to an increased leakage flow through its scalloped backdisc.

A revisitation of White−Metzner viscoelastic fluids

The famous White–Metzner (WM) constitutive equation expresses a relatively simple nonlinear viscoelastic fluid of polymer melts. However, such a differential stress model, substantial with strong hyperbolic and singular problems, has hitherto always obtained unsatisfactory simulations of corner vortex in a typical contraction flow, especially for high Weissenberg numbers. A modified WM model useful for viscoelastic fluid computations is, therefore, proposed herein. As a validation, this model primarily fits the first normal stress difference for characterizing a fluid's elasticity, as well as shear viscosity and extensional viscosity. It is significant to discuss the vortex formation and growth, with the predicted vortex sizes in good agreement with the experimental data.

Numerical simulation of adiabatic/cooled/heated spherical particles with Stefan flow in supercritical water

When droplets or particles are in complex fluid-temperature-environment conditions, the spatial variation in temperature-dependent properties affects the overall particle-laden flow behavior. Particularly, in a high-temperature environment, the components on the particle surface are heated and volatilize to form a mass flow, named the Stefan flow, that influences the mass, momentum, and energy transfer between particles and the fluid. For supercritical fluids, small changes in temperature and pressure cause substantial changes in thermophysical properties. Hence, in this work, we study the characteristics of supercritical water flowing past an adiabatic/cooled/heated sphere for Re = 10–200 with and without Stefan flow. The three-dimensional numerical simulations that are conducted consider the exact water thermophysical properties. The flow field, the Nusselt number (Nu), the drag coefficient (Cd), and the velocity and temperature distribution around the particle are analyzed. The results demonstrate that the vortex is strongly influenced by the variation in viscosity near the particle. The Cd and Nu values of the cooled and heated spheres show different deviations in different conditions. The influence of Stefan flow cannot be ignored as it increases the vortex size and decreases both Cd and Nu. Finally, the effect of Stefan flow on both Cd and Nu of the cooled sphere is greater than that of the heated sphere.

Study on the flow characteristics in the supersonic morphing cavities using direct numerical simulation and proper orthogonal decomposition

Supersonic flows past the morphing cavities with different ramp angles of the trailing wall are studied by the direct numerical simulation (DNS) method. As the ramp angle increases, the sound pressure level of the dominant mode and overall sound pressure level gradually decrease at the last monitor point. The number of the feedback shock waves and the size of the large-scale vortices also gradually decreases. The vortex wave moving downstream slowly disappears. When the ramp angle increases to 30 and 40 degrees, the dominant mode at the front of the cavity shifts from mode 3 to mode 1. In addition, the flow structures in the morphing cavities are analyzed using proper orthogonal decomposition (POD). Results indicate that the energy occupied by the POD modes, the size of the flow structures, and the amplitude of POD coefficients all decrease with the ramp angle increase. Compared with the fixed-geometry cavity with the ramp of the trailing wall, the results show that there is a better noise reduction effect and the flow structure is changed in the morphing cavity. In a word, the morphing cavity control method effectively suppresses cavity noise, greatly weakens the sensitivity of the shear layer, and obviously changes the flow structure in the cavity.

Large Eddy Simulation of three‐dimensional flow structures over wave‐generated ripples

AbstractWe performed a three‐dimensional high‐resolution Large Eddy Simulation using a sinusoidal ripple‐like bedform geometry with spacing and amplitude consistent with equilibrium conditions under the prescribed oscillatory forcing. The simulation results are validated qualitatively and quantitatively with previous laboratory experiments and numerical simulations. Our numerical simulations allow to analyze the presence of “ribs”, strong flow rotational features in the spanwise direction developing perpendicular to the ripple crest. We show that ribs tend to appear on the upslope and crest of ripples and display a dominant spacing, ranging from 0.5λ to λ, during wave phases associated to flow acceleration. When the vortex is transported over the downstream ripple during the flow deceleration, ribs appear for the second time over the upslope of the downstream ripple, with the dominant spacing about 1/8 ripple wavelength. The presence of flow three‐dimensionality corresponds to a large variability of the shear stress over ripples in the spanwise direction, which could ultimately favor the development of three‐dimensional geometry. The three‐dimensional vortex dynamics are evaluated using the concept of vortex strength. Peak vortex strength is observed at the maximum free stream velocity, but the largest variation of the vortex strength and vortex size in the spanwise direction occurs prior to the flow reversal. The variability of the vortex structures might provide a favorable setting for the development of ribs and might relate to the spacing of ribs.

Hemodynamic change in patients with hypertrophic obstructive cardiomyopathy before and after alcohol septal ablation using 4D flow magnetic resonance imaging: a retrospective observational study

BackgroundThe hemodynamics in the left ventricle (LV) and the ascending aorta (AAO) before and after alcohol septal ablation (ASA) in patients with hypertrophic obstructive cardiomyopathy (HOCM) is elucidated. Our objective was to evaluate the pattern changes in AAO and intra-LV flow assessed by four-dimensional (4D) flow magnetic resonance imaging (MRI) before and after ASA and to clarify the association between 4D flow MRI-derived hemodynamic characteristics and the peak pressure gradient (PPG) in patients with drug-refractory HOCM.MethodsIn this retrospective observational study, 11 patients with HOCM underwent 4D flow MRI before and a week after ASA. The 4D flow MRI included blood flow visualization and quantification using streamline images. The combined score of vortex and helix in AAO was analyzed. The duration and phase count of the AAO vortex or helix flow and the size of the intra-LV anterior vortex were quantified. The correlation between the changes in hemodynamics and the resting PPG at LV outflow tract was also analyzed. We used the paired t-test for the comparison between before and after ASA and the Pearson’s correlation coefficient for the analysis.ResultsThe combined score for the incidence of vortex and/or helix flow in AAO after ASA was significantly lower than that before ASA (1.45 ± 0.52 vs. 1.09 ± 0.30, p = 0.046). The duration (744 ± 291 ms vs. 467 ± 258 ms, p < 0.001) and phase count (14.8 ± 4.4 phases vs. 10.5 ± 5.8 phases, p < 0.001) of the vortex or helix flow in AAO were significantly decreased after ASA. The LV anterior vortex area after ASA was significantly larger than that before ASA (1628 ± 420 mm2 vs. 2974 ± 539 mm2, p = 0.009). The delta phase count of the AAO vortex or helix before and a week after ASA was significantly correlated with delta PPG before and a week after ASA (R = 0.79, p = 0.004) and with delta PPG before and 6 months after ASA (R = 0.83, p = 0.002).ConclusionsLower vortex or helix flow in AAO and larger diastolic vortex flow in LV were observed after ASA, which suggests the possibility to detect the changes of aberrant hemodynamics in HOCM.

Impacts of double rotating cylinders on the forced convection of hybrid nanofluid in a bifurcating channel with partly porous layers

Impacts of using double rotating cylinders and partly porous layers in the bifurcating channels on the hydro-thermal performance were numerically assessed. Hybrid nanoparticles were used in water and finite element method was selected as the solver. Effects of Reynolds number, rotational speeds of the cylinders and their locations in the bifurcating channels, porous layer sizes and nanoparticle solid volume fractions on the hydro-thermal performance features were explored. The contribution of different hot wall parts was changed with varying Reynolds number and rotational velocity of the cylinders. Depending upon the rotational direction of the cylinders, the vortex occurrence and size at the bifurcations change significantly. Heat transfer considering all hot walls rise with higher rotational speeds in both directions. The amount of improvement in the heat transfer rate becomes 25% and 19% with varying speeds of the cylinders as compared to motionless cylinders. The pressure coefficient reduces with increasing the second cylinder speed in clockwise direction and this is favorable for thermal performance since the heat transfer also increases. The overall impact of the varying horizontal locations of the cylinders on the heat transfer rate is slight. The separated zones at the branching depends on the porous layer sizes. The overall heat transfer behavior becomes opposite when varying the sizes of the porous layers in the horizontal and vertical channels. By using nanoparticles in the base fluid, 35.75% improvement in the heat transfer rate is achieved for vertical wall at Re = 350 while pressure drop coefficient rises by about 8.5%. The overall improvement in the heat transfer rate by using nanofluid is 26%. Owing to diverse use of bifurcating channels in thermal engineering from fuel cells to electronic cooling, the proposed methods of heat transfer enhancement techniques can be considered simultaneously for effective control the thermal performance of those systems.