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The present comment concerns some doubtful results included in the above paper. • The comment concerns a paper published in JML. • The slip parameter and the local Reynolds number are dimensional and wrong. • The local skin friction coefficient and the local Nusselt number are dimensional and wrong. [ABSTRACT FROM AUTHOR]

This communication concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient numerical scheme to deal with heat transfer problems in pipe flow with a large length/diameter ratio. The generalized finite difference method (GFDM) is combined with a space stepping algorithm (SSA) for the solution. The SSA divides the solution domain into a number of overlapping sections in the length direction of the pipe. Due to the large Peclet number, the heat transport process is dominated by advection, which allows an approximate boundary condition to be applied at the downstream cross section. The problem is then solved section by section. Using the uniform distributed points, the solution matrix for each section does not change, and only the right hand side needs to be refreshed for the changing boundary conditions. This leads to a highly efficient scheme for problems with a large pipe length. To show the accuracy of the numerical scheme, a problem with available analytical solution is studied. Then the method is applied to problems of single pipe with different pipe wall temperature and flow Reynolds number, and concentric annular pipe. Numerical results confirm the stability and efficiency of the GFDM-SSA. The method can be applied to many real world transient heat transfer problems in which the pipe is heated or cooled along its length with arbitrary wall temperature for heat exchange and other purposes. [ABSTRACT FROM AUTHOR]

Understanding spermatozoa transportation in the human female cervical canal, particularly in relation to the fertilization process, holds significant physiological importance. Present paper accords with the assessment of the self-propelling sheet of spermatozoa (SPSS) between porous cervical walls continuously secreting viscoelastic mucus in the human cervical canal (HCC). Mathematical modelling of the biological model yielded two inhomogeneous partial differential equations. These partial differential equations along with Saffman slip conditions are solved for exact solutions. It is delineated that an increase in the Reynolds number, Jeffrey parameter, and slip parameter results in an increase in the propulsive velocity and mucus velocity. Conversely, an increase in Darcy number results in a decrease in both propulsive and mucus velocity. When the secreting velocity is constant, the propulsive velocity is maximal, and when the secreting velocity is exponential, it is minimal. Spermatozoa move through the Jeffrey fluid more quickly than they do in the Newtonian fluid. The propulsive velocity through the channel is higher than in unbounded domain. The propulsive velocity of the spermatozoa in cervical canal is approximately 80 μ m/s in particular environment. [ABSTRACT FROM AUTHOR]

• A new topology approach based on the finite element method coupled with a density approach is proposed. • An alternative projection function and a new objective function are improved and applied. • All parameters and equations are treated as global dimensionless in the proposed approach. • The verification schemes for the proposed approach and the optimized structure performance are carried out. The present work is based on the Finite Element Method as the discretization technique coupled to a density approach, an alternative interpolation function in this paper. A new dimensionless objective function combining minimum energy consumption and maximum thermal performance of topology optimization is proposed, and the performance of the approach and the optimized structure in this paper are verified. The result shows: that the alternative interpolation function can effectively solve the checkerboard and gray cell problems in topology optimization; the new objective function can reduce the vibration problem in the calculation process caused by nonlinearity; in the same conjugate heat transfer systems, the objective function value obtained by the Finite Element Method is 2.24% higher than that of Finite Volume Method and 4.26% higher than that of the Lattice Boltzmann Method; under high Reynolds number, topology structure shows superior comprehensive performance, which is increased by 19.5% -65.2%, and energy consumption per heat transfer can be reduced by up to 38.85%. [ABSTRACT FROM AUTHOR]

The numerical solution of the two–dimensional, time–dependent, incompressible Navier–Stokes equations (NSE) in curvilinear coordinates using the nodal integral method (NIM) is presented in this paper. The developed numerical scheme is applied to solve fluid flow problems in domains discretized using quadrilateral cells. Three test problems are numerically solved to assess the accuracy and efficiency of the method. The scheme is second-order accurate in space for all considered deformation levels and Re numbers. The results of the current scheme are compared with the other numerical results in the literature, and good agreement is obtained for all considered cases. The NIM demonstrates superior accuracy per cell compared to other second–order finite–volume schemes considered in this work. New benchmark results obtained from the solution on fine meshes are presented. • The time-dependent, 2D, incompressible Navier-Stokes equations are numerically solved in curvilinear coordinates using nodal integral method. • The accuracy and efficiency of the numerical scheme are assessed through three numerical test problems. • The scheme is found to be second-order accurate in space for all considered deformation levels and Reynolds numbers. • The developed scheme shows superior per-cell accuracy compared to other considered second-order finite-volume schemes. • The developed scheme is capable of simulating incompressible flows accurately using coarse meshes. [ABSTRACT FROM AUTHOR]

Wall-modeled large eddy simulation (WMLES) is considered to be a powerful method in high Reynolds number wall-bounded fluid dynamics calculations. However, little research on aero-acoustic simulation by lattice Boltzmann method (LBM) combined with LES considering wall model has been found. Moreover, the discussion of the dominant geometric parameters of the wall model, which is dedicated to curved boundary modeling and based on a non-fitted Cartesian mesh, is rarely addressed. This paper proposes a WMLES algorithm based on a hierarchical Cartesian mesh and utilizing LBM, including the treatment of dominant geometric parameters. Firstly, based on the Green's formula, a strategy for obtaining detection point positions is developed using the mathematical formulas to solve the boundary free parameters, such as the normal direction of the curved surface and the distance from the lattice point to the solid-fluid boundary in the given direction. Secondly, a new wall model adapted to non-fitted Cartesian mesh is proposed to improve the precision of pressure fluctuation calculation. This model applies an interpolation bounce-back (IBB) scheme where slip velocity is estimated by an implicit wall function proposed by Spalart, and the eddy viscosity is reconstructed in the near-wall region. Finally, to enhance the accuracy of pressure fluctuation propagation, an appropriate transition zone treatment method of a multi-domain scheme with spatio-temporal second-order is applied and validated with a point source case. The aforementioned algorithms are implemented in a self-developed LBM code and validated through a three-element airfoil 30P30N benchmark, demonstrating their effectiveness and high accuracy in acoustic calculations. [ABSTRACT FROM AUTHOR]

This research paper focuses on CFD analysis for comparative evaluation of different hybrid nanofluids (NFs): MWCNT-Al 2 O 3 /H 2 O, MWCNT-MgO/H 2 O, Al 2 O 3 -CuO/H 2 O performance as working fluid (WF) inside parabolic trough solar collector (PTSC). The performance of the collector is evaluated using different performance indicators, including Nusselt number (Nu), friction factor (f), and Performance Evaluation Criterion (PEC) for different Reynolds number (Re) (10000-50000). Among the investigated hybrid nanoparticles (NPs), MWCNT-Al 2 O 3 emerges as the most promising choice for significantly enhancing the system's thermal performance with the highest PEC value of 1.9. This outcome signifies the superior efficiency of MWCNT-Al₂O₃/H₂O hybrid NF in enhancing convective heat transfer, thus underlining the paramount significance of adopting them in thermal systems operating within the specified Re range. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive support domain scheme is proposed to the in-compressible fluid flow based on the localized radial basis function collocation method (LRBFCM). The idea of the adaptive support domain avoids complex mathematical derivations of the finite difference method (FDM). Unlike other upwind schemes in the LRBFCM, the support domain uses the sampling nodes similar to different finite difference schemes, and the improved LRBFCM is further applied to the in-compressible fluid flows. Considering the Kronecker tensor product and Cholesky decomposition techniques, the improved LRBFCM can be easily used to the lid-driven problems with Reynolds numbers up to 100,000 by a simple mathematical derivation. The proposed LRBFCM has an adaptive support domain similar to the finite difference schemes with much less CPU time costs. [ABSTRACT FROM AUTHOR]

Artificial Intelligence (AI) can be used to model efficient processes. In this paper, AI and CFD are employed to maximize the wall pressure of the impinging jet, which has a wide range of industrial and technological applications. Firstly, the CFD model is validated with the experimental results for various geometrical and flow rate configurations (H/D= {1, 2, 3, 4, 5, 10, 20}, where H is nozzle to flat plate distance and D is nozzle diameter, and Reynolds Number (Re) ranges {Re = 15,000, 25,000, 30,000}. In explanatory data analysis, Pressure and D are slightly negatively correlated. Re and D show a negative relation of −0.2 whereas a slight negative relation appears for D vs H/D. Re vs H/D have a positive correlation of 0.2. Various activation functions were explored to find that tangent hyperbolic performed best model fit under AI. The Artificial Neural Networks (ANNs) are applied to train the model with minimized least squared error. Finally, the trained model is optimized for the maximum wall pressure over the distance. The maximum pressure obtained from the trained model is 383.83 KPa. [ABSTRACT FROM AUTHOR]

Impinging jets are found in many industrial applications and specifically in ventilation systems. Mostly, these jets are turbulent and under certain conditions can be a source of discomfort in closed areas due to the high level of noise it can generates. Therefore, it is very important to understand the flow dynamics that is responsible of generating the acoustic field in order to control and reduce such phenomenon. In this paper, an experimental study of a rectangular impinging air jet on a slotted plate is considered for three different Reynolds numbers producing self-sustaining tones (Re = 4100, 5100, and 5900). The sound pressure and spatial velocity field are obtained simultaneously using four microphones located at different locations and SPIV technique. Results show that Re = 5100 correspond to a critical regime where there is a significant drop in the sound pressure level (SPL) that reached 5 dB when compared to a lower Reynolds number Re = 4100. The flow dynamic analysis suggests that this drop in SPL could be contributed to the path followed by the large coherent structure at Re = 5100, where they are deviated in the transverse direction along the wall leading to low energy transfer from the dynamic field to the acoustic one. However, at Re = 4100 and 5900 the peak in SPL could be contributed to the two paths followed by the large coherent structures and particularly to the path where vortices hit the slotted plate before escaping through it. This path is responsible for the optimization of energy transfer from the dynamic field to the acoustic field. Moreover, at Re = 5900 the spectrogram of the instantaneous frequency and instantaneous flow dynamics results show that the acoustic frequencies (160 Hz and 320 Hz) are generated by symmetric and anti-symmetric modes respectively. This unusual aspect is related to the sudden changes in vortex mode. [ABSTRACT FROM AUTHOR]

Thermoacoustics is about conversion between thermal and acoustical energies to provide alternative green technology for power cycle and cooling system. The oscillatory flow across porous structure inside the system is playing the role of energy conversion between the acoustic wave and the surface of the porous structure. Better understanding of fluid dynamics of oscillatory flow inside thermoacoustic system is therefore important for the thermoacoustic based energy conversion system. This paper presents the 'entrance' and 'exit' effects of the oscillatory flow within a parallel-plate structure that is placed inside a standing-wave thermoacoustic environment. Two-dimensional SST k-ω CFD models which were validated using experimental data and theoretical predictions were used for this investigation. Two different operating frequencies of 14.2 Hz and 23.6 Hz were studied for flow with five different amplitudes that were represented using drive ratios of 0.3%, 0.83%, 1.5%, 2.1% and 3%. These correspond to cases with Reynolds numbers between 5936 and 62926. Due to the cyclic nature of the flow, a region defined as an 'exit' region was observed in addition to the usual 'entrance' region and the fully developed region for flow inside a channel. The change of shape of velocity profiles from the 'm' shape profile, to the 'slug-like' profile and 'parabolic-like' profile was discussed in relation to the 'entrance' and 'exit' effects on flow inside the channel. The 'entrance' and 'exit' effects become bigger as drive ratio increases. The effect of 'entrance' and 'exit' are slightly reducing as frequency increases from 14.2 Hz to 23.6 Hz. This may be related to the shorter travel distance of fluid as the frequency increases. The results shown in this paper suggest that the flow within a 200 mm parallel-plate structure should be treated as developing flow especially for flow with low resonance frequency at drive ratio higher than 1%. [ABSTRACT FROM AUTHOR]

The demand of energy saving and loss mitigation in modern industry gives rise to drag reduction techniques such as micro groove/riblet ever since the last century. Plenty of studies are conducted under straight flow condition showing relevance between drag reduction and flow features. However, the same issue has not been studied adequately for rotational flows, which is typical in turbopumps. In this paper, two-dimensional numerical simulations of rotating disks are performed together with verification experiments to investigate drag reduction effect of micro riblet under rotational flow condition. The numerical results show that riblets with certain dimensions can lessen the resistant torque by a maximum of 8.46% and the drag reduction efficiency depends on rotational Reynolds number and riblet dimensions. Meanwhile, the distributions of static pressure and swirl velocity on surfaces are changed and near-wall turbulence intensity is tranquilized by riblets which are considered as the main reasons to the diminish of drag. Finally, the relevance of vortexes inside riblets to swirl wall shear stress and torque is demonstrated revealing that the configuration of riblets plays an important role in cutting resistance. The results of this paper can be a supplement for the investigation of micro groove/riblet drag reduction mechanism. [ABSTRACT FROM AUTHOR]

This paper investigates modelling strategies on the prediction of lift and drag coefficients of a NACA0012 airfoil at Reynolds number of 360,000. Two computational methods are employed; namely Navier-Stokes equation and panel method, by using different tools for computing lift and drag coefficients. The obtained results are compared against experiment in order to assess the accuracy of each technique. Two turbulence models are employed; Reynolds stress model, which is not based on Boussinesq assumption and accounts for flow anisotropy and realizable model which is based on the Boussinesq assumption for computing Reynold stresses. Grid independent solution is produced using the 2-D URANs by employing the fitting method and the obtained lift and drag coefficients are compared against experiment. The fitting method is found to be efficient in saving computational time and power. It is also found that Boussinesq approximation is efficient in predicting lift coefficient. However, the 3rd order panel method produced a remarkably accurate drag coefficient compared to other investigated computational models. Combining the findings of this paper with the existing computational methods in the literature would significantly in improve the accuracy of predicting lift and drag coefficients and may significantly enhance the accuracy of simulation of several aerodynamics applications. [ABSTRACT FROM AUTHOR]

This article presents a detailed study of the non-Newtonian transient Casson fluid flow behavior in three different rectangular domains with their upper and bottom parallel walls moving horizontally either in same direction or in opposite direction to each other. The numerical computations are carried out applying the dynamic subscales approach of the Algebraic Sub-Grid multi-Scale (ASGS) stabilized finite element method upto a sufficiently high Reynolds number, Re =10000. The flow patterns, which include the generation of the primary and secondary vortices, are highly impacted by the Re values, the structures of the domains and the directions in which the parallel walls are moving. We have observed the appearances of both the symmetric and stable as well as unstable asymmetric types of primary vortices in the domains of aspect ratios ≤ 1, with walls moving in the same direction. On the other hand, we notice the existence of multiple phases of the solutions for the Casson fluid flowing in the rectangular domains of aspect ratio > 1, with walls moving in the opposite direction. Besides, the evolution of the solutions with time are also carried out here. In most of the cases, the solutions achieve the steady state after a certain point of time, except for a particular type of domain, where the fluid flow solutions show time dependent behavior after reaching a critical value of Re. This paper has reported the ranges, where the critical Reynolds number (R e c) lies, indicating the appearance of the first Hopf bifurcation for the fluid flow problem. [ABSTRACT FROM AUTHOR]

• At various AoA, Five SJA parameters are optimised using a multi-objective optimiser. • By coupling a mesh generator to a CFD package, Over 2200 2D-CFD cases are automatically pre-processed and performed. • This paper shows how five SJA parameters need to be tuned for different AoA. • At pre-stall AoA, the injection Angle and SJA position are the key parameters to obtain the maximum lift and efficiency. • At post-stall AoA, higher momentum coefficient is required to obtain a full flow attachment. The use of Active Flow Control (AFC) technologies to modify the forces acting on streamlined bodies is one of the most active research fields in aerodynamics. For each particular application, finding the optimum set of AFC parameters which maximises lift, minimises drag or maximises lift-to-drag ratio (aerodynamic efficiency), has become a necessary design requirement. In the present paper, the AFC technology was applied to the Selig-Donovan 7003 (SD7003) airfoil at Reynolds number 6 × 10 4. Synthetic jets were employed to modify the lift and drag forces acting on the airfoil. Four angles of attack (AoA) of 4 ∘ , 6 ∘ , 8 ∘ and 14 ∘ were considered, alongside five AFC parameters: jet position, jet width, momentum coefficient, forcing frequency and jet inclination angle. A multi objective optimisation based on genetic algorithms (GA) was performed for each angle of attack to find the optimum combination of AFC parameters. Each GA generation was simulated using Computational Fluid Dynamics (CFD). A home-made GA package was linked with a mesh generator and the CFD solver, and the results were automatically fed back to the GA code. Over 2200 CFD simulations were performed in two dimensions, using the Spalart-Allmaras turbulent model. The motivation behind the current study is to understand the dependence of the optimum set of AFC parameters on the AoA. Results show that, as AoA is increased, the potential benefits of AFC become more pronounced, which allows for considerable improvement in aerodynamic efficiency. The physics involved in the interaction between the main flow and synthetic jet are clearly presented and clarifies that the physical phenomenon to obtain maximum efficiency is completely different at pre-stall and post-stall AoA. In particular, the aerodynamic efficiency was increased by 251% from baseline (no actuation) by using a moderate/finite momentum coefficient at AoA= 14 ∘ , while a mere 39% increase was obtained at AoA= 8 ∘. In addition, the interaction between the incoming flow and the synthetic jet pulsating flow at different injection angles has been thoroughly investigated. [ABSTRACT FROM AUTHOR]

• Idea of indirect quantification of interfacial mass transfer velocity k l of bubbles under high Reynolds number conditions. • SI-LIF measurement technique and reconstruction algorithm to attain physical quantities required to derive k l. • 3-D visualization and quantification of mass transfer of single bubbles rising in both quiescent water and homogeneous turbulence. • The measured k l are independent of R e T , and all collapse to the analytical solution of potential flow approximation. • Dominant effect of buoyancy of bubble instead of turbulent eddies on the interfacial mass transfer process is confirmed across the hydrodynamic conditions presented in this paper. Accurate quantification of the mass transfer coefficient k l of bubbles under high Reynolds number conditions has been in desperate need for decades to provide insights into its fundamental physics and reach a general mass transfer model. In this paper, a state-of-the-art SI-LIF technique is developed to quantify k l indirectly based on the law of conservation of mass. The reconstruction algorithms of the required physical quantities are validated numerically, suggesting an overall uncertainty of less than ± 5 % in the estimation of k l. We perform mass transfer experiments of single oxygen bubbles with d eq = 1.5 mm rising in both quiescent water and homogeneous turbulence, with turbulent Reynolds number R e T ranging from 0 to 1114. The measured k l under turbulent conditions are independent of R e T , and all collapse to the analytical solution of potential flow approximation, revealing that the flow in the immediate vicinity of the bubble interface remains undisturbed by the fluctuating liquid motions across all the turbulence settings examined in this paper. [ABSTRACT FROM AUTHOR]

The paper presents a new composite structure made up of a double-layer microchannel structure, an impinging jet structure, and a turbulent flow structure. In this paper, the combination of these three structures improves the overall thermal performance of the model compared to the basic impingement-jet double-layer nested microchannel heat sinks (IDN-MHS) model. At Reynolds numbers ranging from 138.2 to 580.4 (0.25≤u in ≤1.05), the thermal performance of the model within introduction of bifurcations is enhanced compared to traditional models that only contain double-layer microchannel structures and impact jet structures. Using 3D printers and conducting experiments, it was discovered that numerical simulation and experimental images were generally consistent. Additionally, IDN-MHS with streaming vertical bifurcations, n=6 (IDN-MHS-VB6) performed well in numerical simulations, with a temperature decrease of 1.24K over IDN-MHS when compared to IDN-MHS. In addition, this model performs better than IDN-MHS with streaming vertical bifurcations, n=2, IDN-MHS with streaming vertical bifurcations, n=4, and IDN-MHS with streaming vertical bifurcations, n=8 (IDN-MHS-VB2/4/8). Compared to IDN-MHS, IDN-MHS-VB6 has the outstanding advantage of reducing substrate temperature while maintaining a relatively low pressure drop. • This structure is an innovative combination of double layer microchannel structure and bifurcation structure of impact jet structure. • In the designed composite structure, the highest substrate temperature is 1.23 K lower than IDN-MHS. • The innovative structure designed has an acceptable pressure drop. • The designed bifurcation structure can effectively increase the coolant flow rate and reduce the substrate temperature. • The IDN-MHS-VB6 allows the coolant to come into contact with more high-temperature areas, achieving cooling effect. [ABSTRACT FROM AUTHOR]

This paper is the second of a two-part series that presents experimental data and analysis on the liquid nitrogen quenching heat transfer process of a stainless-steel tube with an inner surface low-thermal conductivity thin-film coating. This paper focuses on the effects of different flow directions and two tube wall thicknesses. Additionally, this paper also provides an analysis on the chilldown thermal efficiency of the quenching process. Three flow directions with four different inner surface coating modifications, and three tube wall thicknesses were examined. The experimental data covers the Reynolds numbers ranging from 3500 to 140,000. The chilldown efficiency, along with chilldown time and LN 2 (liquid nitrogen) mass consumption were analyzed to assess the overall performance of the LN 2 line chilldown process. For thin tube wall cases, the chilldown efficiencies cover a range between 3% and 41%, and the maximum chilldown efficiency value is found for the tube with 3 L coating at Re = 5278 in the vertical up flow direction. For thick wall tube cases, the efficiencies cover a range between 4% and 52%, and the maximum chilldown efficiency value was found for the tube with 4 L coating at Re = 5308 in the vertical up flow direction. [ABSTRACT FROM AUTHOR]

Numerically investigated analysis occupying considerations free from long wavelength and creeping flow regime has been addressed in this paper for non-Newtonian Casson fluid induced by peristaltic activity. Rheological measurements have been exposed by fluid progression in the asymmetric conduit influenced by a normally settled magnetic field. The analysis is made without implementation of the lubrication theory which allows the role of inertial forces in the flow model not addresses before. Galerkin formulated finite element method is practiced by simplifying full Navier-Stokes equations to assure the appearance of non-trivial Reynolds number and wave independence in an ongoing study. The solution hinged based on code formulated in MATLAB for velocity distribution, pressure profiles, vorticity lines, and stream function is graphically plotted. It has been deduced that inflating the Casson fluid parameter (0.1 ≤ β ≤ 0.5) drives an inappreciable reduction in velocity close to the central region and vorticity lines to remain unaffected. An appreciable increase in bolus formation is inspected by rising time mean flow (1.1 ≤ Q ≤ 1.6) with the diffusion of streamlines in the provision of a progressive phase in waves. [ABSTRACT FROM AUTHOR]

Future advanced aero-engine features highly complex internal flow mechanisms, such as small gap blade row interactions and coupled fluid-structure interactions. Simulating these is challenging for convectional body-fitted computation fluid dynamics methods. As a first step towards this ultimate goal, this paper presents applications of an immersed boundary (IB) method for internal-flow problems at high Reynolds numbers. A hybrid mesh strategy, with a single-block and structured mesh to fit the physical domain and an IB method to model the internal walls, is adopted to the internal-flow problems. To achieve this, an adaptive forcing distance (AFD) technique is proposed for determining the forcing point locations when large-aspect-ratio cells are involved near the walls. This extends the IB method to curvilinear grids so that the domain boundaries can be resolved by a body-fitted mesh, which significantly reduces the total cell number needed to resolve the boundaries compared to the usage of a Cartesian grid, and thus improve the computational efficiency. The present methodologies are firstly validated on a Cartesian grid through a 2D NACA0012 test case. Subsequently, the methods are tested for two internal flow problems with increasing complexity: a 3D subsonic compressor cascade and a well-known transonic rotor, NASA Rotor 37. These case studies prove that the present method can achieve the same overall accuracy for the pressure distribution with the traditional body-fitted simulations at the attached-flow regions, and further studies are still necessary to improve the accuracy of predicting the friction coefficient and separated flows. [ABSTRACT FROM AUTHOR]

This paper first develops a high-efficient accurate mesh-free scheme (CSPH-SFCD) for multi-dimensional time-dependent spatial fractional convection-diffusion (SFCD) equations based on the Riemann-Liouville (RL) derivative in convex domain by coupling a corrected smoothed particle hydrodynamics (CSPH) method with a numerical integral of RL. Subsequently, for the first application, the proposed CSPH-SFCD coupled with up-wind (UW) scheme (CSPH-SFCD-UW) is tentatively extended to investigate the nonlinear shock-wave phenomena in 2D space-fractional Burgers' problem (SFBP) with fractional Neumann boundary at high Reynolds number. The proposed mesh-free scheme for time-dependent SFCD/SFBP with fractional boundary is mainly motived by: (a) the SFCD model with RL fractional calculus is discretized by employing a numerical integral formula and a CSPH scheme, and then a conditionally stable CSPH-SFCD method is first derived; (b) the UW scheme is introduced to stabilize the numerical investigation of convection-dominated SFBP; (c) the fractional Neumann boundary (FNB) condition can be easily enforced in the proposed discretized scheme, and the integer-order NB condition is treated by employing virtual particles interpolation technique; (d) the MPI parallel computing technique is adopted to enhance the computational efficiency. Firstly, the numerical convergence and stability of the proposed scheme are discussed and illustrated by solving several multi-dimensional benchmarks. Secondly, the cases of two-sided and left-sided RL fractional derivatives are also discussed and demonstrated in the numerical tests. The advantages of the proposed method are demonstrated by simulating the 2D/3D SFCD equations in convex domains or under non-uniform point distribution. Finally, the 2D two-component SFBP with FNBC are numerically investigated by using the proposed method, and compared with the FDM results. The complex nonlinear non-local properties governed by SFBP are numerically predicted by the proposed scheme. All the numerical results show that the proposed mesh-free method for time-dependent spatial SFCD problems is high-efficient, flexible and accurate. • A high-efficient accurate CSPH-SFCD scheme is first developed to 2D/3D SFCD equations. • The CSPH-SFCD-UW scheme is first proposed to investigate shock-wave behavior in 2D SFBP. • The FNB condition can be easily enforced in the proposed approximated scheme. • The advantages of the present scheme are shown by numerical tests on convex domain. [ABSTRACT FROM AUTHOR]

In this paper, the forced convection of forced convection of ferro-nanofluid in a U-shaped tubed subjected to a magnetic field is investigated. Modeling is performed in three sizes of the bending radius. The Reynolds number and Hartmann number ranges are 600 ≤ Re ≤ 1200 and 2 ≤ Ha ≤ 12, respectively. The ferro-nanofluid is composed of water-based Fe 3 O 4 particles that vary in volume fraction from 0.01 to 0.03. The simulation is carried out under a 3-D model, incompressible, laminar and steady-state by using the finite volume method. The results show that at a constant bending radius, as the Hartmann number increases, the current density increases. In addition, in all cases, as the Hartmann number increases, the coefficient of friction increases, and the presence of a magnetic field reduces the velocity of the fluid flow. Also, the maximum and minimum friction coefficients are related to the minimum Reynolds number and the maximum Reynolds number, respectively. The results also show that the effect of flow velocity on the heat transfer rate is much more significant than the intensity of the magnetic field and increasing the bending radius of the tube leads to a further reduction of fluid energy and the fluid receives less heat flux from the wall. [ABSTRACT FROM AUTHOR]

This paper deals with the investigations on entropy generation around a circular plain tube with integral downstream splitter plates with cross flow of air in a rectangular duct. This study is carried out in the Reynolds number range 49 × 103 to 227 × 103 on single plain cylinder and single cylinder of various splitter length-to-tube diameter ratios, L/D = 0, 1/3, 2/3, 1, 3/2, 2 and 5/2. Entropy generation characteristics are studied under constant heat flux and temperature conditions and simulated using the artificial neural network (ANN) algorithm. The analysis of the second law of thermodynamics, which considers both the heat transfer and pressure drop effects, indicated the addition of the plate decreases the entropy generation with increased plate length, the entropy generation number being more sensitive to the Reynolds number as plate length increases. entropy generation reduction was, in general, also evident with increased plate length. Results point towards tube with wake splitter being more efficient than plain tube based on entropy generation. The predicted values of the entropy generation number of augmented design, N S,a , using the ANN algorithm are compared with the calculated results. The results showed that the ANN model has good expectation performances with error approaches zero without conducting extra experiments consuming time, money and effort or solving nonlinear mathematical models. Owing to its performance, ANN is a good choice for modeling the entropy generation around a circular plain tube with integral downstream splitter plates. [ABSTRACT FROM AUTHOR]

Hyperthermia is one of the non-invasive therapy of an Abdominal Aortic Aneurysm (AAA), which is achieved by applying a heat source upon the AAA without surgical operation. This research paper considers laminar flow and heat transfer in a heated abdominal aortic aneurysm using an isothermal boundary condition. Heat is added to explicate the thermal treatment of a diseased artery. The blood is assumed as a non-Newtonian fluid based on the shear-thinning Carreau model. Two unequal aneurysms are assumed in the lower wall to simulate bulges or a disordered artery. Flexible wall segments are assumed in the upper wall and opposing to each aneurysm. The transient momentum and energy equations are solved based on the fluid–structure interaction (FSI) using the Arbitrary-Lagrangian–Eulerian (ALE) method. It is found that the shear stress is much higher for a higher index of the power-law fluid governing the blood viscosity and hence, it is strictly recommended to reduce the viscous nature of the blood in diseased vessels. It is found also that the thermal energy can be greatly transported across the blood at a higher Reynolds number, this means that the hyperthermia therapy becomes effective when blood flows violently through the aortic. [ABSTRACT FROM AUTHOR]

In order to study the flow behavior at high Reynolds numbers, two modified models, known as the multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and large-eddy-simulation lattice Boltzmann method (LES-LBM), have been employed in this paper. The MRT-LBM was designed to improve numerical stability at high Reynolds numbers, by introducing multiple relaxation time terms, which consider the variations of density, energy, momentum, energy flux and viscous stress tensor. As a result, MRT-LBM is capable of dealing with turbulent flows considering energy dispersion and dissipation. In the present paper, this model was employed to simulate the flow at turbulent Reynolds numbers in wall-driven cavities. Two-sided wall driven cavity flow was studied for the first time, based on MRT-LBM, at Reynolds numbers ranging from 2 × 1 0 4 to 1 × 1 0 6 , and employing a very large resolution2048 × 2048. It is found that whenever top and bottom lids are moving in the opposite directions, and the Reynolds number is higher than 2 × 1 0 4 , the flow is chaotic, although some quasi-symmetric properties still remain, fully disappearing at Reynolds numbers between 2 × 1 0 5 and 3 × 1 0 5 . Furthermore, between this Reynolds numbers range, 2 × 1 0 5 < Re < 3 × 1 0 5 , the quasi-symmetric structures turn into a much smaller and fully chaotic eddies. The LES-LBM model implements the large eddy simulation turbulent model into the conventional LBM, allowing to study the flow at turbulent Reynolds numbers. LES-LBM combined with Quadruple-tree Cartesian cutting grid (tree grid) was employed for the first time to characterize the flow dynamics over a cylinder and a hump, at relatively high Reynolds numbers. In order to construct the macroscopic quantities in the virtual boundaries separating two different grid levels, a set of new schemes were designed. The coupling of the LES-LBM and tree grid drastically reduced the computational time required to perform the simulations, thus, allowing to minimize the hardware requirements. LES-LBM model is shown to be much more efficient when combined with the tree grid instead of using the standard Cartesian grid. [ABSTRACT FROM AUTHOR]

This paper aims to seek proper stabilized Galerkin methods for solving the two-dimensional coupled Burgers' equations at high Reynolds numbers. The stabilization techniques employed here include the streamline upwind/Petrov–Galerkin (SUPG) method, the spurious oscillations at layers diminishing (SOLD) method and the characteristic Galerkin (CG) method. The first two methods are combined with the Crank–Nicolson scheme for time discretization and the last one is applied in its semi-implicit version. Different from most of the studies on the equations which are usually devoted to improving the accuracy of computed solution in the case of low Reynolds numbers, this paper mainly focuses on keeping the stability of the solution at high Reynolds numbers, which is significant in practical applications and also challenging in numerical computation. We study two problems, equipped with mixed boundary conditions and only Dirichlet boundary conditions, respectively. Numerical experiments reveal that the SUPG method is optimal for the former problem, and the SOLD method is more appropriate for the latter one. In addition, the performances of these methods demonstrate the difference between the two problems, which is seldom mentioned previously and might be helpful to other conventional methods intending to solve the problems at high Reynolds numbers. And last, since SOLD methods have rarely been utilized to solve nonlinear unsteady problems before, this study also indicates the potential of this class of methods to solve nonlinear unsteady convection-dominated problems. [ABSTRACT FROM AUTHOR]

• The physics of droplet in shear is accurately captured. • Mass of the droplet is fully conserved. • The vorticity magnitude inside of the droplet decreases as viscosity ratio increases. • Highly confined droplet exposed to shear flow exhibits fluctuations in deformation. • Two critical viscosity ratios exists for each confinement ratio. This paper is concerned with a numerical study on the behavior of a single Newtonian droplet suspended in another Newtonian fluid, all subjected to a simple shear flow. Conservative finite-volume approximation on a collocated three-dimensional grid along with a conservative Level-set method are used to solve the governing equations. Four parameters of capillary number (Ca), Viscosity ratio (λ), Reynolds number (Re) and walls confinement ratio are used to physically define the problem. The main focus of the current study is to investigate the effect of viscosity on walls critical confinement ratio. In this paper, the phrase critical is used to specify a state of governing parameters in which divides the parameter space into the subcritical and supercritical regions where droplets attain a steady shape or breakup, respectively. To do so, first, we validate the ability of proposed method on capturing the physics of droplet deformation including: steady-state subcritical deformation of non-confined droplet, breakup of supercritical conditioned droplet, steady-state deformation of moderate confined droplet, subcritical oscillation of highly-confined droplet, and the effect of viscosity ratio on deformation of the droplet. The extracted results are compared with available experimental, analytical and numerical data from the literature. Afterward, for a constant capillary number of 0.3 and a low Reynolds number of 1.0, subcritical (steady-state) and supercritical (breakup) deformations of the droplet for a wide range of walls confinement in different viscosity ratios are studied. The results indicate the existence of two steady-state regions in a viscosity ratio-walls confinement ratio graph which are separated by a breakup region. [ABSTRACT FROM AUTHOR]

Nanoplastic particles (<1 μm) are among the contaminants of emerging concern, and compared to microplastic (<5 mm), our understanding of the transport and fate of nanoplastic in water, sediments and soil is very limited. This paper focuses on developing fundamental insight into the dispersion behaviour (sum of hydrodynamic dispersion and diffusion) of nanoplastic spheres, which are likely the most mobile shape of nanoplastic. We measured the dispersion coefficient and dispersivity of nanoplastic spheres (100 nm, 300 nm and 1000 nm diameter) in granular media with a range of pore sizes. We investigated the mechanisms that control the behaviour at low Reynolds number (smaller than 2), relevant to the dispersion of nanoplastic across the riparian area at water velocities of the common river and shallow groundwater. The measured dispersion coefficients were compared with the predictions by two commonly used models. The results show that there are significant differences between measurements and predictions for the case of colloidal size nanoplastics (MAPE>100%). The retarded dispersion caused by the size-exclusion effect was observed to be important in the case of 1.7 mm and 0.4 mm granular media for 300 nm and 1000 nm nanoplastics, reducing the dispersivity and sensitivity to Reynolds number. The methodology in this paper can be adopted in studies on other sizes and shapes of nanoplastic, assisting with predicting the transport and fate of nanoplastic granular media. [Display omitted] • Nanoplastic can be transported from water body to granular media through riparian zone. • Dispersion coefficients of nanoplastic spehers in granular media are presented. • Comparison of measured data with predictions by existing models shows discrepancy. • Size-exclusion was observed to supress the dispersion of large nanoplastics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Taylor bubble mass transfer considering gas compressibility was investigated. • The bubble shape factor was proposed to describe the deformation degree of bubbles. • Three stages were found for the entire mass transfer process of CO 2 gas Taylor bubble. This paper focused on the mass transfer of Taylor bubbles composed of pure carbon dioxide in organic solvent in microchannels. Combined with the Henry's law, the carbon dioxide concentration at the two-phase interface was dynamically updated by using a compressible fluid model and considering the variation of gas density in the bubble. The critical bubble shape factor could help to judge the dominant mechanism of bubble deformation. The entire mass transfer process was divided into three stages: the rapid dissolution stage, the two-end dissolution stage, and the diffusion-like dissolution stage. The gas–liquid mass transfer capacity and influencing factors of each stage were analyzed, and the dominant mass transfer mechanism of each stage was summarized. It was found that the non-uniform degree of gas density in the bubble was related to the bubble Reynolds number and bubble volume by analyzing the distribution variation of solute density. [ABSTRACT FROM AUTHOR]

Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, to aerostructural deflections of aircraft structures. This study aims to develop and validate a high-fidelity static aeroelastic analysis environment that is efficient and that can be used in an industrial setting. The aerodynamics is represented by numerical solutions of the Reynolds-averaged Navier-Stokes equations with appropriate turbulence closures. The load transfer process uses finite element shape functions in order to distribute the aerodynamic loads into the structural discretization. The structural analysis employs a modal basis approach, and a wingtip deflection convergence study is performed to find an adequate modal basis size. Radial basis functions are used for the fluid mesh displacement, and the influence of the support radius is evaluated to determine the optimal values relative to the wing mean aerodynamic chord. The capability is tested using the static aeroelastic benchmarks of the High Reynolds Aerostructural Dynamics Project (HIRENASD) and NASA's Common Research Model (CRM). The static aeroelastic results demonstrate robustness and consistency for the aerodynamic coefficients, pressure distributions, and structural deflection predictions at different normalized dynamic pressure values and grid refinement levels. • The paper describes the development and testing of a novel framework for performing static aeroelastic analyses. • Detailed studies of static aeroelastic behavior of the HIRENASD and the NASA CRM configurations are presented. • The work demonstrated the importance of structural flexibility in aerodynamic moment coefficients for wind tunnel models. • Guidelines for an adequate support radius for mesh movement in static aeroelastic applications using RBFs are presented. [ABSTRACT FROM AUTHOR]

The present paper, for the first time, examines the influences of utilizing oil-ZnO nanofluid with different volume fractions φ = 0.5 %, 1 %, and 2 % in alternating flattened tubes (AFTs) with different alternating pitch angles of 30°, 45°, 60°, and 90° on the performance of a dual-tube heat exchanger (DTHE). This work is conducted experimentally and numerically for the Reynolds number (Re) range of 300 < Re < 1900 for oil-ZnO nanofluid and Re = 2000 for water. Based on the experimental results, the optimal case is selected for the numerical simulations of AFTs. The performance evaluation criterion (PEC) is defined for the simultaneous evaluation of pressure drop (Δp) and heat transfer coefficient (HTC). The results demonstrate that the overall heat transfer coefficient (U) and Δp are augmented with the inlet flow rate and the alternating angle between the pitches. Therefore, the maximum heat transfer (HT) and Δp correspond to the AFTs with the angle of 90° (AF4) at Re = 1900. The PEC amount of AF4 shows a 56 % enhancement compared to the circular tube. It is also observed that using copper oxide nanoparticles inside the oil improves the HT rate and Δp in the heat exchanger. Besides, an increment in φ increases U and Δp; however, the values of PEC show that the positive effects of the nanofluid are larger than their negative impacts in such a way that the PEC is improved by 64 % when the nanofluid with φ = 2 % is utilized in AFTs compared to the circular tube. [ABSTRACT FROM AUTHOR]

Though scaling effects on estimation of peak wind loads are extensively documented in the literature, there is a lack of systematic comparison of such scaling effects across different model scales tested in wind tunnels. Moreover, the limited studies on large-scale physical models accepted the inadequacy of simulating the large turbulent eddies rather than addressing the missing low-frequency turbulence simulation inherent in such large-scale testing. This study provides an in-depth comparison of estimates of peak wind loads obtained using a range of experimental scaled models (1:100 and 1:6 model scales) of the Wind Engineering Research Field Laboratory (WERFL) building while applying a Partial Turbulence Simulation (PTS) methodology to incorporate the effects of turbulence. Large-scale wind tunnel testing of structures provides the advantage of achieving an improved Reynolds number (Re) similarity, more accurate geometric similarity, and enhanced resolution of flow details such as corner vortices, than is possible with the use of smaller model scales. However, as the model scale increases, achieving turbulence similarity becomes challenging due to limitations in simulating the low-frequency turbulent eddies in the wind tunnel. The PTS method has been used in the recent past to account for the low-frequency turbulence effects in the peak wind load estimation. The method is referred to as 1DPTS when considering longitudinal turbulence components only and 2DPTS when considering both longitudinal and lateral turbulence components in the analysis. The computationally intensive 2DPTS can be further simplified by using a weighted average method as described in this paper as "weighted average PTS." The current study explores the effect of scaling on peak wind load estimation by using the 1DPTS, 2DPTS, and weighted average PTS methods. Results from the multi-scale experimental tests demonstrate that using larger model scales and compensating for the low-frequency turbulence deficit in the post-test analysis significantly improve the agreement with the prototype data owing to the simulation of a higher Reynolds number. Furthermore, comparing the results of the proposed weighted average method with full-scale data reveals its potential as a substitute for the original 2DPTS method, offering enhanced accuracy, particularly at the roof corner for oblique wind directions. While the effects of Re are well known, the findings of this study explore its impact in conjunction with the application of the PTS methods on peak Cp estimation across five different model scales with Re ranging from 3.65 × 104 to 2.43 × 106, the latter being closest to the full-scale (field) Re. The findings provide new insights into how large-scale physical model testing in high Re flows, supported by analytical PTS-based compensation, can enhance the accuracy of peak wind load estimations for critical scenarios including cornering winds that generate conical vortices. ● Systematic comparison of peak wind loads across multiple wind tunnel model scales is explored in this study. ● Enhanced Reynolds number similarity and flow detail resolution are achieved in large-scale wind tunnel testing. ● Application of 1DPTS, 2DPTS, and weighted average PTS to account for low-frequency turbulence effects. ● Proposed weighted average PTS method offers improved accuracy in peak wind load estimation. ● Combined effects of Reynolds number and PTS application on peak wind loads are assessed across multiple model scales. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D numerical study was conducted on a micromixer with an oscillating microbeam. • Effects of oscillation frequency and Reynolds number on mixing were investigated. • The optimum operating condition was found for this micromixer. • Four novel designs were proposed by adding passive techniques to this micromixer. • The maximum mixing index was 88% in 0.4 s. In this research, we numerically studied a three-dimensional (3-D) T-shaped active micromixer which works based on the oscillations of a cantilever microbeam. We explored the influence of microbeam's oscillation frequency (10–40 Hz) and flow Reynolds number (2.5–30) on mixing performance, revealing optimal operating conditions. Under optimal operating conditions, using a simple microbeam in a short straight microchannel, the micromixer achieved a 76.7 % mixing index within just 0.4 s. In the next part of this paper, we introduced modifications to the microbeam and microchannel geometries to enhance mixing performance further. Adding a circular part to the channel improved the mixing index to 85.7 %. In a more complex configuration, characterized by a perforated microbeam and a circular microchannel, the micromixer achieved its highest efficiency of 88 %. Additionally, a novel configuration employing two microbeams within a straight channel achieved a mixing efficiency of 82.2 %. [ABSTRACT FROM AUTHOR]

In this paper, a novel open-source framework is presented for the evaluation of noise emissions produced by aerodynamic bodies exhibiting dominant motion at specific frequencies. This behavior is frequently encountered in propellers used for urban air mobility applications. The reduced order model called harmonic balance is employed to compute the unsteady flow solution, reducing the computational cost. The approach tackles K different frequencies by capturing the flow solution at N discrete time instances within a single period, where N is defined as 2 K + 1. The time history of the conservative variables on the solid surfaces is reconstructed through a Fourier interpolation. The Kirchhoff Ffowcs Williams Hawkings integral formulation, integrated into SU2, is used to compute the sound pressure level perceived by farfield observers. The integral formulation propagates the acoustic solution with a computational cost independent of observer distance. The noise emission of a pitching wing and a propeller is computed with the proposed framework. Regarding a small, isolated propeller operating at low Reynolds numbers in forward flight, we conducted a comparison of the aerodynamic and aeroacoustic results between a fully time-accurate solution and a steady-state Reynolds Averaged Navier-Stokes solution within a rotating reference frame. The harmonic balance results demonstrated improved agreement with the fully unsteady solution across the first three blade-pass frequencies and exhibited this consistency over a broader range of propagation angles. • Exploring the efficacy of the reduced-order model Harmonic Balance in capturing surface pressure oscillations. • Novel coupling of the HB method in SU2 with an FWH formulation to computed farfield sound pressure levels. • Noise directivity of an isolated small-scale propeller closely aligns with a fully time-accurate solutions, reducing computational expenses. • Blade pass frequencies are captured with higher accuracy in respect to a steady RANS solution in a rotating reference frame. [ABSTRACT FROM AUTHOR]

This paper presents novel correlations to predict the drag, lift, and torque coefficients of axi-symmetric non-spherical rod-like particles in a wall-bounded linear shear flow. The particle position and orientation relative to the wall are varied to systematically investigate the influence of the wall on the hydrodynamic forces. The newly derived correlations for drag, lift, and torque on the particle depend on various parameters, including the particle Reynolds number, the orientation angle between the major axis of the particle and the main local flow direction, the aspect ratio of the particle, and the dimensionless distance from the particle centre to the wall. The impact of the wall on the hydrodynamic forces is accounted for as a function of a multiplication factor on the drag force in case of locally uniform flow, and an additional force contribution for the lift and the torque, modifying the resultant forces experienced by a particle in a locally uniform flow. The changes in the hydrodynamic forces prove to be substantial, emphasizing the necessity of accounting for wall effects across all particle types and flow conditions investigated in this study. The coefficients of the correlations are determined through a fitting process utilizing the data generated from our previous study on the interaction forces between a locally uniform flow and an axi-symmetric non-spherical rod-like particles, as well as from data of novel direct numerical simulations (DNS) performed in this work of flow past axi-symmetric rod-like particles near a wall. The proposed correlations exhibit a good agreement compared to the DNS results, with median errors of 2.89%, 5.37%, and 11.00%, and correlation coefficients of 0.99, 0.99, and 0.96 for the correlations accounting for the drag, lift, and torque coefficients of a non-spherical particle in wall-bounded linear shear flow profile, respectively. These correlations can be used in large-scale simulations using an Eulerian–Lagrangian or a CFD/DEM framework to predict the behaviour of axi-symmetric rod-like non-spherical particles in wall-bounded shear flow to locally uniform flow conditions. [Display omitted] • PR-DNS of rod-like particles in wall-bounded linear shear flow are performed. • Novel drag, lift and torque models are derived. • Models are based on existing flow correlations for rod-like particles. • Novel models in good agreement with PR-DNS results. • Applicable to Eulerian–Lagrangian simulations with wall boundaries. [ABSTRACT FROM AUTHOR]

• Effect of acoustic excitation on separated boundary layer is experimentally studied. • Influence of Reynolds number and sound pressure level is examined. • The Kelvin-Helmholtz instability and the Klebanoff streaks have been identified. • Acoustic excitation accelerates the l-t transition onset. • Acoustic excitation leads to shrinking or suppression of separation bubble. The paper discusses experimental results on the effect of broadband acoustic excitation on laminar-to-turbulent transition in a separated shear layer developing on a flat plate subjected to an adverse pressure gradient (APG) and freestream turbulence level equal to Tu ≅ 1 %. The study encompasses the influence of Reynolds number (Re x = 185 000 and 370 000) and sound pressure level (SPL). The inherent complexity of the problem is simplified by providing an acoustic excitation from a controlled source (loudspeaker), acting on the boundary layer developing on the flat plate with a given streamwise pressure gradient. Two types of instabilities were identified in the pre-transitional boundary layer in unexcited flows. One was related to the inviscid Kelvin-Helmholtz (K-H) instability, while the second one was associated with formation of streamwise-oriented Klebanoff streaks (so-called Klebanoff mode). In the low Reynolds number case (Re x = 185 000), the K-H was responsible for transition onset, while in the high Reynolds number flow (Re x = 370 000), the Klebanoff distortions dominated the turbulent breakdown with the minor effect of the K-H instability. In addition to the naturally developing boundary layer, the flow was exposed to a pink noise characterized by SPL = 125 dB and 135 dB. In the low Reynolds number case, the acoustic excitation enhanced the K-H instability. It resulted in an earlier laminar-to-turbulent transition in case with higher sound pressure level (135 dB). In the high Reynolds number flow, the acoustic excitation enhanced the mixed-type transition mechanism with dominant role of the Klebanoff streaks. Shrinking or complete suppression of the separation bubbles was observed, depending on the applied sound pressure level (125 and 135 dB). [ABSTRACT FROM AUTHOR]

Different modes of transitional flows are numerically analyzed in a two-stage low-pressure axial turbine, while being exposed to various clocking of second stator blades and results are presented in this paper. The numerical method utilizes coupled approach of SST k-ω turbulence and γ − R e ˜ θ t transitional models. Kinematic of the wake flow in the blades passage and flow topology are presented and discussed. Different types of transitional flows including "separation induced transition" (i.e., "laminar separation bubble"), "reverse transition" and "bypass transition" are distinguished. Results of surface distribution of pressure and skin friction coefficients, turbulence intensity, intermittency and also transition momentum thickness Reynolds number are presented for the worst and optimum clocking cases, in detail. Results show that the onset points of separation induced transition and bypass transition move upstream by 6.64% and 5.47% in the optimum clocking in comparison to the worst case, respectively. In the optimum clocking the separation bubble length decreases by 1.57% and the onset point of the reverse transition moves downstream by 1.2%. All these beneficial effects happen basically as a result of impinging the first stage wake flow on the leading edge of the second stator blade suction side, which in turn, causes transition from laminar to turbulent to occur within the boundary layer. [ABSTRACT FROM AUTHOR]

• In this paper is provided an calculation expression for heat transfer during condensation inside tubes that provides an adequate fit with experimental data available from a total of 22 fluids, including refrigerants, water, and a variety of substances organic. This paper presents a mathematical deduction of a new improved model for heat transfer during condensation inside tubes. This new model has been developed with the aid of the Gaussian Equation for an infinite straight line, considering this relation with the differential equations that govern the heat transfer process. The proposed model was verified by comparison with available experimental data of 22 different fluids, including various refrigerants, water, and organic substances, which condense inside vertical, inclined and horizontal tubes. The proposed model is valid for an reduced pressure values ranging from 0.0008 to 0.91, values of Reynolds number for single-phase between 68 and 84,827 and for Reynolds number for two-phase between 900 and 59,4373, a range of internal diameters ranging from 2 to 50 mm, vapor quality from 0.01 to 0.99, P r values for single-phase from 1 to 18 and mass flux rates in the ranges of 3 to 850 kg/(m2s). The mean deviation found for the analyzed data for horizontal tubes was 11.8%, while for the vertical and inclined tubes data the mean deviation was 13.0%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design. [ABSTRACT FROM AUTHOR]

• This paper unveils a new type of self-excited flapping jets. • Flutter of a film fixed at the nozzle exit excites the emerging jet to flap. • A hysteresis occurs in film flutter: the upper critical velocity > the lower one. • Flutter domain reduces as the film bending stiffness grows. • Flapping frequency increases with decreasing film length or increasing jet velocity. This paper reports a new type of flapping turbulent jets that are self-excited by flutter of a flexible film with a leading edge fixed axially and centrally at a round nozzle exit. Both flutter conditions of a film and flapping-jet characteristics are investigated by varying the film material and dimensions of length (L), span (S) and thickness (δ). Visual observation, flow visualization and hot-wire anemometry are used to examine the flapping jet versus the free counterpart without involving any film. Experiments are made at L/D = 0.5 ∼ 2.0 and the jet Reynolds number of Re = 10,000 to 50,000; where Re ≡ U o D /ν with D , U o and ν being the jet-exit diameter, exit-averaging velocity and fluid viscosity, respectively. Results show that the film's flutter domain reduces with increasing its overall stiffness and varies with the film's shape, size and thickness. The jet-flapping frequency f F rises as either L decreases or U o increases. For the rectangular FEP film of L/D = 0.5 ∼ 2.0, the jet-flapping Strouhal number St F ≡ f F D / U o varies over the range of 0.05 ≤ St F ≤ 0.23. This St F is noticeably lower than that (≈ 0.5 ∼ 0.7) of the primary vortex passage in the non-flapping free jet, but extraordinarily one to two orders of magnitude higher than those for the self-excited oscillation of a jet from conventional fluidic nozzles. [ABSTRACT FROM AUTHOR]

Abstract Winglet pairs are promising longitudinal vortex generators which can be used to produce streamwise vortices that do not decay until further downstream and consequently increase heat transfer rate with comparatively lower pressure penalty. This paper deals with the effect of delta winglet vortex generator (DWVG) pairs on thermal and flow behaviors in a circular tube for Reynolds numbers (Re) range of 5000–25000. The DWVG pairs involved are the pitch ratio (PR = 9.6), four attack angles (α = 10°, 20°, 30° and 40°), three winglet height (h = 5 mm, 7.5 mm and 10 mm) and three spacing between leading edges (s = 10 mm, 15 mm and 20 mm). The experimental results indicate that the Nusselt number (Nu) increases with Re while friction factor (f) decreases with Re. Nusselt number and friction factors both are increasing with attack angle and winglet height, while the middle spacing yields the highest Nu and f. Maximum Nusselt number increment (Nu / Nu 0) with the DWVG pairs was observed as being 73% larger than that of smooth tube, while the maximum friction factor increment (f / f 0) was 2.5 times larger. Thermal enhancement factor (TEF) decreases with Re. The largest TEF obtained, 1.44, is with the combination of α30°s15 h 7.5 at Re = 5000. Compared with other types of VGs in published experimental research papers, the current DWVG pairs show better thermal performance than many of them. Vortices downstream of the DWVG are visualized with smoke flow for better understanding of the flow behavior. [ABSTRACT FROM AUTHOR]

Highlights • Endwall step immediately upstream of the cooling holes deteriorates the film cooling performance. • Coolant were separated into two parts due to the interaction between typical secondary flow and step vortex. • Accompanied with endwall step, increasing the blowing ratio decreases the film cooling effectiveness. • The film effectiveness was improved when moving the cooling holes far away from the endwall step. Abstract Endwall is one of the critical regions to perform film cooling for gas turbine because of not only the increase of turbine inlet temperature but also the complicated secondary flow. Typical endwall film cooling configuration includes leakage slot at combustor-vane interface and discrete cooling holes on the wall. This paper mainly studied the effect of endwall step on the cooling performance of downstream cooling holes. The combustor-turbine interface in this paper is a kind of backward-facing step, causing an interrupted slot. The detailed characteristic of the interrupted slot has been investigated in the previous study. Three dimensional Reynolds-averaged Navier-Stokes equations with shear stress turbulence model (SST) k-ω was solved to perform the calculations of endwall film effectiveness. The adiabatic film effectiveness on the flat endwall was compared with that on the stepped endwall with and without the interrupted slot. Results showed a significant impact of the endwall step on the adiabatic film cooling effectiveness. Coolant jet downstream of the step is split into two parts due to the effects of step vortex (SV) and cross flow. Detailed flowfields in spanwise, pitchwise and axial planes explain the formation and development of secondary flow near the cooling holes. For a range of blowing ratio from 0.6 to 1.2, increasing the blowing ratio of cooling holes deteriorates the adiabatic film cooling effectiveness upstream and downstream of the cooling holes due to the jet liftoff. It is found that cooling effectiveness is strongly dependent on the axial position of the hole. Placing the cooling holes downstream at leading edge plane of the cascade little effect of the step vortex on the film effectiveness and, subsequently, relatively uniform coolant coverage was observed on the endwall. [ABSTRACT FROM AUTHOR]

Highlights • Method of images is successfully adopted to predict the LVG vortex dynamics. • A mixed LVG configuration is suggested to enhance the heat transfer performance. • LVG aspect ratio and channel height are very critical to the LVG effectiveness. Abstract This paper reports a numerical investigation of fluid flow and heat transfer in a rectangular channel with delta-shaped winglet longitudinal vortex generators (LVGs) under different configurations. In addition to the conventional common-flow-down configuration and the common-flow-up configuration, a unique mixed configuration is suggested. The "method of images" is successfully adopted to analyze the dynamics of the longitudinal vortices due to wall interference. The Nusselt number, friction factor and overall performance coefficient for the three configurations are compared at various Reynolds numbers (all less than 2200), LVG row numbers, channel heights, and LVG aspect ratios. It is found that the channel height and LVG aspect ratio are the two most critical factors influencing the effectiveness of the different LVG configurations, which may explain why inconsistent conclusions have been presented by previous studies comparing the performance of the common-flow-down and common-flow-up configurations. When the channel height is relatively small, the unique mixed configuration is found to be the most effective at enhancing fluid mixing (and therefore improving heat transfer) at streamwise cross sections. When the LVG aspect ratio becomes large, the common-flow-down configuration outperforms the common-flow-up configuration. This paper sheds some insight on how to design the optimal LVG configuration for enhancing heat transfer performance. [ABSTRACT FROM AUTHOR]

Highlights • Composite fin with high thermal conductivity coatings deliver large heat transfer enhancement. • At high Re typical of Engine Section Stator vanes, the coating thickness should be around 100 μm. • Composite vanes would be more effective at low Re, as predicted also for composite fins. • Using the internal web structure of vanes can improve heat transfer in long vanes. Abstract This paper main goal is aimed at a paradigm shift in the enhancement of heat transfer rate between finned surfaces and surrounding fluid by presenting a novel approach in composite fins. This approach consists in using high thermally conductive coatings on top of the finned substrate in order to increase the local temperature along the fin washed surface. In the present paper a high thermal conductivity coating has been applied to an aeroengine vane of different shape and dimensions subject to icing conditions at high Reynolds numbers and where the main aim was to keep the vane warm as to avoid icing in aerospace applications. Numerical simulations have been carried out to ascertain the range of thickness of the coatings to be used to maximise the wanted effect. Both short Engine Section Stator (ESS) and longer fan Outlet Guide Vane (OGV) have been modelled, having different final goals. In the case of longer OGV, an additional novel design modification has been suggested to enhance further the heat transfer along the vane length by the use of the internal webs. The experimental validation also carried out at much higher Reynolds numbers than that reported in Buffone et al. (2005), demonstrate that the novel concept of heat transfer enhancement in composite fins is a simple and yet powerful strategy in a wide range of Reynolds numbers. A fin analysis has been performed of both the present ESS vane the fins tested in Buffone et al. (2005) at much lower Reynolds numbers and shows that the improvement obtained with the coated fins tested in Buffone et al. (2005) is much larger than the coated ESS vanes investigated in the present study. This said, the present study demonstrates that the use of high conductive coatings in composite fins can keep the ESS vanes ice free, something that was not possible with uncoated vanes. It is important to note that the actual optimal thickness of the thermally conductive coatings is a function of Biot number, fin shape, dimensions and thermal conductivities of fin substrate and coating; depending on the application, a proper design of the fin substrate and coating should be carried out. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Design of bubble column reactor for various types of bioelectrochemical processes. • First use of a highly flexible bubble column reactor in bioelectrochemistry. • Proof of principle was carried out with two different process. • Reactor characterization was done allowing better comparison with other BES. • Suggestion of scale-up parameters for bioelectrochemical systems. Abstract In times of energy revolution, bioelectrochemistry is a growing field of research, either for the generation of electrical energy from organic substrates or the use of electrical energy to produce various products. By now, this technology is on the turning point from lab scale to industrial applications. Unfortunately, there is still a lack of well characterized, scalable reactor systems that are capable of hosting different bioelectrochemical processes, linking lab scale research to industrial application. In this paper, we introduce a two-chamber bioelectrochemical bubble-column reactor (one liter working volume), which can be used as microbial fuel cell as well as for microbial electrosynthesis and is especially advantageous for processes with gaseous substrates. It is designed flexible in terms of electrode material and area, membrane material and area, and capable of hosting continuous processes. It is a promising replacement of lab-scale H-cells for wider screening possibilities with regard to industrial applications. We characterized the reactor by giving key values such as k L a and gas hold up, and suggest scale-up parameters. These are, for example, dimensionless numbers like Reynolds and Wagner number and different ratios that should be kept constant during scale-up. Therefore, this paper can be a guideline for the development and scale-up of bioelectrochemical systems. [ABSTRACT FROM AUTHOR]