Numerical Investigation Of Flow Research Articles

Numerical investigation of flow boiling characteristics of R134A in a smooth horizontal tube

Three-dimensional transient simulations using ANSYS Fluentʼs mixture multiphase model was conducted to investigate the impact of heat flux, mass flux, and saturation temperature variations on pressure drop behaviour and heat transfer characteristics during flow boiling of R134a refrigerant in smooth horizontal tubes of different diameters. The simulations employ an implicit numerical method to solve the governing equations, with relevant source terms for mass and energy transfer, incorporating the continuum surface force (CSF) and shear stress transport (SST) κ-ω models to account for surface tension and flow turbulence respectively. The results are presented in both dimensional (heat transfer coefficient and pressure drop) and non-dimensional (Nusselt number and two-phase frictional factor) forms. The Nusselt number shows a direct relationship with the Reynolds number, while the two-phase friction factor exhibits different behaviour. At higher vapor quality, mass flux significantly affects heat transfer performance and pressure drop. Heat flux plays a crucial role in heat transfer, but its impact on pressure drop is negligible. Higher saturation temperatures enhance heat transfer while reducing pressure gradients. The obtained results demonstrate good agreement with existing correlations, with mean absolute deviations (MAD) as low as 1.2 % for the heat transfer coefficient and 23.7 % for the pressure drop behaviour. This highlights the model's accuracy in predicting flow boiling behaviour of R134a in smooth horizontal channels, providing valuable insights for thermal analysis. The findings contribute to the understanding of flow boiling processes and aid in designing and optimizing efficient heat exchangers for various engineering applications.

Numerical investigation of flow past a cylinder using cumulant lattice Boltzmann method

This paper presents simulations of flow past a circular cylinder within the subcritical Reynolds number (Re) range from 3900 to 2 × 105, utilizing the parameterized cumulant lattice Boltzmann model. In this study, a three-dimensional characteristic boundary condition for incompressible flow has been integrated into the lattice Boltzmann method at the outflow boundary to minimize spurious reflection. The flow field, wake statistics, hydrodynamic force, and power spectra results of Re = 3900 from the cumulant lattice Boltzmann model are exhaustively compared with the laboratory data and other numerical models. Relative to other numerical models employing turbulence closure, the cumulant lattice Boltzmann simulations demonstrate enhanced agreement with the experimental data even with relatively coarser grid resolution. The resolution-spanning feature for the cumulant lattice Boltzmann model in turbulent flows, without using explicit turbulence model, aligns with the previous benchmark case studies. The stability-preserving regularization process in the present model is analyzed. Results indicate that the influence of the regularization parameter is mitigated with improved grid resolution. A specific regularization parameter for flow around cylinder simulations is recommended. Variations in flow properties and hydrodynamic forces within the subcritical Reynolds number range of 3900 to 2 × 105 are analyzed. The results confirm that the parameterized cumulant lattice Boltzmann model can accurately simulate practical engineering flows, characterized by complex separation and recirculation, within the subcritical range. Moreover, the computational efficiency and parallel scalability are compared with other numerical methods.

Numerical investigation of flow boiling behavior in a vertical tube of a shell‐and‐tube phase change heat storage unit

AbstractPhase Change Materials (PCMs) demonstrate significant potential as latent heat storage systems for direct steam generation. This investigation explores the heat transfer dynamics of an upward‐flowing heat transfer fluid (HTF) boiling within a vertical tube, concurrently examining the solidification process of PCM outside the tube. A two‐dimensional model of a shell and tube heat storage device is established for this purpose. The simulation employs the Volume of Fluid (VOF) model coupled with the Lee model to simulate HTF boiling inside the tube. Concurrently, the enthalpy‐porosity model is utilized to analyze the PCM solidification process. The findings reveal that PCM solidification and heat discharge are influenced by the temperature and thermal conductivity of the HTF, leading to uneven solidified PCM thickness along the tube's length over time. Additionally, variations in tube length, inlet velocity, and inlet temperature impact both the vapor quality of HTF and the thickness of solidified PCM. Tube length correlates with boiling time, affecting the accumulation of steam quality throughout the coupling process. Inlet velocity dictates the heat transfer of HTF with PCM within a limited distance, and insufficient heat exchange resulting in the cessation of HTF boiling. Inlet temperature determines the appropriate device size, lower inlet temperatures necessitate longer tubes to extend the heat charging duration until boiling initiation.

Numerical investigation of forced convection flow of a complex Bingham–Papanastasiou fluid between two concentric

This research presents a numerical investigation of the flow field and heat transfer of a Visco-plastic fluid, The Bingham-Papanastasiou model is used to examine the flow field and forced convection heat transfer of a Viscoplastic fluid between two concentric cylinders with a wavy inner surface. By focusing on this particular configuration (wavy inner cylinder shape), where the inner surface exhibits as the hot wall while the outer surface is considered as the cold wall. This investigation is numerically achieved by using the Comsol Multiphysics, which is based on the finite‐volume method, employing Galerkin’s method for solving the governing equations. The parameters studied in this research are expressed with the following values: r/
 R=1/3, Reynolds number (Re=1, 10, 50), and undulation number (nu=0, 6, 12, 24). Increasing the inertia parameter results in a higher intensity of thermal buoyancy, positively influencing heat transfer, particularly at Re=50. Furthermore, the acceleration of flow within the investi-gated space improves the hydrodynamic behavior, facilitating the exchange of thermal energy between the hot and cold walls. Additionally, it has been discovered that an undulating shape 
 with a specific number of undulations (nu=6) maximizes hydrothermal performance within the investigated volume. The presence of these undulations enhances fluid mixing and dis-rupts the formation of stagnant regions ,which leading to improved heat transfer.

Resolution assessment of Reynolds stress model-based DES methods for high-lift device flow over 30P30N configuration

Flows over high-lift devices (HLD) contain abundant complex physical characteristics such as flow separation, free shear layer transition, and turbulent vortex evolution, which cause challenges to the numerical prediction of unsteady flow characteristics over the HLD. The recently developed detached-eddy simulation (DES) based on the Reynolds-stress model (RSM) is expected to resolve the complex flow characteristics with high fidelity due to the RSM model holding fewer modeling assumptions than classical eddy-viscosity models (EVM). To assess the flow resolution performance of the RSM-based DES method and its dynamic version on the HLD, they are adopted in the numerical investigation of flow over a 30P30N multielement airfoil, a canonical HLD configuration with sufficient experiment measurements. The widely used EVM-based DES method, the shear-stress transport (SST)-based DES method, is also applied for the numerical investigation as the benchmark DES method for the flow resolution performance assessment of RSM-based DES methods. The results are compared with the available experimental data and the benchmark DES method, including average quantities, fluctuation quantities, and instantaneous flow field. It is found that RSM-based DES methods can overcome the prediction delay matter of free-shear layer instability appearing in the SST-based DES method. The dynamic RSM-based DES method can predict the fluctuation flow characteristics in the slat cove of 30P30N configuration more exactly than the other two methods and resolve finer vortex structures in the flow field.

Numerical Investigation of Flow and Scour around Complex Bridge Piers in Wind–Wave–Current Conditions

A sea-crossing bridge is typically constructed in a marine environment with complex piers, and is susceptible to severe scour at the foundation. This study presents a numerical investigation on flow and scour around a complex pier, specifically focusing on a real-world sea-crossing bridge in China. A comprehensive CFD model incorporating hydrodynamic, free surface, sediment transport, and morphological models is employed for numerical modeling. Additionally, a wind shear stress model is considered to accurately simulate wind generation. The validation of the CFD model is achieved through comparison with experimental data of scour around a cylinder, demonstrating its capability to accurately replicate scour morphology and the temporal evolution of scour depth. Subsequently, the validated model is utilized for full-scale simulation of scour around the complex bridge pier under different wind, wave, and current conditions. The results indicate that compared to single piers with uniform cross-sectional shapes, flow patterns around complex piers are much more complicated. Scour predominantly occurs around the first row of group piles, while downstream piles experience less scour due to the sheltering effect from upstream piles. Furthermore, it becomes evident that the current exerts greater influence on pier scour than waves and wind, while the latter two factors primarily influence the superstructure of the bridge.

Numerical investigation of flow past a triangular cylinder at various Reynolds numbers

Numerical simulation of flow around a triangular cylinder placed both in left and right position at Reynolds number Re = 80–200 is presented in this study. The single relaxation time lattice Boltzmann method is used. The results are obtained in terms of vorticity contour visualization, drag and lift coefficients, and force statistics. Regular vortex shedding is observed for both cases, but the vortices generated for a triangular cylinder placed in the right position move toward the top downstream position as the range of Reynolds number increases due to effect of pressure (effect of thrust). The drag coefficient is constant, and lift coefficient is containing negative values from Re = 80–150 for that case, but negative Cdmean values are not observed for a triangular cylinder placed in the left position. In that case, it is due to the reason that the effect of thrust diminishes. The maximum value of Cdmean is obtained at Re = 200, that is, 1.5006 for the left triangular cylinder, but the value of the mean drag coefficient for the right triangular cylinder is zero throughout the cases for Re = 80–200. No fluid forces are produced for right triangular case. The Strouhal number (St) values increased by increasing the Reynolds number, i.e., Re = 80–200, for the right triangular cylinder, and it has a mixed trend for the left triangular cylinder. In literature, a lot of work has been found on rectangular and square cylinders, but triangular cylinder has not been studied much.

Numerical investigation of flow across three co-rotating cylinders in side-by-side arrangement

Flow across three side-by-side co-rotating cylinders is investigated at a Reynolds number of 100 and non-dimensional rotation rates varied from 0 to 8, for spacing ratios of L/D=1.5, 2, and 4 through two-dimensional numerical simulations, where D and L are cylinder diameter and the center-to-center spacing between the cylinders, respectively. For L/D=1.5 and 2, the wakes are classified into regime FF (flip-flopping) at smaller rotation rates and regime SB (single-body) at higher rotation rates. Each regime can be further divided into sub-regimes based on the wake patterns. Regime FF is a regime where the flow switches between two patterns intermittently. The three sub-regimes of SB at L/D=1.5: vortex shedding (SB-VS), steady state (SB-SS), and secondary instability (SB-SI) are the same as those of a single rotating cylinder as the flow through the gap is too weak to have effect on global wake. A new sub-regime single-body quasi-steady (SB-QS) is found for L/D=2, where the two shear layers in the wake of the three cylinders interact weakly with each other but do not form strong vortices. For L/D=4, two new regimes are found: regime 3V-to-3S (transition from three vortex shedding wake to three steady wake), where the vortex shedding from the three cylinders are suppressed consecutively one by one with the increase in the rotation rate, and regime TB (two-body) where two of the three cylinders behave as a single body. Regime TB for L/D=4 has two sub-regimes: steady state (TB-SS) and secondary instability (TB-SI). The effects of the flow regimes on the force coefficients are quantified. For all the spacing ratios L/D=1.5, 2, and 4, the standard derivation drag and lift coefficients are significantly greater than that of a single cylinder when vortex shedding occurs.

Numerical investigation of flow and heat transfer behavior on vortex cooling with an optimal convergent coolant chamber for different nozzle aspect ratio arrangement mode

A computational model including convergent coolant chamber, nozzles and vortex chamber is established. The vortex cooling flow and thermal exchange features are investigated under different nozzle aspect ratio arrangement mode based on an optimal convergent coolant chamber. The nozzle aspect ratio arrangement mode consists of two parts, namely eight nozzle aspect ratio sizes and three kinds of nozzle aspect ratio axial variations. Results indicate that the erosion velocity increases due to the smaller windward area with the increasing nozzle size. The convergent coolant chamber makes the mass flow and pressure increases, the reflux phenomenon appears. And the increasing nozzle size leads to the first increase and then decrease with high pressure and Nusselt number area. For the nozzle aspect ratio arranged from high to low, the airflow stiffness and turbulent kinetic energy at the sixth nozzle are the largest, the thermal transfer feature enhances. For the nozzle aspect ratio arranged from low to high, the airflow impact strength and heat exchange characteristic decreases. But the drag coefficient is minimal that has a positive effect on flow features. The thermal exchange capacity is the highest with the nozzle aspect ratio 2.0. Consequently, this study can provide reference for gas turbine design.

Three-dimensional numerical investigation of flow and heat transfer performances of novel straight microchannel heat sinks

Four-type novel single crystal diamond (SCD) straight microchannel heat sinks with different shapes (symmetrically inclined, turned symmetrically inclined, V-shaped, and X-shaped) are designed and investigated by the three-dimensional computational fluid dynamics method. These four-type microchannel heat sinks are evaluated in terms of fluid flow and heat transfer capabilities compared to the conventional rectangular straight microchannel (RSMC) heat sink. Our research indicates that the newly designed novel SCD microchannel heat sinks can enhance the heat dissipation effect in comparison to the conventional RSMC heat sink, thereby substantiating its potential for enhancing thermal management in electronic devices. Each V-shaped and X-shaped straight microchannel heat sink has a higher heat transfer capacity than the RSMC heat sink. Among the heat sinks involved in this work, the V-shaped SCD heat sink has the best surface temperature uniformity. The symmetrically inclined heat sink shows the lowest pumping power, with 14.1 % lower than that of the RSMC heat sink. The X-shaped SCD heat sink exhibits a significantly lower thermal resistance, with an 8.5 % reduction compared to the RSMC heat sink. Additionally, it demonstrates a substantially higher Nusselt number, with a 27.6 % increase relative to the RSMC heat sink. The X-shaped SCD heat sink has the highest heat transfer coefficient of up to 1.08 × 105 W/(m2·K), which is 20.4 % higher than that of RSMC heat sink. Owing to the highest performance evaluation criterion of 1.22, the X-shaped straight microchannel heat sink is the most optimal of the designed heat sinks.

Numerical Investigation of Flow and Heat Transfer in Vane Impingement/Effusion Cooling with Various Rib/Dimple Structure

Numerical Investigation of Flow and Heat Transfer in Vane Impingement/Effusion Cooling with Various Rib/Dimple Structure

Numerical investigation of flow and heat transfer of supercritical carbon dioxide in the vertical helically-coiled tube under half-side heating condition

ABSTRACT The supercritical boiler is one of the ways to enable sustainable energy development. Its revolution cannot be separated from the study of the characteristics of supercritical carbon dioxide in a spiral pipe. This research article provided an industrially compliant model of a water-cooled wall spiral pipe with one-side heating for heat transfer. The simulation was set for various parameters including P = 30.42 MPa, Tin = 578–643 K, q = 105–180 kW/m2, G = 1784–2348 kg/m2s. The article discussed in detail factors such as buoyancy and secondary flow for these cases. The results showed that in the range of high parameters, mass fluxes, heat fluxes, and inlet temperature all had a substantial influence on the temperature and velocity fields, with the mass flux showing a non-monotonic trend on the HTC and the heat flux having a more subtle influence on the HTC. The inhomogeneous heating pattern affected the buoyancy and secondary flow motion, changing the temperature field in the tube, and enhancing the velocity field at the bend and on the heating side. A new empirical correlation for supercritical CO2 with non-uniform heating was proposed.

Numerical Investigation of Flow and Structural Characteristics of a Large High-Head Prototype Pump–Turbine during Turbine Start-Up

Transient processes that occur in pumped storage power plants can cause high-pressure conditions, which in turn can result in vibrations in the pump–turbine structure and even damage to structural components. It is therefore crucial to research the transient process of the large pump–turbine units and the flow-induced vibrations of the structural components. The three-dimensional flow field and structural field models of a high-head prototype pump–turbine were constructed to study its flow characteristics and structural characteristics under the turbine start-up. Calculations and analyses were performed on the pressure variation and the flow-induced stress concentrations of the pump–turbine during start-up in turbine mode. The simulated pressure distributions during the turbine start-up were mapped onto the finite element calculation model of the structures of the pump–turbine to calculate the flow-induced stress concentrations. This study provides a reference to improve the design and operation of high-head prototype pump–turbines based on the findings of the flow and structural characteristics.

Experimental and numerical investigation of flow and thermal characteristics of aluminum block exchanger using surface-modified and recycled nanofluids

PurposeThe purpose of this study is to numerically and experimentally survey the thermal efficiency of a block-type heat exchanger operated in different working conditions by using pure water and two nanofluids as heat transfer fluids.Design/methodology/approachAn aluminum block-type heat exchanger integrated with Peltier thermoelectric element was designed and installed to operate in a cycle, and the thermal performance of the heat exchanger, heat transfer rate, Nusselt and heat transfer coefficient variations were examined at different bath water temperatures by using recycled nanofluids. New generation surface-modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol/water nanofluid was used as heat transfer fluid in the cycle. In addition, CFD simulation was performed using ANSYS/Fluent to investigate the temperature distribution and fluid flow structure in the used heat exchanger.FindingsExperiments were carried out by using numerical and experimental methods. In the experiments, the operating conditions such as flow rate, volume fraction of the nanofluid and water bath temperature were changed to find the effect of each parameter on the thermal efficiency. The Reynolds number varied depending on the test conditions, which was calculated in the range of approximately 100 < Re < 350. In addition, Nusselt number and heat transfer coefficient of test fluids were very close to each other. For 0.4% nanofluid, the maximum h value was obtained as 3837.1, when the Reynolds number was measured as 314.4.Originality/valueIn the scientific articles published in the field of heat exchangers operated by nanofluids, little attention has been paid to the stability of the nanofluids and sedimentation of particles in the base fluids. In addition, in most cases, experiments were implemented using an electrical resistance as a heat source. In this research, stable surface-modified nanofluids were used as heat transfer fluids, and it was found that the Peltier thermoelectric can be used as heat sources with acceptable efficiency in flat-type heat exchangers and even non-circular channels.

Numerical Investigation of Flow Around Finite Height Rectangular

Three-dimensional flow features of the slender rectangular prism with cross-section height (H) to streamwise depth (D) ratio or side ratio (D/H = 0.5) were investigated numerically using the Large-eddy simulations (LES) turbulence model with Reynolds number Re = 22000. Four different aspect ratios (L/H = 2.5 – 10) were employed in this research to study the effect of the spanwise variation of the prism model on the flow pattern around the prism. Moreover, the instability-induced motion of the prism was modeled to predict the alteration of flow characteristics of stationary to vibrating states of the test model. The global quantities such as drag force, pressure coefficient, and Strouhal frequency characteristics are presented, which suggests that the structure end tip effect plays an essential role in the dependency of flow features variation. The velocity vector variations at streamwise and spanwise positions are also demonstrated. The prism model with a small aspect ratio (L/H = 2.5) exhibited Karman vortex suppression at the prism's vicinity, and the streamwise vortices region shrank. The flow features of the vibrating prism show different behaviors from the stationary prism model

Numerical investigations of flow in nuclear fuel assembly with spacer grid and OpenFOAM validation

Abstract Spacer grids with mixing vanes have complex geometry and are used to support the fuel rods in nuclear fuel assemblies as well as to improve heat transfer by generating turbulence downstream of the spacer grid in the cores of the pressurized water reactors. To validate the CFD code OpenFOAM for relevant spacer grid geometries, numerical analyses on the OECD/NEA MATiS-H benchmark were performed. The flow behind two different types of spacer grid designs was analysed: split- and swirl-type. Initially, an appropriate inlet velocity profile was generated. In a next step, Computer-Aided Design models of the spacer grids were prepared and then meshed using ANSYS Mesher 19.2. Transient URANS simulations were performed with the k-ω-SST turbulence model and the results were compared with data. Good agreement was obtained for the mean velocity profile and the vorticity in the swirl-type configuration, while the numerical results slightly overestimated the transverse velocity profile at some measurements locations of the split-type configuration. The content of this article was initially presented at the 33rd German CFD Network of Competence Meeting, held on March 22–23 at GRS in Garching, Germany.

3D Numerical investigation of flow and heat transfer from an immersed vertical cylinder with the constant rotation speed in an unbounded stationary fluid

3D Numerical investigation of flow and heat transfer from an immersed vertical cylinder with the constant rotation speed in an unbounded stationary fluid

Numerical investigations of flow over wavy cylinders at sub-critical Reynolds number

Numerical investigations of flow over wavy cylinders at sub-critical Reynolds number

Numerical investigation of flow past a circular cylinder modified with a single groove at low Reynolds number

Flow past a circular cylinder modified by grooves is one of the passive control techniques to control the drag and lift forces. The presence of grooves tends to reduce the hydrodynamic drag and lift. The aim of this work was to numerically investigate the influence of a single groove modification on a circular cylinder and how it was impacting the hydrodynamic coefficients based on its position and shape at low Reynolds numbers. Three types of grooves were considered, namely, dimple, square, and triangular, with identical width and depth which is 0.1 times the diameter. The Reynolds numbers considered were 100, 150, and 200. The computational domain was set to a blockage ratio of 0.01 after carrying out a detailed domain independence test. It was observed that the drag and lift reduction was maximum at groove location 90° with the decrements being more for the square groove shape. The viscous drag showed a decrease in its values for all the groove positions located on the flow-facing side of the cylinder; however, the pressure drag showed an increment in its values for these groove locations, and these increments were relative of larger magnitudes, thus influencing a net increase in the total mean drag when compared to the smooth case; this was evident at groove locations 120° and 150°. The vorticity patterns for the grooves located on the front side showed large irregularities in magnitude between the anticlockwise and the clockwise vortices with the groove side vortices being of larger magnitudes, and for the wake side, the irregularities were negligible. The coefficient of pressure and separation angles were also investigated. The CP vs θ plots showed discontinuity at groove locations with abrupt variations at the front face of the cylinder; for the wake side grooves, these discontinuities were low and almost coincided with the CP vs θ plots of the smooth cylinder. The grooves located at 90° showed a delay in separation and at 60° the boundary layer tends to detach earlier.

Numerical Investigation of Flow and Dispersion over Two-Dimensional Semi-Open Street Canyon

A semi-open street canyon is able to protect pedestrians from unpleasant situations such as direct sunlight and rain. However, the protruding elements of the two opposite building facades that form the semi-open configuration can affect the air quality of the urban canopy layer (UCL). Therefore, this paper investigated the influence of the eave structures on the flow and pollutant dispersion over an idealized 2D street canyon with a unity aspect ratio. The length of the eaves was varied into 0.25H and 0.5H (H is the building height) and placed either on the leeward wall, the windward wall, or on both building facades located at the same elevation as the street canyon. Numerical simulations were performed using the steady-state Reynolds-averaged Navier-Stokes (RANS) equations in conjunction with Re-Normalization Group (RNG) k-ε as the turbulence closure model. The pollutant was released from a line source in the center of the bottom of the target canyon with uniform flow rate. Six different eave configurations were simulated in the wind direction perpendicular to the canyon axis, representing the worst condition of canyon ventilation. The evolution of the primary vortex, which occupied the entire canyon with the characteristic of skimming flow, showed less dependence on the length and position of the eave, except for the longest eave on the windward wall. However, the position of the vortex center depicted opposite results. The pollutant concentration is always higher near the leeward wall, but for the eave that protrudes from the windward wall with a length of 0.5H, the pollutant accumulates near the windward region. The ratio of pollutant concentration showed higher concentration in the semi-open configurations compared to the fully open layout as a result of limited penetration of shear flow into the canyon, which leads to deterioration of pollutant removal.